Lss module 2 chpt 6 water, solution, suspension

Module 2:
Matter Around Us
Chapter 6 Water, Solutions And Suspensions
1© Copyright Star Publishing Pte Ltd

Chapter 6 Water, Solutions
And Suspensions
6.1 What are Solutions and
Suspensions?
6.2 Why is water a universal solvent?
6.3 What are the factors that affect the
solubility of a solute in a solvent?
rate of dissolving?
6.5 What are Acids and Alkalis?

Objectives
 Explain what is meant by the terms
solute, solvent and solution
 Give examples of uses of solvents and
solutions at home, in industries and in
medicine
 Deduce the nature of solutions and
suspension by simple laboratory tests
(e.g. passing a beam of light, filtering
using filter paper)

What is a solution?
 A solution is a liquid mixture.
 In the salt solution, salt is called the
solute and water is called the solvent.
© Copyright Star Publishing Pte Ltd 4

Sugar solution
solution = solute + solvent
 When sugar is added to water and stirred, the
solid sugar is the solute and it dissolves in
water as the solvent and forms a sugar
solution.

Copper(II) sulfate solution
 If the solute is coloured, for example,
copper(II) sulfate, then the solution
produced will be clear and coloured
as shown.

Properties of solutions
 Solutions are homogeneous. This
means that the colour, physical and
chemical properties are the same
throughout the solution.
 Solutions will not separate back into
the solute and solvent even if they are
left to stand.
 When filtered, the solution will pass
through the filter paper completely.

What is a suspension?
 When a solid does not dissolve in a liquid, a
suspension is formed.
 For example, sand cannot dissolve in water.
Muddy water containing sand is an example of a
suspension.
talcum powder suspended in watersand is not soluble in the water

Properties of suspensions
 When a solid cannot dissolve in a liquid, the
mixture formed will look cloudy.
 Muddy water looks cloudy.
 When left to stand, the sand will sink to the
bottom, resulting in a clear layer of water above.

Properties of suspensions
 Suspensions are non-homogeneous.
This means that the colour, physical
and chemical properties are not the
same throughout the suspension.
 The insoluble solids will settle to the
bottom of the solvent when left to
stand. When filtered, the insoluble
solids will remain on the filter paper.

Differences between
solutions and suspensions
Activity Book Link
Activity 6.1
Physical Properties of Solutions and
Suspensions

Differences between
solutions and suspensions

And Suspensions
Suspensions?
rate of dissolving?

Objectives
 Recognise that water dissolves many
substances

Water is as a solvent
 Water is a very good solvent as it
can dissolve many substances such
as sugar, salt, alcohol and soluble
food substances.
water used to make souptable salt and sugar are water soluble

Water is as a solvent
 Water makes up almost
90% of our body mass.
 Much of these are found
as water in blood. Water
is important to our body
because it helps to
dissolve and transport
mineral salts, food and
gases to various parts of
our body.
a vitamin C tablet
dissolves in water
Activity Book Link
Activity 6.2
Water as a Solvent

Use of Solvents and Solutions
 Solutions and solvents are very
useful at home, in industries,
agriculture and medicine.
Hydroponics is a technique of growing plants in water without soil. The nutrients are
dissolved in water and the plants absorb the nutrients through their roots.

And Suspensions
Suspensions?
6.3 What are the factors that affect
the solubility of a solute in a
solvent?
rate of dissolving?

Objectives
 Investigate the factors that affect the
solubility of materials (e.g. type of
solute/solvent, temperature).

Solubility of a substance
 The solubility of a substance is the
maximum amount of the substance
that can dissolve in a given amount
of solvent (e.g. 100 cm3 of water) at a
given temperature (e.g. 25°C).
 Different types of solids will have
different solubilities in a solvent.

Solubilities of some common
substances

Factors affecting solubility
 The solubility of substances is affected
by the type of solute.
more salt can dissolve in 100cm3 of water than baking soda

by the type of solvent.
more iodine dissolves in alcohol than in water

by the temperature.
more salt dissolves in hot water than in water at room temperature
Activity Book Link
Activity 6.3
Factors Affecting the Amount of Substance that can
Dissolve in a Fixed Amount of Water

And Suspensions
Suspensions?
6.4 What are the factors that affect
the rate of dissolving?

Objectives
 Investigate the factors that affect the
rate of dissolving (e.g. temperature,
surface area, stirring).

Factors Affecting the Rate of Dissolving
of Substances
 Which of the following cups of coffee
will dissolve faster?

of Substances

of Substances
Activity Book Link
Activity 6.4
Factors Affecting the Rate of Dissolving of Substances

What is the rate of dissolving
?
 The rate of dissolving is a measure of
how fast a solute can dissolve
completely in a solvent.
 The rate of dissolving a solute in a
solvent depends on the following
factors:
(a) Temperature of solvent
(b) Surface area of solute
(c) Rate of stirring

Temperature of solvent
 Heating a solution increases the rate of
dissolving.
 For example, hot water dissolves sugar
faster than cold water.

Surface area of solute
 Breaking the solute into smaller pieces increases the
rate of dissolving as the total surface area of the solid
is increased.

For example, fine sugar powder dissolves faster than
rock sugar blocks.

Rate of stirring
 A greater amount of solute can dissolve in a
solvent if the mixture is stirred faster.
 For example, stirred coffee powder
dissolves faster than if it was not stirred.

And Suspensions
Suspensions?
rate of dissolving?

Objectives
 Describe acidity, neutrality and
alkalinity in terms of the pH scale
(whole numbers only)
 Show an understanding that indicators
are substances that change colour
when an acid or alkali is added to
them
 Investigate the effect of acidic, alkaline
and neutral solutions on indicators
(Universal and litmus indicators)

Acids and Alkalis
 Two common chemicals
are acids and alkalis
which are both
solutions.
 Acids are sour in taste.
 Examples of household
items that contain acids
are lemon juice and
vinegar is an example of a
food acid

Alkalis
 Alkalis are bitter in
taste.
 Alkalis belong to a larger
group of chemicals
known as bases. Alkalis
are bases that are
soluble in water.
 Detergents and baking
powder can dissolve in
water to form alkalis. © Copyright Star Publishing Pte Ltd 39
soap solution is a natural
alkali

Using Indicators
 Indicators are used to
find out if a solution is
an acid or an alkali.
 Two common indicators
are:
(a) Litmus paper
(b) Universal indicator
litmus solution

Litmus paper
 A blue litmus paper
turns red when
placed in an acid
 A red litmus paper
turns blue when
placed in an alkali

Universal indicator
the universal indicator can tell us how acidic or
alkaline the solution is through its range of colours

Universal indicator
 The colours of the universal indicator can be compared against a
pH colour chart with pH values.
 The pH value ranges from 0 (most acidic) to 14 (most alkaline).

pH
 Acids have a pH value less than 7
while alkalis have a pH value greater
than 7.
 A solution with a pH value of 7 is
described as neutral (neither acidic
nor alkaline).
Activity Book Link
Activity 6.5
Identifying Acidic, Alkaline and Neutral Solutions

Lss module 2 chpt 6 water, solution, suspension

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