Chemistry practical = Heating in a crucible

Question 1

How many times do we weigh the crucible before the experiment?

Answer 1

2 times:
Empty, clean dry crucible w lid
Crucible with solid

Question 2

What is done with the crucible and hydrated ionic salt?

Answer 2

Heated with a bunsen burner flame for a couple mins and weighed every so often at regular intervals

Question 3

For how long is the crucible heated with a Bunsen burner flame?

Answer 3

Until the mass weighed measurement is constant

Question 4

When is this method of heating in a crucible used?

Answer 4

Remove water in hydrated Ionic salt
Mass loss in thermal decomposition
Mass gain when magnesium reacts with oxygen

Question 5

Should a lid be placed on the crucible?

Answer 5

Yes- improves accuracy to prevent loss of solid
BUT LOSE FITTING to allow for gas escape; prevents build up of pressure

Question 6

Why is the lid on the crucible lose fitting?

Answer 6

Allows for gas to escape

Question 7

Why should the crucible be dry before starting

Answer 7

Otherwise water in wet crucible would evaporate on heating so measure a larger loss in mass than reality:
USING dry one gives more accurate measurement

Question 8

Why use small mass of solid?

Answer 8

So thermal decomposition can go to completion

Question 9

Why avoid using a very small mass of solid?

Answer 9

Otherwise the measurement uncertainties are too high

Question 10

How to find moles of water in hydrated salt

Answer 10

Moles of hydrated salt / moles of water
Taken from above experiment

Question 11

Mass of water

Answer 11

Starting mass of solid-end mass of solid when no change in mass of water occurs