Water Quality: pH

Introduction

The pH of a body of water is very important as an indication of water quality, because of the sensitivity of aquatic organisms to the pH of their environment. Small changes in pH can endanger many kinds of plants and animals; for example, trout and various kinds of nymphs can only survive in waters between pH 7 and pH 9. If the pH of the waters in which they live is outside of that range, they may not survive or be able to reproduce.

Water contains both hydrogen ions and hydroxide ions. The relative concentrations of these two ions determine the pH value. Water with a pH of 7 has equal concentrations of these two ions and is considered to be a neutral solution. If a solution is acidic, the concentration of hydrogen ions exceeds that of the hydroxide ions. In a basic solution, the concentration of hydroxide ions exceeds that of the hydrogen ions. On a pH scale of 0 to 14, a value of 0 is the most acidic, and 14 the most basic. A change from pH 7 to pH 8 in a body of water represents a ten-fold increase in the hydroxide ion concentration.

In this experiment, you will measure the pH of several water sources.

Objectives

In this experiment, you will

• Use a computer and an NXT to measure pH.
• Compare water from different sources.
• Learn to distinguish acidic, neutral, and basic pH values.