lss module 2 chpt 6 water, solution, suspension

Module 2: Matter Around UsChapter 6 Water, Solutions And Suspensions

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Chapter 6 Water, Solutions And Suspensions6.1 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?

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

6.5 What are Acids and Alkalis?© Copyright Star Publishing Pte Ltd

ObjectivesExplain what is meant by the

terms solute, solvent and solutionGive 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.


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 solutionsSolutions 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 water

sand 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 suspensionsSuspensions 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 betweensolutions and suspensions


Activity Book Link Activity 6.1 Physical Properties of Solutions and Suspensions

Differences betweensolutions and suspensions



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?6.4 What are the factors that affect

the rate of dissolving? 6.5 What are Acids and Alkalis?


ObjectivesRecognise 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 solventWater 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.

Use of Solvents and Solutions



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?



ObjectivesInvestigate the factors that affect

the solubility of materials (e.g. type of solute/solvent, temperature).


Solubility of a substanceThe 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


The solubility of substances is affected by the type of solvent.


more iodine dissolves in alcohol than in water


The solubility of substances is affected 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

ObjectivesInvestigate 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?


Factors Affecting the Rate of Dissolving of Substances Which of the following cups of

coffee will dissolve faster?


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.


ObjectivesDescribe 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 AlkalisTwo 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.


vinegar is an example of a food acid

AlkalisAlkalis 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.


soap solution is a natural alkali

Using IndicatorsIndicators 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 oralkaline 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). © Copyright Star Publishing

Pte Ltd

pHAcids 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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