Question

5.0g of bleaching powder was suspended in water and volume made up to half a litre. 20 mL of this suspension when acidified with acetic acid and treated with excess of potassium iodide solution liberated iodine, which required 20 mL of a deci-normal hypo solution for titration. Calculate the value of 10 × x, where x is the percentage of available chlorine in bleaching powder?

Answer 1

The value of 10 × x, where x is the percentage of available chlorine in bleaching powder is 14.2%

Calculate the moles of hypochlorite consumed:

Molarity of hypo solution = 0.1 mol/L (deci-normal)

Volume of hypo solution used = 20 mL = 0.02 L

Moles of hypochlorite consumed = Molarity * Volume = 0.1 mol/L * 0.02 L = 0.002 mol

Relate hypochlorite moles to available chlorine:

The balanced chemical equation shows that 1 mole of hypochlorite reacts with 1 mole of available chlorine.

Calculate the mass of available chlorine in the sample:

Moles of available chlorine

= Moles of hypochlorite consumed = 0.002 mol

Molar mass of chlorine = 35.5 g/mol

Mass of available chlorine

= Moles * Molar mass

= 0.002 mol * 35.5 g/mol = 0.071 g

Calculate the percentage of available chlorine in the bleaching powder:

Mass of bleaching powder used = 5.0 g

Percentage of available chlorine

= (Mass of available chlorine / Mass of bleaching powder) * 100%

Percentage of available chlorine

= (0.071 g / 5.0 g) * 100% = 1.42%

Therefore, the value of 10 × x is 14.2%