Testing the Water




Observation: When I was rinsing out my bowl of red cabbage soup the water turned green.

Step 1: Hypothesis: I Believe the Cabbage in the Cabbage Soup Changes Color to Green When It Comes in Contact With Certain Other Substances. I Also Believe There Must Have Been Traces of One of These Substances in My Water.

Step 2: Supplies:

you will need:
- 9 plastic cups
- a red cabbage
- a pot
- distilled water
- paper towls
- gloves
- a plastic spoon
- a dropper
Test Items:
-distilled water
-tap water
- vinegar
- bleach
- salt
- baking soda
- soap
- a clear soft drink

Step 3: Step 1. Preparing for Soup:

Important note: Be sure to use DISTILLED WATER not tap water.

I gently wiped out the pot with a dry towel. I poured some distilled water into the pot and made circular motion with the pot to clean it. I dumped it and repeated the water step once more to ensure that nothing was left behind. It is not necessary to rinse the red cabbage.

Step 4: Step 2. Making the Soup:

I added a cup and a half of distilled water to the pot. I heated it to just barely boiling. Next I added about three leaves and cooked them for three to five minutes until they lose their color. Look at the picture that compares faded to fresh. Then I fished them out and added more leaves. I repeated this until I had used about ten full leaves.

Notes: I made a small batch of soup. It might be a good idea to make more soup depending on the size of the cups you intend to use.

Step 5: Step 3. Preparing to Mix:

I started by lining up the test items on a table in no partcular order. I placed a layer of paper towels across the table in front of the test items and lined up one cup across from each item. I wrote the corresponding abbreviation on it. Example: On the one across from the vinegar I wrote, vin. Then I filled each cup with an equal amount of soup.

Step 6: Step 4. Start Mixing:

I put on my rubber gloves and got started. I added one teaspoon or one dropper full of the test items to their cup. One of the cups was for testing tap water. I also had a cup with distilled water that was for cleaning the dropper and teaspoon in between uses.
* Make sure that your dropper holds at least a teaspoon.
* The soap can be added with either a teaspoon or a dropper. If you use a dropper you might want to add soap last because the soap is hard to get out of the dropper.
* The gloves are not needed until you get to the steps with vinegar and bleach.
* The bleach should be handled very carefully and it is a good idea to have the towels within reach before pouring.

Step 7: Step 5. Prepare to Analyze Data:

I double checked that the cups were all properly labled. Then I lined the cups up according to color from reddest to greenest. After that I positioned the test items behind their cups.

Step 8: Results:

Here are my results. The items are listed according to the color they produce. The list starts with reddest then goes down to greenest.
distilled water (the control item)
tap water
baking soda

Notes and Observations:
* I added three teaspoons of the tap water, instead of one, so I could make a distinction between it and distilled water.
* The soap's blue color may have interfered with its results.
* It is hard to tell the color difference between salt and tap water. Since I added more water than salt I concluded that salt turned the soup more green.

Step 9: Conclusion:

My conclusion agrees with my hypothesis:
Cabbage reacts to certain substances by changing color. There are substances that make the soup turn red as well as substances that turn cabbage green. Because the distilled water didn't change color, there must have been traces of some substance in the tap water.

Step 10: Research Compared to My Results:

I researched why the soup changed color and found that red cabbage contains an indicator. An indicator is a substance that changes in some way due to the PH level. The PH scale is used to measure how acidic or alkaline (also none as basic) something is. The cups that turned red were acidic, the cups that stayed purple were neutral and the cups that turned green are bases. Because the sample with tap water turned green, my tap water must contain traces of a substance that is basic. (Now if you have heart burn, which is caused by too much acids, you know how to neutralize it safely.)

I looked up the PH levels of the test items and I found my experiment's results to be consistent with the real PH scale. The only exception was soap. I believe that this error was due to the blue coloring in the soap. An example of a PH scale is listed above.

Step 11: More Fun Before Cleaning Up:

You may have noticed that baking soda is an base and vinegar is an acid. That is why when you mix them they react.
I grabbed the baking soda cup, the vinegar cup and the soap cup left over from my experiment. I put down three layers of paper towels, you might even want to do this experiment outside. I added two more teaspoons of baking soda to the baking soda cup and two more dropper fulls of vinegar to the vinegar cup making them very potent. Then I poured the soap cup into the baking soda cup. Last, I poured the vinegar into the soap and baking soda cup. Three things happened:
1. the color will neutralize to purple
2. the baking soda and vinegar should make gass
3. the soap sould make bubbles around the gass
These combined to make a color changing bubbly volcano.

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    34 Discussions


    2 years ago

    I would dissolve 95% ethanol into cabbage (Red) to get a powerful indicator. This would preserve for several months the solution.


    2 years ago

    Any suggestion on how to prevent bacteria from consuming and turning the solution rotten. I may suggest adding 50% of 95% ethanol. Or soaking the cabbage slowly while heating in 35-50% ethanol to preserve the samples. That what they do in the lab with other indicatiors.


    5 years ago on Step 8

    i suggest using less baking soda in your cabbage soup next time you cook. ;-)


    5 years ago

    we do this as a science experiment with kids: put a few cabbage leaves in a microwave safe bowl and nuke for a couple of minutes until juice starts appearing in the dish; fry an egg in the cabbage juice to get a green egg, serve with ham!


    5 years ago on Introduction

    The stock that comes from cooking a red cabbage can be used to tell if other substances are acidic or alkaline/base. When I was a kid I used to make litmus paper by soaking a neutral white paper in in red cabbage stock and then drying it.

    My greatest memory of using it was when I used it to check the volcanic dust that had settled over everything after Mt. Saint Helens blew. The news kept saying it might be acidic and not to wash it off. I found that it was slightly alkaline. We washed off the cars and house.

    1 reply

    Reply 5 years ago on Introduction

    The chlorine in water supplies is typically in the form of chloramine. It is more stable and takes longer to off-gas.


    5 years ago on Introduction

    Commercial vinegars (like Heinz distilled white vinegar) are changed to have 5% acidity. But an interesting experiment!


    5 years ago on Introduction

    I do this as an entry acid/base lab for Grade 10 students, but solution is not boiled. I put half a head of red cabbage, cut up in chunks into a blender and then add one cup of distilled water. Blend to a puree and strain the liquid off. We use round filter paper at school and soak it in the liquid for up to 10 minutes and then hang the filter paper in the fume hood to dry. I have also done this with my nephews and nieces using coffee filters and then hanging them to dry outside. Gets fairly smelly so I recommend the outdoor hanging. Once dry, filters can be either stored in Ziploc bags in the freezer or used right away. Students (or my kids) fold the paper in half, half again and then half again twice more -- makes 8 pie wedges. Label the circular edge with whatever substance you are testing the pH for, grab some droppers (have used plastic spoons in a pinch) and start adding your testers. Cheap way to introduce acid /base.


    5 years ago

    Nice experiment. I've come across cabbage as a PH indicator in old chemistry books but never tried it myself. I think salt is considered not to have a PH which is why it wouldn't change the colour.

    2 replies

    Reply 5 years ago

    It would make sense that salt doesn't have a PH. Thanks for pointing this out.


    Reply 5 years ago on Introduction

    pH is actually a measure of the activity of a hydrogen ion, and salts do have an effect on this.


    5 years ago

    On the spit and saliva front, they as substances tend to be near enough neutral which shows green on the pH scale(this is of course affected by what you eat and drink so not always).

    1 reply