Procedure:
- Mass a crucible and record in data table.
- Place about 2 grams of the hydrate in the crucible and record the mass of the crucible, cover and hydrate salt.
- Gently heat the crucible and its contents for about 10 minutes.
- During the last minute of hearing remove the cover so that any moisture which has collected on the underside of the cover can evaporate.
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When the crucible has cooled completely, determine the mass of the crucible, cover and contents.
- Replace the cover and heat the crucible for 5 minutes removing the cover for the last minute of the heating as you did above.
- Cool and determine the mass of the crucible, cover and its contents.
- This last mass should agree with the previous mass within plus or minus0.01 grams.
Note: if it does not, repeat this heating until a constant mass is reached.
This is called heating a constant mass and is the only way of insuring that the reaction is complete and all the waters of hydration have been driven off (dehydrated).
Do not heat the crucible to red hot, or the salt’s sulfate portion will start to break down. This will give you yellowish contents. If this happens, you have to start over!
Results:
Data Manipulation:
2.00g. of hydrate (CuSO4 x xH2O)
-0.8g. of water
1.2g. of CuSO4
.8 g H2O x 1 mol = .044 moles of H2O
18.0g.
1.2g. CuSO4 x 1 mol = .0075 moles of CuSO4
159.5g.
.044 = 6
.0075
.0075 =1
.0075
Formula: CuSO4 x 6H2O
2.00g. of hydrate (MgSO4 x xH2O)
-1.0g. of water
1.0g. of MgSO4
1.0g.H2O x 1 mol =.056 mol H2O
18.0g.
1.0g. MgSO4 x 1mol = .0083 mol MgSO4
120.4g.
.056 = 7
.0083
.0083 =1
.0083
Formula: MgSO4 x 7H2O
Conclusion:
In the Formula of a Hydrate Lab, our hypothesis was correct. When we heated the hydrated salts, the hydrates evaporated and we were able to find the formula of the salts. When we heated the compounds, we got a formula of CuSO4 x 6H2O for the copper sulfate, and MgSO4 x 7H2O for the magnesium sulfate. Our copper sulfate formula was very close to the answer of CuSO4 x 5H2O, but by heating the hydrate for another minute, or removing the crucible cover for a minute longer, we would have achieved that number by allowing the hydrate to evaporate the other waters of hydration. Although we don’t know the correct answer for the magnesium sulfate, MgSO4 x 7H2O was our best guess.