Two solutions were prepared as follows: Solution U1: Prepared by dissolving 2.12 g of sodium carbonate (Na₂CO₃) in 250 cm³ of water Solution U2: Contains hydrochloric acid of unknown concentration You are to determine the concentration of U2 using titration with methyl orange as indicator. Instructions: • Fill the burette with U2 • Pipette 25.0 cm³ of U1 into a conical flask • Add 2–3 drops of methyl orange and titrate with U2 • Repeat until three concordant titres are obtained and calculate the average

1. What was the colour change observed during the titration? (2 mk)
2. What was the colour change observed during the titration? (0 mk)
3. Write a balanced chemical equation and ionic equation for the reaction. (4 mk)
4. Write a balanced chemical equation and ionic equation for the reaction. (0 mk)
5. Calculate the concentration of solution U1 in mol/dm³. (5 mk)
6. Calculate the concentration of solution U1 in mol/dm³. (0 mk)
7. If the average titre is 25.0 cm³, calculate the number of moles of HCl used. (0 mk)
8. If the average titre is 25.0 cm³, calculate the number of moles of HCl used. (4 mk)
9. Determine the concentration of HCl in mol/dm³. (0 mk)
10. Determine the concentration of HCl in mol/dm³. (6 mk)
11. Convert your answer in (e) to g/dm³. (Molar mass of HCl = 36.5 g/mol) (4 mk)
12. Convert your answer in (e) to g/dm³. (Molar mass of HCl = 36.5 g/mol) (0 mk)

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In a study of the effect of temperature on reaction rate, a student was given: Solution V1: 0.1 M potassium iodide Solution V2: 0.1 M hydrogen peroxide Solution V3: 1 M sulfuric acid Starch solution The student was instructed to mix 5 cm³ of each solution in a test tube, add two drops of starch and record the time taken for a blue-black colour to appear. This was repeated at temperatures 30°C to 70°C. Page 2 of 3

1. What causes the blue-black colour in this experiment? (2 mk)
2. What causes the blue-black colour in this experiment? (0 mk)
3. Complete the table below: (0 mk)
4. Complete the table below: (5 mk)
5. Write the ionic equation for the reaction between hydrogen peroxide and iodide in acidic medium. (4 mk)
6. Write the ionic equation for the reaction between hydrogen peroxide and iodide in acidic medium. (0 mk)
7. What effect does increasing temperature have on the rate of this reaction? (0 mk)
8. What effect does increasing temperature have on the rate of this reaction? (2 mk)
9. What precaution must be taken when measuring time during this experiment? (2 mk)
10. What precaution must be taken when measuring time during this experiment? (0 mk)

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A salt labeled Z is suspected to be ammonium chloride. Carry out the following tests to confirm the ions: Page 3 of 3

1. Describe the appearance of salt Z. (0 mk)
2. Heat a small amount in a dry test tube and test the gas evolved with damp red and blue litmus. (0 mk)
3. Add a portion to water and test with sodium hydroxide. Warm gently and test the gas evolved. (0 mk)
4. Add silver nitrate solution followed by nitric acid to a fresh portion. (0 mk)
5. Record your observations and inferences in a clear table. (0 mk)
6. Identify the cation and anion in salt Z. (0 mk)
7. Write balanced equations for: – The reaction with NaOH – The reaction with AgNO₃ (0 mk)
8. Suggest two physical properties of salt Z that help identify it before any chemical test. (0 mk)

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