Water does many strange things to many elements. It sometimes changes to an entirely different state. This lab focuses on compounds that are formed in water, especially Copper (2) Sulfate. For every mole of CuSO 4 , there are five moles of H 2 O in the crystal. A compound with water removed from it is called anhydrous, while a compound with the water still in it is hydrous.

Objectives

In this experiment, you will:

•  heat a specific amount of hydrated magnesium sulfate to remove the water.

•  find the experimental and theoretical percentages of water in the hydrate.

•  predict an empirical formula for hydrated magnesium sulfate.

Equipment

•  Goggles and apron

•  Hot plate

•  Evaporating dish

•  Balance

•  Beaker (400 or 600 cm 3 )

•  Forceps

Precautions

•  Avoid breathing fumes.

•  Always wear safety goggles.

•  Handle porcelain dish only with forceps after heating for the first time.

•  Do not put dish on balance when hot.

Procedures

1. Prepare data table and put on safety goggles.
2. Turn on hot plate to high and let warm.
3. Wash off the porcelain evaporating dish and dry by placing it on the hot plate for a few minutes.
4. Carefully remove the dish with the forceps and let it cool.
5. Measure the mass of the evaporating dish to the nearest 0.01 grams with a balance.
6. Add about 3 grams of MgSO 4 to the dish and measure the mass to the nearest 0.01 grams again.
7. Place the evaporating dish on a hot plate and cover with a 400 or 600 cm3 beaker. Observe the inside of the beaker for a few minutes and write down your observations.
8. Carefully remove beaker and continue heating dish for about ten minutes.
9. Remove the evaporating dish from the hot plate, let cool, then measure the mass.
10. Reheat dish and contents for a few minutes and measure mass again, making sure this mass comes within 0.02 grams of the last reading, if it doesn't you must reheat and remeasure the mass until this happens.
11. After the final reading, return MgSO 4 crystals to a special container designated by the teacher.

Analysis

Table 8-1

Observations

2. (a) 1.46/3 x 100=48.67

(b) 126.14/246.52 x 100=51.17

(c) (51.17-48.67)/51.17=.049

Conclusion

I think that this lab was a great success. I learned a lot from it. I learned that it is very important to be accurate in your readings or the whole lab will go wrong.

1. The number of moles of anhydrous MgSO 4 was .013, and the number of moles of water in the hydrate was .081. I think hydrated MgSO 4 is much a much larger formula than that.

2. The method we used to find the percentage of water in the crystals cannot be used for all hydrates because a) they might not lose their water by evaporating and b) they may not be able to fit in the dish and c) they may not be crystals.

3. (a) It is necessary to let the dish cool before measuring because the scale is an electronic and if you put the hot dish on the metal plate, it may fry the circuits underneath.

(b) If you measure the mass after too long a period things may have changed and consolidated, giving you a different reading.

4. There are some difference because not all of the evaporating dishes have the same mass and they may have put slightly more or less crystals in the dish.

5. A dessicator is a machine that helps cool things. If we would have used this, the masses would have changed and we would have gotten entirely different readings.

Some possible mistakes that could have happened are: we could have put the dish on the balance while still hot and screwed up the balance, we could have put much more MgSO 4 than we should have into the dish, or we could have forgotten to wash out the remnants of MgSO 4 from previous labs, altering our readings also.