Materials RequiredMilk of Magnesia, 50 mL (876010)Ultra-Spec 2000 Safety Glasses (213695)Carolina™ Standard-Grade Beaker, 600 mL (731011)Bogen Universal Indicator, 1 mL (848263)Vinegar, 10 mL (898110)Corning® Digital Hot Plate/Stirrer (701025)Microchemistry Plastic Pipet, 1 mL (736984)Tap WaterSulfuric Acid, 1 M, 75 mL (893381) (optional)

OptionalTo neutralize the MOM quickly, use sulfuric acid, 1 M. Expectto use approximately 75 mL. The solution will turn clearwhen neutralized.

Activity Procedure1. In a 600-mL beaker, mix 50 mL of milk of magnesia (MOM)

with 200 mL of water.

2. Add 1 mL Bogen universal indicator solution to the beaker.The solution will turn violet, indicating a pH of 10 or higher.

3. Using a pipet, add 1 mL vinegar to the beaker. The solutionturns yellow (acidic), then green, blue, and violet (basic) asthe magnesium hydroxide neutralizes the acid and addi-tional magnesium hydroxide dissolves.

4. Continue adding vinegar in 1-mL increments and observethe color changes.

MOM’s RainbowThis colorful activity demonstrates solubility and Le Châtelier’s principle at work in the reaction between a base andan acid.

SafetyFollow and model basic laboratory safety rules. Wear safety eyewearand gloves.

carolina tips™QuickQuick

Results/SummaryMilk of magnesia is a suspension of magnesium hydroxide in water. In this experiment, MOM is treated with vinegar (CH3CO2H), an acid.The balanced chemical equation for the reaction of milk of magnesia and vinegar is as follows:

Mg(OH)2(s ) + 2CH3CO2H(aq ) → Mg(CH3CO2)2(aq ) + 2H2O(l )

The amount of magnesium hydroxide in the solution (and thus its availability to react) is determined by the equilibrium shown below:Mg(OH)2(s ) Mg2+(aq ) + 2OH-(aq )

This equilibrium lies far to the left, leaving very little magnesium hydroxide in the solution. As acid reacts with the hydroxide ions,removing them from the solution, more magnesium hydroxide dissolves. This shift is an example of Le Châtelier’s principle. This processcontinues until all the magnesium hydroxide is neutralized, leaving only a clear solution of magnesium acetate.

Additional InformationView more information, content links, and products related to this activity at www.carolina.com/takeaways.

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