Question

What is the pH value for a neutral solution?

Answer 1

Hint:Pure water is a neutral solution. The amount of hydronium and hydroxyl ions in water is equal at the given temperature. The salts formed from a strong acid and a strong base are also neutral solutions.

Complete step by step solution:
Let’s look at the answer to the given question:
> A neutral solution is a solution in which the number of hydronium and hydroxyl ions is equal at a given temperature and concentration.
Example: pure water
> The pH of a solution is defined at the negative of the log of the concentration of the hydronium ions present in the solution at a given temperature and concentration. It gives the strength of the acidity of the solution.
pH = -log$\left[ {{H}^{+}} \right]$
> The pH range is a scale having numbers from 0 to 14. On this scale, the strength of a solution is defined from highly acidic to neutral to highly basic.
> The pH of a solution which is neutral is 7.
Solutions having pH lower than 7 are acidic while solutions having pH greater than 7 are basic.
> Let’s see take the example of water
> At $25{}^\circ C$, the concentration of the ions present in water is as follows:
\[\left[ {{H}^{+}} \right]\,=\,{{10}^{-7}}\] and \[\left[ ^{-}OH \right]\,=\,{{10}^{-7}}\]
Now, we will calculate the pH of water:
> The formula for calculating pH is:
\[pH\,=\,-\log \left[ {{H}^{+}} \right]\]
\[pH\,=\,-\log \left[ {{10}^{-7}} \right]\]
\[pH\,=\,-(-7)\log 10\]……using $\log \,{{x}^{a}}\,=\,a\log x$
\[pH\,=\,7\]
Where, $\log 10\,=1$
Hence, the pH of a solution which is neutral is 7.

Note: Students should remember that the pH of a solution depends on dilution and temperature. On dilution the pH increases. On increasing temperature, the pH decreases but the pH of water does not change as the concentration of both hydronium and hydroxyl ions change proportionally.