7 h solutions (boardworks)

KS3 Chemistry

7H Solutions
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© Boardworks Ltd 2004
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Contents

7H Solutions
Introducing solutions
Separating mixtures
Chromatography
More about solubility
Summary activities
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Mixtures and solutions
A mixture is two or more substances that are mixed together
but not chemically joined.
A solution is a special type of mixture that is made when
a solid dissolves and mixes a liquid.
For example, a cup of instant coffee
is a solution.
The solid that dissolves (e.g. coffee
granules) is called the solute.
The liquid that does the dissolving
(e.g. hot water) is called the solvent.
How many other examples of
solutions can you think of?
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Solute + solvent

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Solubility experiment

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Contents

7H Solutions
Separating mixtures
Chromatography
Summary activities
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Salty water
Where does the salt around the Dead Sea come from?

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Separating mixtures
Sea water is a salty mixture
that contains water, salt,
sand and other substances.
The Dead Sea is a salty lake
that contains some of the
saltiest water in the world!
The Dead Sea is almost six times more salty than the ocean,
so nothing is able to live in it and that’s why it is called “dead”.
The substances in a mixture, such as salty water, are not
chemically joined which means they can be separated.
How is salt separated from salty water?
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How are solids separated out of mixtures?
Separating an insoluble solid and a liquid
If a solid is insoluble (e.g. sand in water) then
it is easy to separate it by filtering the mixture.
The insoluble solid cannot pass through the filter
paper but the water can.
Separating a soluble solid and a liquid
To separate a soluble solid from a liquid
(e.g. salt and water), evaporation can be used.
The solution is heated so that the water
evaporates and leaves the dissolved solid behind.
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Filtering

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Evaporation

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Separating salt from sea water
The main salt dissolved in sea
water is “common salt”.
In hot areas, how can the Sun
be used to separate the salt
from sea water?
The heat of the Sun evaporates
the water, the salt is left behind
and collected in salt beds.
Salt can also be obtained from
‘rock salt’ found in layers under
the ground.
How are dissolving, filtering and evaporating used to separate
the salt from rock salt?
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Separating solvents
Evaporation can be use to separate and collect the solute in
a solution. How can the solvent be collected?
The technique use to obtain
a solvent from its solution is
called distillation.
Distillation has three steps:
 evaporating;
 condensing;
 collecting.
The solution is heated so that the solvent (a liquid) evaporates
and is turned into a gas. The solute is left behind.
The gas cools in the condenser and turns back into a liquid.
This liquid is collected and is pure solvent.
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Distillation

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Which separation technique?

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Contents

7H Solutions
Separating mixtures
Chromatography
Summary activities
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What is chromatography?
Chromatography is used to separate mixtures of coloured or
non-coloured substances that are soluble in the same solvent.
Method A
Method B
pipette
spot of
mixture
solvent

solvent
spot of
mixture

A spot of the mixture is placed on some filter paper.
In method A, the solvent is soaked up the paper.
In method B, the solvent or is slowly dripped onto the paper.
The substances in the mixture get separated because
more soluble substances spread along the paper faster.
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Chromatography experiment

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Identifying dyes in a mixture
Chromatography can be used to find out if a dye is made up
of a single coloured substance or a mixture.
The
mixture
consists
of dyes
3 and 5.
1 2

3

4 5 6

mixture

1 2

3

4 5 6

mixture

Dots of known single dyes are placed alongside the dot for
the unknown mixture.
After the solvent washes through the paper, the pattern of
the dyes in the mixture is compared with the single dyes.
Which dyes does the mixture consist of?
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Identifying dyes in a mixture
Which dyes are in the mixture?

1

2

3

4

5

6

mixture

1

2

3

4

5

6

mixture

The mixture consists of
dyes 1 and 4.

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Contents

7H Solutions
Separating mixtures
Chromatography
Summary activities
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Conservation of mass experiment

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Conservation of mass
If 10 g of salt is added to 50 g of water, what is the mass
of the solution?

10 g
50 g

?
60 g

How much salt will be recovered if the mixture is separated
by evaporation?
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Conservation of mass – extension
If 10 g of salt is added to 50 g of sea water, what is the mass
of the solution?

10 g
50 g

?
60 g

How much salt will be recovered if the mixture is separated
by evaporation?
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Does a solid keep dissolving?

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How does temperature affect solubility?
Does sugar dissolve in a cup of cold tea?
The sugar does dissolve but not as much
as in a cup of hot tea.
The sugar is more soluble at higher
temperatures.
The amount of a solute that can dissolve at
a given temperature is called its solubility.
How does the solubility of a substance change
with temperature?
The solubility of a substance usually increases as
the temperature increases.
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Contents

7H Solutions
Separating mixtures
Chromatography
Summary activities
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Glossary
dissolving – The mixing of a solid with a liquid to make a
solution.

mixture – Two or more substances that are mixed together
but are not chemically joined.

saturated – A solution containing the maximum amount of
solute that it can hold.

soluble – A substance that can dissolve in a solvent.
solubility – A measure of how much solute can dissolve in
a solvent at a given temperature.

solute – Solid that dissolves in a solvent to make a solution.
solution – Mixture made when a solute dissolves in a solvent.
solvent – Liquid in which a solid dissolves to make a solution.
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Anagrams

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Word pairs activity

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Wordsearch

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Multiple-choice quiz

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