Question

Mark the correct statement.

• A. Both bases and alkalis are soluble in water.
• B. Alkalis are soluble in water but all bases are not.
• C. $C_2{H}_{5}OH$ is a base because it has $OH$ group.
• D. Bases are soluble in water but alkalis are not.

Answer 1

The correct option is B

Alkalis are soluble in water but all bases are not.

The explanation for the correct option (B):

• Bases are chemical substances that when dissolved in Water (${\mathrm{H}}_2\mathrm{O}$) dissociate to produce Hydroxide (${\mathrm{OH}}^{-}$) ions.
• Example: $\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$
• The solubility of bases depends on the strength of the base (weak or strong). In general, all strong bases are soluble in water.
• Alkalis are known as water-soluble bases. Hence, they are soluble in water.
• Hence, all bases are generally not soluble but alkalis are water-soluble.

The explanation for the incorrect options:

• (A) Generally, strong bases are water-soluble. The compound Copper(I) oxide ($\mathrm{CuO}$) is a base but it is not soluble when dissolved in water.

$\mathrm{CuO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)$

• (C) According to the definition of bases, Ethanol (${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$) is not a base as it does not dissociates in water to produce ${\mathrm{OH}}^{-}$ions.

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{l}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{aq}\right)$

• (D) Alkalis are soluble in water.

Example: Sodium hydroxide ($\mathrm{NaOH}$) is an alkali. The reaction of $\mathrm{NaOH}$ with ${\mathrm{H}}_2\mathrm{O}$ is:

$\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$

Final Answer: Hence, option (B) is correct. The correct statement is Alkalis are soluble in water but all bases are not.