Practical P1 - Filtration and Crystallisation

Question 1

what does filtration do

Answer 1

separate insoluble solids from liquids

Question 2

what is filtration used for

Answer 2

1) if your product is an insoluble solid that needs to be separated from a liquid
2) can be used in purification - solid impurities in the reaction mixture can be separated out

Question 3

what are the ways to separate a soluble solid from a solution
2 points

Answer 3

1) evaporation
2) crystallisation

Question 4

what is the method for evaporation
4 points

Answer 4

1) pour the solution into an evaporating dish
2) slowly heat the solution, the solvent will evaporate and the solution will get more concentrated
3) eventually crystals will start to form, keep heating it until you only have dry crystals left
4) this is really quick but can only be used of the salt doesn’t decompose when it’s heated - use crystallisation instead

Question 5

what’s the method for crystallisation
4 points

Answer 5

1) pour the solution into an evaporating dish and gently heat, some solvent will evaporate and the solution will get more concentrated
2) when crystals start to form (the point of crystallisation) remove the dish from the heat and leave the solution to cool
3) the salt should start to form crystals as it becomes insoluble in the cold highly concentrated solution
4) filter the crystals out of the solution and leave them in a warm place to dry (can use a drying oven or desiccator)

Question 6

what is rock salt

Answer 6

a mixture of salt and sand (salt dissolves in water and sand doesn’t)

Question 7

how can filtration and crystallisation be used to separate rock salt
4 points

Answer 7

1) grind the mixture to make sure the salt crystals are small, so will dissolve easily
2) put the mixture in water and stir, the salt will dissolve but the sand won’t, (heating the mixture will help the salt dissolve)
3) filter the mixture, the grains of sand won’t fit through the filter paper and will be collected in it - the salt passes through it as it’s part of the solution
4) evaporate the water from the salt so it forms dry crystals (could use crystallisation if you want bigger crystals)