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Water of crystallisation

Water of crystallisation. L.O.: Explain the terms anhydrous, hydrated and water of crystallisation. Calculate the formula of a hydrated salt. Workshop today at 1:45pm: Winifred Henry Anna Keverne Esther Adeduntan. Copper sulfate.

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Water of crystallisation

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  1. Water of crystallisation L.O.: Explain the terms anhydrous, hydrated and water of crystallisation. Calculate the formula of a hydrated salt.

  2. Workshop today at 1:45pm: Winifred Henry Anna Keverne Esther Adeduntan

  3. Copper sulfate • Copper sulfate comes in a hydrated form (copper sulfate pentahydrate) and a anhydrous form http://uk.youtube.com/watch?v=kp7yaxlYk08

  4. 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

  5. Writing out the formula for hydrated compounds • There are two ways in which a formula can be written if it is a hydrated compound: • Empirical formula, Which you know and love OR • Dot formula, So copper sulfate pentahydrate becomes Cu SO3 • 5H2O NOTE: This dot is very important!!!!!

  6. Hydrated substances and water of crystallisation • Some substances can trap water molecules inside of them. • The water contained is called the water of crystallisation

  7. Finding the formula of hydrated copper(II) sulfate Note: see worked example in page 27

  8. FeSO4·xH2O

  9. FeSO4·xH2O

  10. FeSO4·xH2O • 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 = 0.03 • 3) Calculate molar ratio • FeSO4 : H2O = 0.01: 0.03 • 4) Divide be the smallest number 0.01: 0.03 = 1:3

  11. Other examples of hydrated compounds: • Cobalt chloride hexahydrate • Sodium sulfate decahydrate Write out the formula for these compounds using the “dot formula” notation

  12. Convert these into the Dot Formula • Calcium chloride dihydrate • Calcium chloride hexahydrate • Zinc chloride hexahydrate • Barium hydroxide octahydrate

  13. Answers • Calcium chloride dihydrate = CaCl2•2H2O • Calcium chloride hexahydrate = CaCl2•6H2O • Zinc chloride hexahydrate = ZnCl2•6H20 • Barium hydroxide octahydrate = Ba(OH)2•8H2O

  14. Write these out in Dot formula • Hydrated Cobalt chloride CoCl2H12O6 • Hydrated Calcium carbonate CaCH6O6 • Hydrated Magnesium sulphate MgSH12O10

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