Concept explainers
Interpretation:
The mass of gold that can be extracted from 25.0 g of sodium cyanide should be calculated.
Concept introduction:
The ratio of mass of substance to its molar mass is said to be number of moles of that substance.
The ratio of amount of any two compounds involved in a

Answer to Problem 71A
The mass of gold extracted from 25.0 g of sodium cyanide is
Explanation of Solution
Given:
The balanced chemical equation:
The molar mass of sodium cyanide is 49.00 g/mol. The number of moles of sodium cyanide is calculated as shown:
From the balanced chemical reaction, the mole ratio of gold and sodium cyanide is 4:8 that is 1:2 which means 1 mole of gold reacts with 2 moles of sodium cyanide. So, the number of moles of gold reacted with 0.51 mol of sodium cyanide is:
Now, the mass of gold reacted with 25.0 g of sodium cyanide is calculated as:
The molar mass of gold is 196.97 g/mol. So,
Hence, the mass of gold extracted from 25.0 g of sodium cyanide is
Interpretation:
The percentage of the gold in ore should be calculated if the mass of the ore is 150.0 g.
Concept introduction:
The percentage of gold in ore is calculated by dividing the mass of gold extracted by the mass of ore. The formula used is:

Answer to Problem 71A
The percentage of the gold in ore is
Explanation of Solution
The mass of gold extracted from 25.0 g of sodium cyanide is
Substituting the values:
Hence, the percentage of the gold in ore is
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