Activity: The acid test - Level 4
Achievement Objectives - Whāinga Paetae: Te Aka
4.1 (ii) Classify familiar materials according to their chemical properties, and devise a way of testing everyday substances for acidity. Te Marautanga o Aotearoa: (p. 101) Ō Kawekawe, Ngā Āhutanga me ngā Panoni Matū. 1(i).
Learning Outcome
I will be able to:
- make a solution from flower petals
- test everyday substances for acidity using the flower solution.
Success criteria
| Success criteria | Self-assessment | Peer assessment | Teacher assessment | ||||||
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| I can make a solution from flower petals. | |||||||||
| I can test everyday substances for acidity using the flower solution. | |||||||||
In this investigation you will be using petal water to test various substances to see if they are acids or bases. Before you carry out your investigation, first make a prediction about whether your test substance is and acid or a base.
| Test substance | Prediction whether your test substance is an acid or a base |
|---|---|
| vinegar | |
| oven cleaner | |
| toothpaste | |
| washing up liquid | |
| kiwifruit juice |
Equipment
- Flowers of the same type (alternatively red cabbage can be used)
- White plastic ice cube tray
- Dropper made from a short piece of drinking straw with reusable adhesive pushed in one end
- Various substances for testing including lemon juice, baking soda, vinegar, oven cleaner, toothpaste, washing up liquid, baking powder, kiwi fruit juice.
Method
- Take off the petals of your selected flower and put them into a plastic zip lock bag. NOTE: all the petals must be the same colour and from the same type of flower.
- Add about a tablespoon of water to your petals. Be careful! Don’t add too much. This solution (a liquid which has something dissolved in it) must be concentrated. Crush the petals inside the bag until the water changes colour.
- Write down the colour change in the table below in row(a).
- Use a teaspoon or a dropper made from a straw to transfer about five drops of your petal water into another section of the ice cube tray.
- Add a drop of lemon juice to your drop of petal solution. Write down the colour change in the table below in row (b). This is the colour of your solution when an acid is added.
- To your drop of petal solution add a few grains of baking soda. Write down the colour change in the table below in row (c). This is the colour of your solution when a base is added.
- To your drop of petal solution add a drop of your test substance. Write down the colour change in the table below.
- Repeat this for all your test solutions. For each test solution compare the colour with the water, lemon juice and baking soda, and write down if your test solution is acid, base or neutral. The blank rows are left for you to test your own substances.
| Test substance | Colour of petal water when test solution was added | Is your test substance an acid, base or neutral? |
|---|---|---|
| a) water | Neutral | |
| b) lemon juice | Acid | |
| c) baking soda | Base | |
| d) vinegar | ||
| e) oven cleaner | ||
| f) toothpaste | ||
| g) washing up liquid | ||
| h) juice from a fruit | ||
| i) | ||
| j) |
- Which of the above substances are acids? What is common about these substances?
- Which of the above substances are bases? What is common about these substances?
Where to next?
In what situations would it be important to test for acids and bases? Why would it be important?
For teachers
If students struggle with the above question encourage them to find out about swimming pools or effluent from factories and farms.