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Current Question (ID: 18687)

Question:

$\text{When an excess of aqueous KCN is added to an aqueous solution of copper sulphate, what coordination entity is formed?}$

Options:

1. $\text{K}_2[\text{Cu(CN)}_6]$
2. $\text{K}_3[\text{Cu(CN)}_4]$
3. $\text{K}_2[\text{Cu(CN)}_4]$
4. $\text{K}_2[\text{Cu(CN)}_3]$

Solution:

$\text{With CN}^- \text{ ligand, Cu forms a stable complex in a } +2 \text{ oxidation state.}$ $\text{The coordination entity formed in the process is } \text{K}_3[\text{Cu(CN)}_4]$ $\text{When an excess of aqueous KCN is added to an aqueous solution of copper sulphate then multiple reactions occur and } \text{K}_3[\text{Cu(CN)}_4] \text{ is obtained as a product.}$ $\text{In this reaction, Cu(II) salt is treated with excess KCN at room temperature, cyanogen is evolved and the copper is reduced. The reduced form of Cu reacts with CN}^- \text{ and } \text{K}_3[\text{Cu(CN)}_4] \text{ is obtained as a product.}$ $\text{The reactions are as follows:}$ $\text{Cu}^{2+} + \text{CN}^- \rightarrow \text{Cu(CN)}_2$ $\text{Cu(CN)}_2 \xrightarrow{\text{decompose}} \text{CuCN} + (\text{CN})_2 \text{ (cyanogen)}$ $\text{CuCN} + \text{CN}^- \text{ (excess is used) } \rightarrow \text{K}_3[\text{Cu(CN)}_4] \text{ or } [\text{Cu(CN)}_4]^{3-}$

Import JSON File

Upload a JSON file containing LaTeX/MathJax formatted question, options, and solution.

Expected JSON Format:

{
  "question": "The mass of carbon present in 0.5 mole of $\\mathrm{K}_4[\\mathrm{Fe(CN)}_6]$ is:",
  "options": [
    {
      "id": 1,
      "text": "1.8 g"
    },
    {
      "id": 2,
      "text": "18 g"
    },
    {
      "id": 3,
      "text": "3.6 g"
    },
    {
      "id": 4,
      "text": "36 g"
    }
  ],
  "solution": "\\begin{align}\n&\\text{Hint: Mole concept}\\\\\n&1 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\text{ moles of carbon atom}\\\\\n&0.5 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\times 0.5 \\text{ mol} = 3 \\text{ mol}\\\\\n&1 \\text{ mol of carbon} = 12 \\text{ g}\\\\\n&3 \\text{ mol carbon} = 12 \\times 3 = 36 \\text{ g}\\\\\n&\\text{Hence, 36 g mass of carbon present in 0.5 mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6].\n\\end{align}",
  "correct_answer": 4
}