HYDRATED CRYSTALS LAB
CONCEPT
Some crystalline salts retain water as a component of their chemical formulas. This water is
molecularly bonded to the crystalline salt molecule. An example of a hydrated compound is
Sodium carbonate decahydrate, Na2CO3•10H2O. Notice that in this compound there is a 1:10
ratio between the Na2CO3 and the H2O. This ratio will always be a whole number.
Heating a hydrated compound will remove the water and the salt will become anhydrous,
meaning “without water”. This process is analogous to placing clothing in the dryer in order
to separate water from clothing.
OBJECTIVE
•
Use mass measurements to determine an empirical formula, or ratio, between water and
anhydrous compound for:
Magnesium sulfate - MgSO4• XH2O and
Copper (II) Sulfate - CuSO4 •XH2O.
EQUIPMENT
Metal crucible and cover
Clay triangle
Ring stand and ring
Bunsen burner
PROCEDURE
1. Measure the mass of a clean crucible and cover. Record in Data Table.
2. Put one full measuring spoon (plastic) of Magnesium sulfate in the metal crucible, cover,
and measure the total mass. Record in Data Table.
3. Heat for 10 minutes. Let cool for 15 minutes and remove from the ring stand.
4. When no longer warm to the touch (room temperature) measure mass of crucible, cover
and sample. Record in Data Table.
5. Complete necessary calculations to determine empirical formula and percent error.
Name: ______________________________________ Period: ________ Date: ______________
HYDRATED CRYSTALS LAB
DATA TABLE
Magnesium sulfate
MgSO4•XH2O
Copper II Sulfate
CuSO4 •XH2O
Crucible, cover & sample
39.47
g
g
Crucible and cover
35.44
g
g
g
g
hydrated sample
Crucible, cover & heated sample
37.84
g
g
Crucible and cover
35.44
g
g
Anhydrous sample
g
g
H2O in sample
g
g
Moles of H2O in sample
mol
mol
Moles of anhydrous sample
mol
mol
Calculations:
1.
Calculate the moles of H2O in each sample (mass of H20 from data table / molar mass H20) enter in DATA
TABLE above.
Copper II Sulfate
2.
Magnesium Sulfate
Calculate the moles of each anhydrous compound (compound without water attached) and enter in DATA
TABLE above.
Copper II Sulfate
Magnesium Sulfate
3.
Derive an empirical formula (ratio between H20 and anhydrous compound) for each hydrated samples
from your lab results. Use the number of moles of each calculated in steps 1 and 2. This ratio becomes the
coefficients in the compound:
__CuSO4•__H20
or
__MgSO4•__H2O
Copper II Sulfate
4.
Calculate the percent of water in a perfect sample (Use the formulas: CuSO4•5H2O and MgSO4•7H2O) of
each hydrated compound.
Copper II Sulfate
5.
Magnesium Sulfate
Calculate the percent of water in each hydrated compound from your lab results. (Use the formula you
calculated in step 3 based on your mole ratio)
Copper II Sulfate
6.
Magnesium Sulfate
Magnesium Sulfate
Calculate your percent of error based on results of 4 and 5. (Use your final % answers and plug in to %
error formula: ( | Actual – Experimental | / Actual ) x 100
Copper II Sulfate
Magnesium Sulfate