Question

Fill in the following blanks with suitable words:
(a) Acids have a pH...........than 7.
(b) Alkalis have a pH.............. than 7.
(c) Neutral substances have a pH of ................
(d) The more acidic a solution, the ................. the pH.
(e) The more alkaline a solution, the............... the pH.

Answer 1

To answer this question, you should recall the concept of pH scale and the properties of acid and base. It ranges from 1 to 14 and is the negative logarithm of the hydrogen ion concentration.

Complete step by step answer:
The pH scale is a logarithmic scale that is used to measure the acidity or the basicity of a substance. The possible values on the pH scale range from 0 to 14. The term pH is an abbreviation of potential for hydrogen.
Acidic substances have pH values ranging from 1 to 7 and alkaline or basic substances have pH values ranging from 7 to 14. A perfectly neutral substance would have a pH of exactly 7.
The pH of a substance can be expressed as the negative logarithm of the hydrogen ion concentration in that substance. Similarly, the pOH of a substance is the negative logarithm of the hydroxide ion concentration in the substance. These quantities can be expressed via the following formulae:${\text{pH }} = {\text{ }} - {\text{log}}\left[ {{{\text{H}}^{\text{ + }}}} \right]$ and ${\text{pOH }} = {\text{ }} - {\text{log}}\left[ {{\text{O}}{{\text{H}}^{\text{-}}}} \right]$. Hence the statements can be filled as:
(a) Acids have a pH lower than 7.
(b) Alkalis have a pH greater than 7
(c) Neutral substances have a pH of 7.
(d) The more acidic a solution, the lower the pH.
(e) The more alkaline a solution, the higher the pH.

Note:
You should know about the limitations of pH Scale
pH values do not reflect directly the relative strength of acid or bases: A solution of pH = 1 has a hydrogen ion concentration 100 times that of a solution of pH = 3 (not three times).
pH value is zero for $1{\text{N}}$ the solution of the strong acid. The concentration of $2\;{\text{N}},{\text{ }}3\;{\text{N}},{\text{ }}10\;{\text{N}},$etc. gives negative pH values.
A solution of an acid having very low concentration, say ${10^{ - 8}}\;{\text{N}},$ shows a pH = 8and hence should be basic, but actual pH value is less than 7.