CXC CSEC Chemistry — Paper 02 (Structured and Extended Response), Practice Paper B

Total marks: 100 · Duration: 2 hours 30 minutes

Instructions to candidates

• This paper consists of SIX compulsory questions in two sections. Answer ALL questions.
• Section A has THREE structured questions worth 55 marks. Question 1 is a data analysis question worth 25 marks; do NOT spend more than 30 minutes on it.
• Section B has THREE extended response questions worth 15 marks each (45 marks).
• In the January 2027 sitting this paper is "hybrid": you read the questions on screen and write your answers in the answer booklet.
• A silent, non-programmable calculator may be used. Show all working in calculations and give units.
• Relative atomic masses: H = 1, C = 12, O = 16, Na = 23, S = 32, Cl = 35.5, Ca = 40, Cu = 64.
• The molar volume of any gas at room temperature and pressure (r.t.p.) is 24 dm³. The Faraday constant is 96 500 C mol⁻¹.

Paper

Section A — Structured Questions (55 marks)

Question 1 (data analysis)

Keisha investigated the rate of reaction between marble chips (calcium carbonate) and dilute hydrochloric acid. She added an excess of marble chips to 25.0 cm³ of hydrochloric acid in a conical flask and collected the carbon dioxide in a gas syringe. She read the volume of gas every 30 seconds. Her results are shown in the table.

(a) (i) On graph paper in your answer booklet, plot a graph of the volume of carbon dioxide (vertical axis) against time (horizontal axis). Draw a smooth curve through the points. (4 marks)

(ii) Use your graph to find the volume of carbon dioxide collected after 45 seconds. (1 mark)

(iii) Calculate the average rate of reaction, in cm³ s⁻¹, over the first 60 seconds. (2 marks)

(iv) Using your results, describe how the rate of reaction changes during the experiment and explain this change in terms of particles. (2 marks)

(v) Explain why no more gas was collected after 210 seconds. (1 mark)

(b) (i) Write a balanced equation, with state symbols, for the reaction between calcium carbonate and hydrochloric acid. (2 marks)

(ii) Calculate the number of moles of carbon dioxide in the final volume of gas collected at r.t.p. (1 mark)

(iii) Hence state the number of moles of hydrochloric acid that reacted. (1 mark)

(iv) Calculate the concentration, in mol dm⁻³, of the hydrochloric acid Keisha used. (2 marks)

(c) Keisha repeated the experiment using the same mass of marble in powdered form and an identical volume of the same acid. Describe how the curve for this second experiment would differ from the first, and explain why the final volume is the same. (2 marks)

(d) Plan and design an experiment to investigate how temperature affects the rate of the reaction between marble chips and hydrochloric acid. Your answer should include:

(i) a hypothesis (1 mark)

(ii) the method, including the apparatus you would use (3 marks)

(iii) TWO variables you would control (1 mark)

(iv) a results table with suitable headings (1 mark)

(v) the results you would expect if your hypothesis is correct (1 mark)

Total 25 marks

Question 2

The table gives information about two elements, X and Y. (X and Y are not their chemical symbols.)

(a) (i) Write the electronic configurations of X and Y. (2 marks)

(ii) State the group and the period of the Periodic Table in which Y is found. (2 marks)

(iii) What are isotopes? (1 mark)

(iv) State the number of neutrons in an atom of each isotope of Y. (2 marks)

(v) Naturally occurring Y is 75% Y-35 and 25% Y-37. Calculate the relative atomic mass of Y. (2 marks)

(b) X and Y react together to form a compound.

(i) State the type of bonding in this compound. (1 mark)

(ii) Describe, in terms of electrons, how atoms of X and Y form the compound, and give its formula. (3 marks)

(iii) Explain why the compound conducts electricity when molten but NOT when solid. (2 marks)

Total 15 marks

Question 3

P, Q and R are three organic compounds, each containing two carbon atoms.

• P has the molecular formula C₂H₄.
• Q has the molecular formula C₂H₆O and burns with a clean blue flame.
• R has the molecular formula C₂H₄O₂ and turns blue litmus red.

(a) (i) Name the homologous series to which each of P, Q and R belongs. (3 marks)

(ii) Describe a chemical test that would distinguish P from ethane, giving the result for each compound. (2 marks)

(iii) P is converted to Q in industry. State the reagent and ONE condition used. (2 marks)

(iv) Q can be converted to R in the laboratory. Name a suitable reagent and state the colour change you would observe. (2 marks)

(b) Q reacts with R to form a sweet-smelling compound.

(i) Name the compound formed. (1 mark)

(ii) Write a balanced equation for the reaction, using structural or condensed formulae. (2 marks)

(iii) State the condition needed for this reaction. (1 mark)

(iv) State ONE use of compounds of this type. (1 mark)

(c) P can form the polymer poly(ethene). State the type of polymerisation involved. (1 mark)

Total 15 marks

Section B — Extended Response (45 marks)

Question 4

(a) (i) What is an electrolyte? (1 mark)

(ii) Distinguish between a strong electrolyte and a weak electrolyte, giving ONE example of each. (3 marks)

(b) Aqueous copper(II) sulfate is electrolysed using inert carbon electrodes.

(i) Name the product formed at EACH electrode and write the ionic half-equation for each. (4 marks)

(ii) State and explain what happens to the colour of the solution as electrolysis continues. (1 mark)

(c) The experiment in (b) is repeated using copper electrodes.

(i) Write the half-equation for the reaction at the anode. (1 mark)

(ii) Explain how this process is used to purify copper for electrical wiring. (2 marks)

(d) A current of 0.50 A is passed through aqueous copper(II) sulfate for 1930 seconds. Calculate the mass of copper deposited at the cathode. (3 marks)

Total 15 marks

Question 5

(a) A student placed small pieces of three metals, J, K and L, into solutions of each other's nitrates. Her observations were:

• J placed in a solution of the nitrate of K: a coating formed on J.
• J placed in a solution of the nitrate of L: no change.
• K placed in a solution of the nitrate of L: no change.

Arrange J, K and L in order of reactivity, most reactive first, and explain how you used the observations. (3 marks)

(b) Iron is extracted from iron(III) oxide in a blast furnace using coke, limestone and hot air.

(i) Explain the role of coke in the furnace. (2 marks)

(ii) Write a balanced equation for the reduction of iron(III) oxide. (2 marks)

(iii) State the purpose of the limestone. (1 mark)

(c) (i) State the TWO conditions needed for iron to rust. (2 marks)

(ii) Describe ONE method of preventing rusting and explain how it works. (2 marks)

(d) Many Caribbean territories now collect aluminium drink cans for recycling. Give THREE reasons why recycling aluminium is better than extracting new aluminium from bauxite. (3 marks)

Total 15 marks

Question 6

(a) (i) Define an acid in terms of protons. (1 mark)

(ii) Solutions of hydrochloric acid and ethanoic acid have the same concentration. Explain why the ethanoic acid has the higher pH. (2 marks)

(b) Describe how you would prepare a pure, dry sample of copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid. Include a balanced equation in your answer. (6 marks)

(c) In a titration, 25.0 cm³ of sodium hydroxide solution was exactly neutralised by 20.0 cm³ of sulfuric acid of concentration 0.100 mol dm⁻³.

2NaOH(aq) + H₂SO₄(aq) → Na₂SO₄(aq) + 2H₂O(l)

(i) Calculate the number of moles of sulfuric acid used. (1 mark)

(ii) Calculate the number of moles of sodium hydroxide that reacted. (1 mark)

(iii) Calculate the concentration of the sodium hydroxide solution in mol dm⁻³. (2 marks)

(iv) Express this concentration in g dm⁻³. (1 mark)

(d) The temperature of the mixture rose during the titration. State what this tells you about the energy change in the reaction. (1 mark)

Total 15 marks