Substances with the property to change color when they come into contact with an either acidic or basicsolution are called pH indicators. This is used in pH strips that changes color when they come into contactwith hydrogen ions (H+) and hydroxide ions (OH-).
Usually, pH strips are bought in packages with either 50 or 100 strips. pH strips are most useful for demonstration experiments or experiments where accuracy of the measured pH is of minor importance.
Using pH strips is simple. The strip is simply submerged in the aqueous solution and the reading of pH is done by comparing the color on the pH strip with the color on the package that the pH strips came in.
The accuracy of any pH reading is within 0.5 pH units.