Question

3. Identify which reactants are amphoteric species in the following reactions. For those species, determine if the compound is also amphiprotic. Reaction Amphoteric Reactant Amphiprotic? (Y or N) HCO3 + HBr = H2CO3 + Br- 3 HCI + Al(OH)3 = AlCl3 + 3 H2O 2 HBr + ZnO = ZnBr2 + H2O

Answer 1

Amphoteric substance are those substance which can act as either an acid or base while the amphiprotic substance are the substance which can accept H as well as donate H ion. Now
1) HCO₃^- can act as both amphoteric as well as amphoprotic because-

HCO₃^- + H₂O----------> CO₃^- + H₃O⁺ ( acts as acid)

HCO₃^- + H₂O----------> H₂CO₃ + OH^- (acts as base)

Similiarly,

HCO₃^- + H⁺------> H₂CO₃ ( accepting proton)

HCO₃^- -----------> CO₃^-2 + H⁺ (donating proton)

2) Al(OH)₃ + H₂O----> Al(OH)₄^- ( acting as acid)

Al(OH)₃ --------> Al(OH)₂⁺ + OH^- (acting as base)

But it is not amphoprotic

3) ZnO is also amphotetic in nature because

ZnO + 2HCl-------> ZnCl₂ + H₂O

ZnO + 2NaOH-------->Na₂ZnO₂ + H₂O

Again it is not amphoprotic as it can accept proton but can't donate proton. So above all of them, only HCO₃^- acta as both amphotetic as well as amphoprotic