Carboxylic acids

This question is about polymers.

A section of the polymer PVC is shown.

Name the monomer used to make PVC.

Draw the structure of the monomer used to make PVC.

Structure

State why PVC is not biodegradable.

Diisobutyl phthalate (DIBP) is a plasticiser added to PVC to modify its properties.

State how the properties of PVC are modified by the addition of DIBP.

An incomplete equation for the reaction used to make DIBP is shown.

Complete the equation.

Give the name of the mechanism for this reaction.

Deduce the empirical formula of DIBP.

Empirical formula of DIBP

A different plasticiser, DEHA, is added to PVC used for food packaging.

The structure of DEHA is

Identify the organic compound that would react with hexanedioic acid to form DEHA.

DEHA can be absorbed into food from PVC packaging.

In an investigation, 1 kg samples of three different foods are stored in PVC packaging for 30 days.

Table 1 shows the water content, fat content and mass of DEHA in each type of food after 30 days.

Use your knowledge of intermolecular forces to explain these results.

The polymer nylon 6,6 can be made from hexanedioyl dichloride and hexane-1,6-diamine.

Figure 2 shows an incomplete mechanism for the first steps in this reaction.

Draw the missing intermediate in the box in Figure 2.

Complete Figure 2 by adding the curly arrows and any relevant lone pairs of electrons involved in these steps in the mechanism.

The polymer nylon 6 can be made by heating caprolactam with water.

Figure 3 shows the species involved in the first three steps of the mechanism for this reaction.

Complete Figure 3 by adding the curly arrows and any relevant lone pairs of electrons involved in these steps in the mechanism.

This question is about rapeseed oil.

Figure 2 shows the structure of compound Q found in rapeseed oil. Each branch in the molecule is formed from a different long-chain carboxylic acid.

State the type of stereoisomerism shown in Branch A.

Q can be reacted with methanol to form three different esters.

State the number used to identify the position of the C=C bond in the name of the ester formed from Branch A.

State the number of different stereoisomers of the ester formed from Branch B.

Give a use for these esters.

Number used in the name of the ester

Number of stereoisomers

Q also reacts with NaOH

State the formula of the product, formed by Branch B in Figure 2, in this reaction.

State a use for this product.

This question is about the preparation of an ester.

Ester F can be prepared from propan-2-ol and ethanoic acid.

Give an equation for this reaction.

Name ester F.

Equation

This method is used to prepare a sample of ester F.

Step 1 Mix 10 cm³ of propan-2-ol with 10 cm³ of ethanoic acid. Add 5 drops of concentrated sulfuric acid. Reflux this reaction mixture for 20 minutes.

Step 2 Transfer the cooled reaction mixture to a separating funnel. Add 20 cm³ of aqueous sodium carbonate and shake the mixture.

Step 3 Transfer the organic layer to a beaker and add 5 g of anhydrous magnesium sulfate. Decant off the organic liquid.

Step 4 Collect the ester using simple distillation.

Describe how Step 1 should be done.

In your description you should

• give details of suitable equipment used to add each reagent to the reflux apparatus

• draw a labelled diagram of the apparatus used for refluxing the reaction mixture

• explain any safety precautions needed other than eye protection.

In Step 2 the reaction mixture from Step 1 is shaken with aqueous sodium carbonate.

State the purpose of the sodium carbonate.

Suggest a precaution that should be taken while this mixture is shaken in the separating funnel.

Give a reason for your suggested precaution.

Purpose of sodium carbonate

Suggest how the purity of the ester can be confirmed during the distillation in Step 4.

Compounds V, W, X and Y are isomers with the molecular formula C₅H₁₀O₂

Isomers V and W are carboxylic acids with formulas that can be written as C₄H₉COOH

Give an equation for the reaction of C₄H₉COOH with sodium hydrogencarbonate.

Isomer V has an asymmetric carbon atom.

Deduce the structure of V.

Isomer W has four peaks in its¹H NMR spectrum.

Deduce the structure of W.

Deduce the integration ratio for the four peaks in the¹H NMR spectrum of W.

Integration ratio

Table 2 shows information about the peaks in the¹H NMR spectrum of isomer Y.

Draw the parts of the structure of Y that can be deduced from each of these peaks.

Deduce the structure of Y.

State how many peaks are in the¹³C NMR spectrum of Y.

Part of structure from peak at δ = 3.65 ppm

Part of structure from peak at δ = 1.19 ppm

The structure of 2-hydroxybenzenecarboxylic acid is shown.

Give the equation for the reaction of 2-hydroxybenzenecarboxylic acid with methanol.

In your equation, include the skeletal formula of the organic product.

Aspirin is produced from 2-hydroxybenzenecarboxylic acid by reaction with ethanoic anhydride in the presence of concentrated phosphoric acid.

Method

1. Add 2-hydroxybenzenecarboxylic acid to a conical flask.

2. Add excess ethanoic anhydride.

3. Add a few drops of concentrated phosphoric acid.

4. Heat the flask to 85 °C for 10 minutes.

5. Cool the flask and pour the contents into 150 cm³ of cold water.

6. Filter and wash the impure solid aspirin.

7. Recrystallise the aspirin using a 50:50 mixture of water and ethanol.

8. Check the purity of the aspirin.

Aspirin can also be produced by reacting 2-hydroxybenzenecarboxylic acid with ethanoyl chloride.

State why ethanoic anhydride is preferred to ethanoyl chloride for this preparation.

Give the name of the mechanism for the reaction of 2-hydroxybenzenecarboxylic acid with ethanoic anhydride.

Suggest the role of the concentrated phosphoric acid.

Suggest why reflux is not essential when the flask is heated to 85 °C for 10 minutes.

Complete and label the diagram to show how the impure solid is filtered.

Suggest the identity of two impurities present in the filtered solid aspirin before it is washed in Step 6 of the method.

Describe the recrystallisation process used to purify the aspirin.

Include the method and apparatus used.

State the physical property that is measured to check the purity of the aspirin.

Describe two ways the result would show that the product is impure.

Physical property

Which compound is formed by the acid hydrolysis of phenyl benzenecarboxylate?

A student plans a series of chemical tests to confirm the identities of four organic

This is the student’s method.

To separate test tubes containing samples of each liquid:

Test 1 add potassium dichromate(VI) solution and warm gently

Test 2 add Fehling’s solution and cool in iced water

Test 3 add sodium hydrogencarbonate solution and test any gas produced with a lighted splint

Test 4 add bromine water and shake at room temperature.

Identify the missing reagent needed in Test 1.

In addition to the missing reagent in Test 1, there is a mistake in the method for two of the other tests.

State the two mistakes.

Suggest how each of the mistakes should be corrected.

The missing reagent is added and the mistakes are corrected.

Identify the liquid(s), J, K, L and M, that would react in each test.

State the expected observation for each reaction.

Liquid(s) that react in Test 1

Expected observation

Liquid(s) that react in Test 2

Expected observation

Liquid(s) that react in Test 3

Expected observation

Liquid(s) that react in Test 4

Expected observation

Figure 10 shows the apparatus that is used to separate a mixture of liquids K and M using fractional distillation.

Suggest labels that should be added to positions S, T and U in Figure 10.

Explain why fractional distillation is preferred to simple distillation to separate liquids K and M.

This question is about biofuels.

Palmitic acid, CH₃(CH₂)₁₄COOH, can be made by hydrolysis of the triester in palm oil under acidic conditions. Palmitic acid can be used as a biofuel.

Complete the equation for the hydrolysis of the triester in palm oil under acidic conditions.

Palmitic acid burns in air.

In a calorimetry experiment, combustion of 387 mg of palmitic acid increases the temperature of 0.150 kg of water from 23.9 °C to 37.5 °C

Calculate a value, in kJ mol^–1, for the enthalpy of combustion of palmitic acid in this experiment. Give your answer to the appropriate number of significant figures.

The specific heat capacity of water is 4.18 J K^–1 g^–1

State how the value calculated in Question 08.2 is likely to differ from data book values.

Give one reason, other than heat loss, for this difference.

A sample of a different biofuel, made from sewage sludge, is found to contain 37.08% carbon, 5.15% hydrogen and 24.72% oxygen by mass. The rest of the sample is sulfur.

Calculate the empirical formula of this biofuel.

Empirical formula

Complete combustion of the biofuel made from sewage sludge produces the greenhouse gas carbon dioxide.

Suggest one other possible environmental problem with the complete combustion of this biofuel.

State the formula of the pollutant responsible for this problem.

Environmental problem

Ethanol is a biofuel that can be produced by the fermentation of glucose.

Glucose has the structural formula shown.

Table 3 shows some mean bond enthalpy values.

Use the equation and the data in Table 3 to calculate an approximate value of Δ H for the fermentation of glucose. For this calculation you should assume that all the substances are in the gaseous state.

The carbon dioxide produced from fermentation can be reacted with steam to make more ethanol.

The equation for this reaction is

Table 4 shows some standard enthalpies of formation.

Use the data in Table 4 to calculate a standard enthalpy change value for this reaction.

Ethyl ethanoate can be made by reacting ethanol with ethanoic acid in the presence of concentrated sulfuric acid.

1. A mixture of ethanol, ethanoic acid, and concentrated sulfuric acid, with anti-bumping granules, is heated under reflux for 10 minutes.

2. The apparatus is rearranged for distillation.

3. The mixture is heated to collect the liquid that distils between 70 and 85 C

4. The distillate is placed in a separating funnel. Aqueous sodium carbonate is added, and a stopper is placed in the funnel. The mixture is shaken, releasing pressure as necessary.

5. The lower aqueous layer is removed and the upper organic layer is placed in a small conical flask.

6. Anhydrous calcium chloride is added to the sample in the conical flask. The flask is shaken well and left for a few minutes.

7. The liquid from the flask is redistilled and the distillate is collected between

State the role of concentrated sulfuric acid in this reaction.

The reaction mixture is flammable.

Suggest how the reaction mixture should be heated in step 1.

Figure 1 shows how a student set up the apparatus for reflux in step 1. You should assume that the apparatus is clamped correctly.

Identify two mistakes the student made in setting up the apparatus. State the problem caused by each mistake.

State why sodium carbonate is added to the distillate in step 4.

Explain why there is a build-up of pressure in the separating funnel.

Give a reason why two layers form in the separating funnel.

Suggest why ethyl ethanoate forms the upper layer.

State why anhydrous calcium chloride is added in step 6.

A student uses the method to prepare some ethyl ethanoate.

The student adds 10.0 cm³ of ethanol (M_r = 46.0) to 5.25 g of ethanoic acid (M_r = 60.0) and obtains 5.47 g of ethyl ethanoate (M_r = 88.0).

For ethanol, density = 0.790 g cm^–3

Determine the limiting reagent.

Calculate the percentage yield of ethyl ethanoate.

Suggest a reason why the percentage yield is not 100%.

Consider this reaction scheme.

Which step is shown with a correct reagent and a correct condition?

This question is about esters.

Figure 4 shows an incomplete mechanism for the reaction of an ester with aqueous sodium hydroxide.

Add three curly arrows to complete the mechanism in Figure 4.

Name the type of reaction shown in Figure 4.

Deduce the role of the CH₃O⁻ ion in step 3 shown in Figure 4.

A triester in vegetable oil reacts with sodium hydroxide in a similar way.

Give a use for a product of this reaction.

Which pair of reagents does not produce ethanol?

Coconut oil contains a triester with three identical R groups. This triester reacts with potassium hydroxide.

Complete the equation by drawing the structure of the other product of this reaction in the box.

Name the type of compound shown by the formula RCOOK

Give one use for this type of compound.

The triester in coconut oil has a relative molecular mass, M_r = 638.0 In the equation shown at the start of Question 01, R represents an alkyl group that

A 1.450 g sample of coconut oil is heated with 0.421 g of KOH in aqueous ethanol until all of the triester is hydrolysed. The mixture is cooled. The remaining KOH is neutralised by exactly 15.65 cm³ of 0.100 mol dm^–3 HCl

Calculate the percentage by mass of the triester (M_r= 638.0) in the coconut oil.

Suggest why aqueous ethanol is a suitable solvent when heating the coconut oil with KOH.

Give a safety precaution used when heating the mixture. Justify your choice.

Safety precaution

This question is about equilibrium.

1 mol of a diester with molecular formula C₇H₁₂O₄ is added to 1 mol of water in the presence of a small amount of catalyst. The mixture is left to reach equilibrium at a constant temperature.

At equilibrium, mol of ethanoic acid are present in the mixture.

Complete Table 2 by deducing the amounts, in terms of , of the diester, water and diol present in the equilibrium mixture.

Deduce the structure of the diester in Question 05.1

A new equilibrium mixture of the substances from Question 05.1 is prepared at a different temperature.

Table 3 shows the amount of each substance in this new equilibrium mixture.

The value of the equilibrium constant, K_c is 0.161 at this temperature.

Calculate the amount of water, in mol, in this new equilibrium mixture. Show your working.

This question is about the structural isomers shown.

Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI).

State the expected observation when acidified potassium dichromate(VI) reacts.

Expected observation

State the type of structural isomerism shown by isomers P, Q, R and S.

Describe fully how infrared spectra can be used to distinguish between isomers R, S and T. Use data from Table A in the Data Booklet in your answer.

State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.

Which compound is formed when phenyl benzenecarboxylate is hydrolysed under acidic conditions?

This question is about esters including biodiesel.

An ester is formed by the reaction of an acid anhydride with CH₃CH₂OH

Complete the equation. In your answer show clearly the structure of the ester. Give the IUPAC name of the ester.

In a reaction to form biodiesel, one mole of a vegetable oil reacts with an excess of methanol to form two moles of an ester with molecular formula C₁₉H₃₄O₂ and one mole of an ester with molecular formula C₁₉H₃₆O₂

Draw the structure of the vegetable oil showing clearly the ester links.

You should represent the hydrocarbon chains in the form C_xH_y where x and y are the actual numbers of carbon and hydrogen atoms.

The compound C₁₉H₃₄O₂ is the methyl ester of Z,Z-octadeca-9,12-dienoic acid.

Part of the structure of the acid is shown.

Complete the skeletal formula to show the next part of the hydrocarbon chain to carbon atom number 14. In your answer, show the Z stereochemistry around both C=C double bonds.

Give an equation for the complete combustion of the ester C₁₉H₃₄O₂

Combustion of biodiesel produces greenhouse gases such as carbon dioxide that cause global warming. Part of the infrared spectrum of carbon dioxide is shown in Figure 3.

State how the infrared spectrum of carbon dioxide in Figure 3 is not what you might predict from the data provided in Table A in the Data Booklet.

Explain how carbon dioxide causes global warming.

Which compound is formed by acid hydrolysis of phenylmethyl ethanoate?

A student is required to dry a liquid sample of pentanoic acid.

Which drying agent is suitable?

Which statement is correct about both 2-methylbutan-1-ol and 2-methylbutan-2-ol?

Draw a structural formula for the diester C₆H₁₀O₄

A small amount of catalyst was added to a mixture of 0.470 mol of ethanoic acid and 0.205 mol of ethane-1,2-diol.

The mixture was left to reach equilibrium at a constant temperature.

Space for working

Write an expression for the equilibrium constant, K_c, for the reaction.

The total volume of the mixture does not need to be measured to allow a correct value for K_c to be calculated.

Justify this statement.

Expression

A different mixture of ethanoic acid, ethane-1,2-diol and water was prepared and left to reach equilibrium at a different temperature from the experiment in Question 5.2

The amounts present in the new equilibrium mixture are shown in Table 2.

The value of K_c was 6.45 at this different temperature.

Use this value and the data in Table 2 to calculate the amount, in mol, of ethanoic acid present in the new equilibrium mixture. Give your answer to the appropriate number of significant figures.

Amount of ethanoic acid
mol

You are provided with samples of each of the four compounds.

Describe how you could distinguish between all four compounds using the minimum number of tests on each compound.

You should describe what would be observed in each test.