Question

250 ml solution of unknown molarity of CuSO₄ in water was electrolysed using platinum anode and copper cathode after the passage of a current of 2×10^-3 A for 19.3 minute the absorbance power of CuSO₄(aq.) was reduced to 50% of it's original value . The molarity of CuSO₄ was :

Answer 1

Absorbance indicates the amount of light absorbed by the coloured substances.
In general a concentrated copper sulphate solution will absorb more light and hence it is darkly coloured and a dilute solution will absorb less light and hence it is pale coloured.
It is given by the Beer-Lambert Law that absorbance is directly related with concentration of the solution. So when absorbance is reduced by 50% the concentration is also reduced by 50%