Question

Two voltameters containing copper sulphate and
acidulated water respectively are connected in
series and the same current is passed for some time.
If the amounts of copper and hydrogen obtained at
cathode are 0.3177 g and 1.008 x 10 g respectively,
calculate the equivalent mass of copper. (Eq. mass of
hydrogen = 1.008).
[Ans. 31.771​

Answer 1

Explanation:

Given:

Mass of hydrogen: 1.008g

Mass of copper: 0.3177g

To find: equivalent mass of copper

Solution:

•  The reaction is redox so the number of electrons exchanged is equal, hence the number of equivalents is equal.

• Number of equivalents of hydrogen = $\frac{mass of hydrogen}{equivalent mass of hydrogen}$

                                                           =$\frac{1.008*10^{-2} }{1.008 }$  =$10^{-2}$

• Number of equivalents of copper =$\frac{mass of copper}{equivalent mass of copper}$

                                                $10^{-2}$=$\frac{0.3177}{equivalent mass of copper}$    

• Equivalent mass of copper = $\frac{0.3177}{10^{-2} }$ = 31.77g

Answer:

31.77g

Answer 2

The equivalent mass of copper is 31.7 grams.

Explanation:

• The problem can be solved by using Faraday's second law of electrolysis.  
• Weight of Cu deposited/ weight of H2 deposited = eq. wt. of Cu/ eq. wt. of H2  
• So, 0.317/ 1.008 x 10^-2 = eq. wt of Cu / 1.008 (equivalent wt. of hydrogen)  
• So, eq. wt of Cu = 0.317 x 1.008 / 1.008 x 10-2  = 31.7 gm
• Thus the equivalent mass of copper is 31.7 grams.