The pH scale measures what chemical property?

• A. Temperature
• B. Hydrogen ion concentration (acidity/alkalinity)
• C. Osmolality
• D. Volume

Answer: (B)

pH measures how acidic or basic a solution is, based on the activity of hydrogen ions. It is defined as the negative logarithm of the hydrogen ion activity, so lower pH means higher hydrogen ion activity and more acidity, while higher pH means lower hydrogen ion activity and more basicity. Neutral water at room temperature sits around pH 7; acidic solutions have pH below 7 and basic solutions have pH above 7. The other properties like temperature, osmolality, or volume describe different characteristics of a solution and do not determine its pH. In practice, pH can be measured with a pH meter that responds to hydrogen ion activity or with indicators that change color as the hydrogen ion concentration shifts.