Question

What is the pH of Pure Water?

Answer 1

Part 1: pH

• The pH of any solution is defined as the negative log of Hydrogen ion concentration.
• Mathematically, $\mathrm{pH}=-{\log }_{10}\left[{\mathrm{H}}^{+}\right]$
• pH is used to determine the nature of the solution whether it is acidic, basic, or neutral.

Solution	pH range
Acidic	1 - 6.9
Neutral	7
Basic	7.1 - 14

Part 2: Identifying the pH of the Water

• Depending on the values of pH we can further classify the solution as strongly and weakly acidic and basic.
• Water is a weak electrolyte but is ionized to produce an equal number of hydrogen and hydroxide ions.
• The ionization reaction can be represented as:

$\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\rightleftharpoons \underset{\mathrm{Hydrogen}\mathrm{ion}}{{\mathrm{H}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}$

• Since water produces the equal number of hydroxide and hydrogen ions. So, water is neutral.
• At 25°C, the pH of the pure water is 7. It is neither acidic nor basic. As it is neutral with a pH value of 7, the pure water is tasteless, odourless, and colourless.
• The safe drinking water that is supplied to our house keeps their water supply at a pH range of 6.5 to 8.5.