Question

Which ions show the amphoteric nature when dissolved in excess of $NaOH/{NH}_{4}OH$ ?

• A. Aluminium
• B. Zinc
• C. Copper
• D. Lead

Answer 1

Answer: (A), (B)

The correct options are
A Zinc
B Aluminium

$A{l}_{\left(s\right)}+NaO{H}_{\left(aq\right)}⟶Al{\left(OH\right)}_{3\left(aq\right)}+N{a}_{\left(s\right)}$

$A{l}_{\left(s\right)}+N{H}_{4}O{H}_{\left(aq\right)}⟶Al{\left(OH\right)}_{3\left(aq\right)}+N{H}_{3\left(g\right)}$

Also,

$Z{n}_{\left(s\right)}+NaO{H}_{\left(aq\right)}⟶Zn{\left(OH\right)}_{2\left(aq\right)}+N{a}_{\left(s\right)}$

$Z{n}_{\left(s\right)}+N{H}_{4}O{H}_{\left(aq\right)}⟶Zn{\left(OH\right)}_{2\left(aq\right)}+N{H}_{3\left(g\right)}$

Thus, since in these reactions $Al{\left(OH\right)}_3$ and $Zn{\left(OH\right)}_2$ can act as both acids and bases. Hence, they are amphotesic in nature.