JEE Advanced 2019 · Paper 2 · Chemistry Q1

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ChemistryMultiple correct+4 / -1Question 19 of 54

The cyanide process of gold extraction involves leaching out gold from its ore with $\ce{CN-}$ 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)

Q is

\ce{O2}

T is Zn

Z is

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

R is

\ce{[Au(CN)4]-}

Answer and worked solution

Official answer: A, B, C

Leaching. Gold dissolves in cyanide only in the presence of oxygen:
$\ce{4Au + 8CN- + 2H2O + O2 -> 4[Au(CN)2]- + 4OH-}.$
So Q is $\ce{O2}$ and R is $\ce{[Au(CN)2]-}$ , gold(I), not $\ce{[Au(CN)4]-}$ .

Recovery. Zinc displaces the gold:
$\ce{2[Au(CN)2]- + Zn -> 2Au + [Zn(CN)4]^{2-}}.$
So T is Zn and Z is $\ce{[Zn(CN)4]^{2-}}$ .

(A), (B) and (C) are true; (D) is false. (A), (B), (C)

Topics:Extraction of specific metals Stability and applications

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JEE Advanced 2019 · Paper 2, Chemistry question 1