1. In This Section We Will Be Studying These Topics:
SOLUTIONS
In This Section We Will Be Studying These Topics:
What are solutes, solvents, solutions and mixtures?
The effect of heating and stirring a solution.
How to separate impurities.
How to get the solvent back from a mixture.
Chromatography.

2. SOLUTIONS
When a solid dissolves in a liquid a mixture called a solution is made.
The solid is called the solute.
The liquid it dissolves in is called the solvent.
The mixture that is made is called a solution.
SOLUTE SOLVENT  SOLUTION

3. SOLUTIONS
The molecules in the solute (solid) mix with the molecules in the solvent (liquid) to form a solution. + 
solute
solvent
solution
The total number of molecules stays the same.
Number of molecules in solute + number of molecules in solvent = number of molecules in solution.
How could we work out the mass of the solution?

4. Mass of solution = mass of solvent + mass of solute.
SOLUTIONS
Answer:
Mass of solution = mass of solvent + mass of solute.
Nothing has been lost or gained so the total mass must stay the same.

5. There is a limit to how much solute can dissolve in a solvent.
SOLUTIONS
There is a limit to how much solute can dissolve in a solvent.
When no more solute can be dissolved, the solution is said to be saturated.
If a solid can be dissolved, the solid is said to be soluble.
If a solid cannot be dissolved, the solid is said to be insoluble.
Solids may dissolve in some liquids but not in others.
For example, gloss paint will not dissolve in water but it will dissolve in white spirit.

6. SOLUTIONS
The warmer a solvent is, the faster the solute will dissolve.
Solutes will dissolve faster if the solvent/solution is stirred.

7. SOLUTIONS Why do the following speed up dissolving? Heating Stirring
Answer:
Heating gives the molecules more energy.
This allows the molecules to move faster.
The molecules mix up faster.
Stirring helps mix up the molecules.

8. SOLUTIONS Answer: Separating mixtures:
Here are some ways of separating a mixture into the different substances it contains:
Filtering
Evaporating
Distilling
Chromatography
One of the above can only be used when an insoluble solid is mixed with a liquid. Which one?
Answer:

9. SOLUTIONS Filtering: Solid particles. Liquid molecules.
Filtering separates insoluble solids (often called impurities) from liquids.
The solids are too large to pass through the filter. The liquid will pass through.
Solid particles.
Liquid molecules.
Filtering is a good way of
separating sand from water.

10. SOLUTIONS Evaporating:
Evaporating a solution separates the solute from the solvent.
The solvent evaporates into the surroundings.
The solute is left behind.
In a solution, the molecules
of the solute and solvent are
mixed up.
The liquid evaporates.
The solid is left behind.
Evaporating is a good way of getting salt out of sea water.
The warmer the solution is, the faster it evaporates.

11. SOLUTIONS
Assuming they are at the same temperature and the same kind of liquid, which of the liquids below would evaporate more quickly?
Why?
Answer:
The liquid in the wider container will evaporate faster.
This is because it has a bigger surface area.
This means there is more room for the evaporating molecules to escape from the liquid.
Why do liquids evaporate faster when they are warmer?
Heat gives the molecules more energy.
This allows the molecules to move more freely and behave like the molecules of a gas.

12. SOLUTIONS Distilling:
If you evaporate sea water, you will be left with the salt but the water will have evaporated into the air.
Distillation is a method of collecting both the solute and the solvent from a solution.
Name one advantage of distillation compared with filtration.
Name one disadvantage of distillation compared with filtration.

13. SOLUTIONS Answers: Advantages of distillation:
Distillation lets you collect the liquid and the solid.
Distillation can be used to separate two liquids that are mixed together, as well as separating a solid from a liquid.
This works if the two liquids have different boiling points. The one with the lower boiling point will turn to a gas and travel down the condenser while the other is still in liquid form in the flask.

14. SOLUTIONS Answers: Disadvantages of distillation:
Much more complicated.
Equipment is more expensive.
Task
Look at this apparatus with your teacher and find out the names of all of the parts.

15. SOLUTIONS This is a sketch of the condenser that Liebig used.
A Liebig condenser is attached to a conical or round bottomed flask which contains sea water and is heated by a Bunsen.
Pure water (solvent) is collected from the output of the condenser.
Salt (solute) is left in the flask.

16. SOLUTIONS Chromatography:
Chromatography is used when a solution contains more than one solute.
It is used to separate the solutes from each other.
It can be used to identify which solutes a solution contains.
A drop of ink is placed on
a piece of damp filter paper.
The different dyes in the ink
separate and form a chromatogram.

17. SOLUTIONS
Using simple apparatus we can find out the different colours of ink in black felt tip pens.
These two CHROMATOGRAPHS are from different makes of black felt tip pen.
A spot of ink has been placed on the pencil line at the bottom of the paper and the paper below the line was dipped in water.
The inks have moved up the paper (‘run up’) and some colours have ‘travelled’ a shorter distance than others.

18. SOLUTIONS Separation task Method Chromatography Distillation
Match each of the methods below with the best way of separating the mixtures given. Each method can only be used once.
Separation task
Method
Getting the sugar out of a
sugar and water mixture.
Chromatography
Finding out what coloured
dyes are in orange juice.
Distillation
Getting the water back out of a cup of black coffee.
Filtration
Getting some iron filings out
of a bucket of water.
Evaporation

19. SOLUTIONS Separation task Method Chromatography Distillation
Answers:
Separation task
Method
Getting the sugar out of a
sugar and water mixture.
Chromatography
Finding out what coloured
dyes are in orange juice.
Distillation
Getting the water back out of a cup of black coffee.
Filtration
Getting some iron filings out
of a bucket of water.
Evaporation

20. SOLUTIONS That a solute dissolves in a solvent to make a solution.
What Have We Learned?
That a solute dissolves in a solvent to make a solution.
When no more solute can be dissolved the solution is saturated.
The speed that a solute dissolves can be increased by heating and stirring the solution.
Impurities can be removed from the solution by filtration.
Evaporation separates the solute from the solvent. The wider the container or the hotter the solution the faster the evaporation.
Distillation can be used to collect the solvent during evaporation. It can also be used to separate two liquids.
Chromatography can be used to separate and identify two or more solutes.