Question

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

(i) Sodium chloride, (ii) magnesium oxide, (iii) calcium carbonate

Answer 1

(i) We know that,

Molar mass= sum of constituent atomic masses

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

Number of moles of a substance= \(\frac{\text{Molar mass of substance in grams}}{\text{Molecular mass of the substance}}\)

0.2=\(\frac{x}{58.5}\)

x = 0.2×58.5 = 11.7g

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

(ii) Molar mass of MgO= 24 + 16 = 40 g/mol

Number of moles of a substance= \(\frac{\text{Molar mass of substance in grams}}{\text{Molecular mass of the substance}}\)

0.2=\(\frac{x}{40}\)

x = 0.2×40 = 8g

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

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

Number of moles of a substance= \(\frac{\text{Molar mass of substance in grams}}{\text{Molecular mass of the substance}}\)

0.2=\(\frac{x}{100}\)

x =0.2×100= 20 g

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