In a Marsh-type test, 0.396 g of As2O3 (As 75, O 16) is reduced by zinc and acid: As2O3 + 6Zn + 12H+ -> 2AsH3 + 6Zn^2+ + 3H2O. Taking the molar volume at STP as 22.4 L mol^-1 and Zn = 65, the volume of AsH3 at STP and the mass of zinc consumed are

JEE Advanced levelSingle correct optionDifficulty 3 of 3qc055

In a Marsh-type test, $0.396 g$ of $As X_{2} O X_{3}$ (As 75, O 16) is reduced by zinc and acid: $As X_{2} O X_{3} + 6 Zn + 12 H X^{+} 2 AsH X_{3} + 6 Zn X^{2 +} + 3 H X_{2} O$ . Taking the molar volume at STP as $22.4 L mo l^{- 1}$ and Zn = 65, the volume of $AsH X_{3}$ at STP and the mass of zinc consumed are

M (As X_{2} O X_{3}) = 2 \times 75 + 48 = 198

, so

n = 0.396/198 = 0.0020 mol

. The equation gives

2 mol

AsH X_{3}

and

6 mol

Zn

per mol

As X_{2} O X_{3}

, i.e.

0.0040 mol

AsH X_{3}

and

0.0120 mol

Zn

. Volume

= 0.0040 \times 22400 = 89.6 mL

and mass of Zn

= 0.0120 \times 65 = 0.78 g

. Arsenic goes from

+ 3

- 3