Question

pH stands for:
(A). Power of hydrogen
(B). Power of hydroxide
(C). Purity of hydrogen
(D). Purity of hydroxide

Answer 1

- Hint: pH notation was devised by the Danish biochemist Soren Sorensen in 1909. It is the logarithm of the reciprocal of the hydrogen ion concentration. It provides a convenient way to represent a range of concentrations that spans many powers of ten.

Complete step-by-step solution -
We can also define pH as the negative logarithm of the hydrogen ion concentration i.e.
$$\text{pH=-log }[{\text{H}}^{+}]$$
Because of the negative sign in the expression, if $[{\text{H}}^{+}]$ increases, pH would decrease and if it decreases, pH would increase.
Therefore, pH stands for Power of hydrogen.
In pure water at ${25}^{\text{o}}\text{C}$ (298K)
$[{\text{H}}^{+}]$$=1.0\text{x1}{\text{0}}^{-7}\text{mol}{\text{L}}^{-1}$
$\text{pH=-log }[{\text{H}}^{+}]=-\text{log(1}{\text{0}}^{-7})=7$
Since, in pure water at ${25}^{\text{o}}\text{C}$(298K)
$\text{O}{\text{H}}^{-}=1.0\text{x1}{\text{0}}^{-7}\text{mol}{\text{L}}^{-1}$
Also, pOH=7
The relationship between $\text{p}{\text{K}}_{\text{w}}$,pH and pOH is
14=pH+pOH
There is a great importance of pH in our daily life-

(a). pH in human and animals
Most of the biochemical reactions taking place in our body are in a narrow pH range of 7.0 to 7.8. Even a small change in pH disturbs these processes.

(b). pH in plants
Plants have a healthy growth only when the soil has a specific pH range which should be neither highly alkaline nor highly acidic.

(c). Acid Rain
When the pH of rain water falls below 5.6, it is called acid rain. When acid rain flows into rivers, the pH of the river water also falls and it becomes acidic. As a result, the survival of aquatic life becomes difficult.

Thus, the correct option is A. Power of Hydrogen.

Note: We should know that the method of calculation of pH used in this unit is valid for
(i). Solutions of strong acids and bases only and
(ii) Solutions of acids or bases should not be extremely dilute and the concentrations of acids and bases should not be less than ${10}^{-6}\text{mol}{\text{L}}^{-1}$.