Q.
KMnO4 can be prepared from K2MnO4 as per the reaction, 3MnO42−+2H2O⇌2MnO4−+MnO2+4OH−
The reaction can go to completion by removing OH− ions by adding
To remove OH- ion a weak acid (H2CO3) is required because a strong acid can reverse the reaction. So here HCl is a strong acid so it reverse the reaction.
KOH is strong base which will increase OH- concentration. SO2 will react with water to form a strong acid H2SO4 . CO2 combines with OH− ion to give carbonate which is easily removed.