F4 Chem(allkali,electrolysis)

1)
Firstly, the alkali used in this reaction is usually a strong alkali, e.g. NaOH or CaO.
Secondly, when heating ammonia solution alone, ammonia gas is evolved. Therefore, it is meaningless to use ammonia as the alkali to react with ammonium salts.

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2)
In the solution, HNO3 is ionized as H+(aq) and NO3-(aq) ions, while water is slightly ionized to give H+(aq) and OH-(aq) ions.

Consider the cathode. The only cation H+(aq) migrate to the cathode. (This is because the cathode is connected to the negative pole of a battery and thus the positively charged cations are attracted.) The H+(aq) ions are then discharged (gain electrons) at the cathode.
2H+(aq) + 2e- → H2(g)

Consider the anode. OH-(aq) and NO3-(aq) ions migrated to anion. (This is because the anode is connected to the positive pole of a battery and thus the negatively charged anions are attracted.) Since OH-(aq) ion is oxidized more readily than NO3-(aq) ion (because NO3- ion is too bulky to migrate), OH-(aq) ion is preferentially discharged but NO3-(aq) would NOT be discharged.
4OH-(aq) → 2H2O(l) + O2(g) + 4e-

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3)
In acidification, the role of the acid is to add H+(aq) to the solution.
Since HCl is a weak reducing agent, it is not used to acidified an oxidizing agent.
HNO3 is a strong oxidizing agent. If it is used to acidify KMnO4 or K2Cr2O7, the case would become complicated because the solution contains two oxidizing agent.­

Dilute H2SO4 is used as the acidifying agent. This is because dilute H2SO4 is neither an oxidizing agent nor a reducing agent.
In some lab manuals, a small amount of conc. H2SO is used. This is because H2SO4 would become dilute when a small amount of conc. H2SO4 is added to a certain amount of aqueous solution.

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4)
Conc. HCl is a reducing agent, but the reducing power is not high.