Question

Q7) A 1.23 g sample, which contains gold (Au), silver (Ag) and metal oxides, is treated with concentrated nitric acid (HNO;), which dissolves all the metals and metal oxides with the exception of the gold. The mass of yellow metal remaining is 7.4 x 10 g. The solution is then treated with aqueous sodium chloride (NaCI), which precipitates silver chloride (AgCI) and nothing else. A total of 0.196 g of AgCl is obtained. What is the percent gold and silver in this ore? Page 3/14

Answer 1

The percentage of Gold is The mass of yellow metal remaining 7 middot 4 times 10^-2 g 0.074 g weight of sample = 1.23 g 0.074/1.23 times 100 = 6 middot 0 % of Au The left Au is mass of Agcl = 0.196 g molar mass of Agcl = 143g/mole 0.196 g Agcl times 1 mol/143 g 1 middot 370 times 10^-3 0.00137 moles Agcl 0.00137 moles of Ag (0.00137 moles of Ag) times (108 g) 0.147 almostequalto 0.15 g of Ag Thus (0.15 g/1.23) times 100 = 12 middot 0 % of Ag Au = 6.0 % Ag = 12.0 %