Determining a Chemical Formula of a Hydrate As you’ve learned in class, hydrates are chemical compounds which contain loosely bound water molecules. Because these water molecules are loosely bound, they can be easily removed or replaced. In this lab your job will be to find the empirical formula of magnesium sulfate hydrate. MgSO4 �nH2O Safety concerns: This lab is fairly safe, though the usual burns/spills may occur. It is, of course, vital that students wear goggles at all times and equally vital that students NOT wear rubber gloves (rubber gloves, when in contact with hot equipment, may melt to the skin). The dehydrated magnesium sulfate may be safely stored or ground with mortar and pestle and used as a reagent in the future. Before lighting the burner, remember to confine loose clothing and long hair. Remember to handle the crucible and cover with tongs. The crucible and cover are very hot after heating!

1. Set up your apparatus as shown above. Wait for teach approval before continuing.

2. Mass an empty crucible (or evaporating dish). Record. Leave it on the scale.

3. Move the MgSO4 �nH2O close to the dish and add about 2.5 grams of it to the dish. Record.

4. Move the dish with MgSO4 �nH2O to the heating apparatus and gently heat for 3 minutes.

5. Now, turn up the heat and heat about ten minutes longer.

6. Remove heat, let cool, weigh dish and anhydrous salt, MgSO4 . Record.

7. Reheat the dish and anhydrous salt, MgSO4 for five more minutes. Record. The mass should

be the same or lighter.

8. While the apparatus is cooling complete the data analysis section.

9. Clean up materials as you found them.

Name _____________________________________ Date ____________ Hour _____________

Mass of crucible empty .............................................. ______________ g

Mass of crucible, and MgSO4 �nH2O........................................... ______________ g

Mass of crucible & anhydrous salt, MgSO4 after 1st heating...... ______________ g

Mass of crucible & anhydrous salt, MgSO4 after 2nd heating .... ______________ g

Calculations: Show your computations in the spaces provided below. Include labels. Place your answers

in the calculations table.

1. Calculate the mass of water driven from the hydrate. 2. Calculate the moles of water driven from the hydrate. 3. Calculate the mass of the anhydrous salt. 4. Calculate the moles of anhydrous salt. 5. The reaction for this experiment is: MgSO4 ·nH2O (s) -------› MgSO4 (s) + nH2O hydrate anhydrous salt n = the number of moles of water driven off per mole of anhydrous. Determine this mole ratio to the nearest whole number, and write the chemical equation for the formation of the hydrate.

6. Determine the mass of the hydrate used. Record

Mass of anhydrous salt ........................................... _____________ g

Moles of anhydrous salt .......................................... _____________ mol

Mass of water driven from hydrate....................... _____________ g

Moles of water driven from hydrate...................... _____________ mol

Mole ratio of water to anhydrous......................... mol H2O _____________ mol anhydrous

Mass of Hydrate ………………………………… _____________ g Hydrate

TURN PAGE

Data Table

∆H

Calculations Table

GOING FURTHER

1. Determine the % Composition of water in your sample experiment.

2. Determine the % Composition of water in MgSO4� 7H2O

3. Determine the amount of error in your experiment. % Error = Ι accepted value – experimental value Ι x 100 accepted value 4. List 3 possible reasons for error.