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CHEMISTRY, M7 2025 HSC 25

A student produced the ester propyl butanoate in the school laboratory, by refluxing 0.267 mol of propan-1-ol and 0.298 mol of butanoic acid with a catalyst.

Use the data in the table to calculate the percentage yield of the ester.   (3 marks)

\begin{array}{|l|c|c|c|}
\hline
\rule{0pt}{2.5ex}\textit{Product} & \textit{Volume produced} &\quad \textit{Density} \quad   & \quad \textit{Molar mass } \quad \\
\text{} \rule[-1ex]{0pt}{0pt}& \text{(mL)} &(\text{g mL}^{-1}) &(\text{g moL}^{-1}) \\
\hline
\rule{0pt}{2.5ex}\text{propyl butanoate} \rule[-1ex]{0pt}{0pt}& 12.2 & 0.873 & 130.2 \\
\hline
\end{array}

Show Answers Only

\(30.6\%\)

Show Worked Solution
  • The reflux reaction that takes place between propan-1-ol and butanoic acid is
  • \(\ce{C3H8O + C4H8O2 \leftrightharpoons C7H14O2 + H2O}\)
  • As the reaction occurs in \(1:1:1\) mole ratio, propan-1-ol is the limiting reagent of the reaction. Hence the theortical number of moles of propyl butanoate produced is 0.267 mol.
  • The actual moles of propyl butanoate that are produced are:
  •   \(\text{mass = density \(\times\) volume}\ = 12.2 \times 0.873 = 10.6506\ \text{g}\)
  •   \(n_{\text{actual}} = \dfrac{m}{MM}= \dfrac{10.6506}{130.2} = 0.0818\ \text{mol}\) 
  • Hence the percentage yield of the ester \(=\dfrac{0.0818}{0.267} \times 100 = 30.6\)%.

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 \(Z\)?
 

Show Answers Only

\(D\)

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, M7 EQ-Bank 23

  1. Design a procedure that can be used to produce the ester, ethyl ethanoate, in a school laboratory.   (4 marks)

  2. Describe a safety precaution in the production of an ester in a school laboratory.   (2 marks)

Show Answers Only

a.   Methodology:

  • STEP 1: Reflux equipment using a hot plate heating source.
  • STEP 2: Pour 10 mL of ethanol into a round bottom flask. Add 20 mL of glacial (water-free) acetic acid.
  • STEP 3: Add 1 mL of concentrated \(\ce{H2SO4}\) (sulfuric acid) to the mixture. Boiling stones/chips can be added to smooth the boiling process before heating under reflux for 45 minutes.
  • STEP 4: Allow the solution to cool. The contents should then be transferred to a separating funnel.
  • STEP 5: Distilled water should be used to wash the contents which will remove excess alcohol and acetic acid. The ester layer has a density less than 1 g/mL and will therefore form a layer above the aqueous solution.
  • STEP 5: Remove the aqueous solution using the separating funnel.
  • STEP 6: By adding a solution of 1 mol L ¯1  \(\ce{Na2CO3}\) (sodium carbonate), all remaining acid will be removed. Similarly to Step 4, the ester can be isolated by removing the lower layer.

b.   Safety precaution:

  • Ethanol presents a danger due to its combustibility.
  • A safety precaution that reduces the fire threat is through the use of a hot plate for heating rather than a naked flame.
Show Worked Solution

a.   Methodology:

  • STEP 1: Reflux equipment using a hot plate heating source.
  • STEP 2: Pour 10 mL of ethanol into a round bottom flask. Add 20 mL of glacial (water-free) acetic acid.
  • STEP 3: Add 1 mL of concentrated \(\ce{H2SO4}\) (sulfuric acid) to the mixture. Boiling stones/chips can be added to smooth the boiling process before heating under reflux for 45 minutes.
  • STEP 4: Allow the solution to cool. The contents should then be transferred to a separating funnel.
  • STEP 5: Distilled water should be used to wash the contents which will remove excess alcohol and acetic acid. The ester layer has a density less than 1 g/mL and will therefore form a layer above the aqueous solution.
  • STEP 5: Remove the aqueous solution using the separating funnel.
  • STEP 6: By adding a solution of 1 mol L ¯1  \(\ce{Na2CO3}\) (sodium carbonate), all remaining acid will be removed. Similarly to Step 4, the ester can be isolated by removing the lower layer of aqueous solution using the separating funnel. 

b.   Safety precaution:

  • Ethanol presents a danger due to its combustibility.
  • A safety precaution that reduces the fire threat is through the use of a hot plate for heating rather than a naked flame.

CHEMISTRY, M7 2018 HSC 3 MC

An esterification reaction is to be performed.

Which of the following substances, when added, would increase the yield of the product?

  1. Water
  2. Boiling chips
  3. More alkanol
  4. Dilute sulfuric acid
Show Answers Only

`C`

Show Worked Solution
  • The addition of more alkanol increases one of the reactants in a reversible reaction.
  • By Le Chatelier’s principle, this would shift the equilibrium to the right hand side (increase yield).

`=>C`

CHEMISTRY, M7 2016 HSC 22

This apparatus was set up to produce methyl butanoate.
 

  1. Identify a safety issue in this experiment.   (1 mark)

  2. Using structural formulae, write the equation for the production of methyl butanoate.   (2 marks)

  3. Justify the use of apparatus `X` in this experiment.   (2 marks)

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a.   Flame could ignite one of reagents which is flammable.

b.   
     

c.    Esterification is a relatively slow reaction.

  • Heating the reaction makes it go faster. However, the low boiling points of the reactants make them volatile as they readily convert into gas.
  • The cooling condenser `X` prevents the gas reactants from escaping the experiment by condensing them back into the reaction mixture. This process allows the reaction to proceed at higher temperatures.
Show Worked Solution

a.   Flame could ignite one of reagents which is flammable.
 

b.   
     


 


♦ Mean mark (b) 52%.

c.    Esterification is a relatively slow reaction.

  • Heating the reaction makes it go faster. However, the low boiling points of the reactants make them volatile as they readily convert into gas.
  • The cooling condenser `X` prevents the gas reactants from escaping the experiment by condensing them back into the reaction mixture. This process allows the reaction to proceed at higher temperatures.

♦♦♦ Mean mark (c) 14%.

CHEMISTRY, M7 2019 HSC 34

The following reaction scheme can be used to synthesise ethyl ethanoate.
 


 

Outline the reagents and conditions required for each step and how the product of each step could be identified.   (7 marks) 

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Step 1:

  • To synthesise chloroethane (A) into ethanol (B), \(\ce{NaOH}\) is added and heated. \(\ce{KMnO4 / H+}\) is then added and heated.
  • The mixture is then treated with concentrated sulfuric acid and refluxed.
  • Ethanol (B) can be identified using infrared spectroscopy by looking for a broad absorption between 3230 cm ¯1 and 3550 cm ¯1, which indicates the presence of an \(\ce{O-H}\) bond. This absorption would not be present in chloroethane (A).
  • Alternative ways to identify ethanol include: mass spectrum analysis (single ion peak at m/z = 46), reactivity tests, and \( \ce{^1H NMR}\) spectrum analysis (3 signals vs 2 for chloroethane). 

Step 2:

  • Ethanol (B) can be converted into ethanoic acid (C) by combining it with a strong oxidant like sodium carbonate, which produces carbon dioxide bubbles, confirming the presence of a carboxylic acid.
  • Ethanol will not react as above and the compounds can be distinguished.
  • Alternative ways to identify ethanoic acid include: IR or \( \ce{^13C NMR}\) spectrum analysis, litmus indicators, mass spectrum analysis (ion peak at m/z = 60 vs m/z = 46) 

Step 3

  • Ethyl ethanoate (D) can be synthesised by heating a mixture of ethanol, ethanoic acid and concentrated sulfuric acid under reflux.
  • A \( \ce{^1H NMR}\) spectrum can be used to identify ethyl ethanoate as it will have 3 signals versus ethanol and ethanoic acid that will only have 2 each.
  • Alternative ways to identify ethyl ethanoate include: a distinct smell, no \(\ce{O-H}\) peaks in the IR spectrum or mass spectrum analysis (ion peak at m/z = 102).
Show Worked Solution

Step 1:

  • To synthesise chloroethane (A) into ethanol (B), \(\ce{NaOH}\) is added and heated. \(\ce{KMnO4 / H+}\) is then added and heated.
  • The mixture is then treated with concentrated sulfuric acid and refluxed.
  • Ethanol (B) can be identified using infrared spectroscopy by looking for a broad absorption between 3230 cm ¯1 and 3550 cm ¯1, which indicates the presence of an \(\ce{O-H}\) bond. This absorption would not be present in chloroethane (A).
  • Alternative ways to identify ethanol include: mass spectrum analysis (single ion peak at m/z = 46), reactivity tests, and \( \ce{^1H NMR}\) spectrum analysis (3 signals vs 2 for chloroethane). 

Step 2:

  • Ethanol (B) can be converted into ethanoic acid (C) by combining it with a strong oxidant like sodium carbonate, which produces carbon dioxide bubbles, confirming the presence of a carboxylic acid.
  • Ethanol will not react as above and the compounds can be distinguished.
  • Alternative ways to identify ethanoic acid include: IR or \( \ce{^13C NMR}\) spectrum analysis, litmus indicators, mass spectrum analysis (ion peak at m/z = 60 vs m/z = 46) 

Step 3

  • Ethyl ethanoate (D) can be synthesised by heating a mixture of ethanol, ethanoic acid and concentrated sulfuric acid under reflux.
  • A \( \ce{^1H NMR}\) spectrum can be used to identify ethyl ethanoate as it will have 3 signals versus ethanol and ethanoic acid that will only have 2 each.
  • Alternative ways to identify ethyl ethanoate include: a distinct smell, no \(\ce{O-H}\) peaks in the IR spectrum or mass spectrum analysis (ion peak at m/z = 102).

♦♦ Mean mark 38%.

CHEMISTRY, M7 2015 HSC 9 MC

What are the reactants used to make this compound?

  1. Butan-1-ol and butanoic acid
  2. Butan-1-ol and propanoic acid
  3. Propan-1-ol and butanoic acid
  4. Propan-1-ol and propanoic acid
Show Answers Only

`C`

Show Worked Solution
  • Compound is an ester
  • Oxygen double bond comes from butanoic acid (eliminate B and D)
  • The other carbon chain comes from propan-1-ol

`=>C`

CHEMISTRY, M7 2017 HSC 4 MC

Esterification can be carried out in a school laboratory using the equipment shown.
 


 

How could the safety of the process shown be improved?

  1. Place a stopper on top of the condenser.
  2. Add concentrated sulfuric acid to the flask.
  3. Change the direction of water flow through the condenser.
  4. Replace the Bunsen burner with an electric heating mantle.
Show Answers Only

`D`

Show Worked Solution

By elimination

A:  Resulting pressure build up is dangerous (incorrect)

B:  Adds to the catalytic effect but not a safety reduction measure  (incorrect)

C:  Direction is optimal as water flow is coolest where vapours are hottest (incorrect)

D:  Heating mantle reduces the chance of vapours igniting (correct)

`=>D`

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?
 

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`A`

Show Worked Solution
  • Compound: Ethyl pentanoate
  • Reactants: Ethanol and Pentanoic acid (only the former is listed in the table)

`=>A`

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 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 2021 HSC 4 MC

The structure of ethyl pentanoate is shown.
 

Which pair of chemicals would produce ethyl pentanoate by esterification?

  1. Ethene and pentan-1-ol
  2. Ethane and pentanoic acid
  3. Ethanol and pentanoic acid
  4. Ethanoic acid and pentan-1-ol
Show Answers Only

`C`

Show Worked Solution
  • Esterification involves a reaction between a carboxylic aciand an alcohol.
  • Creating ethyl pentanoate requires ethanol (which is an alcohol) and pentanoic acid (which is a carboxylic acid).
  • Ethanol + pentanoic acid  ↔ ethyl pentanoate + water

`=> C`