Copper ore (0.5100 g) is dissolved in acid and reacted with I–. Calculate the mass %Cu present if 24.08 0.2500 Na2S2O3 are needed to titrate the I2 formed.
2Cu2+(aq) + 4I–(aq)
2CuI(s) + I2(aq)
I2(aq) + 2S2O32–(aq) 2I–(aq) + S4O62–(aq)
2Cu2+(aq) + 4I–(aq)
2CuI(s) + I2(aq)I2(aq) + 2S2O32–(aq)
2I–(aq) + S4O62–(aq) | c(S2O32–) V(S2O32–) | n = cV Step 1 | n(S2O32–) |
Step 2 | n(I2) |
Step 3 | n(Cu2+) | | n(Cu) | m = nM Step 5 | m(Cu) | uses m(ore) Step 6 | %(Cu) |
n(S2O32–) = 24.08 × 10–3 × 0.2500 mol
m(Cu) = 63.55 gmol–1 × 6.020 × 10–3 mol
m(Cu) = 0.382571 g
| 3.010 × 10–3 mol | = | n(Cu2+) |
| 1 | 2 | |
| n(Cu2+) = 6.020 × 10–3 mol n(Cu) = 6.020 × 10–3 mol | ||
| 6.020 × 10–3 mol | = | n(I2) |
| 2 | 1 | |
| n(I2) = 3.010 × 10–3 mol | ||
then
m(Cu) = 63.55 g
m(Cu) = 0.382571 g
| %Cu | = | 0.38254692 | × 100% = 75.01% |
| 0.5100 |
Step 1: Use given information (concentration and volume) to calculate n(known).
Steps 2, 3 and 4: Calculate n(unknown) from n(known), relating both to n(I2) because the I2 produced in the first reaction is consumed in the second reaction.
Step 5: Use the calculated n(unknown) and the known M(unknown) to calculate m(unknown).
Step 6: Calculate the desired percentage.
Steps 2, 3 and 4: Calculate n(unknown) from n(known), relating both to n(I2) because the I2 produced in the first reaction is consumed in the second reaction.
Step 5: Use the calculated n(unknown) and the known M(unknown) to calculate m(unknown).
Step 6: Calculate the desired percentage.