Question

What does pH measure?

Answer 1

It measures the concentration of h+ ions.

Answer 2

• pH is the negative log of the H+ concentration in mol/L in any medium
• In chemistry, pH is a measure of the acidity or basicity of a solution. It approximates but is not equal to p[H], the negative logarithm (base 10) of the molar concentration of dissolved hydronium ions (H3O+);
• a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration.
• Crudely, this negative of the logarithm matches the number of places behind the decimal point,
• so for example
• 0.1 molar hydrochloric acid should be near pH 1 and 0.0001 molar HCl should be near pH 4 (the base  10 logarithms of 0.1 and 0.0001 being -1, and -4, respectively). Pure  water is neutral, and can be considered either a very weak acid or a  very weak base (center of the 0 to 14 pH scale), giving it a pH of 7 (at  25 °C (77 °F)), or 0.0000001 MH+
• However, pH is not precisely p[H], but takes into account an activity factor.
• This represents the tendency of hydrogen ions to interact with other  components of the solution, which affects among other things the  electrical potential read using a pH meter.
• As a result, pH can be affected by the ionic strength of a solution - for example, the pH of a 0.05 M potassium hydrogen phthalate