A solution that is neither acidic nor basic is neutral and has a pH of 7. The pH scale, which ranges from 0 to 14, indicates how acidic or basic a substance is. A substance that has a pH below 7 is and acid and a substance with a pH above 7 is a base.
The hydrogen ion, H+, is responsible for an substance being acidic and the hydroxide ion, OH-, makes a substance basic. When the concentrations of these two ions are equal the substance is neutral. Pure distilled water is an example of a neutral solution. A very small amount of water ionizes, and in doing so it produces equal numbers of H+ and OH- ions.
The pH scale is a logarithmic scale, meaning that it's based on powers of 10. The pH value of a substance is the negative logarithm of the H+ concentration. The product of the H+ and OH- concentrations of an aqueous solution is 10^(-14), so in a neutral solution both have a concentration of 10^(-7) and the pH is therefore 7.
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