51221647 Form 2 Science Chapter 5
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Transcript of 51221647 Form 2 Science Chapter 5
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FORM 2
Science
Chapter 5
Water and solution
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Content
5.1 The physical properties of water
5.2 Composition of water
5.3 The process of water evaporation
5.4 Solutions and solubility of substances
5.5 Acid and alkali
5.6 Methods of purifying water
5.7 Water supply system
5.8 Preserving water quality
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5.1
The Physical Properties of Water
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The Physical Properties of Water
� Water is colourless, tasteless and odourlessliquid
� Water exists in three states, which are solid,liquid and gas
� Water can change from one state to another
� The density of water is 1 g/cm3
� Impurities in water can affect
freezing and boiling point
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Change of state of water
Liquid ( Water )
Gas (Vapour )
Freezing
Boiling //
Evaporation Solid ( Ice )
Condensation
Melting
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Kinetic theory of freezing point of water
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http://fizik-fizik.blogspot.com 9The temperature of steam is taken as the boiling point of water.
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Kinetic theory of boiling point of water
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5.2
Composition of Water
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Composition of Water
Water is a chemical compound that made up of two atoms of hydrogen and one atom of oxygen. (The ratio of
hydrogen to oxygen is 2:1)
Water can be break up into hydrogen and oxygen
through the process of electrolysis.electrolysis.
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In the process of electrolysis, oxygen is discharged at the anode (positive electrode) and hydrogen is
discharged at the cathode (negative electrode)
Electrolysis
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� Oxygen is tested with a glowing wooden splint. The wooden splint lights up when oxygen is present.
� Hydrogen is tested with a lighted wooden splint. ‘Pop’sound is produced when hydrogen is present
Confirmation test of water composition
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5.3
The Process of Water Evaporation
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Evaporation of water
• Water evaporation is a process where water molecules are released as vapourinto the air below boiling point of water.
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Application of evaporation of water
• The knowledge of evaporation applied in daily life.
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Factors that influence the rate of water evaporation
The higher the temperature, the faster the rate of the
water evaporation.
Surrounding temperature
The wider the surface area, the faster the rate of the
water evaporation.
Surface area
Water particles can escape easily when the
atmosphere is dry. Therefore, evaporation process
occurs faster
Air humidity
Moving air (wind) quicken the evaporation process
by blow away the water particles from the water surface
into the atmosphere.
Air movement
(wind)
DescriptionDescriptionFactorsFactors
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How to increase evaporation rate in daily life
• Drying hair using hair-
dryer ( the blower
increase air
movement )
• Spread out the
clothes to increase
surface area.
• Wet clothes dry under
hot sun.
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Differences between evaporation and boiling
Does not influenced by the
temperature surrounding, air
movement, air humidity and
surface area
Influenced by the temperature
surrounding, air movement, air
humidity and surface area
Occurs throughout the waterOccurs only at water surface
Vigorous processSlower process
Takes place at boiling point
only, that is 100 oC
Takes place at any
temperature below
boiling point
BoilingBoilingEvaporationEvaporation
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5.4
Solutions and Solubility of Substances
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Solvent, solute and solution
Solvent:Solvent:
A liquid that dissolve a substance (solute)
Solute:Solute:
A substance that soluble or dissolve in a solvent
Solution:Solution:
A mixture of one or more solutes that dissolved in solvent
Dissolves in
to form
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Dilute solution, concentrated solution and saturated solution
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The solubility of solutes
� The solubility is the number of gram of solute that can dissolve in 100 ml of water at a specific temperature, to form a saturated solution.
� For example, the solubility of potassium nitrate in water is 90 g per 100 ml of water at 50 oC. This means that 90 g of potassium nitrate salt are dissolved in 100 ml of water at a temperature of 50 oC to form a saturated solution of potassium nitrate.
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The solubility of solutes
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The factors that influence the solubility rate of substances
The higher the temperature, the faster the solute can dissolve in the solvent
Temperature
of solvent
Solutes dissolve more easily in a bigger volume of solvent
Volume of solvent
Solutes dissolve more easily if stirredStirring
The smaller the size of the solute, the faster it can dissolve in the solvent
Size of the solutes
Description Factor
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Water as a solvent
Water is known as universal solvent because water can dissolve many types of substances.
The importance of water as a universal solvent.
i. Dissolve oxygen and food so that these can be transfer to body cells.
ii. Most chemical reactions in humans body need water as a solvent.
iii. Dissolve carbon dioxide and oxygen for aquatic organisms.
iv. Dissolves mineral salts and this enables the roots of plants to absorb.
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Suspension
• The suspended substances is a substance that
do not dissolve in water.
• When a suspended substances is added into a
solvent, it forms a suspension
• A suspension can be separated by filtration.
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Organic solvent
• There are also substances that do not dissolves in water but dissolve in organic solvent such as ether, benzene and alcohol
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Organic solvent
to stick plastic
substances
PlasticChloroform
to stick rubber sheetsRubber, greaseBenzene
to dilute paint to make it
easier to use
Grease, paint, tarTurpentine
to make cosmetics such as lipstick and nail polish
Oils, fats, greaseEther
Uses
Substances that can be dissolves
Organic solvent
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5.5
Acid and Alkali
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Acid and alkaline
Acid and alkali will show their properties in the presence of water
In the presence of water
a) acid will change the colour of
litmus paper from blue to red
b) alkali will change the colour of litmus paper from red to blue
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Acid
Acid exists in three states, which are solid, liquid and gas.
Acid are chemical substances that contain hydrogen atom.
Weak acids usually found in food.
Examples are lactic acid, tannic acid, acetic acid, formic acid .
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Sources of acids
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The properties of acid
1. Taste sour
2. Corrosive
3. Have pH value smaller than 7.
4. Change the colour of litmus paper from blue to red
5. React with carbonates to form salt and water and release carbon dioxide
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The properties of acid
6. React with reactive metal (magnesium/aluminium) to form salt and release hydrogen
7. React with alkali to form salt and water (neutralisation process).
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• Alkali is a hydroxide or metal oxide that dissolves in water.
• Examples of alkali:
Alkaline
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1. Taste bitter
2. Corrosive
3. Have pH value greater than 7
4. Feel slippery like soap when touched
5. Change the colour of litmus paper from red to blue
The properties of alkali
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6. React with ammonium salts to give off ammonia gas when heated.
Examples:
sodium hydroxide + ammonium chloride �
sodium chloride + water + ammonia gas
7. React with acids to form salt and water (neutralisationprocess)
The properties of alkali
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pH values
Click here to watch video
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Neutralisation
• Neutralisation is a chemical reaction in which an acid and an alkali react to form salt and water.
acid + alkali ���� salt + water
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Titration
• Titration is a method used for neutralisation.
• At the neutralisation point, all the acid completely reacts with the alkali and the solution has a pH value of 7
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5.6
Methods of Purifying of Water
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Natural source of water
• Natural water contains impurities and needs to be treated before it is safe for drinking.
• Example of natural source of water :
rivers, well, rain , pond, sea, lake, stream..
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Methods of water purification
1. Boiling
2. Chlorination
3. Filtration
4. Distillation
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Boiling
• Use heat to kills the microorganisms in the water.
• Advantages
Water is free from dangerous microorganisms
• Disadvantages
Dissolved impurities and suspended impurities still exists in water
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Chlorination
• Chlorine is added to water to kill microorganisms
• Advantages
Water is free from dangerous microorganism
• Disadvantages
Dissolved impurities and suspended impurities still exists in water
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Filtration
• To remove suspended impurities from the water
• Advantages
Water is clear and free from suspended particles
• Disadvantages
Dissolved impurities and
microorganisms still exists in water
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Distillation
• To remove suspended impurities and dissolved impurities from the water
• AdvantagesWater is free from all microorganisms, suspended and
dissolved impurities
• Disadvantages
Does not contain minerals which our bodies need.
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Distillation
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The application of water purification methods in our daily life
(a) Boiling– Piped water is boiled before drinking
(b) Filtration– River water is filtered before being supplied to consumers house
(c) Distillation– Clinics and hospitals use distilled water to prepared medicines
(d) Chlorination– Chlorine is added to the water in the swimming pool to kill microorganisms
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5.7 Water Supply System
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Water used
• River water and rain water is our main source of water
• The water will then be pump to water purification plants to be purified before it is supplied to consumers home.
• There are several ways to save water
(a) Make use of recycled water
(b) Beware of pipe leakage
(c) Turn off the tap immediately when not in use
(d) Do not turn on the tap full
(e) Wash cloths in big quantities
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5.8
Preserving Water Quality
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Water pollution
• Water pollution occurs when water is
contaminate with waste product.
• Polluted water is not suitable for living
organisms.
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Domestic waste
• Effect of water pollutants
Contains dangerous microorganisms that causes diseases such as cholera.
• Ways to control water pollution
i. Dispose the rubbish in a proper way
ii . Make use of recycle materials instead of using plastic materials
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Agricultural waste
• Effect of water pollutants
Poison the aquatic organisms and affect human’s health
when eaten.
• Ways to control water pollution
Reduce the used of fertilisers and pesticides
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Industrial waste
• Effect of water pollutantsRadioactive wastes and chemical residues will destroy body cells and causes skin cancer
• Ways to control water pollution
Enforce the law strictly to prevent the factories from letting harmful chemical residues into the open drain
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Oil spills
• Effect of water pollutants
Kills marine life thus affecting the income of fisherman .
• Ways to control water pollution
Impose heavy penalties and fines to the ships which
found to pollute the sea
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Waste water today
- Live in a desert tomorrow.