Magnesium carbonate has the formula MgCO₃ - Edexcel - GCSE Chemistry - Question 3 - 2022 - Paper 1

Solid magnesium can conduct electricity because it consists of metallic bonding with free-moving electrons. In contrast, solid magnesium carbonate is an ionic compound, and while the ions are present, they are held in fixed positions within the crystal lattice, preventing movement. Hence, solid magnesium carbonate cannot conduct electricity.

To find the percentage by mass of magnesium in MgCO₃, we first calculate the molar mass of the compound:

• Molar mass of MgCO₃ = Mg (24.0) + C (12.0) + 3×O (3×16.0) = 24.0 + 12.0 + 48.0 = 84.0 g/mol.

Next, the percentage by mass of magnesium is given by the formula: $\text{Percentage by mass of Mg} = \left( \frac{\text{Mass of Mg}}{\text{Molar Mass of MgCO₃}} \right) \times 100$

Substituting the values: $\left( \frac{24.0}{84.0} \right) \times 100 = 28.57\%$

The balanced equation for the reaction of magnesium carbonate with dilute hydrochloric acid is:

$\text{MgCO}_3 + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\text{O} + \text{CO}_2$