A student was given: • V1: A solution of nitric acid with unknown concentration • V2: A standard solution of sodium carbonate prepared by dissolving 5.3 g of Na₂CO₃ in 500 cm³ of water The student was instructed to determine the concentration of V1 by titrating it against V2 using methyl orange as indicator. Instructions: • Pipette 25.0 cm³ of V2 into a conical flask • Add 2–3 drops of methyl orange • Titrate with V1 from the burette until the colour changes • Repeat and calculate the average volume used (a) State the colour change observed during titration. (b) Write the balanced chemical and ionic equations for the reaction. (c) Calculate the concentration of V2 in mol/dm³. (d) If the average titre of V1 was 25.0 cm³, calculate the number of moles of HNO₃ used. (e) Hence calculate the concentration of HNO₃ in mol/dm³. (f) State the mass of HNO₃ in 250 cm³ of this acid solution. (Molar mass = 63 g/mol)

1. State the colour change observed during titration. (1 alama)
2. Write the balanced chemical and ionic equations for the reaction. (3 alama)
3. Calculate the concentration of V2 in mol/dm³. (3 alama)
4. If the average titre of V1 was 25.0 cm³, calculate the number of moles of HNO₃ used. (3 alama)
5. Hence calculate the concentration of HNO₃ in mol/dm³. (2 alama)
6. State the mass of HNO₃ in 250 cm³ of this acid solution. (Molar mass = 63 g/mol) (2 alama)

Boresha ili kuona majibu ya mfano.

You are given: • 0.2 M sodium thiosulphate (Y1) • 0.1 M hydrochloric acid (Y2) • Stopwatch, beaker, and a paper marked with “O” You are to study the effect of concentration of Y1 on the rate of reaction. Keep the volume of Y2 constant and dilute Y1 progressively while maintaining the total volume constant. Questions (a) Why does the mark “O” disappear during the reaction? (b) Complete the following table: Trial Y1 (cm³) Water (cm³) Y2 (cm³) Time (s) 1 10 0 10 19 2 8 2 10 25 3 6 4 10 34 4 4 6 10 48 5 2 8 10 71 (c) Write the full and net ionic equations for the reaction. (d) Explain how the concentration of Y1 affects the rate of the reaction. (e) List two possible errors to avoid when recording time.

1. Why does the mark “O” disappear during the reaction? (2 alama)
2. Complete the following table: (0 alama)
3. Write the full and net ionic equations for the reaction. (4 alama)
4. Explain how the concentration of Y1 affects the rate of the reaction. (3 alama)
5. List two possible errors to avoid when recording time. (2 alama)

Boresha ili kuona majibu ya mfano.

A salt labeled F is suspected to be a nitrate of a heavy metal. Carry out the following tests to identify the cation and confirm the anion: (a) Record the physical appearance of salt F. (b) Heat a small amount in a dry test tube and observe the gas evolved. (c) Dissolve a portion in water and test with aqueous sodium hydroxide dropwise and then in excess. (d) Test another portion with aqueous ammonia dropwise and in excess. (e) Add iron(II) sulfate and concentrated sulfuric acid down the side of the test tube. (f) Test a fresh portion with barium chloride and dilute HCl. Questions (i) Record your observations and give inferences in a table. (ii) Identify the cation and anion in salt F. (iii) Write two balanced chemical equations from the above reactions. (iv) What special test confirms the presence of a nitrate ion?

1. Record the physical appearance of salt F. (1 alama)
2. Heat a small amount in a dry test tube and observe the gas evolved. (2 alama)
3. Dissolve a portion in water and test with aqueous sodium hydroxide dropwise and then in excess. (2 alama)
4. Test another portion with aqueous ammonia dropwise and in excess. (2 alama)
5. Add iron(II) sulfate and concentrated sulfuric acid down the side of the test tube. (2 alama)
6. Test a fresh portion with barium chloride and dilute HCl. (2 alama)
7. Record your observations and give inferences in a table. (0 alama)
8. Identify the cation and anion in salt F. (2 alama)
9. Write two balanced chemical equations from the above reactions. (2 alama)
10. What special test confirms the presence of a nitrate ion? (1 alama)

Boresha ili kuona majibu ya mfano.