1.
Chemical energy can be directly converted to electrical energy by devices such as batteries and
fuel cells. The nickel-cadmium (Ni-Cd) battery is a type of rechargeable battery used in many
portable devices like hand phones and cameras. The cathode is made of a nickel compound,
NiO(OH)(s) and the anode is made of cadmium The electrolyte is aqueous potassium hydroxide.
When the battery discharges, Ni(OH)2(s) and Cd (OH)2(s) are formed ( Construct the ionic half-
equation at the anode and cathode, respectively of this Ni-Cd battery during the discharging
process. (20 marks) (ii) Write the overall cell reaction on discharge of battery in part (i). (5
marks)
Solution
We know that in at anode oxidation takes place and at cathode reduction takes place.
Here in zinc cadmium battery at anode oxidation of cadmium will takes place hence it will
accumulate electronic from the solution and forms negative electrode.
While at cathode reduction of cadmium takes place
And get the positive charges and act as positive electrode.
1) discharging reaction
At cathode: -
NiOOH (s) + H2O+ e -
---> Ni (OH)2(aq) + OH -
At anode
Cd (s) + 2OH -
---->Cd (OH)2 + 2 e
2) overall cell reaction
2NiOOH + Cd + 2H2O ---> 2Ni(OH)2 + Cd (OH)2
So we will get the over all cell reaction as shown above

2.
And if we will reverse the cell reaction and apply external current it will be charged.