Question

A constant current of 30 amperes ispassed through an aqueous solution of NaCl for 1 hour. How many grams of NaOH will be formed in the reaction ? Also find out the volume of `Cl_(2)` evolved at S.T.P.

Answer 1

The redox reaction taking place on electrolysis is an follows :
`2Cl^(-)(aq) to Cl_(2)(g)+2e^(-)`
`(2H_(2)O(l)+2e^(-) to H_(2)(g)+2OH^(-)(aq))/(2Cl^(-)(aq)+2H_(2)O(l) to H_(2)(g)+Cl_(2)(g)+2OH^(-)(aq)`
Step I. Calculation of the mass of NaOH formed
Quantity of charge passed=(30 amp)xx(60xx60 s)=108000 Coulombs
Now, 96500 C of charge from NaOH=40 g
108000 C of charge will form NaOH `=(40g)xx((108000C))/((96500C))=44.77 g=1.12 mol`.
Step II. Calculation of volume of `Cl_(2)` evolved at S.T.P.
According to the equation,
No. of moles of `Cl_(2)` evolved`=1//2xx"No"`. of mole of NaOH formed `=1//2xx1.12=0.56 mol`
1 mole of `Cl_(2)` at S.T.P. will correspond to volume =22.4L
0.56 mole of `Cl_(2)` at S.T.P. will correspond to valume`=((22.4L))/((1 mol))xx(0.56 mol)=12.54 L`