e-Consult | Revision Qns

1.

(c) Write balanced chemical equations for the reactions of $Al_2O_3$ and $ZnO$ with hydrochloric acid ($HCl$).

\$Al2O3\$ with HCl:

\$Al2O3(s) + 6HCl(aq) \rightarrow 2AlCl3(aq) + 3H2O(l)\$

\$ZnO\$ with HCl:

\$ZnO(s) + 2HCl(aq) \rightarrow ZnCl2(aq) + H2O(l)\$

2.

The following statement is about amphoteric oxides: "Amphoteric oxides can act as both acids and bases." Explain this statement in terms of the ions present in the oxide and how they interact with acids and bases. Give one example of an amphoteric oxide and describe the products formed when it reacts with a strong acid and a strong base.

The statement "Amphoteric oxides can act as both acids and bases" refers to the ability of these oxides to react with both acids and bases, demonstrating dual character. This is because amphoteric oxides contain metal ions that can exist in different oxidation states. The metal ion can lose electrons to form a positive ion (acting as an acid) or gain electrons to form a positive ion (acting as a base).

For example, aluminium oxide (Al₂O₃) is an amphoteric oxide.

Reaction with a strong acid (e.g., HCl):

Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l)

In this reaction, the aluminium ions (Al³⁺) in the oxide react with the hydrogen ions (H⁺) from the hydrochloric acid to form aluminium chloride (AlCl₃) and water. This shows the acidic behavior of the oxide.

Reaction with a strong base (e.g., NaOH):

Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2Na[Al(OH)₄](aq)

In this reaction, the oxide ions (O^2-) in the oxide react with the protons (H⁺) from the strong base (NaOH) to form the tetrahydroxoaluminate(III) ion, [Al(OH)₄]^-. This shows the basic behavior of the oxide.

3.

(a) Define the term 'amphoteric oxide'.

An amphoteric oxide is a metal oxide that can react with both acids and bases.

Acids, bases and salts - Oxides (3)