Secondary 3 Chemistry Practice Paper 1

TuitionGoWhere Practice Paper - Chemistry Secondary 3 - Mark Scheme

Total Marks: 60

Section A: Short Answer Questions [20 marks]

1. Define the term 'acid' in terms of the ions it produces in aqueous solution. [1]

Answer: A substance that produces/releases hydrogen ions (H⁺) in aqueous solution Mark: 1 mark for H⁺ ions mentioned

2. State the pH range for acidic solutions. [1]

Answer: Less than 7 / 0-6.9 / Below 7 Mark: 1 mark for correct range

3. Name the salt formed when potassium hydroxide reacts with nitric acid. [1]

Answer: Potassium nitrate Mark: 1 mark for correct name

4. Write the chemical formula for sulfuric acid. [1]

Answer: H₂SO₄ Mark: 1 mark for correct formula

5. State two safety precautions that should be taken when handling concentrated acids. [2]

Answer: Any two from: Wear safety goggles/eye protection; Wear gloves; Use fume cupboard; Add acid to water (not water to acid); Keep away from skin/clothing Mark: 1 mark each for any two valid precautions

6. Complete the word equation: Metal carbonate + Acid → _______ + _______ + _______ [1]

Answer: Salt + Water + Carbon dioxide Mark: 1 mark for all three products correct

7. Name the indicator that shows a range of colours depending on pH. [1]

Answer: Universal indicator Mark: 1 mark for correct indicator

8. State what is meant by the term 'neutralization'. [1]

Answer: The reaction between an acid and a base/alkali to form salt and water / H⁺ + OH⁻ → H₂O Mark: 1 mark for correct definition

9. Give the chemical test for hydrogen gas. [1]

Answer: Lighted splint produces a 'pop' sound / Burns with a squeaky pop Mark: 1 mark for correct test and observation

10. Name two acids that occur naturally in foods. [2]

Answer: Any two from: Citric acid (citrus fruits); Ethanoic acid (vinegar); Tartaric acid (grapes); Lactic acid (sour milk) Mark: 1 mark each for any two correct acids

11. State the colour change when red litmus paper is placed in an alkaline solution. [1]

Answer: Red to blue / Turns blue Mark: 1 mark for correct colour change

12. Write the ionic equation for neutralization. [1]

Answer: H⁺ + OH⁻ → H₂O Mark: 1 mark for correct ionic equation

13. Name the process used to obtain pure water from salt water. [1]

Answer: Distillation Mark: 1 mark for correct process

14. State whether ammonia solution is acidic, neutral, or alkaline. [1]

Answer: Alkaline Mark: 1 mark for correct classification

15. Give one use of hydrochloric acid in industry. [1]

Answer: Any one from: Cleaning metals; Making plastics (PVC); Food processing; Making other chemicals Mark: 1 mark for any valid industrial use

16. Name the compound responsible for acid rain. [1]

Answer: Sulfur dioxide / SO₂ (or nitrogen oxides/NOₓ) Mark: 1 mark for correct compound

17. State the effect of dilution on the pH of an acidic solution. [1]

Answer: pH increases / Becomes less acidic / Approaches 7 Mark: 1 mark for correct effect

18. Write the chemical formula for calcium hydroxide. [1]

Answer: Ca(OH)₂ Mark: 1 mark for correct formula

Section B: Structured Questions [40 marks]

19. A student investigates the reactions of acids with different substances. [10 marks]

(a)(i) Write a balanced chemical equation for this reaction. Include state symbols. [2]

Answer: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g) Mark: 1 mark for correct equation and balancing, 1 mark for state symbols

(a)(ii) Name the gas produced in this reaction. [1]

Answer: Hydrogen Mark: 1 mark for correct gas

(a)(iii) Describe the chemical test for this gas. [2]

Answer: Apply a lighted splint to the gas. The gas burns with a squeaky pop/explosive sound. Mark: 1 mark for lighted splint, 1 mark for squeaky pop observation

(b)(i) Write a balanced chemical equation for this reaction. Include state symbols. [2]

Answer: CuCO₃(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l) + CO₂(g) Mark: 1 mark for correct equation and balancing, 1 mark for state symbols

(b)(ii) State two observations the student would make. [2]

Answer: Any two from: Effervescence/bubbles of gas; Copper carbonate dissolves; Solution turns blue/green; Solid disappears Mark: 1 mark each for any two valid observations

(c) Explain why copper metal does not react with dilute hydrochloric acid. [1]

Answer: Copper is below hydrogen in the reactivity series / Copper is less reactive than hydrogen Mark: 1 mark for correct explanation

20. Titration experiment [15 marks]

(a) Name apparatus X and Y. [2]

Answer: X: Burette; Y: Conical flask (or pipette if X is conical flask) Mark: 1 mark each for correct apparatus names

(b)(i) Calculate the average volume of hydrochloric acid used. [2]

Answer: Concordant results: 24.1, 24.0, 23.9 cm³ Average = (24.1 + 24.0 + 23.9) ÷ 3 = 24.0 cm³ Mark: 1 mark for identifying concordant results, 1 mark for correct calculation

(b)(ii) Calculate the number of moles of hydrochloric acid in the average volume used. [2]

Answer: Volume = 24.0 cm³ = 0.0240 dm³ Moles = concentration × volume = 0.100 × 0.0240 = 0.00240 mol Mark: 1 mark for volume conversion, 1 mark for correct calculation

(c)(i) State the mole ratio of NaOH to HCl in this reaction. [1]

Answer: 1:1 Mark: 1 mark for correct ratio

(c)(ii) Calculate the number of moles of sodium hydroxide in 25.0 cm³ of solution. [1]

Answer: 0.00240 mol (same as HCl due to 1:1 ratio) Mark: 1 mark for correct answer

(c)(iii) Calculate the concentration of the sodium hydroxide solution in mol/dm³. [2]

Answer: Volume of NaOH = 25.0 cm³ = 0.0250 dm³ Concentration = moles ÷ volume = 0.00240 ÷ 0.0250 = 0.0960 mol/dm³ Mark: 1 mark for correct formula and setup, 1 mark for correct answer

21. Salt preparation [11 marks]

(a) Name this method of salt preparation. [1]

Answer: Neutralization / Acid + insoluble base / Direct combination Mark: 1 mark for correct method name

(b) Explain why this method is suitable for preparing zinc sulfate. [2]

Answer: Zinc oxide is insoluble in water, so excess can be easily removed by filtration. Zinc sulfate is soluble, so it remains in solution. Mark: 1 mark for insoluble reactant, 1 mark for soluble product

(c) Describe the experimental procedure. [4]

Answer: Step 1: Add excess zinc oxide to dilute sulfuric acid and stir/warm until no more dissolves Step 2: Filter to remove unreacted zinc oxide Step 3: Evaporate the filtrate to crystallization point Step 4: Cool to allow crystals to form and dry Mark: 1 mark each for correct description of each step

(d)(i) Calculate the number of moles of zinc oxide used. [2]

Answer: Mr of ZnO = 65 + 16 = 81 Moles = mass ÷ Mr = 1.63 ÷ 81 = 0.0201 mol Mark: 1 mark for Mr calculation, 1 mark for moles calculation

(d)(ii) Calculate the theoretical yield of zinc sulfate. [2]

Answer: From equation: 1 mol ZnO produces 1 mol ZnSO₄ Moles of ZnSO₄ = 0.0201 mol Mr of ZnSO₄ = 65 + 32 + (4 × 16) = 161 Theoretical yield = 0.0201 × 161 = 3.24 g Mark: 1 mark for mole ratio and Mr, 1 mark for mass calculation

(d)(iii) Calculate the percentage yield. [2]

Answer: Percentage yield = (actual yield ÷ theoretical yield) × 100% = (3.22 ÷ 3.24) × 100% = 99.4% Mark: 1 mark for correct formula, 1 mark for correct calculation

22. Uses of acids and alkalis [4 marks]

(a) Give one use of each: [3]

(i) Sulfuric acid: Car batteries / Making fertilizers / Making detergents / Refining petroleum (ii) Sodium hydroxide: Making soap / Making paper / Cleaning drains / Food processing (iii) Ammonia solution: Cleaning / Making fertilizers / Making nylon Mark: 1 mark each for any valid use

(b) Explain why farmers add lime to soil. [2]

Answer: Lime is alkaline/basic. It neutralizes acidic soil, increasing the pH to make it suitable for plant growth. Mark: 1 mark for alkaline nature, 1 mark for neutralizing acidic soil

(c) Describe how acid rain is formed and state one harmful effect. [3]

Answer: Formation: Sulfur dioxide (from burning fossil fuels) dissolves in rainwater to form sulfuric acid / SO₂ + H₂O → H₂SO₃ Harmful effect: Any one from: Damages buildings/statues; Kills fish in lakes; Damages forests; Corrodes metals Mark: 2 marks for formation (1 for SO₂ source, 1 for acid formation), 1 mark for harmful effect

Total: 60 marks