Education in chemistry

1. Solutions and Suspensions
Ali Nasir
Class 8th
Orange
Beacon House School Systems

2. Solutions
A solution contains both solute and solvent.
solute
substance that the
solute dissolves in
Generally, there are three types of solutions:
1. Dilute solution – contains small amount of solute dissolved in large
amount of solvent
2. Concentrated solution – contains large amount of solute dissolved in
small amount of solvent
3. Saturated solution – contains maximum amount of dissolved solute in
a given amount of solvent at a given temperature
substance that dissolves
solvent
=
=
+ solution
=
mixture in which its
components are evenly
mixed

3. When a substance dissolves in a solvent, it is soluble in that
solvent.
Water is known as the universal solvent
as many substances can dissolve in it.
Aqueous solution is thus a solution which
has water as the solvent.
Nature of solutions
When a solution is formed,
solute particles are evenly and
completely mixed with the
solvent particles. evenly mixed
Can solutions be separated by physical methods?
solvent solute
Alcoholic drinks

4. Homogeneous (solution) = physical (e.g. colour) and chemical
properties are the same in every part
The solute does not settle to the bottom
or float to the top when the iodine in
alcohol solution is left to stand
Light passes through the solution
when light is shone through it.
Reason : The tiny solute particles
are too small to block any
light passing through the solution.
Filtration cannot be used to separate
solutes from its solvent.
Reason : The tiny solute particles can pass
through the filter paper.

5. Suspensions
A suspension = mixture containing insoluble solid particles
suspended in a liquid
A suspension can also consist of liquid droplets or fine solids in a gas
Some example of suspensions
chalk dust
and water
calamine
lotionhazy environment medicine
Nature of suspensions
When a suspension is formed, solute particles remain as
large visible insoluble solid particles

6. Heterogeneous (suspension) = physical (e.g. colour) and
chemical properties are
different in every part
The insoluble particles will settle to the bottom or float to
the top when the suspension is left to stand
Light cannot pass through the
suspension when light is shone through it
Reason : large insoluble particles are
large enough to prevent light passing
through the suspension
Filtration can be used to separate solute from
its solvent and the residue collected is the
solute
Reason : The insoluble particles are too large to
pass through the filter paper

7. Factors Affecting the
Solubility of Substances
Solubility = maximum amount of a solute which can dissolve
in 100 g of solvent at a fixed temperature
For example: 200 g of salt in 100 g of water at 30
°C
Factors affecting the solubility of a solute in a solvent:
• nature of the solute
• nature of the solvent
• temperature of the solution
Solubility of solids and liquids
when temperature
Solubility of gases
when temperature

8. Factors Affecting the Rate of
Dissolving of Substances
Rate of dissolving = time taken for solute to completely
dissolve when it is added to a
fixed amount of solvent
Factors affecting the rate of dissolving a solute in a given
volume of solvent:
• surface area of the solute
• temperature of the solution
• rate of stirring
Faster rate of dissolving
85 °C 15 °C
Faster rate of dissolving

9. Applications at Home and in the Industry
Many substances that we use are in the form of solutes, solvents and
solutions.
Hence, it is important to know about factors affecting the solubility
and rate of dissolving of substances
At home: washing machine uses hot water and rotating drum to
increase the solubility and rate of dissolving of detergent in water
In fizzy drinks industry:
Temperature
of water,
Solubility and rate of
dissolving extracts
BUT,
Temperature
of water,
Solubility and rate of
dissolving of carbon
dioxide gas
So how do we increase the solubility and rate
of dissolving of the extracts and gas at the
same time?

10. Acids and Alkalis
acid alkali
Acids and alkalis are two common types of
aqueous solutions we use every day.
Acids
Acids can be found all around us:
Citrus fruits
Contains: Citric acid
Tea
Contains: Tannic acid
Stomach secretions
Contains:
Hydrochloric acid

11. General Properties of Acidic Solutions
• Acids are generally corrosive – they can burn our skin and
react with many materials
• All acids have sour taste
• Acids turn blue litmus paper red
• Dilute acids react with
reactive metals to
produce hydrogen gas
• Aqueous solutions of acids are good
electrical conductors
Test for hydrogen gas:
a ‘pop’ sound is heard when a
burning splint comes into contact
with the hydrogen gas
Sodium + dilute hydrochloric acid sodium chloride + hydrogen
(metal) (acid) (salt) (gas)
Word equation:

12. Test of carbon dioxide: Clear
limewater will turn chalky when
carbon dioxide passes through it
(white precipitate formed)
• Dilute acids react with carbonates to produce carbon
dioxide gas
calcium carbonate + dilute nitric acid calcium nitrate + carbon dioxide + water
(carbonate) (acid) (salt) (gas)
Alkalis
Alkalis can also be found all around us:
Household cleaners
Contains:
Ammonia solution
Soap
Contains:
sodium hydroxide

13. General Properties of Alkaline Solutions
• Alkalis are generally corrosive – they can burn our skin and
can cause bleaching
• All alkalis taste bitter and feel soapy
• Alkalis turn red litmus paper blue
• Alkalis are good electrical conductors
• Alkalis react with acid to form salts can water only
Potassium hydroxide + nitric acid potassium nitrate + water
(alkali) (acid) (salt)

14. Indicators
To determine how acidic or alkaline a solution is, we use a
suitable indicator (e.g. litmus paper, Universal Indicator)
Acidity increases Alkalinity increases
Indicator = substance
which changes colour
according to whether the
solution is acidic, alkaline
or neutral
Universal Indicator
• mixture of several types of indicators
• shows a variety of colours according to the different
degrees of acidity or alkalinity of the solution
• comes with a colour chart for comparing the colour shown on it
(representing degree of acidity or alkalinity) with colour chart
Compare the colour changes of the different indicators