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

Solid magnesium carbonate (MgCO₃) cannot conduct electricity because it consists of fixed ions in a lattice structure, which do not move freely. In contrast, solid magnesium can conduct electricity because it contains delocalized electrons that are free to move throughout the metallic lattice, allowing for the conduction of electric current.

To calculate the percentage by mass of magnesium in magnesium carbonate (MgCO₃), first determine the molar mass of MgCO₃. The molar mass is calculated as follows:

• Magnesium (Mg): 24.0 g/mol
• Carbon (C): 12.0 g/mol
• Oxygen (O): 16.0 g/mol × 3 = 48.0 g/mol

Total molar mass of MgCO₃ = 24.0 + 12.0 + 48.0 = 84.0 g/mol

The percentage by mass of magnesium is then given by:

$\text{Percentage} = \left( \frac{\text{mass of Mg}}{\text{molar mass of MgCO₃}} \right) \times 100 = \left( \frac{24.0}{84.0} \right) \times 100 \approx 28.57\%$

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

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