The pH scale

The pH scale measures the acidity or alkalinity of a solution.

= 7neutral
\textgreater 7alkaline

The pH of a solution can be estimated using universal indicator and a colour chart, or measured using a pH meter.

Using an indicator

  1. dip a clean glass rod into the solution
  2. transfer one drop of solution to a piece of universal indicator paper on a white tile
  3. wait 30 seconds for the colour to develop, then match the colour to the colour chart
Universal indicator colours.Universal indicator colours and pH values

Using a pH meter

The pH of a solution can be measured using a pH meter:

  1. wash the pH probe with distilled water
  2. put the end of the probe into the solution
  3. record the reading on the pH meter
A pH meter with a probe which is in a beaker of yellow liquid. The meter reads 3.20
A pH meter with its pH probe in an acidic solution

The pH meter may need calibrating first. This is done by adjusting the reading to match the pH of a buffer solution, a solution with a known pH.