Author: Maddie Van Beek
In past experiments, you’ve learned about acids and bases. For example, you learned about acid-base reactions when you made an eggshell disappear and exploded a plastic bag: http://discoveryexpress.weebly.com/homeblog/experimenting-with-eggs-acid-base-reactions-and-osmosis
Since you already know about acid-base reactions, today we are going to learn how to test different substances to not only tell whether they are an acid or a base, but also determine their pH levels.
Why is it important to test for pH? Just one reason that scientists use pH testing in the real world is to check the quality of the water you use. If your water is too acidic or too alkaline, it could be dangerous.
How will we do this activity without a complicated test kit? You are going to make your own pH level test kit simply with red cabbage!
In past experiments, you’ve learned about acids and bases. For example, you learned about acid-base reactions when you made an eggshell disappear and exploded a plastic bag: http://discoveryexpress.weebly.com/homeblog/experimenting-with-eggs-acid-base-reactions-and-osmosis
Since you already know about acid-base reactions, today we are going to learn how to test different substances to not only tell whether they are an acid or a base, but also determine their pH levels.
Why is it important to test for pH? Just one reason that scientists use pH testing in the real world is to check the quality of the water you use. If your water is too acidic or too alkaline, it could be dangerous.
How will we do this activity without a complicated test kit? You are going to make your own pH level test kit simply with red cabbage!
Photo Copyright Fundamental Photographs, NYC, www.fphoto.com
Why red cabbage? The extract from red cabbage changes color based on substances’ alkalinity or acidity levels. (Alkaline is just another word for base. Remember, an alkaline is on the opposite end of the spectrum as an acid). Alkaline/Acid levels are rated on a pH scale. The higher the number, the more alkaline a substance is. The lower the number, the more acidic a substance is. A pH of 7 is neutral.
Let’s say you test a liquid that reads at a level 4 pH. Is that liquid acidic or alkaline?
How about if the liquid turns out to be a level 12 pH. Is that liquid acidic or alkaline?
Depending on that pH number, the red cabbage extract will change color. Thus, red cabbage extract is a pH indicator.
Check out the image below.
Let’s say you test a liquid that reads at a level 4 pH. Is that liquid acidic or alkaline?
How about if the liquid turns out to be a level 12 pH. Is that liquid acidic or alkaline?
Depending on that pH number, the red cabbage extract will change color. Thus, red cabbage extract is a pH indicator.
Check out the image below.
http://4.bp.blogspot.com/-UJOL0fv8WlM/TzgVaLpNecI/AAAAAAAAAo8/LhKIu87FZ1Y/s640/red+cabbage+indicator.jpg
If the pH is at 8, what color will the red cabbage extract be?
If the pH is at 12, what color will the red cabbage extract be?
Let’s test it out!
Before you can test any liquids for their pH level, you need to make your pH indicator.
YOU WILL NEED
- Red cabbage
- Water
- Measuring cups
- Food processor/blender
- Strainer
- Bowl
- Small cups
Here’s what to do!
- Cut up a head of red cabbage into small pieces. Measure about 2 cups of red cabbage pieces and dump it into the food processor.
- Add 1 cup of water to the red cabbage in the food processor.
- Cover the cabbage and turn on the food processor until the cabbage is fully blended.
- Place a strainer over a bowl and dump the blended red cabbage into the strainer.
- Remove the strainer and set aside. You should now have a bowl of red cabbage extract. This is your pH indicator!
- Now that you have your indicator, you can test some household substances for their pH levels.
- Label one small cup vinegar and add 1/2 cup vinegar. Label a second small cup baking soda and add 1/2 cup water and 1 teaspoon baking soda. Stir until the baking soda dissolves. Label a third small cup ammonia and add 1/2 cup laundry ammonia.
- Make a chart to track your results. Use markers to color your chart and then estimate the pH level based on the pH scale above. Your chart may look similar to the one below:
9. Add 1 teaspoon of pH indicator to each cup. Observe. What colors did each liquid change to? Record your results.
10. Find other household substances to test out! See how many different pH levels you can find in your home.
Here’s an example of substances you could test:
10. Find other household substances to test out! See how many different pH levels you can find in your home.
Here’s an example of substances you could test:
http://www.webinnate.co.uk/science/images/rc09.jpg
