In the electrolytic refining of blister copper, the total number of main impurities, from the following, removed as anode mud is ______________
Pb, Sb, Se, Te, Ru, Ag, Au and Pt

Solution

Chemistry ma’am · 3 steps

Ask what each metal does at the anode: whatever cannot dissolve falls off and settles as anode mud.

1. The set-up. Impure blister copper is the anode, a thin sheet of pure copper is the cathode, and acidified CuSO₄ solution is the electrolyte. Copper dissolves at the anode as Cu²⁺ and pure copper deposits on the cathode.
2. What stays behind. Impurities that do not go into solution at the anode loosen and settle below it as anode mud. The noble metals Ag, Au and Pt are less reactive than copper, so they are not oxidised. The NCERT list of main anode-mud impurities from blister copper is antimony, selenium, tellurium, silver, gold and platinum.

   Impurity	Main anode-mud impurity?
   Pb	No. It is more reactive than copper, so it is oxidised at the anode. It is not in the list of main anode-mud impurities.
   Sb, Se, Te	Yes, 3
   Ru	No. It is not a main impurity of blister copper.
   Ag, Au, Pt	Yes, 3 (noble metals, not oxidised)

3. So. Sb, Se, Te, Ag, Au and Pt go into the anode mud. That is 3 + 3 = 6.

The common slip: 7. Counting Pb as anode mud gives 7. Lead is more reactive than copper and is oxidised at the anode, so it is not one of the main anode-mud impurities.

The idea to keep. In electrolytic refining, metals less reactive than the one being refined do not dissolve at the anode and settle as anode mud. For copper, remember the NCERT list: Sb, Se, Te, Ag, Au, Pt.

Answer from the NTA final answer key. Solution by PrepWiser.