Stoichiometry- extraction of gold from its ore

Question

1. To extract gold from its ore, the ore is treated with sodium cyanide solution in the presence of oxygen and water.

4Au(s) + 8NaCN(aq) + O2 (g) + 2 H2O(l) → 4NaAu(CN)2 (aq) + 4NaOH(aq)

a) Determine the mass of gold that can be extracted if 25.0 g of sodium cyanide is used.

b) If the mass of the ore from which the gold was extracted is 150.0 g, what percentage of the ore is gold?

Answer 1

4Au(s) + 8NaCN(aq) + O₂ (g) + 2H₂O(l) → 4NaAu(CN)₂ (aq) + 4NaOH(aq) ... balanced equation

molar mass NaCN = 49.0 g / mol

atomic mass Au = 197 g / mol

(a). 25.0 g NaCN x 1 mol NaCN / 49.0 g x 4 mol Au / 8 mol NaCN x 197 g Au / mol = 50.3 g Au

(b). 50.3 g / 150.0 g (x100%) = 33.5%