Heating in a crucible and using a gas syringe

Question 1

How to check whether all the water has been removed

Answer 1

Reheat and observe whether the mass changes

Question 2

Method

Answer 2

1. Weigh an empty clean dry crucible and lid .
2. Add 2g of hydrated calcium sulphate to the crucible and weigh again
3. Heat strongly with a Bunsen for a couple of minutes 4. Allow to cool
4. Weigh the crucible and contents again
5. Heat crucible again and reweigh until you reach a constant mass (do this to ensure reaction is complete).

Question 3

Large amounts of the solid should not be added because…

Answer 3

the decomposition is likely to be incomplete

Question 4

The crucible needs to be dry otherwise…

Answer 4

a wet crucible would cause mass loss to be too large as the water would be lost when heating

Question 5

Small amounts of the solid should not be used as…

Answer 5

percentage uncertainties in weighing will be too high

Question 6

The lid improves accuracy as …

Answer 6

it prevents loss of solid from the crucible but should be loose fitting to allow gas to escape

Question 7

Volume of gas depends on

Answer 7

Temperature

Pressure

Question 8

Potential errors in using a gas syringe

Answer 8

• gas escapes before bung inserted
• syringe sticks
• some gases like carbon dioxide or sulphur dioxide are soluble in water so the true amount of gas is not measured