Assume that impure copper contains only iron, silver and a gold as impurities. After passage of `140A`, for `482.5` sec, of the mass of the anode decreased by `22.260g` and the cathode increased in mass by `22.011g`. Estimate the % iron and % copper originaly present.

Explanation

The increase at the cathode is due to copper only. Hence, there is 22.011 g of copper and rest impurities of iron, gold and silver.
Mass of impurities `=(22.260-22.011)=0.249 g`
At anode, only copper and iron are oxidised, the gold and silver collect below anode in the form of anodic mud.
`underset("Copper and iron")(M)rarr M^(2+) +2e^(-)`
No. of moles of metal oxidised `=(140xx482.5)/(2xx96500)=0.35`
No. of moles of copper `=22.011/63.5=0.3466`
No. of moles of iron `=(0.35-0.3466)=0.0034`