Percent Composition Lab

Purpose: To measure the percent of water in a series of crystalline compounds called hydrates.

Procedure:

 1) Label each test tube with the name of the compound. Measure and record the masses.

 2) Add 2-3 grams of each compound to the appropriate tube. Measure and record the mass of each test tube and compound.

 3) Heat contents of test tubes over Bunsen burner, holding at 45 degree angle. Not any changes in appearance.

 4) Heat from 2-4 minutes. Repeat steps 2 and 3 twice.

 5) Allow each tube to cool, then measure and record the mass of each test tube and heated compound.

Data:

Calculations:

9.38g-7.58g=1.8g.     (.18g/1.8g)x100=10% water

9.69g-7.56g=2.13g.   (.58g/2.13g)x100=27.23% water

9.21g-7.58g=1.63g.   (.52g/1.63g)x100=32.9% water

Calculations Check:

Conclusion:

In this lab the percentage of water in compounds were found by indirectly with use of evaporation and some calculations. To check the answers, mole conversions were used to find the empirical formula for each compound. The results were fairly reasonable and accurate, and other than human error, few errors were identifiable in this lab. Some generalities in rounding to arrive at the empirical formulas could also have contributed to inaccuracy in the answers.