JEE Advanced · 2019 · 27 May 2019 · Paper 2 · General Principles and Processes of Isolation of Metals

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The cyanide process of gold extraction involves leaching out gold from its ore with CN⁻ in the presence of Q in water to form R. Subsequently, R is treated with T to obtain Au and Z. Choose the correct option(s).

(A)T is Zn✓ Correct
(B)R is $[Au (CN)_{4}]^{-}$
(C)Z is $[Zn (CN)_{4}]^{2 -}$ ✓ Correct
(D)Q is $O_{2}$ ✓ Correct

Answer: (A), (C), (D)

Solution

The cyanide process involves two key reactions:

Gold is leached with CN⁻ in the presence of O₂ (Q):

4 Au (s) + 8 CN^{-} (aq) + 2 H_{2} O (aq) + O_{2} (g) \to 4 [Au (CN)_{2}]^{-} (aq) + 4 OH^{-} (aq)

So R is

[Au (CN)_{2}]^{-}

, not

[Au (CN)_{4}]^{-}

The complex is then treated with Zn (T):

2 [Au (CN)_{2}]^{-} (aq) + Zn (s) \to [Zn (CN)_{4}]^{2 -} (aq) + 2 Au (s)

So Z is

[Zn (CN)_{4}]^{2 -}

.

Therefore, options (A), (C), and (D) are correct.

JEE Advanced · 2019 · 27 May 2019 · Paper 2 · One or more correct options

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JEE Advanced · 2019 · 27 May 2019 · Paper 2 · General Principles and Processes of Isolation of Metals

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