Calculate the hydroxide ion concentration of pure water.
Use the fact that the pH of pure (neutral) water is 7.00. The look up the definition of pH. You can also get it from the dissociation costant of the H2O -> H+ + OH- reaction.
To review that, see
http://www.sensorex.com/support/education/pH_education.html
To calculate the hydroxide ion concentration of pure water, we need to understand the concept of pH.
pH is a measure of the acidity or alkalinity of a solution. It is defined as the negative logarithm (base 10) of the hydrogen ion concentration ([H+]). In pure water, the concentration of hydrogen ions is equal to the concentration of hydroxide ions ([H+] = [OH-]), so the pH is neutral and equal to 7.
The dissociation of water can be represented by the following equation:
H2O -> H+ + OH-
The dissociation constant (Kw) is a value that represents the equilibrium constant for this reaction. In pure water, the value of Kw is 1 x 10^-14 at 25 degrees Celsius.
Since the concentration of hydrogen ions is equal to the concentration of hydroxide ions, we can write the equation:
Kw = [H+][OH-]
In pure water, where the pH is 7.00, we can substitute the values into the equation:
1 x 10^-14 = [H+][OH-]
Since [H+] = [OH-] in pure water, we can assign the same value 'x' to both.
1 x 10^-14 = x * x
Taking the square root of both sides, we get:
x = 1 x 10^-7
Therefore, the hydroxide ion concentration of pure water is 1 x 10^-7 moles per liter (M).