Mass Of Water In Hydrated Crystals PP1

Question 1

What is a hydrated solid?

Answer 1

A solid which is hydrated contains ‘water of crystallisation’

Question 2

Name and formula of crystals that are heated

Answer 2

Hydrated iron(II) sulfate, FeSO4·xH2O

Question 3

Safety considerations ?(4)

Answer 3

• Gentle heating should be carried out to reduce risk of FeSO4 decomposing, use a well-ventilated lab
  • Iron(II) sulfate is harmful
  • Wear safety goggles
  • Take care when heating, all apparatus will become very hot

Question 4

What should be avoided in this process?

Answer 4

You should avoid the formation of brown iron(III) oxide if possible, as this reduces the degree of hydration

Question 5

What does heating to constant mass mean?

Answer 5

‘heating to constant mass’ ensures that all the water of crystallisation has been removed from the hydrated crystals.

Question 6

Suggest why the value for the degree of hydration may be lower than expected

Answer 6

• Some anhydrous iron (II) sulfate lost during heating.
• Material ‘spat out’ of the crucible.
• Anhydrous iron (II) sulfate decomposed to brown iron (III) oxide.

Question 7

Why might the value of hydration be higher than expected ?

Answer 7

Not all the water of crystallisation has been removed from the hydrated crystals.

Question 8

How would you improve the accuracy of this experiment ? (3)

Answer 8

• Place a lid over the crucible when heating.
• Continue to heat to ensure constant mass.
• Use a more accurate balance (with a draught shield).

Question 9

How could you improve the reliability of the experiment ?

Answer 9

Repeat results and take an average.