Applying Concepts
These questions test conceptual learning.
Gold can be dissolved from gold-bearing rock by treating the rock with sodium cyanide in the presence of the oxygen in air.
Once the gold is in solution in the form of the [Au(CN)2]-ion, it can be precipitated as the metal according to this unbalanced equation:
(a) Are the two reactions above acid-base or oxidationreduction reactions? Briefly describe your reasoning.
(b) How many liters of 0.075-M NaCN will you need to extract the gold from 1000 kg of rock if the rock is 0.019% gold?
(c) How many kilograms of metallic zinc will you need to recover the gold from the [Au(CN)2]- obtained from the gold in the rock?
(d) If the gold is recovered completely from the rock and the metal is made into a cylindrical rod 15.0 cm long, what is the diameter of the rod? (The density of gold is 19.3 g/cm3.)
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