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Year 9

Practical: red cabbage indicator solution

I can make red cabbage indicator solution and use it to test solutions to find out if they are acid or alkali.

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New
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Year 9

Practical: red cabbage indicator solution

I can make red cabbage indicator solution and use it to test solutions to find out if they are acid or alkali.

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Lesson details

Key learning points

  1. Red cabbage solution is pink or red in an acid, purple in a neutral solution, and green in an alkali.
  2. Different chemical indicators have their advantages and disadvantages.
  3. Universal indicator will turn many different colours depending on pH.

Keywords

  • Universal indicator solution - a solution or paper that will turn different colours depending on pH of the solution.

  • PH scale - is a scale from 1 to 14 used to measure the acidity or alkalinity of solutions. pH7 is for neutral solutions.

  • Pestle and mortar - are tools used to crush and grind substances. The pestle is a grinding club and the mortar a heavy bowl.

  • Chemical indicator - is a chemical that will change colour to indicate the presence of a substance, for example if a solution is an acid or alkali.

  • Solution - formed when a substance dissolves into a liquid.

Common misconception

Pupils often think that the red cabbage will change to the same colours as universal indicator solution.

Remind pupils that there are many different indicators used to show different pH.

Make sure students only cover the cabbage with a suitable volume of water to produce a concentrated red cabbage indicator solution. Other flowers, fruit and vegetables can also be used. Butterfly Pea Flower is a good alternative/addition and is readily available to purchase online.
Teacher tip

Equipment

Red cabbage, kettle, pestle and mortar, beaker, pipette, filter paper, funnel, conical flask, stirring rod, spotting tile, universal indicator, red and blue litmus, solutions with varying pH's.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Match the following keywords to the correct description.
Correct Answer:neutral,a solution with a pH of 7

a solution with a pH of 7

Correct Answer:acidic,a solution with a pH of 3

a solution with a pH of 3

Correct Answer:alkaline,a solution with a pH of 14

a solution with a pH of 14

Q2.
Which of the following statements about solvents is correct?
Correct answer: A liquid in which a substance dissolves.
The mixture formed when a solid dissolves in a liquid.
The ability of a substance to dissolve in a liquid.
A liquid in which a substance will not dissolve.
Q3.
Which two of the following keywords can be used to describe a substance that can dissolve in a liquid?
Correct answer: solute
Correct answer: soluble
solution
solvent
Q4.
Some pH scales have a range from 0 to 14. Which of the following would describe a substance with a pH of 0?
Correct answer: very strong acid
very strong alkali
neutral
Q5.
The pH range most commonly used is from 1 to 14. What does the term 'range' mean?
The largest value in an experiment.
The smallest value in an experiment.
The sum of the maximum and minimum values.
Correct answer: The difference between the maximum and minimum values.
Q6.
The lower the concentration of hydrogen ions in a solution, the the pH of the solution.
Correct Answer: higher

Exit quiz

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6 Questions

Q1.
A pupil uses red cabbage to make an indicator. The solution produced is too pale to show a colour change. How could the method to make the indicator be improved?
Use more water and less red cabbage.
Correct answer: Use less water and more red cabbage.
Use less water and less red cabbage.
Use green cabbage instead of red cabbage.
Q2.
Which of the following describe what a mortar and pestle are used for?
Correct answer: crushing substances
mixing substances
dissolving substances
heating substances
Q3.
Match the following colours of red cabbage indicator to the correct type of the substance.
Correct Answer:pink or red,acidic solution

acidic solution

Correct Answer:green,alkaline solution

alkaline solution

Correct Answer:purple,neutral solution

neutral solution

Q4.
Which of the following statements explain why red cabbage and litmus are less effective than universal indicator at indicating the pH of a substance?
Correct answer: Litmus does not clearly indicate when a solution is pH 7.
Red cabbage does not indicate when a solution is pH 7.
Correct answer: Universal indicator turns a different colour for each pH from 1 to 14.
Red and blue litmus are more effective as indicators of pH than red cabbage.
Q5.
Different chemical indicators turn different colours at the same pH. Match the colour to the correct indicator if a solution has a pH of 7.
Correct Answer:red,red litmus

red litmus

Correct Answer:blue,blue litmus

blue litmus

Correct Answer:green,universal indicator

universal indicator

Correct Answer:purple,red cabbage indicator

red cabbage indicator

Q6.
A soluble substance dissolves in a solvent. If the solvent is water, what name is given to a soluble base?
acid
Correct answer: alkali
hydrogen
neutral