Question

A solution of ${\mathrm{MgCl}}_2$ in Water is

• A. $<7$
• B. $>7$
• C. 7
• D. 14.2

Answer 1

The correct option is A

$<7$

The explanation for the correct option (A):

• Salt is a compound formed from an acid by the replacement of the Hydrogen ($\mathrm{H}$) in the acid by a metal.
• Example: Hydrochloric acid ($\mathrm{HCl}$) is an acid. When the $\mathrm{H}$ of $\mathrm{HCl}$ is replaced by a metal atom, say a Sodium atom ($\mathrm{Na}$), then it results in the formation of a salt Sodium chloride ($\mathrm{NaCl}$).
• Magnesium chloride (${\mathrm{MgCl}}_2$) is a salt. The aqueous solutions of many salts are neutral (pH = 7) but some salts form acidic or basic solutions when dissolved in Water (${\mathrm{H}}_2\mathrm{O}$).
• The acidic and basic nature of some salt solutions can be determined by the hydrolysis of salts.
• The salts of strong acids and strong bases produce solutions that are neutral in nature.
• The salts of strong acids and weak bases produce solutions that are acidic in nature.
• The salts of weak acids and strong bases produce solutions that are basic in nature.
• The hydrolysis of ${\mathrm{MgCl}}_2$produces Hydrochloric acid ($\mathrm{HCl}$) and Magnesium hydroxide ($\mathrm{Mg}{\left(\mathrm{OH}\right)}_2$). The equation is:

${\mathrm{MgCl}}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Mg}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)$

• In this reaction $\mathrm{HCl}$ is a strong acid and $\mathrm{Mg}{\left(\mathrm{OH}\right)}_2$ is a weak base and therefore, the aqueous solution of ${\mathrm{MgCl}}_2$is acidic in nature. For the acidic solution, the value of pH is less than 7 ($<7$).

Final Answer: Hence, option (A) is correct. A solution of ${\mathrm{MgCl}}_2$ in Water is $<7$.