A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes

Question

(a) A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series containing electrolytes FeSO₄ and ZnSO₄ until 2.8 g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the cathode of cell Y. (Molar mass: Fe = 56 g mol^–1 Zn = 65.3 g mol^–1 , 1 F = 96500 C mol^–1 ) 

(b) In the plot of molar conductivity (A_m ) vs square root of concentration (c^1/2), following curves are obtained for two electrolytes A and B: 

Answer the following: 

(i) Predict the nature of electrolytes A and B. 

(ii) What happens on extrapolation of (A_m) to concentration approaching zero for electrolytes A and B?

Answer 1

(a)  According to Faraday's first law 

2.8=\(\frac{(56)\times2\times t}{2\times96500}\)=4825s=80min, 41s

Wt. of Zn deposited =\(\frac{65.3}{2\times96500}\)x 2 x 4825 =3.265g

(b) (i) A represents the strong electrolyte whereas B represents the weak electrolyte. 

(ii) It can be found from the graph that for a strong electrolyte A, as the concentration approaches the zero value, the molar conductance approaches a limiting value called molar conductance at infinite dilution

The curve for a weak electrolyte B is a rectangular hyperbola and does not intercept the y-axis. Even though the concept of molar conductance at infinite dilution exists for a weak electrolyte, graphically the value cannot be evaluated.