To extract gold from its ore, the ore is treated with sodium cyanide solution in the presence of oxygen and water.
4 Au(s) + 8 NaCN(aq) + O2(g) + 2 H2O(l) 4 NaAu(CN)2(aq) + 4 NaOH(aq)
(a) Determine the mass of gold that can be extracted if 21.4 g sodium cyanide is used.
If the mass of the ore from which the gold was extracted is 126.0 g, what percentage of the ore is gold?
I can't tell the difference between reactants and products because you don't have an arrow to indicate the separation; however, you can work this by following the example here. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html
To determine the mass of gold that can be extracted, you need to use the stoichiometry of the balanced chemical equation. The balanced equation tells you that for every 4 moles of gold (Au), you need 8 moles of sodium cyanide (NaCN).
First, let's convert the mass of sodium cyanide to moles. The molar mass of NaCN is 49.01 g/mol.
Number of moles of NaCN = mass of NaCN / molar mass of NaCN
Number of moles of NaCN = 21.4 g / 49.01 g/mol
Number of moles of NaCN ≈ 0.436 mol
According to the balanced equation, for every 4 moles of Au, you need 8 moles of NaCN. Therefore, the ratio of moles of Au to moles of NaCN is 4:8, which simplifies to 1:2.
Number of moles of Au = (Number of moles of NaCN) x (1 mol Au / 2 mol NaCN)
Number of moles of Au = 0.436 mol x (1 mol Au / 2 mol NaCN)
Number of moles of Au ≈ 0.218 mol
Now, we can calculate the mass of gold using the molar mass of gold (Au), which is 196.97 g/mol.
Mass of Au = Number of moles of Au x Molar mass of Au
Mass of Au = 0.218 mol x 196.97 g/mol
Mass of Au ≈ 42.90 g
Therefore, approximately 42.90 grams of gold can be extracted if 21.4 grams of sodium cyanide is used.
Now, we can calculate the percentage of gold in the ore using the mass of the ore and the mass of gold extracted.
Percentage of gold = (Mass of gold / Mass of ore) x 100
Percentage of gold = (42.90 g / 126.0 g) x 100
Percentage of gold ≈ 34.05%
Hence, approximately 34.05% of the ore is gold.