What is the pH of a neutral solution at standard room temperature?

• A. 7
• B. 0
• C. 14
• D. -7

Answer: (A)

Neutral pH means the concentrations of hydrogen and hydroxide ions are equal. Since pH is defined as the negative logarithm of the hydrogen ion concentration, when [H+] equals [OH−] at standard room temperature, their balanced condition falls right at the middle of the pH scale. In pure water at 25°C this neutrality corresponds to the value that marks the center of the scale, indicating neither acidity nor basicity. Remember, values below this point indicate acidity and values above indicate basicity. The exact middle value is specific to that temperature because the water autoionization constant Kw changes with temperature, but at standard room temperature the neutral point sits right in the middle.