What is pH?

• A. A measure of how acidic or basic a solution is.
• B. The rate of a chemical reaction.
• C. The temperature of a solution.
• D. The concentration of solutes in a solution.

Answer: (B)

pH is a measure of how acidic or basic a solution is. It reflects the hydrogen ion concentration: more hydrogen ions means stronger acidity, while fewer hydrogen ions (or more hydroxide ions) means basicity. On the usual scale, neutral solutions sit around pH 7, acidic solutions have pH below 7, and basic solutions have pH above 7. The scale is logarithmic, so each unit change represents about a tenfold change in [H+]. This concept distinguishes pH from other properties like how fast a reaction occurs, the temperature of the solution, or the overall concentration of dissolved substances.