Lesson plan

Plant colour chemistry and pH indicators

Change flower petal colours with acid/base and use red cabbage as an acid/base indicator.
Science content
Biology: Features, Adaptations of Living Things (K, 1, 3, 7)
Chemistry: Atoms, Molecules (3-7)
Chemistry: Chemical Changes (2, 7)

Some flowers can change colour depending on the chemical environment they are in.
Do flower colour activity.
Discuss what colours were made, and the molecules responsible.
Flowers can make an array of petal colours by varying the acidic/basic environment (the concentration of H atoms) in their petals. This changes the colour of some pigment molecules, and several pigment molecules can mix to make even more colours.

Chemists often use a pigment that changes colour with acid and base to find out how many H atoms are in something. They call it an indicator.
The scale of how acidic or basic something is can be measured on a scale called the pH scale. So these indicators are called pH indicators.
Make a pH indicator with cabbage juice, and use to measure the pH of household chemicals.

Test fruits and vegetables that are red, blue and purple to find out which ones have pH sensitive pigments.

The concentration of H atoms (technically ions), or the pH, affects the chemistry of many systems, as it affects what chemical reactions happen and what molecules are made. pH is important in water and soil, changing how plants get nutrients and grow, and what minerals are dissolved and precipitated; it is important in our own bodies to make sure we digest food and make new cells for growth and to heal injuries.


Laurier did flower colours and red cabbage dye.
ingridscience afterschool did red cabbage dye and fruit and vegetable colours.
The colouring a white flower activity was added to this lesson plan for a lesson on Coloured plants for After school programs in NY.
Seymour did red cabbage dye, then vegetable colours

Grades taught
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7