OCR A Level Chemistry B (Salters) Scientific literacy in chemistry June 2019 question paper H433/02

Name the functional groups in compounds A and B.

A........

B........

Explain your answer.

Compound A can be made by the reaction in Fig. 1.2.

Calculate the mass of compound A that can be made from 32 g of benzene-1,4-dicarboxylic acid if the yield is 67%.

Give your answer to the nearest whole number.

The polymer strands link together by intermolecular bonds when they are spun to form Twaron. This gives the fabric its tough quality.

Name the strongest intermolecular bonds that can form between the chains.

Mark the positions of the intermolecular bonds by drawing dotted lines on the diagram

A Twaron polymer strand is hydrolysed.

State the conditions that could be used to hydrolyse the polymer.

Draw the formulae of the two organic products of hydrolysis in the boxes.

Strontium carbonate is used in fireworks to colour the flames red.

The red colour comes from lines of specific frequency in the atomic emission spectrum of strontium.

Explain how these lines are formed.

Strontium carbonate decomposes to give strontium oxide when heated.

SrCO₃ → SrO + CO₂

12.0 g of SrCO₃ are heated.

Calculate the volume of CO₂ (in cm³) that would be collected at 290 K and 155 kPa.

Give your answer to an appropriate number of significant figures.

volume of CO₂ =........ cm³

A student says ‘Strontium ions are larger than calcium ions, so the attraction to carbonate ions is weaker. This means that strontium carbonate has a lower thermal stability than calcium carbonate.’

Discuss the student’s statement, giving the correct chemistry where necessary.

A sample of strontium metal has the isotopic composition shown in the table.

How many neutrons are there in an atom of⁸⁴Sr?

Use the data to calculate the relative atomic mass of the strontium sample.

Give your answer to 2 decimal places.

At 0 °C, the solubility of strontium hydroxide in water is 3.4 × 10⁻² mol dm⁻³. (ii)

Calculate the solubility product of strontium hydroxide at this temperature.

Give the units in your answer.

Explain how the solubility of strontium hydroxide in aqueous NaOH at 0 °C compares with 3.4 × 10⁻² mol dm⁻³.

Use the idea of solubility product in your answer.

The melting point of strontium is higher than the melting point of rubidium.

To which block of the Periodic Table do these elements belong?

Explain the difference in melting point.

Chlorine is made by electrolysing sodium chloride solution.

Sodium chlorate(V) is made by letting the chlorine react with the hydroxide ions that are also produced.

The forward reaction in equation 3.1 does not occur under standard conditions.

Use data from Table 3.1 to explain why.

Suggest why the forward reaction in equation 3.1 does occur in the presence of concentrated hydrochloric acid.

A student investigates the reactions of some halogen compounds using the data in Table 3.1

State where the electrons move and which way they are moving when the cell delivers a current.

The E value for the copper electrode at 298 K varies with the concentration of copper ions. The equation for this is shown below.

Calculate the E value for a copper electrode where [Cu²⁺] = 0.010 mol dm⁻³.

From data in Table 3.1, the student knows that chlorine reacts with iodide ions in aqueous solution.

Write an equation for the reaction that occurs.

Name the reducing agent in your reaction in (d)(i).

What will be seen when the reaction in (d)(i) occurs?

Explain, in terms of electrons, why chlorine is more reactive than iodine.

The student uses a simple apparatus to prepare a test-tube full of hydrogen chloride gas in the laboratory.

Draw a diagram of an apparatus the student could use, labelling the reactants.

Dinitrogen pentoxide, N₂O₅ is an oxide of nitrogen that is formed in the stratosphere by reactions such as those shown below.

NO₂ + O₃ → NO₃ + O₂

The dinitrogen pentoxide acts as a ‘sink’ for NO₂, stopping it breaking down ozone.

A student says that oxides of nitrogen catalyse the breakdown of ozone in the stratosphere by the reactions shown below.

NO₂ + O₃ → NO₃ + O₂

O₃ + NO₃ → NO₂ + 2O₂

Discuss the student’s choice of reactions, giving the correct chemistry if necessary.

In the troposphere, dinitrogen pentoxide decomposes as shown below.

2N₂O₅ → 4NO₂ + O₂ Equation 4.1

The table shows how the concentration of 2N₂O₅ varies with time at 315 K.

How does the graph show that the reaction in equation 4.1 is first order with respect to N₂O₅?

Draw construction lines on the graph to explain your answer.

The gradient of the graph at 1000 s is 9.8 × 10⁻⁵ mol dm⁻³ s⁻¹. (c)

Work out the rate constant for the reaction in equation 4.1 at 315 K.

Give the units in your answer.

The reaction in equation 4.1 was repeated with a fixed concentration of N₂O₅ at different temperatures. A graph of l n k against for the reaction in equation 4.1 is given below.

Use the graph to work out a value for the activation enthalpy (in kJ mol⁻¹) for the reaction.

=........ kJ mol⁻¹ E_a

2N₂O₅ → 4NO₂ + O₂ Equation 4.1

A student suggests the following mechanism for the reaction in equation 4.1. The reaction is first order with respect to N₂O₅.

Show that this is a possible mechanism.

Consider which step(s) could be rate-determining.

This question refers to the Advance Notice Article ‘Clearing the air around smoke formation’ that is included as an insert in this paper.

The enthalpy change of combustion of acetylene, C₂H₂, can be calculated using enthalpy changes of formation.

Draw the Hess cycle that shows this, giving formulae and state symbols.

Label the enthalpy changes of formation and show how they can be combined to give the enthalpy change of combustion.

You do not need to give ∆ H values.

The Article refers to a ‘back-of-the-envelope’ calculation. This shows that the number of acetylene molecules combusting is approximately 1.4 times greater than the number of ethane molecules in the same volume of air/fuel mixture.

Use a similar calculation for propane.

Calculate how many more acetylene molecules combust in air in a given volume of air/fuel mixture compared with propane.

(Assume air contains 20% oxygen by volume.)

Number of acetylene molecules combusting is approximately........ times greater than

the number of propane molecules in the same volume.

In an sp² hybrid carbon atom, one s orbital joins with two p orbitals to form three ‘hybrid’ sp² (c) orbitals of the same energy. This leaves one other p orbital of a similar energy containing one electron.

Explain why the remaining p orbital contains one electron.

State what happens to these single p electrons in the structures of ethene and naphthalene.

Fig. 2 in the Article shows the formation of naphthalene from benzene.

Suggest the first step in the formation of a larger PAH from naphthalene.

The equation C₄H₁₀ + M → C₃H₇ + CH₃ + M, is given in the Article. M is a molecule.

Classify this reaction as initiation, propagation or termination with a reason.

Suggest a reason for the involvement of the molecule M.

* Oxygen is involved in the formation of soot in the flame of a burning hydrocarbon.

Discuss the role of oxygen in controlling the flame temperature, causing small molecule reactions and providing competing routes.

Illustrate your answer with equations where appropriate.