Question

A sample of hydrazine sulphate (N₂H₆SO₄) was dissolved in 100 ml. of water, 10 ml of this solution was reacted with excess of ferric chloride solution and warmed to complete the reaction. Ferrous ion formed was estimated and it required 20 ml. of M/50 potassium permanganate solution. Estimate the amount of hydrazine sulphate in one litre of the solution.
Reaction :
$4Fe^{3+} + N_2H_4 \longrightarrow N_2 + 4Fe^{2+} + 4H^+$
$MnO_4^- + 5Fe^{2+} + 8H^+ \longrightarrow Mn^{2+} + 5Fe^{3+} + 4H_2O.$

Answer 1

Meq of 〖MnO〗_4^- required = 20 × 1/50 × 5 = 2 ⇒ Meq of Fe2+ present in solution = 2 ⇒ millimol of Fe2+ present in solution = 2 (n-factor = 1) Also, ∵ 4 millimol of Fe2+ are formed from 1 millimol N2H4 ∴ 2 millimol Fe2+ from 1/4 ×2= 1/2 millimol N2H4 Therefore, molarity of hydrazine sulphate solution 1/2 × 1/10= 1/20 ⇒ In 1 L solution 1/20 mol N2H6SO4 is present. ⇒ Amount of N2H6SO4 = 1/20 × 130 = 6.5 gL-1