Board of Certified Safety Professionals (BCSP) Practice Exam

What does pH measure in a solution?

1. The concentration of total dissolved solids

2. The inverse proportion of hydrogen ions to hydroxide ions

3. The viscosity of the solution

4. The temperature of the solution

The correct answer is: The inverse proportion of hydrogen ions to hydroxide ions

pH measures the concentration of hydrogen ions (H⁺) in a solution, which directly relates to the acidity or basicity of that solution. The concept of pH is rooted in the logarithmic scale, where lower pH values indicate higher concentrations of hydrogen ions and thus greater acidity, while higher pH values signify lower hydrogen ion concentrations and greater basicity (or alkalinity). The pH scale ranges from 0 to 14, with pH 7 being neutral (equal concentration of hydrogen ions and hydroxide ions, H₂O). This implies that as the number of hydrogen ions increases, the number of hydroxide ions (OH⁻) decreases, and vice versa, thereby establishing an inverse relationship. While total dissolved solids, viscosity, and temperature are important characteristics of a solution, they do not relate to the measurement of pH, which is specifically focused on the concentrations of hydrogen ions. Thus, the statement about the inverse proportion of hydrogen ions to hydroxide ions captures the essence of what pH measures.