A Battery charger used to recharge the NiMH batteries used in a digital camera can deliver as much as 0.50 A of current to each battery. If it takes 100. minutes to recharge one battery, how much Ni(OH)2 (in grams) is oxidized to NiO(OH)? First you can calculate the quantity of electricity used to charge the battery using the equation:
Q = It
where
Q = charge in Coulombs (C)
I = current in Amps (A)
t = time in seconds (s)
In the above question then
Q = 0.5 x 100 x60 = 3,000 C
Now the oxidation state of the Ni in Ni(OH)2 is 2+, while the oxidation state of Ni in NiO(OH)2 is 4+, so the change is 2+.
Faraday's constant = 96,500 Cmol-1 so
the moles of electrons available = 3000/96500 = 0.03109
However, 2 moles of electrons are required to oxidise 1 mol of Ni(OH)2 therefore moles of Ni(OH)2 that can be oxidised is 0.03109/2 = 0.015545.
Lastly, we can now convert the moles of Ni(OH)2 to grams by multiplying by its formula mass, which is 92.708 gmol-1, ie
0.015545 x 92.708 = 1.44 g. |
