The Mole (8) Water Of Crystallisation

Question 1

What is meant by a hydrated compound?

Answer 1

When water of crystallisation is present in a crystal compound

Question 2

What is meant by an anhydrous compound?

Answer 2

When all the waters of crystallisation have been removed from a compound

Question 3

Define the term water of crystallisation

Answer 3

The water present in a compound by giving the compound a crystalline appearance (the .xH2O term)

Question 4

CuSO4.XH2O(s) –> CuSO4(s) + XH2O(l)

How could a practical be used to gather results to calculate the value of X?

Answer 4

Procedure:
1 - Weigh an empty crucible
2 - Add some hydrated salt to crucible and reweigh
3 - Heat crucible to evaporate the water of crystallisation, leaving behind the anhydrous salt
4 - Allow to cool - reweigh crucible and anhydrous salt
5 - repeat steps 3 and 4 (heat until constant mass), this ensures all of the water of crystallisation has been evaporate

Question 5

What limitations may be met when trying to obtain the correct mass of anhydrous salt?

Answer 5

• When heated, solids can ‘spit’ - leave crucible
• Bunsen may deposit carbon particulates onto crucible
• Salt may decompose

Question 6

Suggest a modification to the practical that would reduce the percentage uncertainty

Answer 6

• Use greater mass of hydrated salt

- Use more precise tip pan balance