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

(B) Only $\mathrm{Cu}^{2+}$ shows the formation of precipitate by passing $\mathrm{H}_{2}\mathrm{~S}$ in acidic medium; (D) $\mathrm{Cu}^{2+}/\mathrm{Cu}$ has higher reduction potential than $\mathrm{Mn}^{2+}/\mathrm{Mn}$ (measured under similar conditions)

(A) $\mathrm{Mn}^{2+}$ shows the characteristic green colour in the flame test

(C) Only $\mathrm{Mn}^{2+}$ shows the formation of precipitate by passing $\mathrm{H}_{2}\mathrm{~S}$ in faintly basic medium

JEE Advanced · 2018 · 20 May 2018 · Paper 2 · Practical and Analytical Chemistry

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The correct option(s) to distinguish nitrate salts of

Mn^{2 +}

and

Cu^{2 +}

taken separately is (are)

(A) $Mn^{2 +}$ shows the characteristic green colour in the flame test
(B)Only $Cu^{2 +}$ shows the formation of precipitate by passing $H_{2} S$ in acidic medium✓ Correct
(C)Only $Mn^{2 +}$ shows the formation of precipitate by passing $H_{2} S$ in faintly basic medium
(D) $Cu^{2 +} / Cu$ has higher reduction potential than $Mn^{2 +} / Mn$ (measured under similar conditions)✓ Correct

Answer: (B), (D)

Solution

Cu^{2 +}

(not

Mn^{2 +}

) shows characteristic green colour in flame test. The solubility product of CuS is much smaller than that of MnS, so only

Cu^{2 +}

precipitates as CuS in acidic medium when

H_{2} S

is passed. The standard reduction potential

E_{Cu^{2 +} / Cu}^{\circ} > E_{Mn^{2 +} / Mn}^{\circ}

, which is a distinguishing property.

JEE Advanced · 2018 · 20 May 2018 · Paper 2 · One or more correct options

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JEE Advanced · 2018 · 20 May 2018 · Paper 2 · Practical and Analytical Chemistry

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