Separating Techniques Flashcards
When can you use filtration?
- if a product of a reaction is an insoluble solid you can use filtration to separate it from the liquid reaction mixture
How do you do filtration?
- put some filter paper into a funnel and pour your mixture into it
- liquid part of the mixture runs through the paper
- which leaves a solid residue
How do you do crystallisation to separate a soluble solid from a solution?
- pour the solution into an evaporating dish and gently heat the solution
- some of the water will evaporate and the solution will become more concentrated
- when some of the water has evaporated crystals will start to form
- remove dish from heat and leave the solution to cool
- salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
- filter crystals out of solution
- leave them in a warm place to dry
- you could also use a drying oven
How can you use filtration and crystallisation to separate rock salt?
1 Grinding- grind the rock
2 Dissolving- dissolve in beaker and stir
3 Filtering- filter through filter paper in a funnel
4 Crystallisation- evaporate in an evaporating dish
What is observed when you use filtration and crystallisation to separate rock salt?
- the sand does not dissolve so it collects in the filter paper
- the salt is dissolved in the solution- so it does go through
- when the waters evaporated the salt forms as crystals in the evaporating dish
How can you do paper chromatography?
- draw a line near the bottom of a sheet of filter paper (baseline)
- add spots of different inks to the line at regular intervals
- role the sheet and put it in the beaker of solvent (water)
- level of solute is below the baseline
- place a lid on the top of the container to stop the solvent evaporating
- solvent seeps up the paper carrying the inks with it
- each different dye in the inks will move up the paper at different rates
- and form a spot in a different place
- leave the paper to dry when the solvent has reached the top
Why do you use a pencil when doing chromatography?
- pencil marks are insoluble
- so it wont dissolve in the solvent
During chromatography, why is the level of solvent below the baseline?
- you don’t want the inks to dissolve into the solvent
How do you calculate Rf for each chemical?
Rf= distance travelled by solute/distance travelled by solvent
How can you carry out simple distillation to separate out solutions?
- used for separating out a liquid from a solution
- solution is heated and the part of the solution that has the lowest boiling point evaporates
- vapour is then cooled, condenses back into a liquid and is collected
- rest of solution is left behind in a flask
- you can use SD to get pure water from sea water
- water evaporates and is condensed and collected
- you will end up with just salt left in the flask
Why is simple distillation different to fractional distillation?
- if you have a mixture of liquids with similar boiling points you cannot use simple distillation
How can you do fractional distillation to separate a mixture of liquids?
- put your mixture into a flask and put a fractionating column on top, then heat it
- different liquids have different boiling points, so they will evaporate at different temperatures
- liquid with the lowest boiling point evaporates first
- when the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column
- liquids with the highest boiling points might also start to evaporate
- the column in cooler towards the top
- so you will only get part of the way up before condensing and running back down the flask
- when the first liquid has been collected you raise the temperature until the next one reaches the top
