Water is the most abundant substance onearth.Like any other substances, water has its ownunique characteristics.
A. Physical Characteristics of Water1. Water can exist in three states:a. Solid b. Liquid c. Gas5.1 Physical Characteristics of Water
2. At room temperature, pure water is aa. colourless,b. odourless andc. tasteless.5.1 Physical Characteristics of Water
liquid solidFreezing point of water is the temperature atwhich water freezes into ice.5.1 Physical Characteristics of WaterFreezing Point of Water1.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 fixedpositions.Waterfreezes into ice!5.1 Physical Characteristics of Water
liquid gasesBoiling point of water is the temperature atwhich water boils and becomes steam.5.1 Physical Characteristics of WaterBoiling Point of Water1. 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 andleave 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 Water1. Impurities in water can change thephysical characteristics of water. Sometimesthe change is noticeable and sometimes it is not.5.1 Physical Characteristics of Water
PhysicalcharacteristicExampleTaste Purewateristastelessbutseawaterissalty.Odour Purewaterisodourless.Waterwithdecayedmatterhasanunpleasantsmell.Colour Purewateriscolourlessbutmuddywaterisbrownishincolour.Density Purewaterislessdensethanseawater.Electricalconductivity Purewaterwithafewdropsofsulphuricacidcanconductelectricity.Freezingpoint oPurewaterfreezesat0Cbutseawaterfreezesatalowertemperature.Boilingpoint oPurewaterboilsat100Cbutseawaterboilsatahighertemperature.2. Here are some examples:5.1 Physical Characteristics of Water
Hydrogen Oxygen5.2 Composition of WaterComposition of Water1. 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 solution5.2 Composition of Water
Hydrogen isreleased at thecathodeOxygen isreleased at theanode5.2 Composition of Water3. The volume of hydrogen released is alwaystwice the volume of oxygen released.
Hydrogen atomsEach water molecule consists of one atom of oxygen andtwo atoms of hydrogen.5.2 Composition of WaterWater is made up of one part of oxygen and two parts ofhydrogen.Oxygen atom4.
5. Therefore, scientists represent water with thefollowing formula:H2OH – Represents the hydrogen atom2 – Shows that there are two atoms of hydrogenO – Represents the oxygen atom5.2 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 Solubility5.4 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 solutionContains a littledissolved soluteCan dissolve a lotmore soluteConcentrated solutionContains a lot ofdissolved soluteCan dissolve a little bitmore soluteSaturated solutionContains the maximumamount of dissolved soluteCannot dissolve any moresoluteAll these solutions have a clear appearance5.4 Solution and Solubility2. 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, blood5.4 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 giventemperature.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 Solutea. The nature of the solventb. The nature of the solutec. The temperature of the solvent5.4 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 soluteDifferent 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. Temperatureb. Rate of stirringc. Size of solute particles5.4 Solution and Solubility
i. TemperatureThe 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 stirringThe 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 particlesThe 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 theuniversal 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 • Acetone5.4 Solution and SolubilitySome 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 varnishesAlcoholTurpentineAcetoneTo produce various types of inkTo prepare iodine solution (as an antiseptic)To produce perfumeTo produce paintsTo remove paint stainsTo produce nail polishTo remove nail polish5.4 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
3.An acid exist in three state which area. solid – tartaric acidb. liquid – ethanoic acidc. gas – hydrogen chloric4. 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 dioxideand form salt and wateracid + cabonates salt + water + carbon dioxide
f. React with active metals to release hydrogen and formsalt.g. React with alkalis to form salt and wateracid + metal salt + hydrogenacid + alkali salt + water
1.2.An alkalis is hydroxide or metal oxide thatdissolves in water.Example: potassium hydroxide, sodiumhydroxide, calcium hydroxide, ammoniumhydroxide solutions.
acid + alkali salt water+Note:NeutralisationNeutralization is a process whereWhere 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 WaterNatural Sources of WaterFrom Ocean• Salty• Not suitable forhuman consumptionFrom lakes, streams,rivers, ground water(well) and rain• Fresh Water• But not pure, need to be purified5.6 Water Purification
a. Most pureb. Has very little dissolved substances and alittle dust
a. Not cleanb. Has a lot of dissolved substances and dirtsuch as microorganisms and silt
a. Has microorganisms and dissolvedsubstancesb. Cleaner than river
a. Has the most substances of saltb. Has the most of dirt.
Usage of WaterUsage of WaterDomestic Useof Water• Drinking• Washing• WateringPlantsAgricultural Useof Water• Irrigation• Aquaculture •••Direct Use ofRivers andStreamsGenerateHydroelectricPowerRecreationTransportationIndustrial Useof Water• Cooling• Washing• Disposalof Waste5.7 Water Supply System
Chlorine solutionMETHOD OF PURIFICATIONChlorination
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.
b. Distillation Prepares pure ordistilled water Water is freefrom allsuspendedsubstances,microorganismsand dissolvedsubstances.Water doesnot makegooddrinkingbecause itdoes notcontaindissolvedmineralwith ourbody need.
c. Boiling andchlorinationOnly killsmicroorganisms inwater Water is free fromdangerousmicroorganisms Water still hasdissolvedsubstances andsuspendedsubstances.
WATER TREATMENT PLANT1. Refer to your text book pg. 36 and draw figure 5.34PRESERVATION OF WATER QUALITY1. Find out the ways to control water pollution on page 41.