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CHEMISTRY, M7 2025 HSC 27

Mixtures of hydrocarbons can be obtained from crude oil by the process of fractional distillation. Examples include petrol, diesel and natural gas.

  1. Outline an environmental implication for a use of a named hydrocarbon mixture that is obtained from crude oil.   (2 marks)

  2. Ethene is a simple hydrocarbon obtained from crude oil.
  3. Using structural formulae, write the chemical equation for the conversion of ethene to ethanol, including any other necessary reagents.   (3 marks)

  1. When ethanol is reacted with ethanoic acid, ethyl ethanoate is formed, as shown by the equation.
      1. \(\text{ethanol} \ + \ \text{ethanoic acid } \ \rightleftharpoons \ \text{ethyl ethanoate} \ +\ \text{water}\)
  2. The graph below shows the concentration of ethanol from the start of the reaction, \(t_0\), up to a time \(t_1\).
  3. At time \(t_1\), an additional amount of ethanol is added to the system.
  4. Sketch on the graph the changes that occur in the concentration of ethanol between time \(t_1\), and when the system reaches a new equilibrium before time \(t_2\).   (3 marks)

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a.    Environmental implication:

  • The combustion of petrol, a hydrocarbon mixture obtained from crude oil, leads to the release of large amounts of carbon dioxide.
  • Increased \(\ce{CO2}\) levels intensify the enhanced greenhouse effect, contributing to global warming, climate change, and associated environmental impacts such as rising sea levels and extreme weather patterns.
  • A typical component of petrol, octane, burns according to:
  •    \(\ce{2C8H18(l) + 25O2(g) -> 16CO2(g) + 18H2O(g)}\)

b.    
           

c.    
       

Show Worked Solution

a.    Environmental implication:

  • The combustion of petrol, a hydrocarbon mixture obtained from crude oil, leads to the release of large amounts of carbon dioxide.
  • Increased \(\ce{CO2}\) levels intensify the enhanced greenhouse effect, contributing to global warming, climate change, and associated environmental impacts such as rising sea levels and extreme weather patterns.
  • A typical component of petrol, octane, burns according to:
  •    \(\ce{2C8H18(l) + 25O2(g) -> 16CO2(g) + 18H2O(g)}\)

b.    
           

c.    
       

  • There will be a sudden increase at \(t_1\) and then the concentration of ethanol will decrease smoothly until a new equlibrium concentration (greater than the original equilibrium concentration) is reached.

CHEMISTRY, M7 2025 HSC 24

65.0 g of ethyne gas reacts with an excess of gaseous hydrogen chloride to produce chloroethene.

  1. Draw the full structural formula of ethyne and identify the shape of the molecule.   (2 marks)

\begin{array}{|c|c|}
\hline
\rule{0pt}{2.5ex}\quad \quad \text{Structural formula } \quad \quad \rule[-1ex]{0pt}{0pt}& \quad \quad\text{ Shape of molecule } \quad \quad\\
\hline
\rule{0pt}{2.5ex}\rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\rule[-1ex]{0pt}{0pt}& \\
\hline
\end{array}

  1. The molar masses of the compounds in the reaction are provided.

\begin{array}{|l|c|}
\hline \rule{0pt}{2.5ex}\text{Compound} \rule[-1ex]{0pt}{0pt}& \text{ Molar mass } \\
\hline \rule{0pt}{2.5ex}\text{Ethyne} \rule[-1ex]{0pt}{0pt}& 26.04 \\
\hline \rule{0pt}{2.5ex}\text{Hydrogen chloride} \rule[-1ex]{0pt}{0pt}& 36.46 \\
\hline \rule{0pt}{2.5ex}\text{Chloroethene} \rule[-1ex]{0pt}{0pt}& 62.50 \\
\hline
\end{array}

  1. Calculate the mass of chloroethene produced, using the molar masses provided. Include a relevant chemical equation in your answer.   (3 marks)

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a.    Structural formula:

   

The shape of ethyne is linear.

b.    156 grams

Show Worked Solution

a.    Structural formula:

   

The shape of ethyne is linear.
 

b.    The chemical equation for the reacton occuring is shown below:

\(\ce{C2H2(g) + HCl(g) -> C2H3Cl(g)}\)

  • \(n\ce{(C2H2)} = \dfrac{m}{MM} = \dfrac{65.0}{26.04} = 2.496\ \text{mol}\)
  • As the reactants and products are in a \(1:1:1\) ratio, \(n\ce{(C2H2)}_{\text{reacted}} = n\ce{(C2H3Cl)}_{\text{produced}}\)
  • \(m\ce{(C2H3Cl)} = n \times MM = 2.496 \times 62.50 = 156\ \text{grams (3 sig.fig.)}\)

CHEMISTRY, M7 2025 HSC 15 MC

Consider the following sequence of reactions.

  • Prop-2-en-1-ol was reacted with hydrogen gas to form liquid \(X\).
  • \(X\) was oxidised, producing liquid \(Y\) that formed bubbles of a gas when reacted with aqueous sodium carbonate.
  • \(Y\) was heated under reflux with methanol and a drop of concentrated sulfuric acid, producing an organic liquid, \(Z\).

This process has been presented in the flow chart below.
 

  

Which option correctly identifies the structures for \(X\), \(Y\) and \(Z\)?
 

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\(D\)

Show Worked Solution
  • The first reaction that occurs is a hydrogenation addition reaction in which prop-2-en-1-ol reacts under a Pd catalyst to produce propan-1-ol.
  • The primary alcohol propan-1-ol then undergoes oxidation to produce the carboxylic acid propanoic acid. This is confirmed as when it is reacted with sodium carbonate, it undergoes an acid-carbonate reaction to produce carbon dixoide which is observed through the bubbles.
  • The third reaction is an estification reaction in which propanic acid reacts with methanol under relfex to produce methyl-propanoate.
  • All three of the correctly drawn compounds can be observed in \(D\)

\(\Rightarrow D\)

CHEMISTRY, M8 2025 HSC 8 MC

An alkene \(\text{X}\) with only one \(\text{C} \ = \ \text{C}\) bond undergoes an addition reaction with an unknown substance to produce \(\text{Y}\) .

\(\text{X}\ +\ \text{unknown substance} \rightarrow \text{Y}\)

The following table shows the molecular ion peaks for \(\text{X}\) and \(\text{Y}\).

\begin{array}{|c|c|}
\hline
\rule{0pt}{2.5ex}\text{X} \rule[-1ex]{0pt}{0pt}& \text{Y} \\
\hline
\rule{0pt}{2.5ex} \quad \quad 70 \ \text{m/z} \quad \quad\rule[-1ex]{0pt}{0pt}& \quad \quad 90 \ \text{m/z} \quad \quad \\
\hline
\end{array}

Which of the following can be the unknown substance?

  1. Water
  2. Fluorine
  3. Hydrogen
  4. Hydrogen fluoride
Show Answers Only

\(\Rightarrow D\)

Show Worked Solution
  • The molecule ion peaks for \(\text{X}\) and \(\text{Y}\) correspond to their molecular masses.
  • By the law of conservation of mass, the mass of the unknown substance must be the difference in mass between the substances \(\text{X}\) and \(\text{Y}\).
  • Hence the molecular mass of the unknown substance \(=90-70 = 20\ \text{g mol}^{-1}\).
  • This corresponds to the molecular mass of  \(\ce{HF} = 1.008 + 19.00 = 20.008\ \text{g mol}^{-1}\).

\(\Rightarrow D\)

CHEMISTRY, M7 2024 HSC 35

Unknown samples of three carboxylic acids, labelled \(\text{X , Y}\) and \(\text{Z}\), are analysed to determine their identities.

  • Both \(\text{Y}\) and \(\text{Z}\) react rapidly with bromine in the absence of UV light, but \(\text{X}\) does not. A 0.100 g sample of \(\text{Y}\) reacts with the same amount of bromine as a 0.200 g sample of \(\text{Z}\).
  • Separate 0.100 g samples of \(\text{X , Y}\) and \(\text{Z}\) are titrated with 0.0617 mol L\(^{-1}\) sodium hydroxide solution. The titre volumes are shown.

\(
\begin{array}{|l|c|c|c|}
\hline \textit{Acid } & X & Y & Z \\
\hline \begin{array}{l}
\text {Volume of } \ce{NaOH \text{(mL)}} \\
\end{array} & 21.88 & 22.49 & 22.49 \\
\hline
\end{array}
\)
 

  • Both \(\text{Y}\) and \(\text{Z}\) can undergo hydration reactions in the presence of a suitable catalyst. Two products are possible for the hydration of \(\text{Y}\), but only one product is possible with \(\text{Z}\).

Identify which structures 1, 2 and 3 in the table are acids \(\text{X , Y}\) and \(\text{Z}\). Justify your answer with reference to the information provided.   (7 marks)

   

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  • Both sample \(\text{Y}\) and \(\text{Z}\) undergo an addition reaction with bromine and a hydration reaction. Therefore these samples must contain a \(\ce{C=C}\) bond.
  • As sample \(\text{X}\), undergoes neither of these reactions, it must have no \(\ce{C=C}\) bond, thus sample \(\text{X}\) is structure \(2\).
  • Both structure \(1\) and structure \(3\) contain 1 \(\ce{C=C}\) each \(\Rightarrow\) they will react in a \(1:1\) with \(\ce{Br2}\). Hence the same number of moles of the carboxylic acid samples will react with the bromine.
  • Since the mass of sample \(\text{Z}\) that reacts with the bromine is double the mass of sample \(\text{Y}\), the molar mass of sample \(\text{Z}\) must be double the molar mass of sample \(\text{Y}\) following the formula \(m = n \times MM\).
  • Therefore, sample \(\text{Y}\) is structure 1 and sample \(\text{Z}\) is structure 3.

Other information provided that could support identification includes:

  • The two products formed for the hydration of \(\text{Y}\) is due to the asymmetry of structure 1 and the single product formed in the hydration of \(\text{Z}\) is due to the symmetrical nature of structure 3.

The titration values are consistent with the proposed samples and their corresponding structures.

  • \(\ce{n(NaOH)}\) reacted with \(\text{X} = 0.0617 \times 0.02188 = 1.35 \times 10^{-3}\ \text{mol}\)
  • \(\text{n}_{\text{X}}= \dfrac{0.100}{74.078}= 0.00135\ \text{mol}\). Therefore \(\text{X}\) reacts in a \(1:1\) molar ratio as it is a monoprotic acid.
  • \(\ce{n(NaOH)}\) reacted with \(\text{Y}\) and \(\text{Z} = 0.0617 \times 0.02249 = 1.39 \times 10^{-3}\ \text{mol}\)
  • \(\text{n}_{\text{Y}}= \dfrac{0.100}{72.062}= 0.00139\ \text{mol}\). Therefore \(\text{Y}\) reacts in a \(1:1\) molar ratio as it is a monoprotic acid.
  • \(\text{n}_{\text{Z}}= \dfrac{0.100}{144.124}= 0.0006938\ \text{mol}\). Therefore \(\text{Z}\) reacts in a \(2:1\) molar ratio with \(\ce{NaOH}\) as it is a diprotic acid.
  • The equal volumes of \(\text{Y}\) and \(\text{Z}\) used in the titration can be attributed to \(\text{Z}\) having twice the molar mass of \(\text{Y}\) and being a diprotic acid.

Show Worked Solution

  • Both sample \(\text{Y}\) and \(\text{Z}\) undergo an addition reaction with bromine and a hydration reaction. Therefore these samples must contain a \(\ce{C=C}\) bond.
  • As sample \(\text{X}\), undergoes neither of these reactions, it must have no \(\ce{C=C}\) bond, thus sample \(\text{X}\) is structure \(2\).
  • Both structure \(1\) and structure \(3\) contain 1 \(\ce{C=C}\) each \(\Rightarrow\) they will react in a \(1:1\) with \(\ce{Br2}\). Hence the same number of moles of the carboxylic acid samples will react with the bromine.
  • Since the mass of sample \(\text{Z}\) that reacts with the bromine is double the mass of sample \(\text{Y}\), the molar mass of sample \(\text{Z}\) must be double the molar mass of sample \(\text{Y}\) following the formula \(m = n \times MM\).
  • Therefore, sample \(\text{Y}\) is structure 1 and sample \(\text{Z}\) is structure 3.

Other information provided that could support identification includes:

  • The two products formed for the hydration of \(\text{Y}\) is due to the asymmetry of structure 1 and the single product formed in the hydration of \(\text{Z}\) is due to the symmetrical nature of structure 3.

The titration values are consistent with the proposed samples and their corresponding structures.

  • \(\ce{n(NaOH)}\) reacted with \(\text{X} = 0.0617 \times 0.02188 = 1.35 \times 10^{-3}\ \text{mol}\)
  • \(\text{n}_{\text{X}}= \dfrac{0.100}{74.078}= 0.00135\ \text{mol}\). Therefore \(\text{X}\) reacts in a \(1:1\) molar ratio as it is a monoprotic acid.
  • \(\ce{n(NaOH)}\) reacted with \(\text{Y}\) and \(\text{Z} = 0.0617 \times 0.02249 = 1.39 \times 10^{-3}\ \text{mol}\)
  • \(\text{n}_{\text{Y}}= \dfrac{0.100}{72.062}= 0.00139\ \text{mol}\). Therefore \(\text{Y}\) reacts in a \(1:1\) molar ratio as it is a monoprotic acid.
  • \(\text{n}_{\text{Z}}= \dfrac{0.100}{144.124}= 0.0006938\ \text{mol}\). Therefore \(\text{Z}\) reacts in a \(2:1\) molar ratio with \(\ce{NaOH}\) as it is a diprotic acid.
  • The equal volumes of \(\text{Y}\) and \(\text{Z}\) used in the titration can be attributed to \(\text{Z}\) having twice the molar mass of \(\text{Y}\) and being a diprotic acid.
♦ Mean mark 55%.

CHEMISTRY, M7 2016 HSC 15 MC

The table lists some properties of the straight-chained carbon compounds `W, X, Y` and `Z`.
 

Which row of the following table best identifies the compounds `W, X, Y` and `Z`?
 

\begin{align*} 
\begin{array}{c|c}
\rule{0pt}{2.5ex}\text{          }\rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{A.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{B.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{C.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\rule{0pt}{2.5ex}\text{D.}\ \ \ \ \ \rule[-1ex]{0pt}{0pt} \\
\end{array}
\begin{array}{|c|c|}
\hline
\rule{0pt}{2.5ex}\textit{W}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\textit{X}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\textit{Y}\rule[-1ex]{0pt}{0pt}& \rule{0pt}{2.5ex}\textit{Z}\rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\ \ \ \ce{C3H6}\ \ \ \rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ \ \ \ce{C3H8}\ \ \ \rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{CH3OH}\rule[-1ex]{0pt}{0pt}& \rule{0pt}{2.5ex}\ce{C4H9OH}\rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\ce{C3H8}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{C3H6}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{CH3OH}\rule[-1ex]{0pt}{0pt}& \rule{0pt}{2.5ex}\ce{C4H9OH}\rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\ce{C3H6}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{C3H8}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{C4H9OH}\rule[-1ex]{0pt}{0pt}& \rule{0pt}{2.5ex}\ce{CH3OH}\rule[-1ex]{0pt}{0pt}\\
\hline
\rule{0pt}{2.5ex}\ce{C3H8}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{C3H6}\rule[-1ex]{0pt}{0pt} & \rule{0pt}{2.5ex}\ce{C4H9OH}\rule[-1ex]{0pt}{0pt}& \rule{0pt}{2.5ex}\ce{CH3OH}\rule[-1ex]{0pt}{0pt}\\
\hline
\end{array}
\end{align*}

Show Answers Only

`A`

Show Worked Solution
  • Compound W is unsaturated (C–C multiple bonds exist).
  • Compound X is saturated (all C–C bonds are single bonds).
  • Shorter alcohols, such as \(\ce{CH3OH}\) are more soluble.

`=>A`

CHEMISTRY, M7 2017 HSC 7 MC

Three test tubes were set up as shown.


 

Bromine water was added to `X` and `Y` in the absence of UV light.

Which of the following best represents the changes in test tubes `X` and `Y` ?
 

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`C`

Show Worked Solution

By Elimination:

  • Liquids are immiscible (eliminate A and D).
  • Bromine water does not decolourise with with alkanes, but does with alkenes (eliminate B).

`=>C`


♦♦ Mean mark 33%.

CHEMISTRY, M8 2021 HSC 21

Four organic liquids are used in an experiment. The four liquids are

    • hexane
    • hex-1-ene
    • propan-1-ol
    • propanoic acid
  1. State ONE safety concern associated with organic liquids and suggest ONE way to address this safety concern.   (2 marks)

  2. The organic liquids are held separately in four flasks but the flasks are not labelled. Tests were conducted to identify these liquids. The outcomes of the tests are summarised below.   (2 marks)
     
           
    Identify the FOUR liquids.
     
           
  3. What chemical test, other than those used in part (b), could be used to confirm the identification of ONE of the liquids? Include the expected observation in your answer.   (2 marks)

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a.    A safety concern is that the organic liquids are flammable.

To address this, keep substance away from open flames and keep away from ignition sources.
 

b.    Flask 1: propanoic acid  (carboxylic acids can’t be oxidised and are polar)

Flask 2: hex-1-ene (alkenes can be oxidised and are non-polar)

Flask 3: propan-1-ol (primary alcohols can be oxidised and are polar)

Flask 4: hexane (alkanes don’t react with acidified oxidants and are non-polar)
 

c.   Hex-1-ene

  • Could be identified using the bromine water test.
  • The addition of brown bromine water to an alkene causes an addition reaction where the solution changes colours from brown to colourless.

Propanoic acid

  • Could be identified through a neutralisation reaction using `text{Na}_2text{CO}_3`.
  • Effervescent reaction will result.

Propan-1-ol

  • Could be identified through an oxidation reaction using acidified dichromate.
  • The reaction would cause the solution to change from green to orange.
Show Worked Solution

a.    A safety concern is that the organic liquids are flammable.

To address this, keep substance away from open flames and keep away from ignition sources.
 

b.    Flask 1: propanoic acid  (carboxylic acids can’t be oxidised and are polar)

Flask 2: hex-1-ene (alkenes can be oxidised and are non-polar)

Flask 3: propan-1-ol (primary alcohols can be oxidised and are polar)

Flask 4: hexane (alkanes don’t react with acidified oxidants and are non-polar)
 

c.   Hex-1-ene

  • Could be identified using the bromine water test.
  • The addition of brown bromine water to an alkene causes an addition reaction where the solution changes colours from brown to colourless.

Propanoic acid

  • Could be identified through a neutralisation reaction using `text{Na}_2text{CO}_3`.
  • Effervescent reaction will result.

Propan-1-ol

  • Could be identified through an oxidation reaction using acidified dichromate.
  • The reaction would cause the solution to change from green to orange.

CHEMISTRY, M7 2021 HSC 13 MC

A chemist synthesises a substance using the following pathway.

\[\ce{ X ->[{hydration}] {Y} ->[{oxidation}] Z}\]

What are compounds `text{X, Y, Z}` ?

Show Answers Only

`C`

Show Worked Solution

By elimination:

  • Hydration reaction is an addition reaction that can only occur on alkenes, thus  `X` = prop-1-ene  (eliminate A and B)
  • `Y` = propan-2-ol
  • The oxidation of secondary alcohol creates a ketone, thus `Z` = propanone

`=> C`