Mixtures

Question 1

What is a mixture

Answer 1

Consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged

Question 2

How can a mixture be separated

Answer 2

Physical processes such as filtration, crystallization, simple distillation and fractional distillation and chromatography
These chemicals do not involve a chemical reaction and no new substances are made

Question 3

How do you do paper chromatography

Answer 3

Used to separate dyes in an ink

1. Draw a line near the bottom of a sheet of filter paper (pencil as they are insoluble and won’t dissolve in the solvent)
2. Add a spot of the ink to the line and and place the sheet in a beaker of solvent (water)
3. Make sure the ink isn’t full in the solvent
4. Place a lid on top to stop the solvent evaporating
5. The solvent moves up the paper carrying the ink with it
6. Each different dye in the ink will move up the paper at a different rate so the dyes will separate out. Each dye will form a spot in a different place
7. If any of the dyes are insoluble, they’ll stay on the baseline
8. When the solvent has nearly reached the top, take it out and dry it

Question 4

What is filtration

Answer 4

Separates insoluble solids from liquids

Can be used in purification

Question 5

What two ways can you separate soluble solids from solutions

Answer 5

Evaporation

Crystallization

Question 6

What is evaporation

Answer 6

Pour the solution into an evaporating dish
Slowly heat the solution. The solvent will evaporate and the solution will get more concentrated, eventually crystals will start to form
Keep hearing until all you have left are dry crystals

Question 7

What is crystallization

Answer 7

Pour the solution into an evaporating sissy and gently heat
Once some of it has evaporated or when crystals start to form, remove dish from the heat and leave the solution to cool
The salt should start to form crystals as it becomes insoluble in the cold
Filter the crystals out the solution, and leave them in a warm place to dry, you could also use a drying oven

Question 8

How can filtration and crystallization separate rock salt

Answer 8

Salt and sand are both compounds but salt dissolved in water, sand doesn’t

1. Grind the mixture to make sure salt crystals are small so it dissolves easily
2. Put the mixture in water and stir, the salt will dissolve, sand won’t
3. Filter, the grains of sand won’t fit through the holes in the filter paper so they collect. The salt passes through the paper
4. Evaporate the water from the salt so that it forms dry crystals

Question 9

What is simple distillation

Answer 9

Used to separate out a liquid from a solution
Solution is heated, the part of the solution that has the lowest boiling point evaporates first
The vapor is then cooled, condensed and collected
The rest of left behind in the flask
You can get pure water form sea water. The water evaporates and is condensed and collected. Eventually you’ll end up with just salt left in the flask

Question 10

What is the problem with simple distillation

Answer 10

You can only use it to separate things with very different boiling points

Question 11

What is fractional distillation

Answer 11

Put mixture in a flask and put a fractionating column on top and heat it
The different liquids will have different boiling points so they will evaporate at different temperatures
The 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 higher boiling point might also start to evaporate, but the column is cooler towards the top so they will only get part of the way up before condensing and running back down towards the flask
When the first liquid has been collected, you raise the temperature until the next one reaches the top