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Household pH Indicator Experiment

Identify acid and bases in this fun experiment using common household items!

Difficulty: Easy to do and find results


Topics: pH, Acids, and Bases


Materials:

  • Blueberries (10 - 15)

  • Strainer/Filter paper

  • Various Household Ingredients (baking soda, vinegar, lemon juice, etc)

  • Water

  • Cups to hold the reactants

Procedure:

  1. Crush the blueberries in a bowl until they are thoroughly smashed. Add water and stir thoroughly so that a blueberry juice is able to form.


2. Strain the blueberries using filter paper or a strainer to extract the blueberry juice and remove any skin or chunks of blueberry . This magenta-colored solution will be our pH indicator.



3. We will next see how the pH indicator will react with acids and base

4. In our case, we used vinegar to see how our pH indicator will react with acids. Common household vinegar (the one we have) is 5% Acetic acid.

5. Add ¼ cup of the pH indicator to a transparent plastic cup. To this, add about a ½ cup of vinegar. The pH indicator will turn a bright red to pink color with an acid.


6. Now, we will test our pH indicator with a base, using baking soda

7. To another transparent plastic cup, add ¼ cup of pH indicator.

8. Since Baking soda is a powder and not a liquid, we will want to first make a solution of baking soda and water. To do this, mix together ½ cup of water and 1-2 tablespoons of baking soda.

Now to test the pH, pour the baking soda solution into the cup with the pH indicator. We will see that the solution will change to a bluish-green or dark purple color, indicating a base.

9. Here is a comparison of both acidic results (right) to basic results (left), in comparison with the original pH indicator (middle)

How It Works:

A blueberry contains a magenta-colored compound called peonidin in its skin, which also gives blueberries its blue color. This compound belongs to a class of chemicals called anthocyanidins that are pH-sensitive. When we mush the blueberries and add the water, we are able to remove the peonidin from its skin and put it into the water.


When a compound is acidic, when it is dissolved in water, there will be a higher amount of Hydrogen ions (positively charge Hydrogen atoms - H+) dissolved in the water. While, when a compound is basic, there will be fewer Hydrogen ions dissolved in it and more hydroxide (OH-) ions dissolved in it. A compound that is more acidic will have a lower pH, while a compound that is basic will have a higher pH. Since peonidin, is pH sensitive, its color changes when the concentration of H+ ions changes. Below is the chemical structure of peonidin.


When the pH changes, the wavelength of light energy absorbed by the molecule changes, causing the color of the compound to differ as well. This why at lower values of pH, such as at 2.0, peonidin is cherry red, while at higher levels of pH, such as at 8.0, 8.0 it becomes deep blue.


Other Possible Experiments:

- Other anthocyanidins are found in other fruits like blackberries and raspberries. Try using other fruits to make a new type of pH indicator!

- Test out other liquids or compounds such as lemon juices, sodas, candies to see if they are acidic or basic!


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