A solution of FeCl3 in dilute HCl is saturated with H2S. If 0.20 mol of Fe^3+ is present, the observation and mass of sulphur formed (S = 32) are

pale-green solution with milky sulphur turbidity; 3.2 g

pale-green solution with milky sulphur turbidity; 6.4 g

pale-green solution with milky sulphur turbidity; 3.2 g

black precipitate of Fe2S3; 6.4 g sulphur

JEE Advanced levelSingle correct optionDifficulty 3 of 3qc095

A solution of $FeCl X_{3}$ in dilute $HCl$ is saturated with $H X_{2} S$ . If $0.20$ mol of $Fe X^{3 +}$ is present, the observation and mass of sulphur formed (S $= 32$ ) are

2 Fe X^{3 +} + H X_{2} S 2 Fe X^{2 +} + S + 2 H X^{+}

: Fe(III) is reduced to pale-green Fe(II) and

H X_{2} S

is oxidised to colloidal sulphur. Moles of S

= 0.20/2 = 0.10

, mass

= 0.10 \times 32 = 3.2 g

. This is why concentrated

HNO X_{3}

is used afterwards.