During the discharge of a lead storage battery the density of sulphuric acid fell from 1.294 to 1.139g mL−1 . H2SO4 of density 1.294 g mL−1 is 39% and that of density 1.139 g mL−1 is 20% by weight. The battery holds 3.5 L of acid and the volume practically remains constant during the discharge. Calculate the number of Ampere hours for which the battery must have been used. The discharging reactions are:
Pb+SO2−4→PbSO4+2e−(anode)
PbO2+4H++SO2−4+2e−→PbSO4+2H2O(cathode)