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. Graph paper is provided in the booklet.
- A silent, non-programmable calculator may be used. Show all working in calculations and give units.
- Relative atomic masses: H = 1, C = 12, N = 14, O = 16, Mg = 24, Al = 27. The molar volume of any gas at room temperature and pressure (r.t.p.) is 24 dm³.
Paper
Section A — Structured Questions (55 marks)
Question 1 (data analysis)
A student investigated how temperature affects the rate of reaction between magnesium ribbon and dilute hydrochloric acid:
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
For each experiment she added a 0.05 g piece of magnesium ribbon to 50 cm³ of 1.0 mol dm⁻³ hydrochloric acid at a measured temperature and timed how long the magnesium took to disappear. Her results are shown in the table; two values of 1/time have been left blank.
| Temperature / °C | Time for magnesium to disappear / s | Rate, 1/time / s⁻¹ |
|---|---|---|
| 20 | 120 | 0.0083 |
| 30 | 64 | |
| 40 | 34 | 0.0294 |
| 50 | 18 | |
| 60 | 10 | 0.1000 |
(a) State TWO variables that the student should keep constant during this investigation. (2 marks)
(b) Copy and complete the table by calculating 1/time for 30 °C and 50 °C, to 3 significant figures. (2 marks)
(c) On graph paper in your answer booklet, plot a graph of rate (1/time) on the vertical axis against temperature on the horizontal axis. Draw a smooth curve through the points. (4 marks)
(d) Describe how the rate of reaction changes as the temperature increases, using your graph. (2 marks)
(e) Use your graph to find the rate of reaction at 45 °C, and hence estimate the time the magnesium would take to disappear at that temperature. (2 marks)
(f) Explain, in terms of collision theory, why the rate increases with temperature. (2 marks)
(g) Calculate the maximum volume of hydrogen gas, in dm³, produced in each experiment at r.t.p. (3 marks)
(h) Suggest why the time recorded at 60 °C is the least reliable result. (1 mark)
(i) Plan and design an experiment to investigate how the concentration of hydrochloric acid affects the rate of its reaction with magnesium ribbon. 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 halogens are elements in Group VII of the Periodic Table.
(a) (i) State the trend in reactivity of the halogens as you descend Group VII. (1 mark)
(ii) Explain this trend in terms of electronic structure. (2 marks)
(b) Chlorine gas can be produced in the laboratory by reacting manganese(IV) oxide with concentrated hydrochloric acid:
MnO₂(s) + 4HCl(aq) → MnCl₂(aq) + 2H₂O(l) + Cl₂(g)
(i) State ONE safety precaution that should be taken when preparing chlorine gas in the laboratory. (1 mark)
(ii) Describe a chemical test to confirm that the gas produced is chlorine. Include the expected observation. (2 marks)
(c) In Trinidad and Tobago, chlorine is added to water supplies.
(i) State the purpose of adding chlorine to water. (1 mark)
(ii) When chlorine dissolves in water, a mixture of acids is formed. Write a balanced chemical equation for the reaction of chlorine with water. (2 marks)
(d) Chlorine water is added to colourless potassium bromide solution. State what you would observe, and write the ionic equation for the reaction. (3 marks)
(e) State the physical state and colour at room temperature of chlorine, bromine and iodine. (3 marks)
Total 15 marks
Question 3
Carbon compounds are important to Caribbean industries, from the rum distilleries to the fertiliser plants.
(a) Ethanol (C₂H₅OH) is used as a solvent and in the manufacture of alcoholic beverages. State the homologous series to which ethanol belongs. (1 mark)
(b) Ethanol can be produced by the fermentation of glucose using yeast:
C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g)
(i) State ONE condition necessary for fermentation to occur. (1 mark)
(ii) Calculate the maximum mass of ethanol, in grams, that could be produced from 90 g of glucose. (3 marks)
(iii) Explain why fermentation stops when the ethanol concentration reaches about 15%. (2 marks)
(c) (i) State the colour change observed when ethanol is oxidised by acidified potassium manganate(VII). (1 mark)
(ii) Write a balanced chemical equation for the complete combustion of ethanol in oxygen. (2 marks)
(d) Urea, CO(NH₂)₂, is a common nitrogen fertiliser. Calculate the percentage by mass of nitrogen in urea. Show all working. (3 marks)
(e) Ethanol made from sugar cane can be used as a fuel for cars. State ONE advantage and ONE disadvantage of using ethanol in place of petrol. (2 marks)
Total 15 marks
Section B — Extended Response (45 marks)
Question 4
Aluminium is extracted from its ore, bauxite, which is mined in Jamaica and Guyana.
(a) Name the main compound of aluminium present in bauxite. (1 mark)
(b) State the method used to extract aluminium from its purified ore. (1 mark)
(c) (i) Write the ionic half-equation for the reaction at the cathode during the extraction of aluminium. (2 marks)
(ii) Explain why cryolite is added to the purified aluminium oxide during the extraction. (2 marks)
(d) Aluminium is used to make cooking utensils. Suggest TWO properties of aluminium that make it suitable for this use. (2 marks)
(e) Aluminium is a reactive metal, yet aluminium pots do not corrode in use. Explain why. (2 marks)
(f) Describe THREE environmental effects of mining and refining bauxite. (3 marks)
(g) Calculate the maximum mass of aluminium, in kilograms, that can be extracted from 1.00 tonne (1000 kg) of aluminium oxide, Al₂O₃. (2 marks)
Total 15 marks
Question 5
The petroleum industry plays a vital role in the economy of Trinidad and Tobago. Crude oil is a complex mixture of hydrocarbons that must be separated and processed before use.
(a) (i) Define the term "hydrocarbon". (2 marks)
(ii) Name the industrial process used to separate crude oil into useful fractions. (1 mark)
(iii) Describe how this process separates the components of crude oil, referring to the differences in physical properties of the fractions. (4 marks)
(b) Naphtha, a fraction of crude oil, contains hydrocarbons with 5 to 10 carbon atoms. It can be converted into more useful products by catalytic cracking.
(i) State what is meant by the term "cracking". (2 marks)
(ii) Write a balanced equation for the cracking of one molecule of decane (C₁₀H₂₂) to produce octane (C₈H₁₈) and one other product. (2 marks)
(iii) Explain why cracking is an important process in the petroleum industry. (2 marks)
(iv) Describe a chemical test to show that the other product in (b)(ii) is unsaturated. State the result you would expect. (2 marks)
Total 15 marks
Question 6
The combustion of hydrocarbon fuels produces carbon dioxide, a greenhouse gas.
(a) Write a balanced equation for the complete combustion of octane, C₈H₁₈. (2 marks)
(b) When fuel burns in a limited supply of air, carbon monoxide is formed. Explain why carbon monoxide is dangerous. (2 marks)
(c) Evaluate the impact of increasing carbon dioxide levels in the atmosphere on the Caribbean region. In your answer you should:
- discuss the environmental consequences of increased carbon dioxide levels
- assess the potential effects on Caribbean nations
- suggest ONE way that Caribbean countries can reduce their carbon dioxide emissions. (9 marks)
(d) Calculate the mass of carbon dioxide, in kilograms, produced when 1.00 kg of octane (Mr = 114) burns completely. (2 marks)
Total 15 marks