Chemistry 9701/32 May June 2018 | Cambridge AS Level Past Papers With Mark Scheme

### 1. Decomposition of Metal Hydroxide (M(OH)₂):
- In this experiment, you heat a metal hydroxide, M(OH)₂, and identify the metal M based on the mass of residue (metal oxide) and water lost during the decomposition.
- Calculations involve:
- Mean mass of FB 1 (metal hydroxide) used.
- Mean moles of water lost.
- Calculating the relative formula mass of the metal oxide.
- Using the decomposition equation to find the relative atomic mass of M and suggest its identity.
- Analysis includes:
- How to ensure complete decomposition.
- The effect of contamination with MCO₃ (metal carbonate) on the results.

### 2. Enthalpy Change Determination for Calcium Hydroxide Decomposition:
- This experiment involves determining the enthalpy change for the decomposition of calcium hydroxide (Ca(OH)₂) to calcium oxide (CaO) using Hess's Law.
- You perform reactions of calcium hydroxide and calcium oxide with hydrochloric acid (HCl) and calculate the enthalpy changes based on the heat released.
- Calculations include:
- Energy produced during the reaction.
- Moles of calcium hydroxide used.
- Enthalpy changes (ΔH₁ and ΔH₂) for the reactions.
- Use Hess’s Law to find the enthalpy change for the decomposition of calcium hydroxide (ΔHr).
- Analysis includes:
- Reasons for heating the acid before adding calcium hydroxide or oxide.
- How changing the concentration of HCl affects the temperature rise and reaction.

### 3. Qualitative Analysis:
- This involves testing solutions (FB 5, FB 6, FB 7) for the presence of specific cations and anions using various reagents like magnesium ribbon, sodium carbonate, sodium hydroxide, barium chloride, and potassium iodide.
- The observations and ionic equations for reactions with different cations and anions are part of the analysis.