Question

(a) What are amphoteric oxides?

(b) What are amphoteric metals? What happens when aluminum reacts with $\mathrm{KOH}\left(\mathrm{aq}\right)$?

Answer 1

(a) The metallic oxides that show chemical reactions with both bases and acids are commonly referred to as amphoteric oxides. The corresponding products obtained are salt and water$\left({\mathrm{H}}_2\mathrm{O}\right)$.

• For example, Zinc oxide$\left(\mathrm{ZnO}\right)$ and Aluminum oxide$\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$.

(b) Amphoteric metals are metals that exhibit chemical reactions with both acids and bases.

• For example, Aluminum$\left(\mathrm{Al}\right)$, Zinc$\left(\mathrm{Zn}\right)$, and Lead$\left(\mathrm{Pb}\right)$.
• Amphoteric metals like aluminum react with potassium hydroxide $\left(\mathrm{KOH}\right)$ in the presence of heat which leads to the liberation of hydrogen gas.
• Consider the following chemical reaction between aluminum and potassium hydroxide$\left(\mathrm{KOH}\right)$.
• $2\mathrm{Al}+2\mathrm{KOH}+6{\mathrm{H}}_2\mathrm{O}\stackrel{∆}{\to }2\mathrm{KAl}{\left(\mathrm{OH}\right)}_4+3{\mathrm{H}}_2\uparrow$