What is the pH of a neutral solution?

• A. 0
• B. 14
• C. 3
• D. 7

Answer: (D)

pH expresses how acidic or basic a solution is, on a scale from 0 to 14. A neutral solution has equal amounts of hydrogen ions and hydroxide ions, which places it at the middle of the scale. At standard room temperature this balance corresponds to a hydrogen ion concentration of 1×10^−7 M, and pH is defined as the negative logarithm of that concentration, so pH = −log10(1×10^−7) = 7. So a neutral solution has pH 7. The other values are outside neutrality: 0 and 3 are acidic, while 14 is basic. Temperature can shift the neutral point slightly, but under typical conditions neutral is around 7.