Empirical formulae

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.

Compound L (M_r = 88.0) contains carbon, hydrogen and oxygen only.

A 6.56 × 10^–4 mol sample of L burns completely in air to form 2.62 × 10^–3 mol of water and 2.62 × 10^–3 mol of carbon dioxide.

Deduce the formula of L. Show your working.

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.

This question is about compound X with the empirical formula C₂H₄O

Figure 2 shows the infrared spectrum of X.

Figure 3 shows the¹³C NMR spectrum of X.

The¹H NMR spectrum of X shows four peaks with different chemical shift values. Table 3 gives data for these peaks.

Show how information from Figure 2, Figure 3 and Table 3 can be used to deduce the structure of compound X.

The answer space for this question continues on the next page

This question is about olive oil.

A sample of olive oil is mainly the unsaturated fat Y mixed with a small amount of inert impurity.

The structure of Y in the olive oil is shown. Y has the molecular formula C₅₇H₁₀₀O₆ (M_r = 880).

The amount of Y is found by measuring how much bromine water is decolourised by a sample of oil, using this method.

• Transfer a weighed sample of oil to a 250 cm³ volumetric flask and make up to the mark with an inert organic solvent.

• Titrate 25.0 cm³ samples of the olive oil solution with 0.025 mol dm⁻³ Br₂(aq).

A suitable target titre for the titration is 30.0 cm³ of 0.025 mol dm⁻³ Br₂(aq).

Justify why a much smaller target titre would not be appropriate.

Calculate the amount, in moles, of bromine in the target titre.

Calculate a suitable mass of olive oil to transfer to the volumetric flask using your answer to Question 09.1 and the structure of Y. Assume that the olive oil contains 85% of Y by mass.

(If you were unable to calculate the amount of bromine in the target titre, you should assume it is 6.25×10⁻⁴ mol. This is not the correct amount.)

The olive oil solution can be prepared using this method.

• Place a weighing bottle on a balance and record the mass, in g, to 2 decimal places.

• Add olive oil to the weighing bottle until a suitable mass has been added.

• Record the mass of the weighing bottle and olive oil.

• Pour the olive oil into a 250 cm³ volumetric flask.

• Add organic solvent to the volumetric flask until it is made up to the mark.

• Place a stopper in the flask and invert the flask several times.

Suggest an extra step to ensure that the mass of olive oil in the solution is recorded accurately.

Justify your suggestion.

State the reason for inverting the flask several times.

A sample of the olive oil was dissolved in methanol and placed in a mass spectrometer. The sample was ionised using electrospray ionisation. Each molecule gained a hydrogen ion (H⁺) during ionisation. The spectrum showed a peak for an ion with = 345 formed from an impurity in the olive oil. The ion with = 345 was formed from a compound with the empirical formula C₅H₁₀O

Deduce the molecular formula of this compound.

Show your working.

Molecular formula 12

Tschermigite is a hydrated, water-soluble mineral, with relative formula mass of 453.2

The formula of tschermigite can be represented as M.xH₂O, where M represents all the ions present.

Table 4 shows its composition by mass.

In an analysis, it is found that the mineral contains the ions NH₄⁺, Al³⁺ and SO₄²

Calculate the empirical formula of tschermigite and the value of x in M.xH₂O

Describe the tests, with their results, including ionic equations, that would confirm the identities of the ions present.

This question is about citric acid, a hydrated tricarboxylic acid. Its formula can be

A 1.50 g sample of H₃Y.H₂O contains 0.913 g of oxygen by mass. The sample burns completely in air to form 1.89 g of CO₂ and 0.643 g of H₂O

Show that the empirical formula of citric acid is C₃H₅O₄

A 3.00 g sample of H₃Y.H₂O (M_r = 210.0) is heated to constant mass. The anhydrous H₃Y that remains has a mass of 2.74 g

Show, using these data, that the value of = 1

Figure 5 shows the structure of H₃Y

Complete this IUPAC name for H₃Y

State the number of peaks you would expect in the¹³C NMR spectrum for H₃Y

The outer layers of some golf balls are made from a polymer called polyisoprene. The isoprene monomer is a non-cyclic branched hydrocarbon that contains 88.2 % carbon by mass. The empirical formula of isoprene is the same as its molecular formula.

Deduce the molecular formula of isoprene and suggest a possible structure.

Molecular formula

Structure

The insides of some golf balls are made from a mixture of three other polymers. The repeating unit for one of these polymers is shown.

Draw the skeletal formula of the monomer used to make this polymer.

Give the IUPAC name of the monomer.

Skeletal formula of monomer

A second polymer in the mixture has a repeating unit with the structure shown.

The third polymer in the mixture is a stereoisomer of this polymer.

Draw the structure of the repeating unit of the third polymer.

Give a reason why this type of stereoisomerism arises.

Repeating unit

Golf balls recovered from lakes and ponds can be used again even after being in water for several years.

Explain why these golf balls do not biodegrade.

Some compounds with different molecular formulas have the same relative molecular mass to the nearest whole number.

A dicarboxylic acid has a relative molecular mass of 118, to the nearest whole number.

Deduce the molecular formula of the acid.

Molecular formula

A student dissolved some of the dicarboxylic acid from Question 10.1 in water and made up the solution to 250 cm³ in a volumetric flask. In a titration, a 25.0 cm³ sample of the acid solution needed 21.60 cm³ of 0.109 mol dm³ sodium hydroxide solution for neutralisation.

Calculate the mass, in g, of the dicarboxylic acid used. Give your answer to the appropriate number of significant figures.

Compounds with molecular formula C₆H₁₄O₂ also have a relative molecular mass of 118 to the nearest whole number. These include the diol shown.

Deduce the number of peaks in the¹H NMR spectrum of this diol.

Draw the structure of a different diol also with molecular formula C₆H₁₄O₂ that has a ¹H NMR spectrum that consists of two singlet peaks.

The dicarboxylic acid in question 10.1 and the isomers of C₆H₁₄O₂ in Questions 10.3 and 10.4 all have a relative molecular mass of 118

State why the dicarboxylic acid can be distinguished from the two diols by high resolution mass spectrometry using electrospray ionisation.

Which can be both an empirical and molecular formula of a stable compound?