Question

What is anode mud?
A.Fan of anode
B.Metal of anode
C.Impurities collected at anode in electrolysis during purification of metals
D.All of these

Answer 1

Hint: The insoluble impurities of anode in the electrorefining; neither dissolve in solution nor get deposited at cathode. So such impurities remain as sludge in the electrolytic cell. The pure metal from anode gets deposited at the cathode.

Complete step by step answer:
In the electrorefining method: metals such as Copper, Silver, Zinc, Aluminium, Nickel and Chromium. The impure metal is made of the anode of the electrolytic cell, while the cathode is a thin plate of pure metal. Electrolyte is the solution of a double salt of the metal. On passing the electric current pure metal from the anode dissolves and gets deposited at the cathode. The soluble impurities go into the solution while insoluble impurities or less electropositive impurities settle down below the anode as anode mud or sludge.

For example during electrorefining of copper, the electrolytic bath contains an acidified solution of copper sulphate, impure copper acts as anode while cathode is of the pure copper strip. When electric current is passed, there is transfer of pure copper from anode to cathode which results into cathode gradually growing in size. The impurities of iron, zinc, nickel and cobalt dissolve in the solution as sulphates and other impurities like silver and gold settle down below the anode as anode mud. The cathode is removed and copper of about \[99.9\% \] purity is obtained.

Thus, the correct option is C.

Note:
In electrorefining of silver: impure silver is made to be anode and pure silver is made to be cathode. Aqueous silver nitrate and \[1\% \] dilute nitric acid acts as electrolyte. On passing electricity, pure silver is deposited at cathode. Electrorefining of lead is known as the Bett process.