Question

34. The graph between H+ ion concentration and pH is given below. Answer the questions based on it.
Hydrogen ion concentration is more conveniently expressed as pH, which is the logarithm of the
reciprocal of the hydrogen ion concentration in gram moles per litre. Thus, in a neutral solution the
hydrogen ion (H+) and the hydroxyl ion (OH) concentrations are equal, and each is equal to 10-7. A PH
of 7 is neutral. A decrease in pH below 7 shows an increase in acidity (hydrogen ions), while an increase
in pH above 7 shows an increase in alkalinity (hydroxyl ions).
Each pH unit represents a 10-fold change in concentration.
Values of pH lower than 7 indicate that the hydrogen ion
concentration is greater than the hydroxide ion concentration,
and the aqueous solution is termed acidic. The opposite
condition is implied when the pH exceeds 7, and the aqueous
solution is termed basic.
(i) How pH is related to hydrogen ion concentration?
(ii) What is the pH value of distilled water?
(iii) How does the pH value of distilled water change when you add a little amount of common salt
to it? Give reason for your answer.
(iv) Four solutions A, B,C and D with pH values 1,5,8,and 10 are given. Arrange them the decreasing
order of hydrogen ion concentration.
(v)
If pH of a solution changes from 7 to 6, how much the hydrogen ion concentration of the solution
vary?
0
6.0
7.0
8.0
pH​

Answer 1

i) Lower the pH value, more the Hydrogen ion concentration.

ii) Distilled water normally has a pH value of 7. It might get a little acidic after reacting with carbon dioxide in air.

iii) When you add common salt to distilled water, the pH remains the same because common salt is a neutral salt and hence doesn't affect the pH of water.

iv) The given solutions are arranged in decreasing order of Hydrogen ion concentration:

A(1) > B(5) > C(8) > D(10)

v) If the pH of a solution changes from 7 to 6, the Hydrogen ion concentration will increase by ten-fold in the solution.