Question

When Thomas Edison first sold electricity, he used zinc coulometers to measure charge consumption. (In a coulometer the cathode is weighed before a current is passed through it, and then again after the passage of current. The weight increase is proportional to the amount of current that flows through the cathode.) If the zinc plate in one of Edison's coulometers increased in mass by 7.85 g, how much charge had passed through it

Answer 1

When the zinc plate in one of Edison's coulometers increased in mass by 7.85 g, the amount of charge that had passed through it is 23,173 C.

Ionization of zinc

The zinc metal will ionize as shown below;

Zn²₊ + 2e⁻ → Zn

The molar mass of zinc metal is given as 65.38 g/mol

Amount of charge passed through 65.38 g/mol

Amount of charge that will deposite the given mass of zinc is calculated as follows;

e⁻ = 96500 C

2e⁻ = 2 x 96500 C = 193,000 C

Amount of charge passed through 7.85 g

65.38 g -------> 193,000 C

7.85 g -----------> ?

= (7.85 x 193,000)/(65.38)

= 23,173 C

Thus, when the zinc plate in one of Edison's coulometers increased in mass by 7.85 g, the amount of charge that had passed through it is 23,173 C.

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