Calcium reacts with water to form calcium hydroxide, Ca(OH)₂, and hydrogen, H₂ - Edexcel - GCSE Chemistry Combined Science - Question 2 - 2016 - Paper 1

The balanced equation for the reaction between magnesium and steam is:

$2Mg(s) + 2H_2O(g) → 2MgO(s) + H_2(g)$

Calcium is more reactive than magnesium because it has a higher tendency to lose its outer electrons. Magnesium has the electronic configuration of 2.8.2, while calcium has 2.8.8.2. As calcium has two electrons in its outer shell, it will lose these electrons more easily compared to magnesium, which holds on to its outer shell electrons more tightly. This makes calcium more reactive.

To calculate the empirical formula, we first divide the mass by the relative atomic mass:

• For calcium, $\frac{0.2 ext{ g}}{40 ext{ g/mol}} = 0.005 \text{ mol}$
• For bromine, $\frac{0.8 ext{ g}}{80 ext{ g/mol}} = 0.01 \text{ mol}$

Next, we find the simplest ratio:

• Calcium : Bromine = 0.005 : 0.01 = 1 : 2

Thus, the empirical formula for calcium bromide is CaBr₂.