Quote:
Originally Posted by Mohit Pandey
One minute, does it mean that not every solution having lower pH is acidic in nature and vice versa?
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If you define
acidity to mean a pH of less than 7 then hot water would both be slightly acidic and have a pH of slightly less than 7. This slight deviation from pH's definition (which relies on 25 Celsius ) is only important when you are doing something that accurately depends on acidity.
For instance, if you are mixing an acid and a base, let's say hydrochloric acid and sodium hydroxide:
and measuring the result with a pH meter and you need the hydrochloric acid to completely neutralize the sodium hydroxide and the solution isn't at 25 C then you will need to take into account the difference in pH from the standard definition.
Otherwise, you will be fine. Adding an acid to water means more

in the water means more acidic means lower pH.
It's just important to know that the only reason hot water is more acidic is because our deffinition relies on the hydronium, not the hydroxide...
![pH = -log[H^+] pH = -log[H^+]](http://hypography.com/forums/latex/img/9323a7960b59520a7a2ea825af0fc4ec-2.gif)
. If we were using pOH, we would get the opposite result with hot water...
![pOH = -log[OH^-] pOH = -log[OH^-]](http://hypography.com/forums/latex/img/7da391d16d859b9aaf283a568f96eb60-2.gif)
.
-modest