Question

Even though the toxicity of cadmium has become a concern, nickel-cadmium (nicad) batteries are still used commonly in many devices. The overall cell reaction isCd(s) + 2NiO(OH)(s) + 2H₂O(l) → 2Ni(OH)(s) + Cd(OH)₂(s) A certain nicad battery weighs 18.3 g and has a capacity of 300. mA?h (that is, the cell can store charge equivalent to a current of 300. mA flowing for 1 h).(c) What percentage of the cell mass consists of reactants?

Answer 1

(a) the capacity of this cell is 1080 C .

(b) 1.856 g of the reactants is needed to deliver 300 mA hr .

(c)the percentage of the cell  mass consists of reactants is 14% .

(a) Given ,

current = 300 mA = 300 *10^-3 A

Time = 1 hr =3600 s

capacity of the cell is given by ,

= (300*10^-3) * (3600) = 1080 C

Hence ,the cell capacity of the cell is 1080 C .

(b) Given ,

current = 300 mA =300*10^-3 A

We know ,

1 F = 1 mole e^-

96500 C = 1mole e^-

1C = 1/ 96500 mole e^-

1080 C = 1080/96500 mole e^- =0.01119 mole e^-

the two half reaction of the cell is given by ,

Cd +2OH^- ==>2Cd(OH)2 +2e^-

2NiOOH +2H2O +2e^- ==> 2Ni(OH)2 =2OH^-

1 mole Cd = 112.4 g of Cd

2 mole e^- =112.4g of Cd

0.01119 mole e^- = 112.4g(0.01119m mole e^-) /2= 0.6288 g Cd

1mole NiOOH = 91.70 g of NiOOH

2 mole NiOOH = 2*91.70 g of NiOOH

2 mole e^- NiOOH =91.70*2 g of NiOOH

0.01119 mole e^- NiOOH = 91.70 * O.O1119 *2/2 =1.026 g NiOOH

1 mol of H2O = 18.02 g of H2O

2 mol of H2O = 2*18.02 =36.04 g of H2O

2 mole e^- of H2O = 36.04g of H2O

0.01119 mole e^- of H2O = 36.04 *0.01119/2 =0.2016 g of H2O

Mass of reactants needed

= 0.6288 g of Cd + 1.026 g of NiOOH + 0.2016 g of H2O = 1.856 g

Hence 1.856 g of the reactants is needed .

(c) % reactants mass

= mass of reactants *100/ mass of cell

= 1.856 *100 / 13.3 = 14 %

Hence , 14% of the cell mass consists of reactants .

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Question: even though the toxicity of cadmium becomes a concern , but nickel- cadmium ( nicad) batteries are still used commonly in many devices . the overall cell reaction is ,

Cd(s) + 2NiO(OH) (s) + 2H2O (l) ==> 2Ni(OH)(s) +Cd(OH)2(s)

A certain nicad battery weighs 13.3g and has a capacity of 300 mA hr ( that is , the cell can store charge equivalent to a current 300 mA flowing for 1 hr ).

(a) what is the capacity of this cell in coulombs ?

(b) what mass of the reactants is needed to deliver 300 mA hr ?

(c) what percentage of the cell mass consists of reactants ?