Ncert Exercises & Solutions

1. What mass of hydrgen peroxide will be present in 2 L of a 5 molar solution?

2. Calculate the mass of oxygen which well be liberated by the decomposition of 200 mL of this solution.

(i) Molar mass of

H_{2} O_{2} = 34 g {mol}^{- 1}

1 L of 5 M solution of

H_{2} O_{2}

will contain

34 \times 5 g H_{2} O_{2}

2 L of 5 M solution of

H_{2} O_{2}

will contain

34 \times 5 \times 2 = 340 g H_{2} O_{2}

Mass of

H_{2} O_{2}

present in 2 L of 5 molar solution

= 340 g

(ii) 0.2 L (or 200 mL) of 5 M solution will contain

\frac{340 \times 0.2}{2} = 34 g H_{2} O_{2}

\underset{2 \times 34 = 68 g}{2 H_{2} O_{2}} \to 2 H_{2} O + \underset{2 \times 16 = 32 g}{O_{2}}

68 g H_{2} O_{2}

on decomposition will give

32 g O_{2}

∴ 34 g H_{2} O_{2}

on decomposition will give

\frac{32 \times 34}{68} = 16 g O_{2}