Testing the Water

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Introduction: Testing the Water

Scientific Method Contest

Fourth Prize in the
Scientific Method Contest



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.
notes:
* 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.
vinegar
pop
soap
distilled water (the control item)
tap water
salt
bleach
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 Comments

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

    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.

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

    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!

    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.

    Thats really cool

    That was a very good demonstration of the scientific process.

    I wish I had you as a chemistry teacher.

    Tap water is often treated with bleach as well as chlorine during the sanitation process.