🥬 Which kitchen liquids change red cabbage water?

My hypothesis

If I change the liquid added to the cabbage water, then what colour the cabbage water turns, on your 1 to 5 scale will ______, because ______.

🔊 You fill in the blanks. Think about which of these liquids are sour, and which feel slippery like soap. A guess is a good because: the test finds out.

Change, measure, keep the same

Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 5 levels 3 times.

What you need

• 🥬 A quarter of a red cabbage: a quarter of one
• ♨️ Hot water from the tap or kettle, for a grown-up to pour: 2 cups, hot from the tap, never boiling
• 🥣 A big bowl
• 🔻 A kitchen funnel
• ⚪ Round paper coffee filters: 1
• 🫙 A clear jar or tall glass: 1, to hold the cabbage water
• 🍶 White vinegar
• 🍋 Lemon juice
• 🚰 Water from the tap
• 🫧 Dish soap
• 🧂 Baking soda
• 🥛 Clear plastic cups, all the same size: 5
• 🥛 A measuring cup
• 🥄 Measuring spoons
• 🥄 A spoon
• 📄 Paper
• 🖍️ Crayons or markers
• 🔪 A sharp kitchen knife, for the grown-up

Steps

1. Grown-up: A grown-up chops the red cabbage into small pieces.🔊
2. Grown-up: A grown-up puts the pieces in a bowl and pours hot water over them.🔊
3. Wait twenty minutes, until the water turns deep purple.🔊
4. Grown-up: A grown-up pours the purple water through a coffee filter in a funnel into a jar.🔊
5. Let the purple water cool down before you touch it, and put your goggles on.🔊
6. Colour a row of five squares: 1 pink, 2 pink-purple, 3 purple, 4 blue and 5 green.🔊
7. Mix baking soda water (a teaspoon in a quarter cup) and soapy water (3 drops of soap in a quarter cup).🔊
8. Pour a quarter cup of cool purple water into each of five clear cups.🔊
9. Stir a tablespoon of a different liquid into each cup. Never drink any of them.🔊
10. Compare each cup with your colour squares, and write its colour number in your table.🔊
11. Pour out, rinse the cups, and do the whole test two more times.🔊
12. Find the mean colour number for each liquid, and draw a bar graph.🔊

3 steps are a grown-up's, marked above. Write each number down straight away, in the table below, so nothing is lost.

Your results table

From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a bar graph, one bar for each thing you tried.

Why it works

🔊 Red cabbage juice holds a purple colour that changes with how acidic something is. Acids, like vinegar and lemon juice, turn it pink, while bases, like baking soda, turn it blue or green. Plain water leaves it purple, and soapy water usually goes a little bluer.

Going further (7th and up): Change a second thing: mix vinegar and baking soda water in steps, a teaspoon at a time, and graph the colour number against the amount of each.

Board layout

This project at your grade

Every grade this project fits works out a mean. See every project for 4th grade, or print a blank results table.

What a judge will ask

• What did you change, and what did you measure? I changed the liquid added to the cabbage water and measured what colour the cabbage water turns, on your 1 to 5 scale, in colour number, 1 to 5.
• What did you keep the same, and why does that matter? I kept a quarter cup of the same cabbage water in every cup and one tablespoon of each liquid the same, so the only difference was the liquid added to the cabbage water.
• How many times did you test it? 3 times at each of my 5 levels.
• If you did it again, what would you change or test next? I'd mix vinegar and baking soda water in steps, a teaspoon at a time, and graph the colour number against the amount of each.

Make it yours

Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.

Try next

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