1. to determine the percentage of water in an unknown hydrate
2. to determine the moles of water present in each mole of this unknown hydrate, when given the molar mass of the anhydrous salt
3. to write the empirical formula of the hydrate
Supplies
Equipment ring stand and ring
lab burner centigram or digital balance
crucible and lid lab apron
crucible tongs safety goggles
pipestem triangle
Chemical Reagents
Approximately 5g of a hydrate
water
Procedure
1. Put on safety goggles
2. Set up pipestem triangle, iron ring, stand and bunsen burner like in 4C-1 in your workbork (Page 46)
3. Heat the crucible for 3 min and let it cool for 3 min
4. Determine the mass of empty crucible and record the mass in Table 1
5. Place hydrate into the crucible. Determine and record the mass of the crucible and hydrate
6. Place the crucible and contents on the pipestem triangle. Increase heat till the bottom is red and maintain this temperature for 5 min.
7. Turn off the burner and let the crucible cooldown for 5 min. Then determine and record the mass of the crucible and its contents.
8. Reheat the crucible for 5 min then let it cool for 5 min and then determine and record the mass. Step 6 and 7 should be within 0.03g, if it's not, reheat it again.
9. After the final mass reading, and crucible is cooled, add a drop of water into the contents of the crucible and note any observation/changes.
Table 1
Analysis of Results
1. g H20 x 100% = % of water
g hydrate
2. mass of salt = mass after heating - mass of empty crucible
moles of salt = mass of salt x 1 mol
159.6g
3. mass of hydrate = mass of crucible/hydrate - mass of crucible
mass of H20 = mass of hydrate - mass of salt
moles of H20 = mass of H20 x 1 mol
18g
4. moles of H20 = _____
moes salt
5. CuSO4 x __ H20 (copper (II) sulphate pentahydrate)
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