Question

The pH of neutral water at ${{25}^{\circ }}C$ is 7.0. As the temperature increases, ionisation of water increases , however the concentration of ${{H}^{+}}$ ions and $O{{H}^{-}}$ ions are equal. What will be the pH of pure water at ${{60}^{\circ }}C$?
A. Equal to 7.0
B. Greater than 7.0
C. Less than 7.0
D. Equal to 0

Answer 1

Hint: It is found that as the temperature increases, the pH will decrease. The value of pH equal to 7 is neutral, greater than 7 is basic and less than 7 is acidic in nature.

Complete answer:
- As we know that the ionisation of water is increased as the temperature is increased, due to which${{H}^{+}}$ ions are also increased. So, we can write that since ionisation of water increases upon the increasing temperature.
- And if the ions are increased then it means that the value of pH will become less than 7.0 because, if we will see the pH scale then then the range that is below 7 is acidic range and the range below 7 is basic range. And 7 is the neutral or alkaline range.
-So, in short we can say that as the temperature increases, the ionisation of water increases, and the pH of the solution therefore decreases and becomes less than that of 7.
Hence, we can conclude that the correct option is (C).
That is the pH of pure water at ${{60}^{\circ }}C$ is less than 7.0.

Note:
- As we know that pH decreases with the increase in temperature, but we can say that this doesn’t mean that water becomes more acidic at high temperature. A solution is said to be acidic, if there is an excess amount of ${{H}^{+}}$ ions over $O{{H}^{-}}$ ions.
- For example: In pure water there is always the same concentration of hydroxide and hydrogen ions and therefore the water is neutral even if its pH changes.