chap 5 (2)

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Water is the most abundant substance on earth.

Like any other substances, water has its ownunique characteristics.

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A. Physical Characteristics of Water

1. Water can exist in three states:

a. Solid b. Liquid c. Gas

5.1 Physical Characteristics of Water

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2. At room temperature, pure water is a

a. colourless,

b. odourless and

c. tasteless.


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Freezing Point of Water

1.Water changes from liquid to solid at its freezingpoint.

liquid solid

Freezing point of water is the temperature atwhich water freezes into ice.


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2. The freezing point of pure water is 0 oC.

3. The temperature remains constant at 0 oC until waterfreezes completely.


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4. What happens to water particles when water is cooled?

When the temperature drops, the waterparticles move slower.

Therefore, the forces of attraction among theparticles grow stronger.

At 0 oC, the forces of attraction are so greatthat the water particles are held in fixed

positions.

Water freezes into ice!


h i l h i i f

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Boiling Point of Water

1. Water boils at its boiling point.

liquid gases

Boiling point of water is the temperature atwhich water boils and becomes steam.


5 1 Ph i l Ch t i ti f W t

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2. The boiling point of pure water is 100 oC.

3. The temperature remains constant at 100 oC untilwater boils completely.



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4. What happens to water particles when waterboils?

When the temperature rises, the water particlesmove faster and further apart.

Therefore, the forces of attraction among theparticles grow weaker.

At 100 oC, water particles move so fast thatthey overcome the forces of attraction and

leave the liquids surface.

Water becomes steam!



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5. Water conducts heat slowly. Water is a poorthermal conductor.

6. Water is also a poor electrical conductor.7. The density of water varies with temperature.

Pure water has the maximum density of 1 gper cm3 at 4 oC.


5 1 Physical Characteristics of Water

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B. Effects of Impurities on the PhysicalCharacteristics of Water

1. Impurities in water can change thephysical characteristics of water. Sometimesthe change is noticeable and sometimes it is not.


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2. Here are some examples:

ExamplePhysical

characteristic

Pure water is tasteless but sea water is salty.Taste

Pure water is odourless. Water with decayed matter has an unpleasantsmell.Odour

Pure water is colourless but muddy water is brownish in colour.Colour

Pure water is less dense than sea water.Density

Pure water with a few drops of sulphuric acid can conduct electricity.Electrical conductivity

Pure water freezes at 0 oC but sea water freezes at a lowertemperature.Freezing point

Pure water boils at 100 oC but sea water boils at a higher temperature.Boiling point


5 2 Composition of Water

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Composition of Water

1. Water is a compound. It is made of two differentelements.

Water

Hydrogen Oxygen

5.2 Composition of Water


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2. Water can be broken down to its elementsthrough electrolysis.

A method to break down a compound by passingan electric current through its liquid or solution



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Hydrogen isreleased at the

cathode

Oxygen isreleased at the

anode

3. The volume of hydrogen released is alwaystwice the volume of oxygen released.



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Water is made up of one part of oxygen and two parts ofhydrogen.

Oxygen atom

Hydrogen atoms

Each water molecule consists of one atom of oxygen andtwo atoms of hydrogen.


4.


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5. Therefore, scientists represent water with thefollowing formula:

H2O Represents the hydrogen atomH

Shows that there are two atoms of hydrogen2 Represents the oxygen atomO


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Applying the principle of water evaporation

In our daily life.

1. To drying clothes

2. To drying hair3. To drying agricultural produce

4. To drying fish and prawn

5. To cooling the body6. To producing the common salt

5.4 Solution and Solubility

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Solution and Solubility

Solution and Solubility



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A. SOLUTION

1. What is a solution?

A solution is produced when a substancedissolved in another substance.

A solute is thesubstance that dissolves.

A solvent is thesubstance that the solutedissolves in.



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2. Depending on the amount of solutes insolutions, there are three types of solutions.

Solution

Dilute solution Concentrated solution Saturated solution

Contains a littledissolved solute

Contains a lot ofdissolved solute

Contains the maximumamount of dissolved solute

Can dissolve a lotmore solute

Can dissolve a little bitmore solute

Cannot dissolve any moresolute

All these solutions have a clear appearance

o o o y


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B. SOLUTION AND SUSPENSION

1. What is a suspension?

A suspension is a mixture containing insolublesubstances.

2. There are many suspensions around us.

Muddy water, fruit juices, chocolate drink, blood

y


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C. FACTORS AFFECTING SOLUBILITY

1. What is solubility?

The solubility of a solute is the maximum amount of solute ingrams that will dissolve in 100 g of solvent at a given

temperature.

For example, the solubility of sodium chloride is 38 g per 100g of water at 20 oC.

This means that you can dissolve not more than 38 g of sodium

chloride in 100 g of water at 20o

C.

y


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2. Factors Affecting the Solubility of a Solute

a. The nature of the solvent

b. The nature of the solutec. The temperature of the solvent

y


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i. The nature of the solvent- The solubility of a solute differs indifferent solvents.

Example:

Only a little iodine can dissolve in water. Iodine candissolve very well in alcohol.

y


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ii. The nature of the solute

Different solutes have different solubility

in the same solvent.

Example:

At the same temperature, sodium chloride has alower solubility in water compared to copper chloride.


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D. RATE OF DISSOLVING

1. What are the factors affecting the rateof dissolving a solute?

a. Temperature

b. Rate of stirring

c. Size of solute particles


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i. Temperature

The higher the temperature of the solvent, the higher therate of dissolving.

Example:

We use hot water to maketea. One reason for this is

that hot water increasesthe rate of dissolving ofcertain substances in thetea leaves.


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ii. Rate of stirring

The higher the rate of stirring, the higher the rate ofdissolving.

Example:

The faster you stir the

soup, the faster the saltdissolves in it.


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iii. Size of solute particles

The smaller the size of the solute particles, the higher therate of dissolving.

Example:

Smaller pieces of palmsugar can dissolve in water

faster than a big piece ofit.

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Date :

Day :

Experiment : 5.3Title : Rate of dissolving

Aim : To determine the factors affecting the rate of

dissolving

Materials :

Apparatus :

A. Problem :

Hypothesis:

Manipulated variable:

Responding variable :

Fixed variable :

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Procedures: * draw figure 5.17, page 18

1. 100 cm of distilled water is measured and poured into

beaker A and B.

2. The water in a beaker B is heated until the temperature

reaches 70 C, as shown in figure 5.17

3. 1 g of fine salt is added to each beaker

4. The both mixtures are stirred at the same rate.

5. The observation is recorded in my lab.report.

Observation:

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B. Problem:

Hypothesis:

Manipulated variable: rate of stirring

Responding variable : rate of dissolving

Fixed variable : mass of fine salt, temperature of solvent,

volume of solvent

Procedures: * draw figure 5.18, page19

1. The apparatus is set up as shown in figure 5.18

2. The mixtures in beaker A is stirred slowly and the mixture

in beaker B is stirred quickly.

3. The observation is recorded in my lab. Report

Observation:

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C. Problem:

Hypothesis: The smaller size of solute particles,

the higher the rate of dissolving

Manipulated variable : coarse salt and fine salt

Responding variable : rate of dissolving

Fixed variable : mass of solute, temperature of

solvent, volume of solvent,

rate of stirring

Procedures:

1. The fine salt and coarse are used to carry out an

experiment to test the hypothesis.

2. The observation is recorded in my lab. Report.

Observation:

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Conclusion: the factors affecting the rate dissolving :

1. Temperature of solvent

2. Rate of stirring

3. Size of solute particles


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E. WATER AS A SOLVENT

Water is a good solvent. Almost everything can dissolve in it toproduce solutions. Therefore, water is also known as the

universal solvent.

Water acts as a medium in many chemical reactions inour body.

Water dissolves and transports many substances in ourbody such as digested food and waste products.

Water dissolves cleaning agents such as soap powder,dishwasher liquid and toilet cleaner.


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Water dissolves various substances. This enables us touse water in cooking and making drinks.

Water is used extensively in food industry as a solvent.

Water is used to prepare traditional and modern liquidmedicines.

Farmers use water to dissolve pesticides.

Water is needed in plants to transport food anddissolved minerals.


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F. ORGANIC SOLVENTS

Some substances cannot dissolve in water but they candissolve in organic solvents.

What are organic solvents?

Organic solvents are carbon compounds that are usedas solvents.

Examples:

Alcohol Turpentine Acetone


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1. We use many organic solvents in various products.

Alcohol

To produce lacquers and varnishes

To produce various types of ink

To prepare iodine solution (as an antiseptic)

To produce perfume

TurpentineTo produce paints

To remove paint stains

AcetoneTo produce nail polish

To remove nail polish


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2. Organic solvents are very useful to us.

a. They are volatile. Therefore, products such aspaints, lacquers, varnishes and inks become dry in ashort period of time.

b. They can dissolve many solutes that do not dissolvein water.

3. However, products containing organic solventsshould be handled carefully.

a. They are flammable and should be stored awayfrom heat.

b. They are toxic and carcinogenic (likely to causecancer).

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Date :

Day :

Title : Acid and alkali

A. Aim : to identify the properties of acid

and define acid

Material:

Apparatus:Procedures:

1. PH value

a. A piece of pH paper is dipped into a test

tube with 3cm of dilute hydrochloric acid.b. The resulting colour is compared with the

colour chart

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2. Taste

a. Some lemon juice is squeezed into a glass of

drinking water and taste it.

3. Corrosive nature

a. A piece of filter paper is put on a white tile

b. A drop of dilute hydrochloric acid is added

on both pieces of litmus paper.

4. Effect on litmus paper

a. A piece of blue litmus paper an a piece of red

litmus paper are put side by side on a white tile.b. A drop of dilute hydrochloric acid is added on

both pieces of litmus paper.

c. The observation is recorded in my lab.report.

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5. Reaction with metals

a. The surface of magnesium ribbon is cleaned with

sandpaper and is put into a clean test tube.

b. The test tube is filled with about 5 cm of dilute

hydrochloric acid and the observation is recorded.

c. The mouth of the test tube is covered with my

thumb for a few minutes as shown in figure 5.2

d. My thumb is removed and a lighted splinteris placed quickly at the mouth of the test tube.

The gas collected is identified.

Observation:

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Test Observation inference

pH value pH 1 pH value of acidis less than 7

Taste Sour taste Acid taste is sour

Corrosive nature A hole is formedon a filter paper

Acid is corrosive

Effect on litmuspaper

Turn the bluelitmus paper to

red

Acid turns theblue litmus paper

to redReaction withmetals

pop sound isheard.

React with metalto releasehydrogen

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B. To identify the properties of alkali and define alkali

Materials: pH paper, colour chart, dilute Natrium hydroxide,concentrated ammonium hydroxide, filter paper,

distilled water, blue litmus paper and red litmus

paper

Apparatus:test tubes, dropper, white tile

Procedures:

1. PH value

a. A piece of pH paper is dipped into a testtube with 3cm of dilute natrium hydroxide .

b. The resulting colour is compared with the

colour chart

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2. Feel

a. A dropper is used to added and a few drops of dilute

natrium hydroxide are added into a test tube half full

with distilled water . The test tube is shake.

b. The test tube is brought to the sink. One drop of

mixtures are placed onto my forefinger.

The solution is rubbed between my thumb andforefinger to feel it.

c. The solution off your finger is washed with a lot

of water.

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3.Corrosive nature

a. A piece of filter paper is put on a white tile.

b. A dropper is used to added a drop of concentrated

ammonium hydroxide onto a filter paper. The observation

is recorded.

4. Effect on litmus paper

a. A piece of blue litmus paper an a piece of red

litmus paper are put side by side on a white tile.

b. A drop of dilute natrium hydroxide is added onboth pieces of litmus paper.

c. The observation is recorded in my lab.report.

Observation:

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Test Observation inference

pH value pH 14 pH value of alkaliis less than 14

Feel Soapy The feel of alkaliis soapy

Corrosive nature A hole is formedon a filter paper

alkali is corrosive

Effect on litmuspaper

Turn the redlitmus paper to

blue

alkali turns thered litmus paper

to blue

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Discussion : the differences between acid and alkali

Test Acid alkali

pH value

Effect on litmus

paperCorrosivenature

Taste / feel

React to metal -

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Conclusion:

1. The properties of acid are:

a.b.

c.

d.

e.

2. The properties of alkali are

a.

b.

c.d.

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1. An acid is a substance that has a hydrogen

atom, which can be replaced by a metal

or ammonium.

2. Acid can be divided into two groups and

differences are shown below

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ACID

Organic acid Inorganic acid

Example

Acetic acidFormic acid

Lactic acid

Malic acid

Citric acidTannic acid

Tartaric acid

Example

Sulphuric acid

Nitric acid

Hydrochloric acid

Carbonic acid

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3.An acid exist in three state which are

a. solid tartaric acid

b. liquid

ethanoic acidc. gas hydrogen chloric

4. The properties of acids

a. Taste sour

b. Are corrosivec. Change blue litmus paper to red

d. Have pH values of less than 7

e. React with carbonates to release carbon dioxide

and form salt and water

acid + cabonates salt + water + carbon dioxide

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f. React with active metals to release hydrogen and form

salt.

g. React with alkalis to form salt and water

acid + metal salt + hydrogen

acid + alkali salt + water

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1. An alkalis is hydroxide or metal oxide that

dissolves in water.

2. Example: potassium hydroxide, sodiumhydroxide, calcium hydroxide, ammonium

hydroxide solutions.

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5.5 Acid and Alkali

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Neutralisation

acid + alkali salt water+

Note:

Different kinds of acids and alkalis will form different types of salt.

Neutralization is a process where

Where acid reacts with alkali, salt and water are formed.

5.6 Water Purification

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Natural Sources of Water

Natural Sources of Water

From Ocean From lakes, streams,rivers, ground water

(well) and rain Salty Not suitable forhuman consumption Fresh Water

But not pure, need to be purified

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a. Most pure

b. Has very little dissolved substances and alittle dust

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a. Not clean

b. Has a lot of dissolved substances and dirt

such as microorganisms and silt

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a. Has microorganisms and dissolved

substances

b. Cleaner than river

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a. Has the most substances of salt

b. Has the most of dirt.

5.7 Water Supply System

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Usage of Water

Usage of Water

Domestic Useof Water

Agricultural Use

of Water

Direct Use ofRivers and

Streams

Industrial Useof Water

Drinking Washing Watering

Plants

Irrigation Aquaculture Generate

HydroelectricPower

Recreation Transportation

Cooling Washing Disposal

of Waste

METHOD OF PURIFICATION

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Chlorination

Chlorine solution

METHOD OF PURIFICATION

Filtration

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Filtration

Muddy water

Fine sand

Coarse sand

Pebbles

Gravel

filtrate

Boiling

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filtrate

g

i ill i

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Distillation

Muddy

Water

Water

out

Water in

Liebig

condenser

Distilled

water

1 Water from natural sources have various

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1. Water from natural sources have various

impurities such as microorganisms, dissolved gases,

mineral salts and silt.

2. Water from natural sources must be purified so that it

save to drink and use.

3. Table shows the advantage and disadvantage of

water purification.

Water purification method advantage disadvantage

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Water purification method advantage disadvantage

a. Filtration

Only removesimpurities that arecoarse such assuspended substances.

Sand filters arecommonly used

Water is clearand freesuspendedparticles only

Water still hasmicroorganismsand dissolvedsubstances(such asmineral salts)

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b. Disti l lat ion

Prepares pure or

distilled water

Water is freefrom all

suspendedsubstances,microorganismsand dissolvedsubstances.

Water doesnot make

gooddrinkingbecause itdoes notcontain

dissolvedmineralwith ourbody need.

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c. Boiling and

chlorination

Only killsmicroorganisms in

water

Water is free from

dangerousmicroorganisms

Water still has

dissolvedsubstances andsuspendedsubstances.

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WATER TREATMENT PLANT

1. Refer to your text book pg. 36 and draw figure 5.34

PRESERVATION OF WATER QUALITY

1. Find out the ways to control water pollution on page 41.

chap 5 (2)

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