water of crystallisation l.o.: explain the terms anhydrous, hydrated and water of crystallisation. ...
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Water of crystallisation
L.O.:Explain the terms anhydrous, hydrated and water of crystallisation.
Calculate the formula of a hydrated salt.
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Workshop today at 1:45pm:
WinifredHenryAnnaKeverneEsther Adeduntan
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Copper sulfate
• Copper sulfate comes in a hydrated form (copper sulfate pentahydrate) and a anhydrous form
http://uk.youtube.com/watch?v=kp7yaxlYk08
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Anhydrous substances
• Many substances will absorb water from the atmosphere, like NaCl, these are called hygroscopic substances
• An anhydrous compound is one which has no water molecules inside of it
• To make an anhydrous substance you can either heat it to evaporate off the water, or you can dry it in a drying cabinet
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Writing out the formula for hydrated compounds
• There are two ways in which a formula can be written if it is a hydrated compound:
1) Empirical formula, Which you know and love OR
2) Dot formula, So copper sulfate pentahydrate becomes Cu SO3 • 5H2O
NOTE: This dot is very important!!!!!
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Hydrated substances and water of crystallisation
• Some substances can trap water molecules inside of them.
• The water contained is called the water of crystallisation
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Finding the formula of hydrated copper(II) sulfate
Note: see worked example in page 27
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FeSO4·xH2O
Exp 1 Exp 2Mass of crucibleMass of crucible + hydrated saltMass of hydrated saltMass of anhydrous saltMass of water lost
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FeSO4·xH2O
Exp 1 Exp 2 Mean massMass of anhydrous saltMass of water lost
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FeSO4·xH2OMean mass
Mass of anhydrous salt 1.51 g
Mass of water lost 0.54 g
1) Calculate amount in moles of anhydrous salt
n (FeSO4) = 1.51/ 151.8 = 0.01
2) Calculate the amount in moles of water.n (H2O) = 0.54/18 = 0.033) Calculate molar ratioFeSO4 : H2O = 0.01: 0.034) Divide be the smallest number 0.01: 0.03 = 1:3
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Salt Ions presentCaCl2•2H2O
ZnCl2•6H20
Ba(OH)2•8H2O
Cu SO3 • 5H2O
YSO3•6H20
Na ZXSO4
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Hydrated salt
Mass of anhydrous salt
Water lost Identity of salt
XCl•2H2O 5.86 g 9 g
XSO4•3H20 40.53 g 16.2
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Other examples of hydrated compounds:
• Cobalt chloride hexahydrate• Sodium sulfate decahydrate
Write out the formula for these compounds using the “dot formula” notation
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Convert these into the Dot Formula
1. Calcium chloride dihydrate 2. Calcium chloride hexahydrate 3. Zinc chloride hexahydrate4. Barium hydroxide octahydrate
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Answers
1. Calcium chloride dihydrate = CaCl2•2H2O
2. Calcium chloride hexahydrate = CaCl2•6H2O
3. Zinc chloride hexahydrate = ZnCl2•6H20
4. Barium hydroxide octahydrate = Ba(OH)2•8H2O
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Write these out in Dot formula
1. Hydrated Cobalt chloride CoCl2H12O6
2. Hydrated Calcium carbonate CaCH6O6
3. Hydrated Magnesium sulphate MgSH12O10