Help needed with redox reaction question?

Question

Hi, i'm having troubles starting with the following chem question:
Balc'd. equation: 4Au(s) + 8CN-(aq) + O2(g) + 2H2O (l) -> 4[Au(CN)2]-(aq) + 4OH-(aq)
How many liters of 0.22M NaCN solution would be needed to extract the gold from 1000kg of rock, if the rock is 0.063% gold by mass?

Any tips/suggestions would be great :)

Answer 1

assuming 100% is extracted from the ore:

Total gold available from the rock = 1000kg x 0.063 = 63 kg
Hence,
4 moles of Au is equivalent to 8 moles of Cyanide.
MW of gold = 196.967
Total moles of Gold = 63000 x 196.967 = 12408921 moles

Moles CN = Moles gold x [GF] = 12408921 x [8/4] = 24817842 moles

volume of NaCN = 24817842 x 0.22 M = 5459925.24 liters

Answer 2

Tis is just book-keeping. As always when balancing different substances, you go by way of moles.

10^6 g rock x 0.063 x 1/100 = mass Au.

Divide by atomic mass Au to get moles Au.

Each mole Au = 2 moles CN-

And,of course, volume(L) x conc(M) = amount (moles).

Over to you.