mixtures Flashcards
what is a mixture
2 points
1) a mixture consists of two or more elements or compounds not chemically bonded together
2) the chemical properties of each substance in the mixture are unchanged
how can mixtures be separated
through physical processes
what are the main physical processes
5 points
1) evaporation
2) simple distillation
3) filtration
4) chromatography
5) fractional distillation
give two examples of mixtures
1) air
2) crude oil
what is the mixture of air
it’s a mixture of gases, mainly nitrogen, oxygen, carbon dioxide and argon
what is the mixture of crude oil
it’s a mixture of different length hydrocarbon molecules
what are the properties of a mixture
2 points
1) the properties of the separate parts
2) the chemical properties of it aren’t affected by it being in a mixture
what is paper chromatography used for
separating compounds out of a mixture
e.g. dyes in an ink
how do you carry out paper chromatography
8 points
1) draw a line near the bottom of a sheet of filter paper using pencil
2) add a spot of the ink to the line and place the sheet in a beaker of solvent e.g. water
3) make sure the ink isn’t touching the solvent
4) place a lid on top of the container to stop the solvent evaporating
5) the solvent seeps up the paper carrying the solvent with it
6) each dye in the ink will move up the paper at a different rate
7) so the dyes separate out
8) when the solvent has nearly reached the top of the paper take it out of the beaker and leave it to dry
what is the end result of paper chromatography
2 points
1) a chromatogram
2) each dye will form a spot in a different place
what will happen to insoluble dyes in the solvent in paper chromatography
they will stay on the base line of the paper
why do you use pencil in paper chromatography
because pencil is insoluble in solvent
how do you decide what solvent to use in paper chromatography
depends on what is being tested some compounds dissolve well in water sometimes other solvents like ethanol are needed
why do you need to make sure the ink isn’t touching the solvent in paper chromatography
because otherwise ink will dissolve into the solvent
what is filtration used for
separating an insoluble solid from liquids
what do you use for filtration
3 points
1) beaker
2) filter paper in a cone shape
3) funnel
what are the two ways you can separate a soluble solid from solutions
2 points
1) evaporation
2) crystallisation
what is the method for evaporation
4 points
1) pour the solution into an evaporating dish
2) slowly heat the solution using a bunsen burner
3) the solvent will evaporate and the solution will get more concentrated
4) eventually crystals will start forming keep heating until you are just left with dry crystals
when can you not use evaporation
if the salt decomposes when it’s heated so you then use crystallisation
what is the method for crystallisation
7 point
1) pour the solution into an evaporating dish and gently heat it
2) some of the solvent will evaporate and the solution will be more concentrated
3) when you start to see some crystals form (the point of crystallisation)
4) remove the dish from the heat and leave the solution to cool
5) the salt should start to form crystals as it becomes insoluble in the cold highly concentrated solution
6) filter the crystals out of the solution
7) leave the crystals in a warm place to dry - you can also use a drying oven or a desiccator
what is rock salt
it’s a mixture of salt and sand
what are similarities and differences of salt and sand
2 points
1) both compounds
2) but salt dissolves in water sand does not
what are the four steps to separate rock salt - mixture of soluble solid and insoluble solid
4 points
1) grinding: so the salt crystals are small and easy to dissolve
2) dissolving: put the mixture in water and stir and heat to speed
3) filter: grains of sand won’t fit through so collects on the filter paper but salt passes through as it’s part of the solution
4) evaporation: evaporate the water from the salt so you are left with just salt crystals (or use crystallisation for bigger crystals)
what is simple distillation used to separate
used to separate a liquid from a solutions
what is the method for simple distillation
3 points
1) the solution in a flask is heated part of the solution with the lowest boiling point evaporates first
2) the vapour cools and condenses in the condenser and is collected in a beaker
3) the rest of the solution is left behind in the flask
what solutions can simple distillation be used
to get pure water from seawater
and you end up with salt
what is the problem with simple distillation
can only be used to separate things that have very different boiling points
what is fractional distillation used for
to separate a mixture of liquids with similar boiling point
what is the method for fractional distillation
6 points
1) you put your mixture in a flask and put your fractionating column on top and heat it
2) the different liquid will have different boiling point so evaporate at different points
3) the liquid with the lowest boiling point evaporate first
4) when the temperature on the thermometer matches the boiling point it will reach the top of the column
5) then go through the condenser to be collected
6) liquids with higher boiling points might also start to evaporate but the column is cooler towards the top so only gets part of the way up before condensing and returning to the flask
