JEE Advanced 2018 · Paper 2 · Chemistry Q2

ChemistryMultiple correct+4 / -2Question 20 of 54

The correct option(s) to distinguish nitrate salts of $\mathrm{Mn^{2+}}$ and $\mathrm{Cu^{2+}}$ taken separately is (are)

\mathrm{Mn^{2+}}

shows the characteristic green colour in the flame test

Only

\mathrm{Cu^{2+}}

shows the formation of precipitate by passing

\mathrm{H_2S}

in acidic medium

Only

\mathrm{Mn^{2+}}

shows the formation of precipitate by passing

\mathrm{H_2S}

in faintly basic medium

\mathrm{Cu^{2+}/Cu}

has higher reduction potential than

\mathrm{Mn^{2+}/Mn}

(measured under similar conditions)

Answer and worked solution

Official answer: B, D

(A) The green (bluish-green) flame is characteristic of copper, not manganese. False.
(B) CuS has a very small $K_{sp}$ and precipitates even in acid (group II). MnS does not. True.
(C) In faintly basic medium MnS precipitates, but so does CuS. "Only $\ce{Mn^{2+}}$ " is wrong. False.
(D) $E^\circ(\ce{Cu^{2+}/Cu})=+0.34$ V and $E^\circ(\ce{Mn^{2+}/Mn})=-1.18$ V. True.

(B), (D)

JEE Advanced 2018 · Paper 2, Chemistry question 2