A portable CD player that draws 175 milliamperes of current is powered by Ni-Cd

Question

A portable CD player that draws 175 milliamperes of current is powered by Ni-Cd rechargable batteries. Compute the mass of NiO2 consumed when a disk is played for 115 minutes. (enter your answer in grams)

Explanation / Answer

The reaction from the nickel terminal of the battery is: NiOOH(s) + H2O + e- --> Ni(OH)2 + OH- The reaction on the cadmium terminal is: Cd(s) + 2OH- --> Cd(OH)2 + 2e- So, for the redox equations to be balanced, multiply the nickel terminal equation by 2: 2NiOOH(s) + 2H2O + 2e- --> 2Ni(OH)2 + 2OH- 1 milliamp is equal to 6.24 E15 electrons/second so, from what you've given me, we can solve for the number of electrons: n(e-) = 6.24E15 (e-)/sec * 115 min * (60 sec/min) *165 mA / 1 mA n(e-) = 7.104 E21 e- So, for every electron that is used, you also convert 1 molecule of NiOOH to Ni(OH)2 Divide that number by Avogadro's number to get the number of moles of NiOOH that was consumed: 7.104 E21 molecules / (6.02 E23 molecules/mol) = 0.0118 mol NiOOH The molecular weight of NiOOH is 58.69 + 16*2 + 1 = 91.7 g/mol So, 0.0118 mol * 91.7 g/mol = 1.08 g You consumed 1.08 g of NiOOH.

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