Magnesium carbonate has the formula MgCO₃ - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1

Solid magnesium carbonate (MgCO₃) does not conduct electricity because its ions (Mg²⁺ and CO₃²⁻) are fixed in a lattice structure. In this solid state, the charged ions cannot move freely, which is essential for the conduction of electricity.

In contrast, solid magnesium contains metallic bonds where the magnesium atoms share their electrons in a 'sea of electrons', allowing them to move freely. This mobility of electrons in magnesium enables it to conduct electricity effectively. Therefore, the key points are:

• In solid MgCO₃, ions are fixed and cannot move.
• In solid magnesium, electrons are free to flow, allowing conduction.

To calculate the percentage by mass of magnesium in magnesium carbonate (MgCO₃), we first need to determine the molar masses of each component:

• Molar mass of Mg = 24.0 g/mol
• Molar mass of C = 12.0 g/mol
• Molar mass of O = 16.0 g/mol (there are 3 oxygen atoms, so this contributes 3 × 16.0 = 48.0 g/mol)

Calculating the total mass of MgCO₃:

$ext{Molar mass of MgCO₃} = 24.0 + 12.0 + 48.0 = 84.0 ext{ g/mol}$

Now, the percentage by mass of magnesium is calculated as follows:

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

Final Answer: The percentage by mass of magnesium in magnesium carbonate, MgCO₃, is approximately 28.57%.