Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic $8.1$ — Arrangement of elements (Part $\mathrm{(a)}$)
• Topic $2.7$ — Metallic bonding (Part $\mathrm{(b)}$)
• Topic $9.1$ — Properties of metals (Parts $\mathrm{(c)}$, $\mathrm{(d)}$)
• Topic $3.3$ — The mole and the Avogadro constant (Part $\mathrm{(e)}$)
(a) Strontium (Sr)
Explanation: The period number corresponds to the number of occupied electron shells. The Group II element in Period $5$ is Strontium.
(b) Name: Metallic bonding.
Description: It is the electrostatic attraction between positive ions (cations) arranged in a giant lattice and a ‘sea’ of delocalised (mobile) electrons.
(c)(i) Observations: 1. Effervescence (bubbles of gas), 2. The solid calcium dissolves/disappears, 3. The universal indicator solution turns blue (or purple).
(c)(ii) Products: Calcium hydroxide and hydrogen.
Explanation: Metals reacting with water form metal hydroxides and hydrogen gas. Calcium hydroxide is an alkali, which turns universal indicator blue/purple.
(d)(i) Orange-red (or brick-red).
(d)(ii) $2Ca + O_{2} \rightarrow 2CaO$
(e)(i) Water of crystallisation.
(e)(ii) $x = 4$
Calculation:
Moles of $Ca(NO_{3})_{2} = \frac{3.28}{164} = 0.0200\text{ mol}$
Moles of $H_{2}O$ given off (the mass decrease) $= \frac{1.44}{18} = 0.0800\text{ mol}$
Ratio of $Ca(NO_{3})_{2}$ to $H_{2}O$ is $0.0200 : 0.0800$, which simplifies to $1 : 4$. Therefore, $x = 4$.
