MHS Chemistry
Decomposition of a Hydrate

Many chemical compounds decompose when heated. Sometimes the result is the elements of which the compound was made, and other times it is simpler and more stable compounds. In this lab, you will use heat to decompose a hydrateate compound into the anhydrous (dry) compound and water. You will also calculate the percent by mass of water in the original compound.

  1. Weigh a clean, dry crucible to the nearest milligram.
  2. Record the name of the hydrate compound provided.
  3. Add no more than one gram of the hydrate compound to the crucible, and weigh them together. If you have too much, give a little extra to another group, or dispose of it in the waste container. DO NOT put it down the drain!
  4. Heat the sample over the hottest flame of the Bunsen burner for about ten minutes.
  5. Record the mass of the crucible and sample.
  6. Repeat steps 4 and 5 until the mass changes by less than 0.01 g.
  7. Dispose of the remaining sample in the waste receptacle, and clean your crucible


  1. Present all the information about your hydrate, including it’s identity, in a beautiful, clear, and proper data table.
  2. Determine the mass of the original sample.
  3. Determine the mass of water lost.
  4. Determine the percent water (by mass ) in the original sample.
  5. What happened to the missing mass? (In other words, where is it now?)
  6. Briefly describe some sources of error in the experiment (that are not mistakes in carrying out the procedure).

Each partner will pass in their own lab. The lab should be on exactly one sheet (this one will do). The lab is due on _______________.

[% Water in a Hydrate score sheet][MHS Chem page]