mixtures

Question 1

what is a mixture
2 points

Answer 1

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

Question 2

how can mixtures be separated

Answer 2

through physical processes

Question 3

what are the main physical processes
5 points

Answer 3

1) evaporation
2) simple distillation
3) filtration
4) chromatography
5) fractional distillation

Question 4

give two examples of mixtures

Answer 4

1) air
2) crude oil

Question 5

what is the mixture of air

Answer 5

it’s a mixture of gases, mainly nitrogen, oxygen, carbon dioxide and argon

Question 6

what is the mixture of crude oil

Answer 6

it’s a mixture of different length hydrocarbon molecules

Question 7

what are the properties of a mixture
2 points

Answer 7

1) the properties of the separate parts
2) the chemical properties of it aren’t affected by it being in a mixture

Question 8

what is paper chromatography used for

Answer 8

separating compounds out of a mixture
e.g. dyes in an ink

Question 9

how do you carry out paper chromatography
8 points

Answer 9

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

Question 10

what is the end result of paper chromatography
2 points

Answer 10

1) a chromatogram
2) each dye will form a spot in a different place

Question 11

what will happen to insoluble dyes in the solvent in paper chromatography

Answer 11

they will stay on the base line of the paper

Question 12

why do you use pencil in paper chromatography

Answer 12

because pencil is insoluble in solvent

Question 13

how do you decide what solvent to use in paper chromatography

Answer 13

depends on what is being tested some compounds dissolve well in water sometimes other solvents like ethanol are needed

Question 14

why do you need to make sure the ink isn’t touching the solvent in paper chromatography

Answer 14

because otherwise ink will dissolve into the solvent

Question 15

what is filtration used for

Answer 15

separating an insoluble solid from liquids

Question 16

what do you use for filtration
3 points

Answer 16

1) beaker
2) filter paper in a cone shape
3) funnel

Question 17

what are the two ways you can separate a soluble solid from solutions
2 points

Answer 17

1) evaporation
2) crystallisation

Question 18

what is the method for evaporation
4 points

Answer 18

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

Question 19

when can you not use evaporation

Answer 19

if the salt decomposes when it’s heated so you then use crystallisation

Question 20

what is the method for crystallisation
7 point

Answer 20

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

Question 21

what is rock salt

Answer 21

it’s a mixture of salt and sand

Question 22

what are similarities and differences of salt and sand
2 points

Answer 22

1) both compounds
2) but salt dissolves in water sand does not

Question 23

what are the four steps to separate rock salt - mixture of soluble solid and insoluble solid
4 points

Answer 23

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)

Question 24

what is simple distillation used to separate

Answer 24

used to separate a liquid from a solutions

Question 25

what is the method for simple distillation
3 points

Answer 25

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

Question 26

what solutions can simple distillation be used

Answer 26

to get pure water from seawater
and you end up with salt

Question 27

what is the problem with simple distillation

Answer 27

can only be used to separate things that have very different boiling points

Question 28

what is fractional distillation used for

Answer 28

to separate a mixture of liquids with similar boiling point

Question 29

what is the method for fractional distillation
6 points

Answer 29

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