Question

1. For these three oxides, state whether each one is acidic, basic or amphoteric. Explain how cation oxidation state can be used to help predict acid/base behavior.
   1. CrO
   2. CrO₃
   3. Cr₂O₃
2. (a) Briefly explain what amphoterism means; (b) Choose an amphoteric molecular compound and indicate its chemical reaction with an acid and with a base.

Answer 1

The properties of oxides depends on the oxidation states and nature of element as metal forms basic oxides and non metals form acidic oxides.

But depending on the oxidation states the metal form the acidic and amphoteric oxides also .

Generally all these three properties are shown by transtion metals having variable oxidation states

As metal in low oxidation state iy form badic oxide due to low elecronegativity but at medium oxidation state it show amphoteric character (acidic and basic both) undergoes in either direction depending on the reactant nature

and if the oxdation state is to high then due to increase in elctronegaivity it show acidic nature.

So, 1.   CrO is basic in nature as Cr in low (+2)oxidation state.

2. CrO3 is acidic in nature as Cr in high (+6) oxidation state

3. Cr2O3 is amphoteric in nature as Cr in medium (+3) oxidation state

**Amphoteric means having both acidic and basic properties

Vonsider an example ZnO  amphoteric oxide

Acidic behaviour

ZnO + 2HCl -------> ZnCl2(salt)+ 2H2O

Basic behavior

ZnO +2 NaOH -----> Na2ZnO2(salt) + H2O