Question

Arrange the pH values of 0.1 M solution of (I) $HCOONa$, (II) $HCOOH$, (III) $C{{H}_{3}}COON{{H}_{4}}$, (IV) $NaOH$, and (V) $HCl$ in decreasing order is:
(a)- IV > III > I > II > V
(b)- IV > I > III > II > V
(c)- II > III > I > IV > V
(d)- V > II > III > I > IV

Answer 1

The pH of the solution is inversely proportional to the strength of the acid and the pH of the solution is directly proportional to the strength of the base.

Complete answer:
The pH of the solution is inversely proportional to the strength of the acid and the pH of the solution is directly proportional to the strength of the base.
From the given compounds, (IV) $NaOH$ is the strongest base and will have a highly alkaline solution, so it will have the highest pH.
(V) $HCl$ is the strongest acid and will have a highly acidic solution, so it will have the lowest pH.
(II) $HCOOH$ is known as formic acid, so it is also an acid but it is a weak acid, hence it will have pH higher than hydrochloric acid. (I) $HCOONa$ is salt and it is formed by a strong base and weak acid so it will have a pH higher than 7. (III) $C{{H}_{3}}COON{{H}_{4}}$ is also a salt and is formed by weak acid and a weak base, so its pH will be less than sodium acetate.
So the order will be IV > I > III > II > V.

Therefore, the correct answer is an option (b).

Note:
The components of the salt decide whether the solution of the salt is acidic or basic. If the salt is made up of strong acid, then the solution of salt will be acidic and if the salt is made up of a strong base then the solution of the salt will be basic.