Changing the Amount of Epsom Salt
In this task, you will carry out the chemical reaction between Epsom salt and ammonia:

2NH3 + MgSO4 + 2H2O → Mg(OH)2 + (NH4)2SO4.

This time, you’ll use varying amounts of Epsom salt to see how the amount of a reactant affects the amount of product. Review these lab safety requirements before you begin.

Estimated time to complete:

Total time: at least 8 hours
Active time: 1 hour

If you’ve purchased an Edmentum lab kit, remove the safety goggles, protective gloves, and apron from the kit. These materials are italicized in the following list. In addition to the kit materials, gather all the other items appearing in the list.

You’ll need these materials:

safety goggles
protective gloves
apron
3 identical empty disposable water bottles, about 16.9 fluid ounces each
permanent marker
Epsom salt (8.5 tablespoons)
tablespoon measure and -tablespoon measure (or a -teaspoon measure; note that teaspoons equals tablespoon)
-cup measure
water
ammonia (1 cup)
Stay safe! Always follow these safety measures when working with ammonia:

Ammonia should be used only in a well-ventilated area.
Safety goggles, gloves, and an apron should be used when handling ammonia.
Ammonia fumes are strong. Be careful not to breathe them. If your nose or throat becomes irritated from the fumes, leave the area and go to an area with fresh air.
If ammonia splashes in your eyes, immediately flush your eyes with running water for at least 15 minutes. Be sure to remove any contact lenses first. Seek medical attention right away.
If ammonia gets on your skin or clothing, immediately take off the contaminated clothing. Wash your skin thoroughly with water. Wash the clothes before wearing them again.
Ammonia may spill while being poured. Perform this activity in an area that can be cleaned up easily. If possible, pour ammonia over a sink.
To begin the experiment, follow these steps. Use this diagram to help you work through the steps:

Label the three bottles with the numbers 1 through 3 using the permanent marker.
Add the following amounts of Epsom salt to each bottle.
bottle 1: tablespoon
bottle 2: 2 tablespoons
bottle 3: 6 tablespoons
Add cup of water to each bottle.
Add cup of ammonia to each bottle.
Cap each bottle tightly.
Rinse the outsides of the bottles to remove any ammonia that may have spilled onto them.
Swirl the bottles to dissolve the Epsom salt.
Let the bottles sit overnight, or for at least 8 hours.
If solids end up floating on the surfaces of the solutions, tap or gently shake the bottles until the solids sink to the bottom. Wait several minutes for the solids to collect at the bottom of the bottles.
Part A
Compare bottles 1 and 2. How do the amounts of the reactants compare? How do the amounts of the products compare? For these two bottles, does the amount of product appear to be proportional to the amount of Epsom salt used?

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Part B
Compare bottles 2 and 3. How do the amounts of the reactants compare? How do the amounts of the products compare? For these two bottles, does the amount of product appear to be proportional to the amount of Epsom salt used?

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Part C
Compare your answers from parts A and B. If your answers to those questions are different, explain why they’re different.

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Part D
Imagine mixing 10 tablespoons of Epsom salt with cup of ammonia. How much precipitate would be produced? Describe the amount of precipitate by comparing it with the amount in bottle 1, 2, or 3. Explain your prediction.

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Part E
In task 1, you varied the amount of ammonia used in the reaction. In task 2, you varied the amount of Epsom salt. Combining the results of these two tasks, what can you conclude about the amount of product formed by two reactants?

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Dispose of your materials properly:

Rinse the solutions down the sink drain with lots of water.
Rinse out the bottles, and recycle them.
Store unused ammonia and Epsom salt for future use.
Wash the measuring spoons and cups.
Return equipment to where it belongs.