Question

An acid is a substance that increases the concentration of H3O+ ions in solution. Look at the reaction below of phenol (C6H5OH) with water: Which reactant acts as an acid by contributing a H+ ion to create H3O+ in the chemical equation?
a.C6H5OH(aq)
b.H2O(l)
c.C6H5O–(aq)
d.H3O+(aq)

Answer 1

A. C6H5OH is the acid because, on the product side, it becomes C6H5O-. this means it lost a hydrogen, and this is what acids do they give hydrogen away. 

Answer 2

Answer: Option (a) is the correct answer.

Explanation:

The reaction will be as follows.

        $C_{6}H_{5}OH(aq) + H_{2}O(l)$ $\rightarrow$ $H_{3}O^{+}(aq) + C_{6}H_{5}O^{-}(aq)$

Here, phenol is acting as an acid as it's conjugate base is more stabilized due to resonance. Whereas if $H^{+}$ ion is donated by water molecule then it will give a hydroxide ion which is not a strong base.

Therefore, here phenol is acting as an acid as it is donating an $H^{+}$ ion.