What Is pH Paper Used to Determine?

pH measures the acidity or alkalinity of a substance. Substances with a pH below 7 are acids because they have a high concentration of hydrogen ions while alkaline substances have a pH above 7 because they have a high concentration of hydroxide ions.

Liquids

You can determine the pH of liquids, such as water or lemon juice, simply by dipping a strip of pH paper into the solution and comparing the color of the pH paper to the color key.

Solids

You can determine the pH of solids, such as soil, with pH paper by pouring a small amount of distilled water on the solid and then dipping the pH paper in the water. Do not use tap water or rainwater because those water sources may be either acidic or basic (alkaline).

Warning

Depending on your need for precision, pH paper may not be accurate enough for your needs. pH paper only gives a rough approximation based on color rather than the decimal reading given by pH meters.

References

• U.S. Environmental Protection Agency: How to Measure With pH Paper
• Rain: Soil Types and Testing
• University of Wisconsin at Platt: pH Paper Module