H2S is passed into one dm3 of a solution containing 0.1 mole of Zn2+ and 0.01 mole of Cu2+ till the sulphide ion concentration reaches 8.1 ×10-19 moles. Which one of the following statements is true? [Ksp of ZnS and CuS are 3 × 10-22 and 8 × 10-36 respectively]

Question

H2S is passed into one dm3 of a solution containing 0.1 mole of Zn2+ and 0.01 mole of Cu2+ till the sulphide ion concentration reaches 8.1 ×10-19 moles. Which one of the following statements is true? [Ksp of ZnS and CuS are 3 × 10-22 and 8 × 10-36 respectively] (A) Only ZnS precipitates (B) Both CuS and ZnS precipitate (C) Only CuS precipitates (D) No precipitation occurs

Tardigrade Admin · Accepted Answer

Precipitation occurs only when ionic product exceeds the value of solubility product.

1 d m^{3}

of a solution containing

0.1 m o l e

of

Z n^{2 +}, 0.01 m o l e

of

C u^{2 +}

and

8.1 \times 1 0^{- 19} m o l e

of

S^{2 +}

. Let us calculate the ionic product in each case.
Ionic product of

Z n S = [Z n^{2 +}] [S^{2 -}]

= 0.1 \times 8.1 \times 1 0^{- 19} = 8.1 \times 1 0^{- 20}

Ks p

of

Z n S = 3 \times 1 0^{- 22}

∴

Ionic product

> K_{s p}

Ionic product of

C u S = [C u^{2 +}] [S^{2 -}]

= 0.01 \times 8.1 \times 1 0^{- 19} = 8.1 \times 1 0^{- 21}

But it has

K_{s p} = 8 \times 1 0^{- 36}

∴

Ionic product

> K_{s p}

Both

Z n S

and

C u S

have less

K_{s p}

values than their respective ionic products so

Z n S

and

C u S

both precipitates.

Only $Z n S$ precipitates

Both $C u S$ and $Z n S$ precipitate

Only $C u S$ precipitates

No precipitation occurs

Q. H2​S is passed into one dm3 of a solution containing 0.1mole of Zn2+ and 0.01mole of Cu2+ till the sulphide ion concentration reaches 8.1×10−19 moles. Which one of the following statements is true? [Ksp​ of ZnS and CuS are 3×10−22 and 8×10−36 respectively]

Only ZnS precipitates

Both CuS and ZnS precipitate

Only CuS precipitates

No precipitation occurs

Only $Z n S$ precipitates

Both $C u S$ and $Z n S$ precipitate

Only $C u S$ precipitates