Determination of formulae - 3.2 (4)

Question 1

How accurate is an experimental formula - what can be made?

Answer 1

some assumptions and real experiments may not always work out as well

Question 2

Assumption 1 - If the hydrated and unhydrous forms have different colours, what can you then be sure?

Answer 2

that all water has been removed

Question 3

Assumption 1 - What can you only see?

Answer 3

the surface of the crystals and some water could be left inside

Question 4

Assumption 1 - If the hydrated and anhydrous forms are similar colours, what does this suggest?

Answer 4

that it is not as easy to determine if all the water has been lost

Question 5

Assumption 1 - What could be a good solution?

Answer 5

to heat to constant mass - the crystals are reheated repeatedly until the mass of the residue no longer changes - this shows that all water has been removed

Question 6

Assumption - What decomposes further when heated?

Answer 6

many salts

Question 7

Assumption 2 - For example, if heated strongly, what happens to copper (II) sulfate?

Answer 7

it decomposes to form black copper (II) oxide

Question 8

Assumption 2 - What is difficult to judge if there is further or no further decomposition?

Answer 8

if there is no colour change