Question

Pb(s) + PbO2(s) + 2 H2SO4(aq) → 2 PbSO4(s) + 2 H2O(l)

1. If it takes 6.0 seconds of discharge for a car battery to start the engine and the starter drew a current of 230 A, what mass of Pb will be oxidized to PbSO4 in this time?

2. How long will it take to re-charge the battery with an alternator current of 30.0 A?

Answer 1

Ans 1 :

The amount of charge = Q = I. t = 230 x 6.0 = 1380 Coloumbs

1 mole of electrons require a charge of 96487 C

So 1380 C will be utilised by = 1380 / 96487 = 0.0143 moles

Pb = Pb²⁺ + 2e^-

Each mole of Pb releases 2 moles of electrons for its oxidation

So here the number of moles of Pb oxidised = 0.0143 / 2 = 0.00715 moles

Mass of Pb oxidised = 0.00715 x 207.2

= 1.48 grams

Ans 2 :

Since the charge remains the same , i.e 1380 coloumbs ,

So using the same formula Q = I. t

1380 = 30.0 x t

t = 46 seconds

So it will take 46 seconds to recharge the battery.