Chapter 5 Water and Solution
Nov 18, 2014
Chapter 5Water and Solution
Water is the most abundant substance on earth.
Like any other substances, water has its ownunique characteristics.
A. Physical Characteristics of Water
1. Water can exist in three states:
a. Solid b. Liquid c. Gas
5.1 Physical Characteristics of Water
2. At room temperature, pure water is a
a. colourless,
b. odourless and
c. tasteless.
5.1 Physical Characteristics of Water
liquid solid
Freezing point of water is the temperature atwhich water freezes into ice.
5.1 Physical Characteristics of Water
Freezing Point of Water
1.Water changes from liquid to solid at its freezingpoint.
2. The freezing point of pure water is 0 oC.
3. The temperature remains constant at 0 oC until waterfreezes completely.
5.1 Physical Characteristics of Water
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.
Waterfreezes into ice!
5.1 Physical Characteristics of Water
liquid gases
Boiling point of water is the temperature atwhich water boils and becomes steam.
5.1 Physical Characteristics of Water
Boiling Point of Water
1. Water boils at its boiling point.
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
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 liquid’s surface.
Waterbecomessteam!
5.1 Physical Characteristics of Water
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
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
Physicalcharacteristic
Example
Taste Purewateristastelessbutseawaterissalty.
Odour Purewaterisodourless.Waterwithdecayedmatterhasanunpleasantsmell.
Colour Purewateriscolourlessbutmuddywaterisbrownishincolour.
Density Purewaterislessdensethanseawater.
Electricalconductivity
Purewaterwithafewdropsofsulphuricacidcanconductelectricity.
Freezingpoint o
Purewaterfreezesat0Cbutseawaterfreezesatalowertemperature.
Boilingpoint o
Purewaterboilsat100Cbutseawaterboilsatahighertemperature.
2. Here are some examples:
5.1 Physical Characteristics of Water
Hydrogen Oxygen
5.2 Composition of Water
Composition of Water
1. Water is a compound. It is made of two differentelements.
Water
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
Hydrogen isreleased at the
cathode
Oxygen isreleased at the
anode
5.2 Composition of Water
3. The volume of hydrogen released is alwaystwice the volume of oxygen released.
Hydrogen atoms
Each water molecule consists of one atom of oxygen andtwo atoms of hydrogen.
5.2 Composition of Water
Water is made up of one part of oxygen and two parts ofhydrogen.
Oxygen atom
4.
5. Therefore, scientists represent water with thefollowing formula:
H2OH – Represents the hydrogen atom
2 – Shows that there are two atoms of hydrogen
O – Represents the oxygen atom
5.2 Composition of Water
Applying the principle of water evaporationIn our daily life.
1. To drying clothes2. To drying hair3. To drying agricultural produce4. To drying fish and prawn5. To cooling the body6. To producing the common salt
Solution and Solubility
5.4 Solution and Solubility
1. What is a solution?
• A solute is thesubstance that dissolves.
• A solvent is thesubstance that the solutedissolves in.
5.4 Solution and Solubility
Dilute solution
Contains a littledissolved solute
Can dissolve a lotmore solute
Concentrated solution
Contains a lot ofdissolved solute
Can dissolve a little bitmore solute
Saturated solution
Contains the maximumamount of dissolved solute
Cannot dissolve any moresolute
All these solutions have a clear appearance
5.4 Solution and Solubility
2. Depending on the amount of solutes insolutions, there are three types of solutions.
Solution
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
5.4 Solution and 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 sodiumchloride in 100 g of water at 20 oC.
5.4 Solution and Solubility
2. Factors Affecting the Solubility of a Solute
a. The nature of the solvent
b. The nature of the solute
c. The temperature of the solvent
5.4 Solution and Solubility
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.
5.4 Solution and Solubility
ii. The nature of the solute
Different solutes have different solubilityin the same solvent.
Example:
At the same temperature, sodium chloride has alower solubility in water compared to copper chloride.
5.4 Solution and Solubility
1. What are the factors affecting the rateof dissolving a solute?
a. Temperature
b. Rate of stirring
c. Size of solute particles
5.4 Solution and Solubility
i. Temperature
The higher the temperature of the solvent, the higher therate of dissolving.
:
We use hot water to maketea. One reason for this isthat hot water increasesthe rate of dissolving ofcertain substances in thetea leaves.
5.4 Solution and Solubility
ii. Rate of stirring
The higher the rate of stirring, the higher the rate ofdissolving.
:
The faster you stir thesoup, the faster the saltdissolves in it.
5.4 Solution and Solubility
iii. Size of solute particles
The smaller the size of the solute particles, the higher therate of dissolving.
Smaller pieces of palmsugar can dissolve in waterfaster than a big piece ofit.
5.4 Solution and Solubility
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.
5.4 Solution and Solubility
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.
5.4 Solution and Solubility
• Alcohol • Turpentine • Acetone
5.4 Solution and Solubility
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:
1. We use many organic solvents in various products.
To produce lacquers and varnishes
Alcohol
Turpentine
Acetone
To produce various types of ink
To prepare iodine solution (as an antiseptic)
To produce perfume
To produce paints
To remove paint stains
To produce nail polish
To remove nail polish
5.4 Solution and Solubility
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).
5.4 Solution and Solubility
1.
2.
An acid is a substance that has a hydrogenatom, which can be replaced by a metalor ammonium.
Acid can be divided into two groups anddifferences are shown below
ACID
Organic acid
ExampleAcetic acidFormic acidLactic acidMalic acidCitric acidTannic acidTartaric acid
Inorganic acid
ExampleSulphuric acidNitric acidHydrochloric acidCarbonic acid
3.An acid exist in three state which area. solid – tartaric acidb. liquid – ethanoic acidc. gas – hydrogen chloric
4. The properties of acidsa. Taste sourb. Are corrosivec. Change blue litmus paper to redd. Have pH values of less than 7e. React with carbonates to release carbon dioxide
and form salt and water
acid + cabonates salt + water + carbon dioxide
f. React with active metals to release hydrogen and formsalt.
g. React with alkalis to form salt and water
acid + metal salt + hydrogen
acid + alkali salt + water
1.
2.
An alkalis is hydroxide or metal oxide thatdissolves in water.
Example: potassium hydroxide, sodiumhydroxide, calcium hydroxide, ammoniumhydroxide solutions.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
neutral
Acidity increases Alkalinity increases
acid + alkali salt water+
Note:
Neutralisation
Neutralization is a process where
Where acid reacts with alkali, salt and water are formed.
Different kinds of acids and alkalis will form different types of salt.
5.5 Acid and Alkali
Natural Sources of Water
Natural Sources of Water
From Ocean
• Salty• Not suitable forhuman consumption
From lakes, streams,rivers, ground water
(well) and rain
• Fresh Water• But not pure, need to be purified
5.6 Water Purification
a. Most pure
b. Has very little dissolved substances and alittle dust
a. Not clean
b. Has a lot of dissolved substances and dirtsuch as microorganisms and silt
a. Has microorganisms and dissolvedsubstances
b. Cleaner than river
a. Has the most substances of salt
b. Has the most of dirt.
Usage of Water
Usage of Water
Domestic Useof Water
• Drinking• Washing• Watering
Plants
Agricultural Useof Water
• Irrigation• Aquaculture •
••
Direct Use ofRivers and
Streams
GenerateHydroelectricPowerRecreationTransportation
Industrial Useof Water
• Cooling• Washing• Disposal
of Waste
5.7 Water Supply System
Chlorine solution
METHOD OF PURIFICATION
Chlorination
Filtration
Muddy water
Fine sand
Coarse sand
Pebbles
Gravel
filtrate
filtrate
Boiling
Distillation
MuddyWater
Waterout
Water in
Liebigcondenser
Distilledwater
1. Water from natural sources have variousimpurities such as microorganisms, dissolved gases,mineral salts and silt.
2. Water from natural sources must be purified so that itsave to drink and use.
3. Table shows the advantage and disadvantage ofwater purification.
Waterpurificationmethod
advantage disadvantage
a. FiltrationOnlyremovesimpuritiesthatarecoarsesuchassuspendedsubstances.Sandfiltersarecommonlyused
Waterisclearandfree
suspendedparticlesonly
Waterstillhasmicroorganismsanddissolved
substances(suchasmineralsalts)
b. Distillation
Prepares pure ordistilled water
Water is freefrom allsuspendedsubstances,microorganismsand dissolvedsubstances.
Water doesnot makegooddrinkingbecause itdoes notcontaindissolvedmineralwith ourbody need.
c. Boiling and
chlorination
Only killsmicroorganisms inwater
Water is free fromdangerousmicroorganisms
Water still hasdissolvedsubstances andsuspendedsubstances.
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.