Electrolysis Driving Me Crazy!
The electrode reactions for the charging of a lead storage battery are:
P b S O X 4 + 2 e X − P b + S O X 4 X 2 − P b S O X 4 + 2 H X 2 O P b O X 2 + S O X 4 X 2 − + 4 H X + + 2 e X −
The electrolyte in the battery is an aqueous solution of sulphuric acid.Before charging,the specific gravity of liquid was found to be 1.11 (15.7% H X 2 S O X 4 by weight).After charging for 100 hours,the sp.gravity was found to be 1.28 (36.9 % H X 2 S O X 4 by wt.).
If the battery contained 2 litres of the liquid calculate the average current used for charging the battery.
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Initially ; mass of H X 2 S O X 4 = 1 . 1 1 ∗ 2 0 0 0 ∗ 1 5 . 7 / 1 0 0 = 3 4 8 . 5 8 g .
Finally; mass of H X 2 S O X 4 = 1 . 2 8 ∗ 2 0 0 0 ∗ 3 6 . 9 / 1 0 0 = 9 4 4 . 6 4 g .
Now note that the eq.wt of H X 2 S O X 4 in this reaction is 9 8 g (not 4 9 g ) because 2 moles are reacting with 2 electrons in the second reaction.
Intially ; Equivalents of H X 2 S O X 4 = 3 4 8 . 5 8 / 9 8 = 3 . 5 5 6 5
Finally ; Equivalents of H X 2 S O X 4 = 9 4 4 . 6 4 / 9 8 = 9 . 6 3 9 1
Change = 6 . 0 8 2 6 equivalents ; thus the Average current I = 6 . 0 8 2 6 ∗ 9 6 5 0 0 / 3 6 0 0 ∗ 1 0 0 ≈ 1 . 6 3 A .