Question

What Is the pH of Distilled Water?

Answer 1

The $pH$ of a solution is a measure of the concentration of hydrogen ions. The term itself stands loosely for the "power of hydrogen," and it is the negative logarithm of the actual hydrogen ion concentration.

Complete answer:
The concentration of hydrogen ions decreases with increasing $pH$, and a difference of one $pH$ unit represents a tenfold variation in hydrogen ion concentration. The $pH$ scale ranges from 0 to 14. Acidic solutions have a pH between 0 and 7, while basic solutions have a pH between 7 and 14. Pure distilled water should have a $pH$ of 7, but because it absorbs carbon dioxide from the atmosphere, it actually has a $pH$ of 5.8. It is assumed that distilled water has a neutral $pH$ of 7 because it has been purified. However, this is not always the case because distilled water is rarely 100% pure and even less frequently has a pH of exactly 7.
Distillation removes nearly all ionic, mineral, and organic impurities, making it one of the purest forms of water available. However, just because it is labelled as purified water does not imply that it is pure ${H_2}O$. Distilled water actually has a slightly acidic $pH$. This is due to the fact that when distilled water comes into contact with air, carbon dioxide gas dissolves in it, resulting in a dilute solution of carbonic acid. This is also why demineralized water, a type of purified water, reacts poorly with metals such as steel.

Note:
A $pH$ reading of 7 is exactly neutral. A solution with a $pH$ lower than 7 is considered acidic while a solution with a $pH$ higher than 7 is considered alkaline. The further away from 7 the reading is, the more acidic or alkaline it is.