Testing for the Presence of Starch in Foods



Common Household Acids and Bases

Objective: To determine the acidity of common household items using a homemade red cabbage leaf acid/base indicator.

Introduction:

Many common household items that we use, eat, or take when we are not feeling well, are acids or bases. In fact, our stomachs contain a strong acid, hydrochloric acid; and our blood is maintained at a very narrow pH range. We will try to find out if some of the things we are familiar with are acidic, basic, or neutral compounds by making an acid-base indicator using a solution containing compounds extracted from red cabbage leaves.

Book reference: See pages 330-335 of your text book for further discussion.

Project Procedure:

For this project you need the items listed below:

|Red cabbage leaves |Distilled water |White Vinegar |

|Household ammonia |Salt |Sugar |

|Baking soda |Vitamin C |Aspirin tablet (not buffered) |

|Any clear citrus fruit juice |Any clear soft drink |Any clear/white antacid |

|Clear plastic cups and plastic spoons, drinking| |

|straws. | |

Making the red cabbage indicator:

Fill a 2-quart saucepan approximately 2/3 full of distilled water. Bring water to a boil on a stove top or hot plate.

While the water is boiling, shred about two or three leaves of the red cabbage. Choose leaves that have a strong presence of color. Place the shredded leaves into the now boiling water.

Boil the cabbage until the water turns a deep blue color.

Let this solution cool to room temperature.

When cool, pour off the solution from the leaves into any suitable CLEAN container such as a 2 –liter bottle or glass canning jar. Discard the leaves.

The remaining indicator solution may be stored in the refrigerator for up to one week, but the fresher the solution the more accurate your results will be.

Establishing the acidic and basic color of the red cabbage solution for reference:

In order to use the red cabbage acid-base indicator to determine if a compound is acidic, basic or neutral; we need to establish the colors with known acidic, basic, or neutral compounds to be used as references first. We will use the colors of the solution with vinegar for our acid, household ammonia for our base and distilled water for our neutral compound.

Label one of the clear plastic cups “acid,” another cup “base” and a third cup “neutral” using a black permanent marker such as a Sharpie.

To each of the three cups, add approximately ½ cup of the red cabbage solution and an equal amount of distilled water. Mix the two together by stirring with a clean plastic spoon.

To the cup labeled “acid” add 1 tablespoon vinegar

To the cup labeled “base” add 1 tablespoon of household ammonia.

To the third cup labeled “neutral” add 1 tablespoon more of the distilled water. The purpose of adding additional distilled water is to keep all volumes equal and to act as a “blank” or “control” during our experiment. The results we observe we want to observe coming from the sample we are interested in, and not from something unexpected in our water.

Use separate clean plastic spoons to mix each cup so as to avoid cross contamination and possibly throwing off your observed results.

Record the color of each solution in the corresponding blank on your data sheet. Set aside, and refer back to these colors as you test your remaining samples. Do not discard these solutions until you are completely finished with the experimental portion of this project.

The Breath Test:

Take a new plastic cup and add again ¼ cup of the cabbage solution and an equal amount of distilled water. Stir as you did before with a clean, plastic spoon.

Using an eye dropper or 1/4 teaspoon measure, carefully and slowly add a few drops of the household ammonia to this cup until you see it change to a very light blue-green color. It will NOT take very much to do this and the addition of too much ammonia could make the next part of the experiment a lot more difficult.

Blow into the solution using a straw until you see a fading of the color back to its initial color. The time required to get the solution to revert completely back to its initial color will be dependant on how much ammonia you initially added.

Common household items: acids, bases, or neutrals?

For this experiment, you are to observe and record the color of the cabbage solution when common household items are added to it. After adding each compound listed on the sheet, and one or more of your choice; record the color observed as well as state if the solution made is either acid, base or neutral.

Tips for a successful experiment:

1. Always use a dry, clean plastic cup for each sample. If you run out of cups, take a finished experiment, empty out the contents, (safe to throw down the sink) and rinse out with water. Do NOT use soap or detergents as they can leave residues that will cloud your results.

2. Generally use ¼ cup of cabbage solution to ¼ cup of water. You need not be strict about the volume, but the volumes of cabbage solution to water should be as closely equal as possible.

3. Solids, like vitamin tablets should be crushed up before attempting to dissolve in the indicator solution. Usually ½ teaspoon of the crushed solid is more then sufficient to observe your results.

4. Liquids like vinegar or ammonia roughly require only 1 teaspoon.

5. Try to keep the volumes as close to the same as possible when comparing the color changes.

Describe any property you find about this class of compound other than its use as an acid-base indicator. Remember to give credit to the source of your information by giving the website name, the author and the direct URL to the site you found the information. Suggested search words: anthocyanins, red cabbage, dye extract.

Report Form: Briefly describe what you had observed in the blanks of the report sheet provided and indicate if you believe the substance you have tested was either acid, base or neutral.

Remember to answer the questions on the back of the report form.

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Name: Date:

| |

|Results of Red Cabbage Extract With Various Household Compounds |

|Household Item |Color of Solution |Acid, Base or Neutral |

| | |Reference color for a neutral compound |

|Distilled Water | | |

| | | |

|Vinegar (white) | |Reference color for an acid |

| | | |

|Ammonia | |Reference color for a base |

| | | |

|Salt | | |

| | | |

|Sugar | | |

| | | |

|Baking soda | | |

| | | |

|Vitamin C | | |

| | | |

|Aspirin (not buffered) | | |

| | | |

|Squeeze citrus juice | | |

|Antacid (white if using a solid) | | |

| | | |

|Dye free carbonated drink | | |

Answer the following questions, remember to cite sources!

Q. What might you observe if you mixed into a fresh sample of the cabbage solution a substance that gave an acid result with an equal amount of a substance that gave a basic result? What term is used to describe the reaction of acids when they are mixed in equal parts with bases to form a harmless salt and water?

Q. The extracted cabbage dye belongs to a class of compounds known as anthocyanins. Using your favorite internet search program, find what other foods we eat that contain this class of compound that we could have also used to perform this experiment with.

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