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Chapter 3: Problem 74

For many years the recovery of gold-that is, the separation of gold from other materials-involved the use of potassium cyanide: $$ 4 \mathrm{Au}+8 \mathrm{KCN}+\mathrm{O}_{2}+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow 4 \mathrm{KAu}(\mathrm{CN})_{2}+4 \mathrm{KOH} $$ What is the minimum amount of \(\mathrm{KCN}\) in moles needed to extract \(29.0 \mathrm{~g}\) (about an ounce) of gold?

Short Answer

Expert verified
The minimum amount of KCN in moles needed to extract 29.0 g of gold is 0.294 moles.

Step by step solution

01

Convert grams of gold to moles

Using the molar mass of gold (197.0 g/mol), convert the mass of gold given (29.0 g) to moles. Recall that the conversion from grams to moles involves dividing the mass by the molar mass. So \( \frac{29.0 g}{197.0 g/mol} = 0.147 moles \) of Au.
02

Use the molar ratio to find the moles of KCN

The balanced chemical equation shows that 4 moles of Au react with 8 moles of KCN. Therefore, there is a 1:2 molar ratio of Au to KCN. So the moles of KCN required would be \( 0.147 moles \times 2 = 0.294 moles \) KCN.

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If we know the empirical formula of a compound, what additional information do we need to determine its molecular formula?

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