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NEET 2017
Exam
NEET
Year
2017
Subject
Chemistry
Chapter
General Principles and Processes of Isolation of Metals

NEET 2017 · Chemistry · General Principles and Processes of Isolation of Metals

Extraction of gold and silver involves leaching with C N ^ - ion....

Extraction of gold and silver involves leaching with CN−\text{C}{\text{N}}^{-} ion. Silver or gold is later recovered by:

Options

  1. ALiquation
  2. BDistillation
  3. CZone refining
  4. DDisplacement with Zn

Correct answer

D. Displacement with Zn

Step-by-step solution

Zinc metal can displace Ag and Au as Zn being more reactive than Ag and Au. The following reactions are involved in the extraction of gold or silver from their native ores.

From Native ore,

{4Ag+8NaCN+2H2O+O2→Leaching4Na[Ag(CN)2]+4NaOHSolubleSodium dicyanoargentate (I)\begin{cases}4 \text{Ag} + 8 \text{NaCN} + 2 {\text{H}}_{2} \text{O} + {\text{O}}_{2} & \overset{\text{Leaching}}{\to} & 4 \text{Na} \left[\text{Ag} {\left(\text{CN}\right)}_{2}\right] & + 4 \text{NaOH} \\ & & \text{Soluble} & \\ & & \text{Sodium dicyanoargentate (I)} & \end{cases}

{2Na[Ag(CN)2]+Zn→DisplacementNa2[Zn(CN)4]+2Ag↓\begin{cases}2 \text{Na} \left[\text{Ag} {\left(\text{CN}\right)}_{2}\right] + \text{Zn} & \overset{\text{Displacement}}{\to} & {\text{Na}}_{2} \left[\text{Zn} {\left(\text{CN}\right)}_{4}\right] + 2 \text{Ag} ↓\end{cases}
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