Electrochemistry: Problems and solution on Electrolysis Cells

Problem 1

Calculate the mass of copper metal produced from CuSO4 solution by passage of a 3.00-A current for 7250 seconds.

Problem 2

Calculate the time required to deposit 7.00 g of silver from a solution of AgNO3 with a current of 4.00 A.

If two quantities are given and the current is to be calculated,we convert the quantities given to coulombs and seconds and divide them to get the answer.

Problem -3

Calculate the current required to deposit 40.0 g of gold from AuCl3 solution in 7.00 hours.

Even if a metal is not produced, the ratio of moles of electrons involved in the reaction to moles of a chemical substance can be used to calculate the extent of the chemical reaction given in the balanced chemical equation.

Problem 4

Calculate the time required with a current of 10.5 A to reduce 50.0 g of PbO2 to PbSO4 in the lead storage cell (found in most automobile batteries).

Note that despite the oxidation state of lead in the reactant being +4, the ratio of moles of electrons to moles of lead(IV) oxide is 2 : 1 because the final product is not free lead. The number of moles of electrons involved is clearly given in the balanced equation no matter what the final product.The only new concepts that we used in solving these problems were the number of coulombs per mole of electrons and the fact that 1 A = 1 C/s.