PH Scale and its Limitations

Limitations of pH Scale- (i) pH values of the solutions do not give us an immediate idea of the relative strengths of the solutions.

pH is an important quantity that reflects the chemical conditions of a solution. The scale which is used to measure the acidity or alkalinity of a given solution is called the PH– Scale. The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. Numbers less than ‘7’ i.e. 6,5,4… indicate an increase in acidity while numbers more than 7 i.e. 8,9,10… indicate the increase in alkalinity of the solution.

Greater the value of PH of a solution lower will be its hydrogen ions concentration as hence, weaker is the acid. In the case of the acidic solution, the PH value increases after dilution while in the case of alkaline solution the PH decreases after dilution.

Limitations of PH– Scale:-

1. A 10-8 M solution of acid can’t have PH=8 and an acidic solution can’t have PH greater than 7.
2. For an acid of 1M, the concentration must be a concentrated acid but PH is found to be zero. It indicates that acid having concentration such as 2M, 3M, 4M etc will have negative PH
3. The concentrated solution of the strong base can have PH greater than 1. This is something difficult to measure the PH
4. An acidic solution having  ‘1’ has hydrogen ion concentration 100 times than that of a solution of PH ‘3’ but not 3 times.

Hence, A pH value is a number from 1 to 14, with 7 as the middle (neutral) point. Values below 7 indicate acidity which increases as the number decreases, 1 being the most acidic.

Therefore the pH scale and its limitations are explained above.