How Strong is Milk of Magnesia?

In this experiment, students will titrate milk of magnesia (a common laxative medicine) with vinegar (an acid used daily, like dilute acetic acid). The purpose of this experiment is to determine how strong of a base milk of magnesia is. This simple experiment tests students’ knowledge of acid/base chemistry and also introduces a practical application of chemistry.

Chemicals:

1. Milk of Magnesia

2. Red Cabbage Extract (Indicator)

3. White Vinegar

4. Optional--Rice Vinegar

Equipment:

1. Graduate cylinder or another type of measuring devise

2. Flask or a beaker

*Tip: Milk of Magnesia is a thick substance that will adhere to the sides of the flask or beaker. Be sure to use a dilute solution before titrating, to ensure that no volume of milk of magnesia is lost. Directions on diluting are in the methods*

Methods (Part I):

1. Take 1 mL of milk of magnesia and dilute it with 10 mL of distilled water.

2. Place the prepared solution from above in a beaker or a flask.

3. Add 4 drops of red cabbage extract, as an indicator, to the milk of magnesia solution (a green color should appear).

4. Add white vinegar (drop by drop using a buret or an eye dropper) to the milk of magnesia solution. This should be done until the green color disappears.

Data Collection:

1. How many mL of white vinegar was added to the green milk of magnesia solution to turn it back to white?

Methods (Part II):

1. Repeat the above experiment using rice vinegar instead of white vinegar.

Data Collection:

1. How many mL of rice vinegar was added to change the color of milk of magnesia from green to white?