03.09 Molar Mass of Compounds: Determining the Formula of a Hydrate
To determine the formula of a hydrate.
* crucible * Bunsen burner * balance * CuSO4 hydrate
1. Measure the mass of the clean, empty crucible, record the mass. 2. Add one or two scoops of the hydrate to the crucible, record the mass. 3. Heat the crucible and hydrate above a Bunsen burner for at least ten minutes to make sure that all of the water evaporates. 4. Let the crucible cool and then mass the crucible with dehydrated solid inside, record the mass. 5. Calculate the formula of the hydrate.
Data and Observations: | Mass, grams | Mass of empty crucible | 19.508g | Mass of crucible and hydrate | 20.976g | Mass of hydrate | 1.4680g | Mass of crucible and dehydrate | 20.447g | Mass of dehydrate | .9390 |
1. Obtain the mass of the empty crucible. Obtain the mass of the crucible and the hydrate. Subtraction of the mass of the empty crucible from the mass of the hydrate and crucible gives the mass of the CuSO4 hydrate.
1.4680= (20.976) - (19.508) 2. Heat the hydrate. After heating, record the mass of the crucible and the dehydrated compound.
No calculations for this step 3. Subtracting the mass of the empty crucible from the mass of the crucible and dehydrated CuSO4 gives you the mass of the dehydrated compound.
Mass of dehydrate = (mass of the crucible and dehydrated) - (mass of empty crucible)
0.939 =20.447-19.508 4. Subtract the mass of the dehydrated compound from the mass of the hydrate to determine the mass of water that was present in the hydrate.
Mass of water = Mass of hydrate - mass of dehydrate
5. Convert the mass of water to moles of water.
0.529g H2O x (1 mol H2O / 18.0g H2O) = 0.0294 mol H2O 6. Convert the mass of dehydrated compound to moles of the compound. 7. Divide by the lowest mole value to get a whole