Water of crystallisation 1. Explain the terms anhydrous, hydrated and water of crystallisation 2....
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Transcript of Water of crystallisation 1. Explain the terms anhydrous, hydrated and water of crystallisation 2....
Water of crystallisation
Water of crystallisation
1. Explain the terms anhydrous, hydrated and water of crystallisation 2. Calculate the formula of a hydrated salt using percentage composition, mass composition or experimental data. Keywordshydrated
anhydrous
dot formula
Anhydrous copper (II)
sulphate
Hydrated copper (II) sulphate
______________ ______________CuSO4 CuSO4 . 5H2O
Water molecules are trapped within the crystal structure
This is called water of crystallisation
CoCl2.6H2O
CuSO4
5H2O
CoCl2 6H2O
Na2SO4 10H2O
copper sulphate pentahydratecobalt chloride hexahydratesodium sulphate decahydrate
Salt Empirical Formula
Dot Formula
Hydrated magnesium chloride
MgCl2H10O
5
Hydrated sodium carbonate
Na2CH20O1
3
Hydrated calcium nitrate
CaN2H8O10
Rule: use the hydrogens to work the dot formula out NOT the oxygens
What happens if we don’t know the dot formula?
MgCl2 5H2O
Na2CO3 10H2O
Ca(NO3)2 4H2O
What happens if you’re told nothing but still have to work out the water of crystallisation?!
Find the n in BaCl2 . nH2O
You have to do it experimentally:
Mass of crucible: 30.00 gMass of crucible + BaCl2.nH2O crystals: 32.44 gMass of crucible + anhydrous BaCl2: 32.08 g
Use heat to drive off the water! This makes the BaCl2 anhydrous.
Mass of BaCl2 : 2.08 gMass of H2O : 0.36 g
You have to do it experimentally:
Mass of crucible: 30.00 gMass of crucible + BaCl2.nH2O crystals: 32.44 gMass of crucible + anhydrous BaCl2: 32.08 g
Use heat to drive off the water! This makes the BaCl2 anhydrous.
Mass of BaCl2 : 2.08 gMass of H2O : 0.36 g
Substances Anhydrous BaCl2 H2O
1. Masses (g)
3. Number of moles (mass / M)
4. Ratio
5. Empirical formula
2.08 0.36
2.08/208 = 0.01 0.36/18 = 0.02
1:2
BaCl2 . 2 H2O
(RAMs: H=1, O=16, Cl = 35.5, Ba = 137 )
Divide by smallest
Water of Crystallisation
Questions:
1) You are supplied with three empirical formulae. Write down the dot formula of each salt to show the water of crystallisation.
a) BaCl2H4O2 b)ZnSH14O11 c) FeN3H12O15
2) From the data below work out the formula of the hydrated salt.
Mass of CaCl2.xH2O = 6.573 g Mass of CaCl2 = 3.333 g
CaCl2.nH2O: 6.573 ganhydrous CaCl2: 3.333 g
Mass of H2O : 3.24 g
Substances Anhydrous CaCl2 H2O
1. Masses (g)
3. Number of moles (mass / M)
4. Ratio
5. Empirical formula
3.333 3.24
3.333/111 = 0.03 3.24/18 = 0.18
1:6
CaCl2 . 6 H2O
(RAMs: H=1, O=16, 40 = 35.5, Cl = 35.5 )
Divide by smallest
Example questionsA sample of hydrated magnesium sulfate was
strongly heated. The mass of magnesium sulfate before and after heating were recorded in the table below.
Calculate the formula of hydrated magnesium sulfate
Mass of samples before heating (g) 1.232
Mass of sample after heating (g) 0.602
Mass of water lost during heating (g)
Example questionsA sample of hydrated zinc sulfate was
strongly heated. The mass of zinc sulfate before and after heating were recorded in the table below.
Calculate the formula of hydrated zinc sulfate
Mass of samples before heating (g) 2.875
Mass of sample after heating (g) 1.615
Mass of water lost during heating (g)
Example questionsA sample of hydrated magnesium chloride
was strongly heated. The mass of magnesium chloride before and after heating were recorded in the table below.
Calculate the formula of hydrated magnesium chloride
Mass of samples before heating (g) 3.706
Mass of sample after heating (g) 1.906
Mass of water lost during heating (g)
Plenary Complete the exam style questions on water
of crystallisation, ionic and covalent bonding