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 29.3 g sodium cyanide is used.
(b) If the mass of the ore from which the gold was extracted is 146.5 g, what percentage of the ore is gold?
You don't have an arrow. How do you know where the reactants stop and the products begin?
4 Au(s) + 8 NaCN(aq) + O2(g) + 2 H2O(l) --> 4 NaAu(CN)2(aq) + 4 NaOH(aq)
oh sorry, here it is!
mols NaCN = grams/molar mass
Using the coefficients in the balanced equation, convert mols NaCN to mols Au.
Now convert mols Au to g Au. g = mols Au x atomic mass Au. This is the theoretical yield of Au.
b.
%yield = (actual yield/theor yield)*100 = >
To solve both parts of the question, we need to use stoichiometry, which is the calculation of quantities in chemical reactions based on the balanced equation.
(a) To determine the mass of gold that can be extracted using 29.3 g of sodium cyanide, we need to find the molar ratio between sodium cyanide and gold.
1. Start by converting the given mass of sodium cyanide to moles. To do this, divide the mass by the molar mass of sodium cyanide (NaCN). The molar mass of NaCN can be found by adding the atomic masses of sodium (Na), carbon (C), and nitrogen (N).
Molar mass of NaCN = (22.99 g/mol) + (12.01 g/mol) + (14.01 g/mol) = 49.01 g/mol
Number of moles of NaCN = 29.3 g / 49.01 g/mol = 0.598 mol (rounded to 3 decimal places)
2. Now we can use the balanced equation to determine the molar ratio between NaCN and Au. From the balanced equation, we see that 4 moles of Au are produced for every 8 moles of NaCN used.
From the balanced equation: 4 Au(s) + 8 NaCN(aq) + O2(g) + 2 H2O(l) -> 4 NaAu(CN)2(aq) + 4 NaOH(aq)
Molar ratio of NaCN to Au: 8 moles NaCN / 4 moles Au
3. Multiply the moles of NaCN by the molar ratio to find the moles of gold.
Moles of Au = 0.598 mol NaCN * (4 mol Au / 8 mol NaCN) = 0.299 mol (rounded to 3 decimal places)
4. Finally, calculate the mass of gold using the moles of gold and the molar mass of gold (Au).
Molar mass of Au = 196.97 g/mol (from the periodic table)
Mass of gold = 0.299 mol * 196.97 g/mol = 59.38 g (rounded to 2 decimal places)
Therefore, the mass of gold that can be extracted using 29.3 g of sodium cyanide is approximately 59.38 g.
(b) To determine the percentage of gold in the ore, we need to compare the mass of gold to the mass of the ore.
Percentage of gold = (mass of gold / mass of ore) * 100
Given:
Mass of the ore = 146.5 g
Mass of gold = 59.38 g (from part a)
Percentage of gold = (59.38 g / 146.5 g) * 100 = 40.52% (rounded to 2 decimal places)
Therefore, the percentage of gold in the ore is approximately 40.52%.