Question

Calculate the percentage of magnesium in magnesium carbonate.

Answer 1

• The percentage composition of a compound is the percentage weight of each component element present in it.
• Mathematically the percentage of an element in a compound

= $\frac{\mathrm{Total}\mathrm{weight}\mathrm{of}\mathrm{element}\mathrm{present}\mathrm{in}\mathrm{the}\mathrm{compound}}{\mathrm{Molecular}\mathrm{weight}\mathrm{of}\mathrm{the}\mathrm{compound}}$ × 100

• The percentage of Magnesium in Magnesium carbonate (MgCO₃)

1. First determine the components and their atomic masses in them.
2. In Magnesium carbonate(MgCO₃), 1 molecule of MgCO₃ contains 1atom of Magnesium(M), 1atom of Carbon(C), and 3 atoms of Oxygen(O).

1atom of magnesium(M) with atomic mass = 24g

1atom of carbon(C) with atomic mass = 12g

1 atom of oxygen(O) with atomic mass = 16g, since there are 3 Oxygen(O) atoms,

The atomic mass of 3 oxygen atoms = 16×3= 48g

Therefore the relative Molecular mass of Magnesium carbonate(MgCO₃) = Total atomic mass of component elements

= 24 + 12 + 48

= 84g/mol

3. The percentage of Magnesium present in Magnesium carbonate(MgCO₃) = $\frac{\mathrm{Total}\mathrm{weight}\mathrm{of}\mathrm{element}\mathrm{present}\mathrm{in}\mathrm{the}\mathrm{compound}}{\mathrm{Molecular}\mathrm{weight}\mathrm{of}\mathrm{the}\mathrm{compound}}$ × 100

= $\frac{24}{84}$× 100 = 28.57%

Hence the percentage of magnesium present in magnesium carbonate(MgCO₃) is 28.57%