Question

Which of the following ions are present in an aqueous solution of hydrochloric acid?

[0.8 mark]

• A. $H^{+}\text{and}C{l}^{-}\text{only}$
• B. $H_3{O}^{+}\text{and}C{l}^{-}\text{only}$
• C. $H^{+},O{H}^{-},\text{and}C{l}^{-}\text{only}$
• D. $H^{+},H_3{O}^{+},\text{and}C{l}^{-}\text{only}$

Answer 1

The correct option is B $H_3{O}^{+}\text{and}C{l}^{-}\text{only}$

Hydrogen ions, being unstable, do not exist independently in aqueous solutions. These ions combine with water molecules to form hydronium ions in aqueous solutions. The following reactions take place in an aqueous solution of hydrochloric acid:
$H^{+}\left(\mathrm{aq}\right)+H_{2}O\left(l\right)\to H_3{O}^{+}\left(\mathrm{aq}\right)\mathrm{HCl}\left(\mathrm{aq}\right)+H_{2}O\left(l\right)\to H_3{O}^{+}\left(\mathrm{aq}\right)+{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)$

Thus, in an aqueous solution of hydrochloric acid, only $H_3{O}^{+}$ and $C{l}^{-}$ will be present