For how long a current of 1.5 ampere has to be passed through the electrolyte innorder to deposit 1g of Al when the electrode reaction is

Al3+ +3e → Al (Z=27)

Current  = 1.5 A
Given mass of Al = 1 g
Molar mass of Al =27 g
No. of moles of Al = 1/27 moles

according to the balance chemical equation :
 

Al3+ + 3e- Al
To produce  1 mole of Al = 3 moles of electrons are required 

To produce 1/27 moles of Al  = 3 x (1/27) moles of electrons =1/9 moles of electrons

Charge on 1 mole of electrons =96500 C
Charge on 1/9 moles of electrons = 96500/9 C = 10722.22 C

Charge = current x time(sec)

Time  = charge / current = 10722.22/ 1.5 = 7148.1481 seconds

Time (minutes) = 119.14 minutes or 2 hours approximately

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