pH Indicator

Definition

A halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or alkalinity) of the solution can be determined easily.

Application

A pH measurement is important for medicine, biology, chemistry, food science, environmental science, oceanography and many other applications.

Difficulty

Procedure: Easy

Concept: Medium

Concept

The pH is a measure of the acidity or alkalinity of a solution. It is defined as minus the decimal logarithm of the hydrogen ion activity in an aqueous solution.

Pure water is theoretically neutral. The pH for pure water at 25 Celsius is close to 7.0. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline.

A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or alkalinity) of the solution can be determined easily. THis is normally accomplished by changing the color of the solution.

One method for detecting the pH of the solution is to use Hydrion paper, a paper that produces recognizably different colors for each pH unit over a range of pH values for different solutions. Other methods include pH meter that consists of a special measuring probe (a glass electrode) connected to an electronic meter that measures and displays the pH reading.

pH Indicator Paper
pH Meter

The following paragraphs will introduce the use of the hydrion paper for detecting pH values.

Materials

Procedure

References