Neutrality may not be pH 7

The pH of an aqueous solution is a measure of its hydrogen ion concentration; it depends on temperature because the degree of dissociation of an acid does, i.e. K_a changes. Before you go on, write down the definition of pH.

It is: pH = - lg{[H⁺]/mol dm^-3}

Note that the concentration of the hydrogen ion has to be divided by its unit to get a number. You can only take logarithms of numbers, not of physical quantities.

A neutral solution can be at pH 8. How? By being cold. If you look up the values of K_wat 0^oC, 25^oC and 100^oC you will be able to calculate the pH of water at these three temperatures; they are roughly 8, 7 and 6. All of the solutions are, however, neutral. The definition of this is pH-independent:

a neutral solution is one where [H⁺] = [OH^-] .

This is at pH 7 only at 25^oC.