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Transcript of 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!
5.1 Physical Characteristics of Water
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 Physical Characteristics of Water
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.
5.1 Physical Characteristics of Water
5 1 Ph i l Ch t i ti f W t
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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!
5.1 Physical Characteristics of Water
5 1 Ph i l Ch t i ti f W t
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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
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.
5.1 Physical Characteristics of Water
5 1 Physical Characteristics of Water
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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
5.1 Physical Characteristics of Water
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
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
5.2 Composition of Water
5 2 Composition of Water
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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.
5.2 Composition of Water
5 2 Composition of Water
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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.
5.2 Composition of Water
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
5.2 Composition of Water
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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
5.4 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.
5.4 Solution and Solubility
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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.