Question

If 0.2 mol of the following substances are required how many grams of those substances should be taken?

Sodium chloride, magnesium oxide, calcium carbonate

Answer 1

a. We know that,

$\mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{a}\mathrm{substance}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{substance}\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{substance}}$

Molar mass= sum of constituent atomic masses

Molar mass of NaCl= 23 + 35.5 = 58.5 g/mol

$\mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{a}\mathrm{substance}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{substance}\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{substance}}$

$0.2=\frac{\mathrm{x}}{58.5}=11.7$g

We need, 11.7 g of NaCl for obtaining 0.2 moles of NaCl.


b. Molar mass of MgO= 24 + 16 = 40 g/mol

$\mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{a}\mathrm{substance}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{substance}\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{substance}}$

$0.2=\frac{\mathrm{x}}{40}=8$g

We need, 8 g of MgO for obtaining 0.2 moles of MgO.


c. Molar mass of CaCO₃= 40 + 12 + 3 (16) = 100 g/mol

$\mathrm{Number}\mathrm{of}\mathrm{moles}\mathrm{of}\mathrm{a}\mathrm{substance}=\frac{\mathrm{Mass}\mathrm{of}\mathrm{the}\mathrm{substance}\mathrm{in}\mathrm{grams}}{\mathrm{Molecular}\mathrm{mass}\mathrm{of}\mathrm{the}\mathrm{substance}}$

$0.2=\frac{\mathrm{x}}{100}=20$g

We need, 20 g of CaCO₃ for obtaining 0.2 moles of CaCO₃.