Question

A student mixed equal volumes of hydrochloric acid and sodium hydroxide solution of same concentrations in a beaker and tested the pH of the resulting mixture with a pH paper. What will be the colour of pH paper in this case ?
(1) red
(2) yellow
(3) green
(4) blue

Answer 1

Hydrochloric acid is a strong acid and sodium hydroxide is a strong base, the reaction of strong acid and strong base is known as neutralization reaction. When strong acid and strong base reacts concentration of H⁺ and OH^- ion becomes equal, they completely neutralize each other. So, the colour of the pH paper will be green.
$\mathrm{HCl}\left(\mathrm{aq}\right)+\mathrm{NaOH}\left(\mathrm{aq}\right)\to \mathrm{NaCl}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Hence, the correct answer is option 3.