The pH scale measures how acidic or alkaline a solution is. It ranges between 0 and 14.

Acids have a pH of less than 7.

Alkalis ( or bases ) have a pH of over 7.

pH 7 is neutral.

How is pH measured?

pH is measured using an indicator. An indicator is a dye that changes colour in the presence of an acid or alkali.

Commonly used indicators used to determine pH

• Universal indicator
• Litmus
• Methyl orange
• Phenolphthalein

The image below shows the pH chart for Universal Indicator.

Universal Indicator is a mixture of other indicators.

I have a blank version of the image above available for students to use to fill in the example boxes.

Who created the pH scale?

The pH scale was created by a Danish biochemist named Soren Sorensen in 1909.

Simple science experiments for learning about pH

A very basic pH indicator can be made using the liquid left over from boiling red cabbage in water.

The indicator is a purple colour but turns red in the presence of an acid and green if an alkali is added.

A basic indicator can also be made from the leaves of a poinsettia plant!

Last Updated on October 16, 2023 by Emma Vanstone

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