A technician prepared a solution coded S1 by dissolving an unknown mass of sodium hydroxide pellets in water. Another solution, coded S2, was made by dissolving 3.65 g of hydrochloric acid in 1 dm³ of water. You are required to determine the concentration of solution S1 by titrating it with S2 using methyl orange as the indicator. Instructions: • Fill the burette with solution S2 • Pipette 25.0 cm³ of S1 into a conical flask • Add 2–3 drops of methyl orange and titrate to the end point • Repeat the titration and record the average volume of acid used

1. State the colour change observed during titration. (1 mk)
2. What is the balanced chemical equation between S1 and S2? (2 mk)
3. Calculate the concentration of S2 in mol/dm³. (2 mk)
4. Using an average titre of 25.0 cm³, calculate the number of moles of HCl used. (1 mk)
5. Use the mole ratio to determine the number of moles of NaOH in 25.0 cm³. (1 mk)
6. Calculate the concentration of NaOH in mol/dm³ and g/dm³ (Molar mass of NaOH = 40 g/mol). (2 mk)
7. Suggest two reasons why the technician used pellets of NaOH instead of prepared solution. (1 mk)

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You are given: • 0.2 M potassium iodide labeled W1 • 0.2 M hydrogen peroxide labeled W2 • 0.1 M sulfuric acid labeled W3 • Starch indicator • Stopwatch Equal volumes of W1, W2, and W3 are mixed in a clean beaker. A few drops of starch solution are added, and the time for the blue-black colour to appear is recorded. The procedure is repeated at 25°C, 35°C, 45°C, 55°C, and 65°C.

1. What causes the blue-black colour during the reaction? (1 mk)
2. Complete the following table by filling in the temperature in Kelvin and suggest reasonable times. Temperature (°C) Temperature (K) Time (s) 25 72 35 52 45 36 55 24 65 14 (3 mk)
3. Write the net ionic equation for the reaction between hydrogen peroxide and iodide. (2 mk)
4. Plot a graph of temperature (K) against time (s). (1 mk)
5. Explain how temperature affects the reaction rate based on the data above. (2 mk)
6. If the reaction was done at 15°C, what would be the expected trend in time? Explain. (1 mk)

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A salt labeled Y is suspected to be a sulphate of a transition metal. Perform the following tests to identify the ions present: (a) Observe and record the appearance of salt Y. (b) Heat a small amount in a test tube and record observations. (c) Dissolve a portion in water and test with aqueous sodium hydroxide. (d) Test a second portion with aqueous ammonia solution. (e) Test a third portion with barium chloride followed by dilute hydrochloric acid. (f) Test a fresh solution with silver nitrate followed by dilute nitric acid.

1. Construct a table to show observations and inferences. (3 mk)
2. What is the identity of the cation and anion present in salt Y? (2 mk)
3. Write a balanced chemical equation for the reaction with barium chloride. (2 mk)
4. Give one distinguishing property of the salt that confirms it is a transition metal compound. (3 mk)

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