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BIOLOGY, M5 2022 HSC 15 MC

In a plant species, red flower colour (R) is dominant over white flower colour (r).

Two plants of known genotype for flower colour were crossed. A punnet square was used to determine the proportion of genotypes expected in the offspring. Part of the punnet square is shown.
 

Which statement is true for the parents in this cross?

  1. Both parents were homozygous.
  2. Both parents were heterozygous.
  3. Both parents had flowers of the same colour.
  4. Parent 2 must have red flowers and Parent 1 must have white flowers.
Show Answers Only

`C`

Show Worked Solution

→ Parent 1 must be homozygous dominant (RR), making it red.

→ Parent 2 must be heterozygous (Rr), also making it red.

`=>C`

BIOLOGY, M5 2022 HSC 14 MC

An inherited characteristic in a family is mapped in the pedigree shown.
 

Inheritance of this characteristic is

  1. autosomal recessive.
  2. sex-linked recessive.
  3. autosomal dominant.
  4. sex-linked dominant.
Show Answers Only

`A`

Show Worked Solution

By Elimination:

→ The characteristic can be unaffected in the parents but apparent in the offspring.

→ Therefore must be recessive (eliminate C and D).

→ The father in generation 2 is unaffected `text{(X}^text{A}text{Y}` or `text{Aa)}` but the daughter is affected

→ Therefore it cannot be sex-linked (eliminate B).

`=>A`

ENGINEERING, TE 2020 HSC 21d

Electrolytic tough pitch (ETP) copper has many desirable properties that support its use in telecommunications.

In the table, provide an explanation for the importance of each of the listed properties of ETP copper.   (3 marks)
 

Show Answers Only
  1. The electrical conductivity of ETP copper is important in telecommunications because it has low resistance. This characteristic allows for an increased efficiency of both data transfer and electricity transmission.
  2. The ductility of ETP copper is important in telecommunications because it allows the copper to be drawn into very light weight, thin and flexible wire which can be used in cables without risk of failing in a brittle manner under impact.
  3. The corrosion resistance of ETP copper is important in telecommunications because it greatly reduces the risk of systems needing to be replaced due to to the cable breaking down. It also reduces cost as the system will ideally only be installed once, instead of needing constant replacement.
Show Worked Solution
  1. The electrical conductivity of ETP copper is important in telecommunications because it has low resistance. This characteristic allows for an increased efficiency of both data transfer and electricity transmission.
  2. The ductility of ETP copper is important in telecommunications because it allows the copper to be drawn into very light weight, thin and flexible wire which can be used in cables without risk of failing in a brittle manner under impact.
  3. The corrosion resistance of ETP copper is important in telecommunications because it greatly reduces the risk of systems needing to be replaced due to to the cable breaking down. It also reduces cost as the system will ideally only be installed once, instead of needing constant replacement.

ENGINEERING, TE 2020 HSC 21b

The diagram shows a simple logic circuit with inputs `A, B, C` and `D`, and output `Z`.
 

Inputs `A` and `D` are set to 'high' (1).

Determine, using the logic circuit diagram, the combination of inputs at `B` and `C` which will produce a high (1) output at `Z`. Use the truth table to support your answer.   (3 marks)
 

Show Answers Only

Let the output of the AND gate be `E` and the output of the OR gate be `F`

\begin{array} {|c|c|c|c|c|c|c|}
\hline  \   A  \  & \  B \  & \  C \  & \  D \  & \  E \  & \  F \  & \  Z   \\
\hline 1 & 1 & 0 & 1 & 1 & 1 & 0\\
\hline 1 & 1 & 1 & 1 & 1 & 1 & 0\\
\hline 1 & 0 & 1 & 1 & 0 & 1 & 0\\
\hline 1 & 0 & 0 & 1 & 0 & 1 & 0\\
\hline \end{array}

→ As shown in the table, since `D` is always on, the output of the OR gate (`F`) will always be on/1.

→ Therefore, `Z` will always be 0 since it is a NOR gate, i.e. it requires `E` and `F` to be 0, and `F` is always 1.

→ Hence, there are no inputs at `B` and `C` that produce a high output at `Z`.

Show Worked Solution

Let the output of the AND gate be `E` and the output of the OR gate be `F`

\begin{array} {|c|c|c|c|c|c|c|}
\hline  \   A  \  & \  B \  & \  C \  & \  D \  & \  E \  & \  F \  & \  Z   \\
\hline 1 & 1 & 0 & 1 & 1 & 1 & 0\\
\hline 1 & 1 & 1 & 1 & 1 & 1 & 0\\
\hline 1 & 0 & 1 & 1 & 0 & 1 & 0\\
\hline 1 & 0 & 0 & 1 & 0 & 1 & 0\\
\hline \end{array}

→ As shown in the table, since `D` is always on, the output of the OR gate (`F`) will always be on/1.

→ Therefore, `Z` will always be 0 since it is a NOR gate, i.e. it requires `E` and `F` to be 0, and `F` is always 1.

→ Hence, there are no inputs at `B` and `C` that produce a high output at `Z`.

CHEMISTRY, M5 2019 HSC 12 MC

Methanol can be produced from the reaction of carbon monoxide and hydrogen, according to the following equation:

\( \ce{CO(g) + 2H2(g) \rightleftharpoons CH3OH(g)}\ \  \ \ \ \ \text{Δ}H_r ^{\ \ominus} =-90\ \text{kJ mol}^{-1} \)

Which set of conditions will produce the maximum yield of methanol?

  1. Low pressure and low temperature
  2. Low pressure and high temperature
  3. High pressure and low temperature
  4. High pressure and high temperature
Show Answers Only

`C`

Show Worked Solution

→ To maximise the methanol yield, the equation must shift towards the right hand side.

→ Pressure: If the pressure is increased, the system will shift to reduce this increase. In this reaction, a shift to the right hand side will occur because there are fewer gas molecules (1 on right vs 3 on the left).

→ Temperature: If the temperature is decreased, the equilibrium will shift to the exothermic side which absorbs heat (right hand side). This compensation will result in more methanol.

`=>C`

CHEMISTRY, M5 2019 HSC 11 MC

A saturated solution of barium carbonate was stored in a flask. Solid barium carbonate containing radioactive carbon-14 was added to the solution. The mixture was allowed to stand for several days and was then filtered.

Radioactivity could reasonably be expected to be found in

  1. the filtrate only.
  2. the residue only.
  3. both residue and filtrate.
  4. neither residue nor filtrate.
Show Answers Only

`C`

Show Worked Solution

\( \ce{BaCO3(s) \rightleftharpoons Ba^2+(aq) + CO3^2-(aq)} \)

→ In a saturated solution, a dynamic equilibrium exists whereby the solid barium carbonate is dissolving into the solution and the solution is depositing back onto the solid.

→ If the solid barium carbonate contains a radioactive isotope, such as carbon–14, this isotope will be present in both the solid residue and the filtrate solution due to the process of the dynamic equilibrium described above.

`=>C`

CHEMISTRY, M7 2019 HSC 9 MC

All of the following compounds have similar molar masses.

Which has the highest boiling point?

  1. Butane
  2. Ethanoic acid
  3. Propan-1-ol
  4. Propane
Show Answers Only

`B`

Show Worked Solution

→ Carboxyllic acids have a high affinity for hydrogen bonding, the strongest molecular force.

→ They therefore require more heat to break the intermolecular forces to convert liquid to gas versus other substances.

`=>B`

CHEMISTRY, M7 2019 HSC 8 MC

The structure of an organic compound is shown.

Which row of the table correctly gives the name of the compound and one of the reactants used to produce it in a one-step reaction?
 

Show Answers Only

`A`

Show Worked Solution

Compound: Ethyl pentanoate

Reactants: Ethanol and Pentanoic acid (only the former is listed in the table)

`=>A`

CHEMISTRY, M5 2019 HSC 7 MC

How does the addition of a catalyst affect a reversible reaction?

  1. It increases the activation energy of the forward reaction only.
  2. It decreases the activation energy of the forward reaction only.
  3. It increases the activation energy of both the forward and reverse reactions.
  4. It decreases the activation energy of both the forward and reverse reactions.
Show Answers Only

`D`

Show Worked Solution

→ A catalyst helps to make a chemical reaction happen more easily by offering a different pathway for the reaction to occur.

→ This reduction in the required activation energy applies to both the forward and reverse reactions.

`=>D`

CHEMISTRY, M6 2019 HSC 6 MC

The diagram represents the titration curve for a reaction between a particular acid a particular base. 
 

Which of the following equations best represents the reaction described by the titration curve?

  1. \(\ce{NH3 (aq) + HCl(aq) to NH4 Cl (aq)}\)
  2. \(\ce{NaOH(aq) + HCl(aq) to NaCl(aq) + H2O(l)}\)
  3. \(\ce{NH3 (aq) + CH3 COOH(aq) to CH3COONH4(aq)}\)
  4. \(\ce{NaOH(aq) + CH3 COOH(aq) to CH3COONa(aq)+H2O (l)}\)
Show Answers Only

\(A\)

Show Worked Solution

\(\rightarrow\)The titration curve shows the progress of a titration in which a weak base \(\ce{NH3}\) is reacting with a strong acid \(\ce{CHl}\) .

\(\rightarrow\)As the acid is added to the base, the pH of the solution moves lower.

\(\Rightarrow A\)

CHEMISTRY, M8 2019 HSC 4 MC

The diagram shows the mass spectrum of an organic compound.
 

Which compound was analysed?

  1. Butan-1-amine
  2. Butanoic acid
  3. Ethanoic acid
  4. Iron`text{(II)}` sulfide
Show Answers Only

`B`

Show Worked Solution

→ The parent ion in the mass spectrum has a mass to charge ratio (m/z) of 88 that matches the molar mass of butanoic acid.

`=>B`

ENGINEERING, TE 2020 HSC 20 MC

Which of the following describes high frequency wireless transmission when compared to low frequency wireless transmission?

  1. Faster data rates over longer distances with higher interference
  2. Faster data rates over shorter distances with lower interference
  3. Slower data rates over longer distances with lower interference
  4. Slower data rates over shorter distances with higher interference
Show Answers Only

`B`

Show Worked Solution

→ Higher frequency in wireless transmissions increases data rates

→ However, it decreases wavelength which decreases the penetrating power of a transmission (ie the distance a transmission can travel).

`=>B`

ENGINEERING, TE 2020 HSC 12 MC

A geostationary satellite is positioned above the equator.

How many times does the satellite go around Earth's axis in a 24-hour period?

  1. 0
  2. 1
  3. 2
  4. 3
Show Answers Only

`B`

Show Worked Solution

→ Geostationary satellites orbit at a fixed spot above earths surface.

→ Therefore, a satellite above the equator takes the same time to rotate 360° around the earth’s axis as it takes the earth to do the same.

`=>B`


Mean mark 59%.

ENGINEERING, CS 2020 HSC 11 MC

The diagram shows a 10 kg lamp hanging from a cable over a cycle path.
 

What is the tension in cable `A` ?

  1. 44 N
  2. 88 N
  3. 100 N
  4. 110 N
Show Answers Only

`B`

Show Worked Solution

Solve graphically:

→ Draw a 10cm vertical line (scale 1 cm = 10 N)

→ Draw other sides of triangle using a protractor for accuracy

→ Measure side A and convert to Newtons using the scale

`=>B`


Mean mark 56%.

ENGINEERING, CS 2020 HSC 8 MC

The photograph shows a transport viaduct based on a series of Roman arches.
 

By using the Roman arch, engineers today can design structures which

  1. are easy to construct.
  2. are quick to construct.
  3. can span long distances.
  4. place foundations in tension.
Show Answers Only

`C`

Show Worked Solution

By Elimination:

→ The type of bridge (in this case arch) does not necessarily determine the ease or length of construction (eliminate `A` and `B`).

→ Arches place the foundations in compression, not tension (eliminate `D`).

`=>C`

ENGINEERING, AE 2020 HSC 7 MC

Which of the following best describes how an unpowered aircraft will glide, in a controlled descent, when the lift-to-drag ratio is high?

  1. Long distance at a steep glide angle
  2. Short distance at a steep glide angle
  3. Long distance at a shallow glide angle
  4. Short distance at a shallow glide angle
Show Answers Only

`C`

Show Worked Solution

→ High lift to drag ratio means the aircraft will travel a long distance (low drag) at a shallow angle (high lift).

`=>C`

Vectors, EXT2 V1 2022 HSC 14a

  1. The two non-parallel vectors `\vec{u}` and `\vec{v}` satisfy  `lambda vec(u)+mu vec(v)= vec(0)`  for some real numbers `\lambda` and `\mu`.
  2. Show that  `\lambda=\mu=0`.  (2 marks)

  3. The two non-parallel vectors `\vec{u}` and `\vec{v}` satisfy  `\lambda_1 \vec{u}+\mu_1 \vec{v}=\lambda_2 \vec{u}+\mu_2 \vec{v}`  for some real numbers `\lambda_1, \lambda_2, \mu_1` and `\mu_2`.
  4. Using part (i), or otherwise, show that  `\lambda_1=\lambda_2`  and  `\mu_1=\mu_2`. (1  mark)

The diagram below shows the tetrahedron with vertices `A, B, C` and `S`.

The point `K` is defined by  `vec(SK)=(1)/(4) vec(SB)+(1)/(3) vec(SC)`, as shown in the diagram.

The point `L` is the point of intersection of the straight lines `S K` and `B C`.
 
                       
 

  1. Using part (ii), or otherwise, determine the position of `L` by showing that  `vec(BL)=(4)/(7) vec(BC)`.  (2 marks)

  2. The point `P` is defined by  `vec(AP)=-6 vec(AB)-8 vec(AC)`.
  3. Does `P` lie on the line `A L`? Justify your answer.  (2 marks)

Show Answers Only
  1. `text{Proof (See Worked Solution)}`
  2. `text{Proof (See Worked Solution)}`
  3. `text{Proof (See Worked Solution)}`
  4. `P\ text{lies on}\ vec(AL)\ \ text{(See Worked Solution)}`
Show Worked Solution
i.    `lambda vecu+mu vecv` `=0`
  `lambda vecu` `=-mu vecv`

 
`lambda=0\ \ text{or}\ \ vecu=-(mu/lambda)vecv=k vecv\ \ (kinRR)`

`text{S}text{ince}\ \ vecu and vecv\ \ text{are not parallel}`

`=> lambda=mu=0`
 

ii.  `\lambda_1 \vec{u}+\mu_1 \vec{v}=\lambda_2 \vec{u}+\mu_2 \vec{v}`

`\lambda_1 \vec{u}-\lambda_2 \vec{u}+\mu_1 \vec{v}-\mu_2 \vec{v}` `=vec0`  
`(\lambda_1-\lambda_2)\vec{u}+(\mu_1-\mu_2)\vec{v}` `=vec0`  

 

`text{Using part (i):}`

`(\lambda_1-\lambda_2)=0 and (\mu_1-\mu_2)=0`

`:.\lambda_1=\lambda_2  and  \mu_1=\mu_2\ …\ text{as required}`


Mean mark (ii) 56%.
iii.   `vec(BL)` `=lambda vec(BC)`
    `=lambda(vec(BS)+vec(SC))\ \ \ …\ (1)`

 

`vec(BL)` `=vec(BS)+mu vec(SK)`  
  `=-vec(SB)+mu(1/4vec(SB)+1/3vec(SC))`  
  `=-vec(SB)+mu/4vec(SB)+mu/3vec(SC)`  
  `=mu/3vec(SC)+(mu/4-1)vec(SB)\ \ \ …\ (2)`  


♦♦♦ Mean mark (iii) 25%.

`text{Using}\ \ (1) = (2):`

`lambda vec(BS)+ lambda vec(SC)=mu/3vec(SC)+(mu/4-1)vec(SB)`

`mu/3=lambda, \ \ 1-mu/4=lambda`

`mu/3` `=1-mu/4`  
`(4mu+3mu)/12` `=1`  
`(7mu)/12` `=1`  
`mu` `=12/7`  

 
`lambda=(12/7)/3=4/7`

`:.vec(BL)=(4)/(7) vec(BC)\ \ text{… as required}`
 

iv.  `vec(AP)=-6 vec(AB)-8 vec(AC)`

`text{If}\ P\ text{lies on}\ AL, ∃k\ text{such that}\ \ vec(AP)=k vec(AL)`


♦♦♦ Mean mark (iv) 23%.
`-6 vec(AB)-8 vec(AC)` `=k vec(AL)`  
`-6 vec(AB)-8 (vec(AB)+vec(BC))` `=k(vec(AB)+vec(BL))`  
`-14 vec(AB)-8vec(BC)` `=k(vec(AB)+4/7vec(BC))\ \ text{(see part (iii))}`  
`-14 vec(AB)-8vec(BC)` `=kvec(AB)+(4k)/7vec(BC)`  

 
`k=-14, \ \ (4k)/7=-8\ \ =>\ \ k=-14`

`:.\ P\ text{lies on}\ \ AL.`

BIOLOGY, M7 2022 HSC 10-11 MC

Refer to the following information to answer Questions 10 – 11.

Pasteur used swan neck flasks to conduct experiments on microbial contamination of broth. One of Pasteur's investigations is shown.
 

Question 10

Which of the following was the independent variable in this investigation?

  1. The air
  2. The flask
  3. The broth
  4. The microbes

 
Question 11

What is the best explanation for Pasteur's results?

  1. Cells arise from existing cells
  2. Heating prevents broth spoiling
  3. Gases in the air cause broth to spoil
  4. Cells arise by spontaneous generation
Show Answers Only

Q10.  `B`

Q11.  `A`

Show Worked Solution

Q10.

→ The flask was changed in each test therefore it is the independent variable.

`=>B`
 

Q11.

→ Pasteur’s experiment was conducted to show that microbes arise from existing cells in the air, disproving spontaneous generation.

`=>A`


♦ Mean mark (Q11) 40%.

BIOLOGY, M6 2022 HSC 7 MC

Animal cloning involves inserting the nucleus from a somatic cell of one animal into the

  1. plasmid of a bacterium.
  2. uterus of a surrogate animal.
  3. fertilised egg from another animal.
  4. enucleated egg from another animal.
Show Answers Only

`D`

Show Worked Solution

The nucleus must be discarded from a donor egg so that the somatic cell’s nucleus can be inserted.

`=>D`

ENGINEERING, CS 2021 HSC 25b

A truss is fixed to a wall at `A` and `B` as shown. Ignore the mass of the truss.
 


 

  1. Determine the horizontal reaction at `A`.   (2 marks)
  1. Determine, using method of joints, the internal reaction in member `AC`. Indicate the nature of the force in the member.   (3 marks)
  1. Determine, using method of sections, the internal reaction in member `CE`. Indicate the nature of the force.   (3 marks)
Show Answers Only

i.    `3.75\ text{kN ←}`

ii.    `AC=4802\ text{N}`

iii.   `CE = 3\ text{kN (tension)}`

Show Worked Solution

i.   Horizontal reaction at `A`

\(\circlearrowright \Sigma \text{M}_\text{B}\) \(= 0\)  
`0` `= -(A_H xx 4\ text{m}) + (1500\ text{N} xx  10\ text{m})`  
`A_H` `= 3750\ text{N}`  
  `= 3.75\ text{kN ←}`  

 

ii.   Method of joints at A
 
     

→Σ`F_H` `=0`  
`0` `= -3750+AC xx sin(51.34°)`  
`AC` `=3750/sin(51.34°)`  
  `=4802\ text{N}`  

♦♦ Mean mark (ii) 41%.

iii.  Method of Sections

\(\circlearrowright \Sigma \text{M}_\text{B}\) \(=0\)  
`0` `= (1500 xx 10)-(CE xx 5)`  
`CE` `=(15\ 000)/5`  
  `=3000\ text{N}`  
  `=3\ text{kN (tension)}`  

♦♦♦ Mean mark (iii) 30%.

BIOLOGY, M6 2020 HSC 29

Explain how TWO processes that affect the gene pool of populations can lead to evolution.   (5 marks)

Show Answers Only

→ A gene pool is the total genetic diversity of a population. It includes various genotypes and phenotypes which are a result of variability within offspring, the individual and the population. This process as a whole can be referred to as evolution.

 
Gene Flow

→ The movement of alleles in or out of a population, usually as a result of migration.

→ For example, immigration of an animal into a population as a result of environmental pressures or predators can result in the introduction of that animal’s unique phenotype into the gene pool of the population.

 
Genetic Drift

→ The change in allele frequency as a result of a random event.

→ For example, an earthquake or other natural disaster eliminates organisms regardless of their genotype. The remaining individuals will then carry a small sample of the alleles present in the original population, some which might be eliminated.

 
Other answers could include

→ Mutation

→ Natural Selection

→ Sexual reproduction

Show Worked Solution

→ A gene pool is the total genetic diversity of a population. It includes various genotypes and phenotypes which are a result of variability within offspring, the individual and the population. This process as a whole can be referred to as evolution.

 
Gene Flow

→ The movement of alleles in or out of a population, usually as a result of migration.

→ For example, immigration of an animal into a population as a result of environmental pressures or predators can result in the introduction of that animal’s unique phenotype into the gene pool of the population.

 
Genetic Drift

→ The change in allele frequency as a result of a random event.

→ For example, an earthquake or other natural disaster eliminates organisms regardless of their genotype. The remaining individuals will then carry a small sample of the alleles present in the original population, some which might be eliminated.

 
Other answers could include

→ Mutation

→ Natural Selection

→ Sexual reproduction


Mean mark 53%.

BIOLOGY, M8 2020 HSC 27

Exposure to arsenic in drinking water has been associated with the onset of many diseases. The World Health Organisation recommends arsenic levels in drinking water should be below 10 `mu`g L-1 .

An epidemiological study involving 58 406 young adults was conducted over an 11-year period in one country to investigate young-adult mortality due to chronic exposure to arsenic in local drinking water. Each individual's average exposure and cumulative exposure to arsenic over the time of the study were calculated. Age, sex, education and socioeconomic status were taken into account during the analysis of the results.

The graphs show survival rates for males and females over the 11-year period associated with different average levels of exposure to arsenic in drinking water.
 

  1. Identify TWO features of the method used that contributed to the validity of this study.   (2 marks)

  2. The hypothesis put forward was that exposure to arsenic in drinking water increases mortality in young adults.
  3. Discuss the data presented in the graphs in relation to this hypothesis.   (4 marks)

Show Answers Only

a.   Successful answers should include two of the following:

→ The identification of the age and sex of participants

→  Socioeconomic status 

→  Arsenic exposure

→  Large sample size

→  The length of the study period
 

b.   Consider the less than 90 `mu`g L-1 group:

→  The survival rate for both males and females was highest in this “control” group. This is despite the group being exposed to more arsenic than recommended by WHO.

→  In both males and females, increased exposure to arsenic led to lower survival rates.

→  This gradual survival decrease is best seen in males.

→  In females, all doses over 90 `mu`g L-1 lead to similar survival decrease, suggesting other factors, such as a gene or diet, are interacting with the dosage of arsenic.

→ Over the 11 year period, survival progressively declined, supporting the hypothesis.

→  It is important to note, however, that despite the large sample size and time period the study was conducted, survival only dropped by 0.1%.

Show Worked Solution

a.   Successful answers should include two of the following:

→ The identification of the age and sex of participants

→  Socioeconomic status 

→  Arsenic exposure

→  Large sample size

→  The length of the study period
 

b.   Consider the less than 90 `mu`g L-1 group:

→  The survival rate for both males and females was highest in this “control” group. This is despite the group being exposed to more arsenic than recommended by WHO.

→  In both males and females, increased exposure to arsenic led to lower survival rates.

→  This gradual survival decrease is best seen in males.

→  In females, all doses over 90 `mu`g L-1 lead to similar survival decrease, suggesting other factors, such as a gene or diet, are interacting with the dosage of arsenic.

→ Over the 11 year period, survival progressively declined, supporting the hypothesis.

→  It is important to note, however, that despite the large sample size and time period the study was conducted, survival only dropped by 0.1%.

ENGINEERING, PPT 2021 HSC 22b

A 0.2 kg metallic baseplate is to be cast.

What are the advantages of pressure die casting over sand casting?   (3 marks)

Show Answers Only

Advantages of pressure die casting over sand casting

→ Pressure die casting results in a smoother finish than sand casting and provides better dimensional accuracy.

→ There is also less potential for flaws and voids when pressure die casting is used.

→ Permanent metal mould allows for more castings and produces a harder surface than sand casting.

Show Worked Solution

Advantages of pressure die casting over sand casting

→ Pressure die casting results in a smoother finish than sand casting and provides better dimensional accuracy.

→ There is also less potential for flaws and voids when pressure die casting is used.

→ Permanent metal mould allows for more castings and produces a harder surface than sand casting.

CHEMISTRY, M6 2020 HSC 34

The effect of concentration on the pH of acrylic acid `(text{C}_2 text{H}_3 text{COOH})` and hydrochloric acid `(text{HCl})` solutions is shown in the graph. Both of these acids are monoprotic.
 

 

Explain the trends in the graph. Include relevant chemical equations in your answer.   (4 marks)

Show Answers Only

\(\ce{HCl(aq) -> H+ (aq) + Cl– (aq)}\)

\(\ce{C2H3COOH(aq) \rightleftharpoons H+ (aq) + C2H3COO– (aq)}\)

→ \(\ce{HCl}\) is a strong acid that fully dissociates in water, resulting in a high concentration of \(\ce{H+}\) ions and a low pH.

→ Acrylic acid, on the other hand, is a weak acid that only partially dissociates in water, resulting in a lower concentration of \(\ce{H+}\) ions and a higher pH.

→ When the concentration of \(\ce{HCl}\) decreases by a factor of 10, its pH increases by 1 due to the decrease in \(\ce{H+}\).

→ However, when the concentration of acrylic acid decreases by a factor of 10, its pH increases by less than 1.

→ This is due to the change in pH causing the equilibrium to shift right, producing more \(\ce{H+}\) ions in response to the dilution, resulting in a smaller change in the concentration of \(\ce{H+}\), and thus smaller change in pH.

→ At very dilute concentrations, the degree of dissociation of acrylic acid approaches 100% and its pH converges closely to that of \(\ce{HCl}\).

Show Worked Solution

\(\ce{HCl(aq) -> H+ (aq) + Cl– (aq)}\)

\(\ce{C2H3COOH(aq) \rightleftharpoons H+ (aq) + C2H3COO– (aq)}\)

→ \(\ce{HCl}\) is a strong acid that fully dissociates in water, resulting in a high concentration of \(\ce{H+}\) ions and a low pH.

→ Acrylic acid, on the other hand, is a weak acid that only partially dissociates in water, resulting in a lower concentration of \(\ce{H+}\) ions and a higher pH.

→ When the concentration of \(\ce{HCl}\) decreases by a factor of 10, its pH increases by 1 due to the decrease in \(\ce{H+}\).

→ However, when the concentration of acrylic acid decreases by a factor of 10, its pH increases by less than 1.

→ This is due to the change in pH causing the equilibrium to shift right, producing more \(\ce{H+}\) ions in response to the dilution, resulting in a smaller change in the concentration of \(\ce{H+}\), and thus smaller change in pH.

→ At very dilute concentrations, the degree of dissociation of acrylic acid approaches 100% and its pH converges closely to that of \(\ce{HCl}\).

CHEMISTRY, M7 2020 HSC 32

The table shows three compounds and their boiling points.
 

An ester does not always have a lower boiling point than both the alcohol and the alkanoic acid from which it is produced.

Using the information in the table, account for this observation.   (4 marks)

Show Answers Only

→ The boiling points of all compounds are a function of the strength of their intermolecular forces.

→ All three compounds are polar and have dispersion forces between molecules and dipole-dipole interactions.

→ Methanol and propanoic acid can also form hydrogen bonds (strongest type of intermolecular force).

→ Methyl propanoate’s larger size gives it stronger dispersion forces than methanol and propanoic acid, but it cannot form hydrogen bonds.

→ Despite having weaker dispersion forces, propanoic acid can form two hydrogen bonds per molecule, which makes up for its weaker dispersion forces and results in stronger overall intermolecular forces than methyl propanoate.

→ Methanol is a polar molecule that can form strong hydrogen bonds due to its hydroxyl group. However, it has the lowest boiling point due to its small molar mass, resulting in weaker dispersion forces.

Show Worked Solution

→ The boiling points of all compounds are a function of the strength of their intermolecular forces.

→ All three compounds are polar and have dispersion forces between molecules and dipole-dipole interactions.

→ Methanol and propanoic acid can also form hydrogen bonds (strongest type of intermolecular force).

→ Methyl propanoate’s larger size gives it stronger dispersion forces than methanol and propanoic acid, but it cannot form hydrogen bonds.

→ Despite having weaker dispersion forces, propanoic acid can form two hydrogen bonds per molecule, which makes up for its weaker dispersion forces and results in stronger overall intermolecular forces than methyl propanoate.

→ Methanol is a polar molecule that can form strong hydrogen bonds due to its hydroxyl group. However, it has the lowest boiling point due to its small molar mass, resulting in weaker dispersion forces.

CHEMISTRY, M8 2020 HSC 30

A chemist discovered a bottle simply labelled \( '\ce{C5H10O2}' \).

To confirm the molecular structure of the contents of the bottle, a sample was submitted for analysis by infrared spectroscopy and \( \ce{^1H} \)  and \( \ce{^13C NMR} \) spectroscopy. The resulting spectra are shown.
 

 

 

 

Draw a structural formula for the unknown compound that is consistent with all of the information provided. Justify your answer with reference to the information provided.   (7 marks)

Show Answers Only

Infrared Spectrum

→ There’s a signal between 1680 – 1750 cm ¯1, indicating the presence of a  \( \ce{C=O} \)  bond (consistent with carbonyl group).

→ No absorption at 3230 − 3550 cm ¯1 indicates the absence of the  \( \ce{O-H} \)   bond (rules out carboxylic acid\( \ce{-COOH} \)).
 

\( \ce{^13C NMR} \):

→ The \( \ce{^13C NMR} \) spectrum has 4 peaks, indicating that there are 4 unique carbon environments in the compound.

→ This is consistent with the proposed structure of the compound.

→ The peak at 170 ppm is characteristic of the carbonyl carbon, and the peak at 70 ppm corresponds to a carbon nucleus adjacent to an oxygen, which confirms the presence of an ester group.
 

The \( \ce{^1H NMR} \) Spectrum:

→ A septet in the \( \ce{^1H NMR} \) spectrum is consistent with the presence of six neighbouring hydrogen atoms on two \( \ce{CH3} \) groups.

→ A doublet in the spectrum is consistent with one neighbouring hydrogen atom.

→ The combination of a septet and a doublet is consistent with the presence of a  \( \ce{-CH(CH3)2} \)  group in the compound.

→ A singlet in the spectrum is consistent with the absence of neighbouring hydrogen atoms, which would be produced by an isolated methyl group.

Show Worked Solution

Infrared Spectrum

→ There’s a signal between 1680 – 1750 cm ¯1, indicating the presence of a  \( \ce{C=O} \)  bond (consistent with carbonyl group).

→ No absorption at 3230 − 3550 cm ¯1 indicates the absence of the  \( \ce{O-H} \)   bond (rules out carboxylic acid\( \ce{-COOH} \)).
 

\( \ce{^13C NMR} \):

→ The \( \ce{^13C NMR} \) spectrum has 4 peaks, indicating that there are 4 unique carbon environments in the compound.

→ This is consistent with the proposed structure of the compound.

→ The peak at 170 ppm is characteristic of the carbonyl carbon, and the peak at 70 ppm corresponds to a carbon nucleus adjacent to an oxygen, which confirms the presence of an ester group.
 

The \( \ce{^1H NMR} \) Spectrum:

→ A septet in the \( \ce{^1H NMR} \) spectrum is consistent with the presence of six neighbouring hydrogen atoms on two \( \ce{CH3} \) groups.

→ A doublet in the spectrum is consistent with one neighbouring hydrogen atom.

→ The combination of a septet and a doublet is consistent with the presence of a  \( \ce{-CH(CH3)2} \)  group in the compound.

→ A singlet in the spectrum is consistent with the absence of neighbouring hydrogen atoms, which would be produced by an isolated methyl group.


Mean mark 55%.

BIOLOGY, M5 2020 HSC 26

One of the genes involved in determining the colour of a species of fish has two alleles: yellow and orange.

The diagram shows a pedigree chart for the inheritance of colour in the fish.
 

  1. Use the pedigree chart to explain why the yellow allele is recessive.   (2 marks)

  2. Explain how a cross between individuals `text{I}` and `text{II}` could be used to determine whether the inheritance of colour in the fish is sex-linked or autosomal.   (4 marks)

Show Answers Only

a.   → Parents are both orange (exhibiting dominant allele).

→ Some offspring are yellow, indicating that the yellow allele is present in the parents but not expressed.

→ Therefore yellow allele must be recessive.

b.   If sex-linked Inheritance:

→ `text{I}` would be `text{X}^text{A}text{Y}` and `text{II}` would be `text{X}^text{a}text{X}^text{a}`.

→  A cross between these individuals will result in all male offspring being yellow (`text{X}^text{a}text{Y}`) and all female offspring being orange (`text{X}^text{A}text{X}^text{a}`), as shown by the punnet square below.

\begin{array} {|l|c|c|}
\hline  & \text{X}^\text{A} & \text{Y} \\
\hline \text{X}^\text{a} & \text{X}^\text{A}\text{X}^\text{a} & \text{X}^\text{a}\text{Y}\\
\hline \text{X}^\text{a} & \text{X}^\text{A}\text{X}^\text{a} & \text{X}^\text{a}\text{Y}\\
\hline \end{array}

Autosomal Inheritance

→  If the inheritance it autosomal, then `text{II}` would have genotype aa and `text{I}` either AA or Aa.

→  A cross between Aa and aa would result in 50% yellow and 50% orange fish, and a cross between AA and aa will result in all orange fish.

→  Both crosses will have orange fish offspring, but sex does not have any influence on inheritance.
 

Therefore, to determine the inheritance:

→  The absence of orange, male fish would be indicative of a sex-linked inheritance style.

→  The appearance of orange, male fish would confirm the inheritance is autosomal.

Show Worked Solution

a.   → Parents are both orange (exhibiting dominant allele).

→ Some offspring are yellow, indicating that the yellow allele is present in the parents but not expressed.

→ Therefore yellow allele must be recessive.
 

b.   If sex-linked Inheritance:

→ `text{I}` would be `text{X}^text{A}text{Y}` and `text{II}` would be `text{X}^text{a}text{X}^text{a}`.

→  A cross between these individuals will result in all male offspring being yellow (`text{X}^text{a}text{Y}`) and all female offspring being orange (`text{X}^text{A}text{X}^text{a}`), as shown by the punnet square below.

\begin{array} {|l|c|c|}
\hline  & \text{X}^\text{A} & \text{Y} \\
\hline \text{X}^\text{a} & \text{X}^\text{A}\text{X}^\text{a} & \text{X}^\text{a}\text{Y}\\
\hline \text{X}^\text{a} & \text{X}^\text{A}\text{X}^\text{a} & \text{X}^\text{a}\text{Y} \\
\hline \end{array}

Autosomal Inheritance

→  If the inheritance it autosomal, then `text{II}` would have genotype aa and `text{I}` either AA or Aa.

→  A cross between Aa and aa would result in 50% yellow and 50% orange fish, and a cross between AA and aa will result in all orange fish.

→  Both crosses will have orange fish offspring, but sex does not have any influence on inheritance.
 

Therefore, to determine the inheritance:

→  The absence of orange, male fish would be indicative of a sex-linked inheritance style.

→  The appearance of orange, male fish would confirm the inheritance is autosomal.


♦♦ Mean mark (b) 36%.

PHYSICS, M6 2018 HSC 22

  1. A drill spins a magnet above a non-magnetic metal disc which is free to rotate.
     
       
     
    Explain the effect of the rotating magnet on the disc.   (3 marks)
  1. The diagram shows a magnet attached to an electric drill so that it can be rotated between two coils connected to a voltmeter.
     
       
     
    The drill starts from rest and gradually speeds up, reaching its full speed after three revolutions.
     
    Sketch a graph showing the induced emf across the coils during the time that it takes the magnet to reach its full speed.   (3 marks)
     
Show Answers Only

a.    → The rotating magnet causes a changing magnetic flux in the metal disc.

→ This induces eddy currents (Faraday’s Law). By Lenz’s Law, these produce a magnetic field which opposes the change in flux by minimising the relative motion between the disc and the magnet.

→ This will have the effect of the disc rotating in the same direction as the magnet.
 

b.   

         

Show Worked Solution

a.    → The rotating magnet causes a changing magnetic flux in the metal disc.

→ This induces eddy currents (Faraday’s Law). By Lenz’s Law, these produce a magnetic field which opposes the change in flux by minimising the relative motion between the disc and the magnet.

→ This will have the effect of the disc rotating in the same direction as the magnet.
 

b.   

         


♦ Mean mark (b) 50%.

PHYSICS, M7 2018 HSC 15 MC

The diagram shows a simplified model of the Michelson-Morley experiment. It can be assumed that distances `L_1` and `L_2` are equal without affecting the outcome.
 


 

The times taken for the light to travel in both directions along the lengths `L_1` and `L_2` are `t_1` and `t_2` respectively.

What was Michelson attempting to demonstrate in this experiment?

  1. The relativistic contraction of `L_1` would cause `t_1` to be less than `t_2`.
  2. The ether is carried through space with Earth, which would cause `t_1` to be equal to `t_2`.
  3. The times `t_1` and `t_2` would be the same because the velocity of the apparatus was much less than the speed of light.
  4. The motion of the apparatus resulting from Earth's orbital motion around the sun would cause `t_1` to be greater than `t_2`.
Show Answers Only

`D`

Show Worked Solution

→ Michelson was attempting to show that due to the relative motion of Earth through the aether, there would be a difference in travel times for lengths parallel and perpendicular to the direction of Earth’s travel.

`=>D`

PHYSICS, M5 2018 HSC 11 MC

During the launch of a space vehicle from Earth, an astronaut feels an increased downward `g` force.

In which of the following situations would a person also feel an increased downward `g` force?
 

 

Show Answers Only

`D`

Show Worked Solution

→ A feeling of increased downwards `g` force is a result of upwards acceleration.

→ Options A, B and C all involve zero or downwards acceleration.

`=>D`

PHYSICS, M7 2018 HSC 9 MC

A hypothetical journey to a distant star might be accomplished in an astronaut's life span by travelling at relativistic speeds.

What is the key concept which underpins such a hypothetical journey?

  1. From the frame of reference of the spacecraft making the journey, the distance to the star is less.
  2. Clocks on the spacecraft run slower and hence the rate at which fuel is used for the journey is decreased.
  3. Relativistic effects on the spacecraft reduce its mass, making it possible to accelerate to the speeds needed for such a journey.
  4. The relativistic increase in the mass of the fuel on board makes it possible to complete a longer journey with less fuel.
Show Answers Only

`A`

Show Worked Solution

→ Due to the relativistic effect of length contraction, the distance required to travel will decrease.

→ This reduces the travel time.

`=>A`

PHYSICS, M5 2018 HSC 3 MC

The graph shows the altitude of the International Space Station (ISS) during 2017.
 

The altitude can only be boosted by supply craft visiting the ISS.

Why does the altitude decrease in the times between height boosts?

  1. Momentum of the ISS is being transferred to air molecules.
  2. The moon's gravity changes the net force on the ISS as it orbits Earth.
  3. The decrease in altitude makes it possible for a supply craft to reach the ISS.
  4. The total mass of the ISS changes with the deliveries from each supply craft.
Show Answers Only

`A`

Show Worked Solution

→ Collisions between the ISS and air molecules cause the momentum of the ISS to be transferred to air molecules.

→ This causes the velocity of the ISS to decrease. Using the formula

`v=sqrt((GM)/(r))\ \ =>\ \   r=(GM)/(v^2).`

→ Therefore, the orbital radius (altitude) of the ISS decreases.

`=>A`

CHEMISTRY, M5 2020 HSC 26

Nitric oxide gas (`text{NO}`) can be produced from the direct combination of nitrogen gas and oxygen gas in a reversible reaction.

  1. Write the balanced chemical equation for this reaction.   (1 mark)


  2. The energy profile diagram for this reaction is shown. 
     

   

  1. Explain, using collision theory, how an increase in temperature would affect the value of `K_{eq}` for this system. Refer to the diagram in your answer.  (4 marks)

Show Answers Only

a.   \(\ce{N2(g) + O2(g) \rightleftharpoons 2NO(g) }\)
 

b.    → From the graph, the forward reaction is endothermic.

→ The activation energy of the forward endothermic reaction is greater than the activation energy of the reverse exothermic reaction.

→ An increase in temperature would cause the rates of both the forward and reverse reaction due to the higher average kinetic energy, resulting in a larger likelihood of a successful collisions.

→ However, the rate of the forward reaction would increase to a higher extent than the reverse reaction, since it is an endothermic reaction.

→ Using  `K_(eq) = ([text{NO}]^2)/([text{N}_2][text{O}_2])`, as the equilibrium shifts right, the equilibrium constant would increase.

Show Worked Solution

a.   \(\ce{N2(g) + O2(g) \rightleftharpoons 2NO(g) }\)
 

b.    → From the graph, the forward reaction is endothermic.

→ The activation energy of the forward endothermic reaction is greater than the activation energy of the reverse exothermic reaction.

→ An increase in temperature would cause the rates of both the forward and reverse reaction due to the higher average kinetic energy, resulting in a larger likelihood of a successful collisions.

→ However, the rate of the forward reaction would increase to a higher extent than the reverse reaction, since it is an endothermic reaction.

→ Using  `K_(eq) = ([text{NO}]^2)/([text{N}_2][text{O}_2])`, as the equilibrium shifts right, the equilibrium constant would increase.

PHYSICS, M5 2018 HSC 1 MC

A satellite orbits Earth as shown.

Which diagram correctly shows the direction of the satellite's acceleration?
 

 

Show Answers Only

`A`

Show Worked Solution

The direction of acceleration is the same as the direction of force acting on the satellite, which is towards the centre of mass of the Earth.

`=> A`


Mean mark 64%.
COMMENT: A surprising one third of students answered incorrectly.

ENGINEERING, PPT 2021 HSC 27

In engineering practice, freehand sketching, technical drawing and computer aided drawing are used.

Explain the use of each of these drawing methods in engineering practice. Support your answer with relevant examples.   (8 marks)

Show Answers Only

Freehand Sketching:

  • Quick, simple transfer of information
  • Conveys complex ideas visually without complex equipment
  • Only requires paper and pencil
  • Used onsite to resolve issues/explain ideas
  • Examples include concept sketches, illustrating modifications to a design

Technical Drawing:

  • Ensures projects are built to exact standards
  • Technical drawing standards ensure clear communication and no misunderstandings
  • Unambiguous graphical communication can transcend language barriers
  • Gives specific lengths, sizes and tolerances
  • Used for production of formal technical drawings for manufacturers

CAD:

  • Quickly creates technical drawings
  • Allows for quick collaboration and remote access
  • Fast electronic communication of ideas
  • Allows for more detail than technical drawings
  • Can produce 3D models
  • Can perform structural analysis
  • Can quickly create complex shapes
  • Linked to database of material costs to determine cost of project
  • Can be used along with CAM/CNC/3D printing to create prototypes and models
  • Examples include 3D drawing and detailed technical drawing of complex parts
Show Worked Solution

Freehand Sketching:

  • Quick, simple transfer of information
  • Conveys complex ideas visually without complex equipment
  • Only requires paper and pencil
  • Used onsite to resolve issues/explain ideas
  • Examples include concept sketches, illustrating modifications to a design

Technical Drawing:

  • Ensures projects are built to exact standards
  • Technical drawing standards ensure clear communication and no misunderstandings
  • Unambiguous graphical communication can transcend language barriers
  • Gives specific lengths, sizes and tolerances
  • Used for production of formal technical drawings for manufacturers

CAD:

  • Quickly creates technical drawings
  • Allows for quick collaboration and remote access
  • Fast electronic communication of ideas
  • Allows for more detail than technical drawings
  • Can produce 3D models
  • Can perform structural analysis
  • Can quickly create complex shapes
  • Linked to database of material costs to determine cost of project
  • Can be used along with CAM/CNC/3D printing to create prototypes and models
  • Examples include 3D drawing and detailed technical drawing of complex parts

ENGINEERING, PPT 2021 HSC 26b

The diagram shows a box which is at rest on an inclined ramp. The length of the ramp is 3 m and one end is raised `h` metres off the ground.
 


 

The coefficient of friction between the ramp and the box is 0.5.

To what height `(h)` must the ramp be raised for the box to just begin to slide?   (3 marks)

Show Answers Only

`1.34\ text{m}`

Show Worked Solution
`mu` `= 0.5 = tan\ theta`  
`theta`  `= tan^(-1)(0.5)`  
   `=  26.57°`  

 

`sin(26.57°)`  `= h/3`  
`:.h` ` = 3 xx sin(26.57°)`  
  ` = 1.34\ text{m}`  

ENGINEERING, PPT 2021 HSC 25a

Control technologies are used in modern vehicles.

Outline the basic principle behind the operation of ONE of these technologies.   (2 marks)

Show Answers Only

Successful answers should describe the basic principle and one of the following:

Basic principle:

→ Control technologies involve a signal input from the car/driver to a processor which provides an output or action to be taken.
 

Technology examples:

→ Cameras monitoring the position of a car in the lane. If the car exits the lane, the processor detects this and outputs an alarm to the driver.

→ Semi-autonomous driving. The car can activate brakes without driver intervention if a collision/obstacle is detected.

→ Cruise control. A speed is given as an input and a fuel rate is given to the engine to maintain this speed.

→ PID control. Like cruise control, this uses input from LIDAR sensors and cameras to detect obstacles and other cars, to slow down if necessary.

Show Worked Solution

Successful answers should describe the basic principle and one of the following:

Basic principle:

→ Control technologies involve a signal input from the car/driver to a processor which provides an output or action to be taken.
 

Technology examples:

→ Cameras monitoring the position of a car in the lane. If the car exits the lane, the processor detects this and outputs an alarm to the driver.

→ Semi-autonomous driving. The car can activate brakes without driver intervention if a collision/obstacle is detected.

→ Cruise control. A speed is given as an input and a fuel rate is given to the engine to maintain this speed.

→ PID control. Like cruise control, this uses input from LIDAR sensors and cameras to detect obstacles and other cars, and to slow down if necessary.

ENGINEERING, TE 2021 HSC 24b

Outline how voltage can be tested in a circuit.   (2 marks)

Show Answers Only

Successful answers should cover one of the following testing methods:

Voltmeter

→ A voltmeter is placed across 2 points in a circuit in parallel, and measures the potential difference/voltage between these points.

→ The voltmeter does not interfere with the current in the circuit, as its high resistance draws minimal current.
  

Multimeter

→ The probes of a multimeter can be used to measure voltage by testing the potential difference between 2 points, as with a voltmeter.
  

Oscilloscope

→ Use its probes to measure voltage.

→ Give additional information regarding current and wavelength.

→ Visually represent this data in graphical form.

Show Worked Solution

Successful answers should cover one of the following testing methods:

Voltmeter

→ A voltmeter is placed across 2 points in a circuit in parallel, and measures the potential difference/voltage between these points.

→ The voltmeter does not interfere with the current in the circuit, as its high resistance draws minimal current.
  

Multimeter

→ The probes of a multimeter can be used to measure voltage by testing the potential difference between 2 points, as with a voltmeter.
  

Oscilloscope

→ Use its probes to measure voltage.

→ Give additional information regarding current and wavelength.

→ Visually represent this data in graphical form.


Mean mark 53%.
COMMENT: A surprisingly low result here warrants attention.

ENGINEERING, TE 2021 HSC 24a

A telecommunications engineer is designing a Wi-Fi network that will use either a 2.4 GHz or 5 GHz signal in a client's local area network.

How do the 2.4 GHz and 5 GHz signals differ in performance?   (2 marks)

Show Answers Only

→ 2.4 and 5 GHz signals differ in bandwidth, data transfer rate and attenuation (loss of signal strength).

→ A 2.4 GHz signal carries less data per second but suffers from less attenuation than a 5GHz signal.

→ 2.4GHz signals can also be transmitted through more/thicker obstacles.

Show Worked Solution

→ 2.4 and 5 GHz signals differ in bandwidth, data transfer rate and attenuation (loss of signal strength).

→ A 2.4 GHz signal carries less data per second but suffers from less attenuation than a 5GHz signal.

→ 2.4GHz signals can also be transmitted through more/thicker obstacles.

CHEMISTRY, M7 2020 HSC 24

Biodiesel, an alternative fuel to diesel, may be produced from vegetable oil. The chemical reaction which converts oils from biomass into biodiesel is shown. `text{R}_1`, `text{R}_2` and `text{R}_3` are alkyl chains which may vary from 10 to 22 carbons in length.
  


  

  1. Which functional group is present in both the oil and the biodiesel?   (1 mark)

  2. Explain why biodiesel `(text{C}_14 text{H}_30 text{O}_2)` produces less soot than diesel `(text{C}_18 text{H}_38)` when combusted under the same conditions. Support your answer with balanced chemical equations.   (3 marks)

  3. The energy densities of biodiesel and diesel are 38 MJ kg ¯1 and 43 MJ kg ¯1 respectively. The densities of biodiesel and diesel are 0.90 kg L¯1 and 0.83 kg L¯1 respectively.

    When 60.0 L of diesel is combusted in a typical engine, 2141 MJ of energy is released.

    What volume of biodiesel would be required to produce the same amount of energy?   (2 marks)

  4. Explain TWO advantages and TWO disadvantages of using bioethanol (ethanol produced from biomass) as an alternative to a fossil fuel.    (4 marks)

Show Answers Only

a.   Ester functional group.
 

b.   \( \ce{C14H30O2(l) + 41/2 O2(g) → 14 CO2(g) + 15 H2O(l)}\)

\( \ce{C18H38(l) + 55/2 O2(g) → 18 CO2(g) + 19 H2O(l)}\)

→ Soot is produced when a fuel source undergoes incomplete combustion due to insufficient oxygen.

→ Since biodiesel already contains oxygen atoms within its structure, it would require less oxygen to undergo complete combustion compared to diesel, and is therefore less likely to produce soot.
 

c.   `text{m(biodiesel)} = 2141 / 38 = 56.3\ text{kg}`

`text{V(biodiesel)} = 56.3 / 0.90 = 63\ text{L  (nearest L)}`
 

d.    Advantages of bioethanol (two examples needed only):

→ Bioethanol is sustainable because it is produced from renewable resources, whereas petrol is produced from nonrenewable crude oil reserves.

→ Additionally, bioethanol is biodegradable whereas petrol isn’t. As a result, bioethanol would pose less of an environmental threat in comparison to petrol.

→ Ethanol produces less airborne particulates that are associated with lung cancer.
 

Disadvantages of bioethanol (two examples needed only):

→ Bioethanol requires a large amount of arable land in order to grow crops to produce bioethanol. Thus, it would lead to soil erosion and environmental pollution.

→ More energy is also required to produce bioethanol because of the requirement for labour, fertilisation, and distillation of ethanol from fermentation.

→ If fossil fuels are used as the energy source within the manufacturing process of biofuel, it will not achieve carbon neutrality and will contribute to global warming.

Show Worked Solution

a.   Ester functional group.
 

b.   \( \ce{C14H30O2(l) + 41/2 O2(g) → 14 CO2(g) + 15 H2O(l)}\)

\( \ce{C18H38(l) + 55/2 O2(g) → 18 CO2(g) + 19 H2O(l)}\)

→ Soot is produced when a fuel source undergoes incomplete combustion due to insufficient oxygen.

→ Since biodiesel already contains oxygen atoms within its structure, it would require less oxygen to undergo complete combustion compared to diesel, and is therefore less likely to produce soot.


♦♦ Mean mark (a) 39%, (b) 49%.

c.   `text{m(biodiesel)} = 2141 / 38 = 56.3\ text{kg}`

`text{V(biodiesel)} = 56.3 / 0.90 = 63\ text{L  (nearest L)}`

d.    Advantages of bioethanol (two examples needed only):

→ Bioethanol is sustainable because it is produced from renewable resources, whereas petrol is produced from nonrenewable crude oil reserves.

→ Additionally, bioethanol is biodegradable whereas petrol isn’t. As a result, bioethanol would pose less of an environmental threat in comparison to petrol.

→ Ethanol produces less airborne particulates that are associated with lung cancer.
 

Disadvantages of bioethanol (two examples needed only):

→ Bioethanol requires a large amount of arable land in order to grow crops to produce bioethanol. Thus, it would lead to soil erosion and environmental pollution.

→ More energy is also required to produce bioethanol because of the requirement for labour, fertilisation, and distillation of ethanol from fermentation.

→ If fossil fuels are used as the energy source within the manufacturing process of biofuel, it will not achieve carbon neutrality and will contribute to global warming.


♦ Mean mark (d) 55%.

CHEMISTRY, M8 2020 HSC 23

The flow chart summarises an industrial process for the synthesis of ethane-1,2-diol.
 


 

Explain THREE factors that may have been considered in the design of this industrial process. Make specific reference to the flow chart.   (4 marks)

Show Answers Only

→ A catalyst is utilised in reactions 1 and 2 to increase the rate of reaction by lowering the activation energy.

→ Additionally, moderate temperatures are utilised to increase the average kinetic energy of the molecules, increasing the likelihood of successful collisions.

→ These factors reduce energy consumption and make the process more economically viable.

→ Separators were used to separate and recycle the unused reactant gases. Ensuring that the resources were not wasted, again increases the efficiency and economic sustainability of the design.

→ The availability of reagents should be taken into account by locating the process close to a pretrochemical or industrial plant, where ethylene and oxygen gases are readily available.
 

Other possible answers:

→ It is critical that the market for the major end product, ethane-1,2-diol, is assessed beforehand. This would involve researching demand for the product, expected market price, and the associated methods and costs of transport of the product to the end customers.

→ The usage and demand for the by-products of this process is another key factor that addresses the wastage and economics of production.

Show Worked Solution

→ A catalyst is utilised in reactions 1 and 2 to increase the rate of reaction by lowering the activation energy.

→ Additionally, moderate temperatures are utilised to increase the average kinetic energy of the molecules, increasing the likelihood of successful collisions.

→ These factors reduce energy consumption and make the process more economically viable.

→ Separators were used to separate and recycle the unused reactant gases. Ensuring that the resources were not wasted again increases the efficiency and economic sustainability of the design.

→ The availability of reagents should be taken into account by locating the process close to a pretrochemical or industrial plant, where ethylene and oxygen gases are readily available.
 

Other possible answers:

→ It is critical that the market for the major end product, ethane-1,2-diol, is assessed beforehand. This would involve researching demand for the product, expected market price, and the associated methods and costs of transport of the product to the end customers.

→ The usage and demand for the by-products of this process is another key factor that addresses the wastage and economics of production.

CHEMISTRY, M8 2020 HSC 22

A 0.1 mol L ¯1 solution of an unknown salt is to be analysed. The cation is one of magnesium, calcium or barium. The anion is one of chloride, acetate or hydroxide.

Outline a sequence of tests that could be performed in a school laboratory to confirm the identity of this salt solution. Include expected observations and a balanced chemical equation in your answer.   (5 marks)

Show Answers Only

Cation:

→ The cation can be identified via a flame test. 

→ A pale green flame indicates barium, a brick red flame indicates calcium, and no flame colour observed indicates magnesium.
 

Anion:

→ To identify anion, add copper nitrate.

→ If a precipitate forms, it indicates the presence of hydroxide ions.

→ Next, add silver nitrate. If a white precipitate forms, this indicates chloride ions present. If no precipiate forms, it indicates acetate ions present.

\( \ce{Ag+(aq) + Cl-(aq) -> AgCl(s)} \)
 

Other answers

→ Identify anion by testing pH with universal indicator.

→ Interpret result: Neutral (`text{Cl}^-` present), slightly basic (`text{CH}_3text{COO}^-` present), very basic (`text{OH}^-` present).

Show Worked Solution

Cation:

→ The cation can be identified via a flame test. 

→ A pale green flame indicates barium, a brick red flame indicates calcium, and no flame colour observed indicates magnesium.
 

Anion:

→ To identify anion, add copper nitrate.

→ If a precipitate forms, it indicates the presence of hydroxide ions.

→ Next, add silver nitrate. If a white precipitate forms, this indicates chloride ions present. If no precipiate forms, it indicates acetate ions present.

\( \ce{Ag+(aq) + Cl-(aq) -> AgCl(s)} \)
 

Other answers

→ Identify anion by testing pH with universal indicator.

→ Interpret result: Neutral (`text{Cl}^-` present), slightly basic (`text{CH}_3text{COO}^-` present), very basic (`text{OH}^-` present).


♦ Mean mark 49%.

CHEMISTRY, M8 2020 HSC 21

The mass spectrum of an alkane is shown.
 

Use the information provided to identify the alkane and justify your choice.   (2 marks)

Show Answers Only

→ The alkane is propane.

→ The mass spectrum has a molecular ion peak of 44, which indicates that the alkane is \( \ce{C3H8} \) (propane).

Show Worked Solution

→ The alkane is propane.

→ The mass spectrum has a molecular ion peak of 44, which indicates that the alkane is \( \ce{C3H8} \) (propane).

BIOLOGY, M5 2020 HSC 25

Students tested the hypothesis that the number of eggs/young produced was greater in animals using external fertilisation than those using internal fertilisation. They obtained the following data from secondary sources.
 

  1. What conclusion can be drawn from the data? Justify your answer.   (3 marks)

  2. Justify an improvement to the students' experimental design to test the same hypothesis.   (2 marks)

  3. Explain ONE advantage for animals of using external fertilisation.   (2 marks)

Show Answers Only

a.   Conclusion: There is little difference

→ The numbers of eggs laid/young born between different species was similar in both external and internal animals (43, 40).

→ The standard deviation (variability of the data) was significantly high (55, 32).

→ These two factors mean that students may conclude there is little to no difference between the number of young produced and the mode of fertilisation.
 

b.   Potential adjustments to improve design

→ Students have selected only twelve species to use in their investigation, which has led to similar results in both internal and external fertilisation.

→ A much larger number of species should be included in a follow up investigation to increase the likelihood of yielding more accurate results.
 

c.   Successful answers should include one of the following:

→ External fertilisation will expend less energy on gestation, as it occurs outside the body.

→ The large number of young produced in external fertilisation will ensure continuity of the species with minimal parental guidance.

Show Worked Solution

a.   Conclusion: There is little difference

→ The numbers of eggs laid/young born between different species was similar in both external and internal animals (43, 40).

→ The standard deviation (variability of the data) was significantly high (55, 32).

→ These two factors mean that students may conclude there is little to no difference between the number of young produced and the mode of fertilisation.


Mean mark (a) 51%.

b.   Potential adjustments to improve design

→ Students have selected only twelve species to use in their investigation, which has led to similar results in both internal and external fertilisation.

→ A much larger number of species should be included in a follow up investigation to increase the likelihood of yielding more accurate results.


♦♦ Mean mark (b) 38%.

c.   Successful answers should include one of the following:

→ External fertilisation will expend less energy on gestation, as it occurs outside the body.

→ The large number of young produced in external fertilisation will ensure continuity of the species with minimal parental guidance.

BIOLOGY, M6 2020 HSC 23

The following diagram shows a mutation.
 

  1. What type of mutation is shown in the diagram?   (1 mark)

  2. Outline another type of mutation.   (2 marks)

Show Answers Only

a.   Point mutation (substitution of adenosine to thymine, base number 8).

b.   Chromosomal mutation:

This occurs when there is a change in the number or structure of chromosomes within an individual’s genome.

Show Worked Solution

a.   Point mutation (substitution of adenosine to thymine, base number 8).

b.   Chromosomal mutation:

This occurs when there is a change in the number or structure of chromosomes within an individual’s genome.


♦ Mean mark (b) 46%.

BIOLOGY, M7 2020 HSC 22

Outline a benefit and a limitation of using pharmaceuticals such as antibiotics to treat infectious disease.   (3 marks)

Show Answers Only

→ Antibiotics can be used to treat bacterial infections as they inhibit bacterial growth.

→ Excessive, but at times necessary use can lead to antibiotic resistance amongst bacterial strains, reducing antibiotic effectiveness.
 

Other benefits can include:

→ Antibiotics are quick to administer and readily available.

→ Their usage can often lead to a rapid recovery of patients.

Show Worked Solution

→ Antibiotics can be used to treat bacterial infections as they inhibit bacterial growth.

→ Excessive, but at times necessary use can lead to antibiotic resistance amongst bacterial strains, reducing antibiotic effectiveness.
 

Other benefits can include:

→ Antibiotics are quick to administer and readily available.

→ Their usage can often lead to a rapid recovery of patients.


Mean mark 53%.
COMMENT: A surprisingly low mean mark that warrants attention.

BIOLOGY, M7 2020 HSC 21

Cholera is an acute diarrhoeal infection caused by the bacterium Vibrio cholerae. Humans are infected when they consume food or water that is contaminated with the bacterium.

Outline THREE strategies that could prevent the spread of cholera.   (3 marks)

Show Answers Only

Successful answers should include three of the following:

→ Washing yours hands with soapy water after going to the toilet removes bacteria from skin.

→ The filtration and purification of drinking water will help kill and remove bacteria.

→ Proper disposal of sewerage would stop exposure to bacteria present.

→ Thoroughly cooking food, such as vegetables, to eliminate bacteria residing within.

→ Public health campaigns to encourage proper hygiene, cooking, purifying your own water while camping will improve sanitation and safety around bacterial exposure for individuals.

Show Worked Solution

Successful answers should include three of the following:

→ Washing yours hands with soapy water after going to the toilet removes bacteria from skin.

→ The filtration and purification of drinking water will help kill and remove bacteria.

→ Proper disposal of sewerage would stop exposure to bacteria present.

→ Thoroughly cooking food, such as vegetables, to eliminate bacteria residing within.

→ Public health campaigns to encourage proper hygiene, cooking, purifying your own water while camping will improve sanitation and safety around bacterial exposure for individuals.

CHEMISTRY, M6 2020 HSC 14 MC

The equation for the autoionisation of water is shown.

\( \ce{2H2O(l)  \rightleftharpoons  \ H3O+(aq) + OH-(aq)} \)

At 50°C the water ionisation constant, `K_(w)`, is  `5.5 xx10^(-14)`.

What is the pH of water at 50°C?

  1.  5.50
  2.  6.63
  3.  6.93
  4.  7.00
Show Answers Only

`B`

Show Worked Solution

\(\ce{$K_w$ = [H3O+][OH–]}\)

Since \(\ce{[H3O+] = [OH–]}\):

`[text{H}_3 text{O}^+]^2` `=5.5 xx 10^(−14)`  
`[text{H}_3 text{O}^+]` `= 2.3 xx 10^(−7}\  text{mol L}^(–1)`  

 
`text{pH = −log}_(10) (2.3 xx 10^(−7) ) = 6.63`

`=> B`

Statistics, STD1 S1 2022 HSC 13

Kim wants to investigate what students think about the food that is sold at the school's canteen. Kim decides to use a survey to interview a sample group of students to find out their opinions on a number of different issues.

  1. As part of the survey, Kim is thinking about using one of the options listed below.
     

     
    Name ONE advantage for each option.  (2 marks)

  2. After collecting data, Kim drew the following graph to summarise the opinions related to the price of the food.
     
             
     
    What TWO features of the graph make it misleading?  (2 marks)

Show Answers Only

a.   Advantages

Option A → This option would be very easy to collate as there are only 2 choices.

Option B → This option gives a more detailed idea of the students’ thoughts about the food as they can grade their choice from 1 – 10.

 

b.   Misleading features:

→ The scale on the vertical axis is not equal. This makes the “Too Expensive” column (at 50) appear to have more than twice the number of responses as “Okay Prices” (~30) and “Cheap Prices” (~30) which is incorrect.

→ The varying column widths are also misleading as the wider column could be interpreted as being having more weight than the other 2.

Show Worked Solution

a.   Advantages

Option A → This option would be very easy to collate as there are only 2 choices.

Option B → This option gives a more detailed idea of the students’ thoughts about the food as they can grade their choice from 1 – 10.
 

b.   Misleading features:

→ The scale on the vertical axis is not equal. This makes the “Too Expensive” column (at 50) appear to have more than twice the number of responses as “Okay Prices” (~30) and “Cheap Prices” (~30) which is incorrect.

→ The varying column widths are also misleading as the wider column could be interpreted as being having more weight than the other 2.


♦♦ Mean mark 32%.

CHEMISTRY, M7 2020 HSC 12 MC

The structure of part of a polymer chain is shown.
 


 

Which statement best explains why plastics made from this polymer require a temperature of approximately 250°C before they begin to soften?

  1. The carbon–carbon bonds in the polymer chains are strong.
  2. The carbon–hydrogen bonds in the polymer chains are strong.
  3. Extensive dipole–dipole and dispersion forces exist between the polymer chains.
  4. Extensive hydrogen bonds and dispersion forces exist between the polymer chains.
Show Answers Only

`C`

Show Worked Solution

→ The polymer diagram shows the following intermolecular forces: dipole-dipole forces and dispersion forces.

→ High temperatures break some of the intermolecular forces, causing the plastic to soften (polyesters can’t form `text{H}`-bonds).

`=> C`

CHEMISTRY, M5 2020 HSC 11 MC

Equal volumes of two 0.04 mol L ¯1 solutions were mixed together.

Which pair of solutions would give the greatest mass of precipitate?

  1. `text{Ba(OH)}_(2) \ text{and} \ text{MgCl}_(2)`
  2. `text{Ba(OH)}_(2) \ text{and} \ text{MgSO}_(4)`
  3. `text{Ba(OH)}_(2) \ text{and} \ text{NaCl}`
  4. `text{Ba(OH)}_(2) \ text{and} \ text{Na}_(2) text{SO}_(4)`
Show Answers Only

`B`

Show Worked Solution

\(\ce{Ba(OH)2(aq) + MgSO4(aq) → BaSO4(s) + Mg(OH)2(s)}\)

→ Reaction B produces 2 molecules of precipitate

→ Reactions A and D produce 1 molecule of precipitate each

→ Reaction C does not produce a precipitate.

`=> B`

CHEMISTRY, M8 2020 HSC 5 MC

A \( \ce{^13C NMR} \) spectrum is shown.
 


 

Which compound gives rise to this spectrum?

  1. chloroethane
  2. 1-chloropropane
  3. 1, 2-dichloroethane
  4. 1, 2-dichloropropane
Show Answers Only

`A`

Show Worked Solution

→ The \( \ce{^13C NMR} \) spectrum shows two signals, indicating 2 unique carbon environments.

→ Chloroethane is the only compound with 2 unique carbon environments.

`=> A`

CHEMISTRY, M8 2020 HSC 4 MC

Which pair of compounds would be difficult to distinguish using infrared spectroscopy?

  1. Butane and propane
  2. Ethane and propan-1-ol
  3. Propanol and propanoic acid
  4. Methanamine and propanone
Show Answers Only

`A`

Show Worked Solution

→ Infrared spectroscopy is able to identify the functional groups present.

→ Butane and propane are similar in bonds and functional groups, and thus have similar infrared sprectra. The other pairs of compounds have different functional groups.

`=> A`

CHEMISTRY, M8 2022 HSC 33

Analyse how a student could design a chemical synthesis process to be undertaken in the school laboratory. In your response, use a specific process relating to the synthesis of an organic compound, including a chemical equation, and refer to:

  • selection of reagent(s)
  • reaction conditions
  • any potential hazards and any safety precautions to minimise the risk
  • yield and purity of the product(s).   (8 marks)
Show Answers Only

Selecting reagents

→ The student could synthesise ethyl ethanoate through esterification between acetic acid and ethanol.

→ Both readily available in the school laboratory and are relatively safe.

Acetic acid + ethanol  ⇌  Ethyl ethanoate + water

→ Concentrated sulfuric acid should be used as the acid catalyst as it is a strong acid that is also readily available.
 

Reaction conditions

→ Increasing the temperature of the system increases the reaction rate because it increases the average kinetic energy of the reactant molecules, and thus increases the likelihood of successful collisions, producing more product.

→ Additionally, the addition of reactants would increase the likelihood of successful collisions, thus increasing the reaction rate.

→ The reaction should also be undertaken under reflux allowing vaporised molecules to condense and return back to the reaction vessel, increasing the amount of reactants, and thus increasing the rate of reaction. 

→ Concentrated sulfuric acid should also be utilised as a catalyst in order to speed up the reaction and lower the activation energy.
 

Potential hazards and safety precautions

→ The acetic acid and sulfuric acid used is corrosive and may cause skin and eye burns, therefore, appropriate lab coat and safety glasses should be utilised.

→ The organic reactants are highly flammable and may cause fires. The reaction mixture should be heated on a hot plate or heating mantle instead of a bunsen burner.

→ Refluxing may cause pressure build-up, therefore, ensure the reflux condenser is open.

→ Superheating and bumping may occur in apparatus. Boiling chips should be utilised to provide nucleation sites allowing liquids to boil smoothly.
 

Yield and purity

→ Concentrated sulfuric acid, used as a catalyst, also acts as a dehydrating agent that removes water from the system and improves yield.

→ When the reaction reaches equilibrium, the ester can be separated from the mixture by adding excess sodium carbonate solution in order to neutralise the acid.

→ Transfer to a separation funnel to separate the organic layer (containing the ester) from the aqueous layer.

→ Then use fractional distillation to separate the ester from the organic layer.

Show Worked Solution

Selecting reagents

→ The student could synthesise ethyl ethanoate through esterification between acetic acid and ethanol.

→ Both readily available in the school laboratory and are relatively safe.

Acetic acid + ethanol  ⇌  Ethyl ethanoate + water

→ Concentrated sulfuric acid should be used as the acid catalyst as it is a strong acid that is also readily available.
 

Reaction conditions

→ Increasing the temperature of the system increases the reaction rate because it increases the average kinetic energy of the reactant molecules, and thus increases the likelihood of successful collisions, producing more product.

→ Additionally, the addition of reactants would increase the likelihood of successful collisions, thus increasing the reaction rate.

→ The reaction should also be undertaken under reflux allowing vaporised molecules to condense and return back to the reaction vessel, increasing the amount of reactants, and thus increasing the rate of reaction. 

→ Concentrated sulfuric acid should also be utilised as a catalyst in order to speed up the reaction and lower the activation energy.
 

Potential hazards and safety precautions

→ The acetic acid and sulfuric acid used is corrosive and may cause skin and eye burns, therefore, appropriate lab coat and safety glasses should be utilised.

→ The organic reactants are highly flammable and may cause fires. The reaction mixture should be heated on a hot plate or heating mantle instead of a bunsen burner.

→ Refluxing may cause pressure build-up, therefore, ensure the reflux condenser is open.

→ Superheating and bumping may occur in apparatus. Boiling chips should be utilised to provide nucleation sites allowing liquids to boil smoothly.
 

Yield and purity

→ Concentrated sulfuric acid, used as a catalyst, also acts as a dehydrating agent that removes water from the system and improves yield.

→ When the reaction reaches equilibrium, the ester can be separated from the mixture by adding excess sodium carbonate solution in order to neutralise the acid.

→ Transfer to a separation funnel to separate the organic layer (containing the ester) from the aqueous layer.

→ Then use fractional distillation to separate the ester from the organic layer.


♦♦ Mean mark 52%.

CHEMISTRY, M7 2022 HSC 24

The following graph shows the boiling points of some 1-chloroalkanes.
 

Explain the trend shown in the graph.   (3 marks)

Show Answers Only

→ As the molar masses increase, the boiling point of 1-chloroalkanes increases.

→ This is due to molecules with a larger molar mass containing more electrons. This allows for a higher likelihood of unequal electron distribution, thus, causing stronger dispersion forces.

→ Since more energy is required to break stronger dispersion forces, 1-chloroalkanes with higher molar masses have higher boiling points.

Show Worked Solution

→ As the molar masses increase, the boiling point of 1-chloroalkanes increases.

→ This is due to molecules with a larger molar mass containing more electrons. This allows for a higher likelihood of unequal electron distribution, thus, causing stronger dispersion forces.

→ Since more energy is required to break stronger dispersion forces, 1-chloroalkanes with higher molar masses have higher boiling points.