form 2 science Chapter 5

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 http://fizik-fizik.blogspot.com

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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 odourless liquid 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 http://fizik-fizik.blogspot.com

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Change of state of water Gas (Vapour )

Boiling //

Solid ( Ice )

Evaporation

Condensation

Me l ti n g

Fr ee zin g

Liquid ( Water ) http://fizik-fizik.blogspot.com

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Kinetic theory of freezing point of water

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The temperature of steam is taken as the boiling point of water. http://fizik-fizik.blogspot.com

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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.

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Electrolysis In the process of electrolysis, oxygen is discharged at the anode (positive electrode) and hydrogen is discharged at the cathode (negative electrode)

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Confirmation test of water composition
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

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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 vapour into 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 Factors

Description

Surrounding temperature

The higher the temperature, the faster the rate of the water evaporation.

Air movement (wind)

Moving air (wind) quicken the evaporation process by blow away the water particles from the water surface into the atmosphere.

Air humidity

Water particles can escape easily when the atmosphere is dry. Therefore, evaporation process occurs faster

Surface area

The wider the surface area, the faster the rate of the water evaporation. http://fizik-fizik.blogspot.com 19

How to increase evaporation rate in daily life

• Drying hair using hairdryer ( 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 Evaporation

Boiling

Takes place at any temperature below boiling point

Takes place at boiling point only, that is 100 oC

Slower process

Vigorous process

Occurs only at water surface

Occurs throughout the water

Influenced by the temperature surrounding, air movement, air humidity and surface area

Does not influenced by the temperature surrounding, air movement, air humidity and http://fizik-fizik.blogspot.com surface area

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5.4 Solutions and Solubility of Substances

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Solvent, solute and solution Solute: A substance that soluble or dissolve in a solvent

Dissolves in

Solvent: A liquid that dissolve a substance (solute)

to form

Solution: A mixture of one or more solutes that dissolved in solvent http://fizik-fizik.blogspot.com

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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 Factor

Description

Temperature of solvent

The higher the temperature, the faster the solute can dissolve in the solvent

Size of the solutes

The smaller the size of the solute, the faster it can dissolve in the solvent

Stirring

Solutes dissolve more easily if stirred

Volume of solvent

Solutes dissolve more easily in a bigger volume of solvent http://fizik-fizik.blogspot.com

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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. ii. iii. iv.

Dissolve oxygen and food so that these can be transfer to body cells. Most chemical reactions in humans body need water as a solvent. Dissolve carbon dioxide and oxygen for aquatic organisms. Dissolves mineral salts and this enables the roots of plants to absorb. http://fizik-fizik.blogspot.com

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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 Organic solvent

Substances that can be dissolves

Uses

Ether

Oils, fats, grease

to make cosmetics such as lipstick and nail polish

Turpentine

Grease, paint, tar

to dilute paint to make it easier to use

Chloroform

Plastic

to stick plastic substances

Benzene

Rubber, grease

to stick rubber sheets

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5.5 Acid and Alkali

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Acid and alkaline Acid and alkali will show their properties presence of water

in the

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 http://fizik-fizik.blogspot.com

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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 . http://fizik-fizik.blogspot.com

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Sources of acids

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The properties of acid 1. 2. 3. 4.

Taste sour Corrosive Have pH value smaller than 7. Change the colour of litmus paper from blue to red 5. React with carbonates to form salt and water and release carbon dioxide http://fizik-fizik.blogspot.com

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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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Alkaline • Alkali is a hydroxide or metal oxide that dissolves in water. • Examples of alkali:

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The properties of alkali 1. 2. 3. 4. 5.

Taste bitter Corrosive Have pH value greater than 7 Feel slippery like soap when touched Change the colour of litmus paper from red to blue

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The properties of alkali 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 (neutralisation process)

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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 http://fizik-fizik.blogspot.com

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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 http://fizik-fizik.blogspot.com

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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 http://fizik-fizik.blogspot.com

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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 http://fizik-fizik.blogspot.com

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Distillation

• To remove suspended impurities and dissolved impurities from the water • Advantages Water is free from all microorganisms, suspended and dissolved impurities • Disadvantages http://fizik-fizik.blogspot.com 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 http://fizik-fizik.blogspot.com

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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 http://fizik-fizik.blogspot.com

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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

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Effect of water pollutants Contains dangerous microorganisms that causes diseases such as cholera.

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Ways to control water pollution i. Dispose the rubbish in a proper way ii . Make use of recycle materials instead of using plastic materials http://fizik-fizik.blogspot.com

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Agricultural waste

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Effect of water pollutants Poison the aquatic organisms and affect human’s health when eaten.

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Ways to control water pollution Reduce the used of fertilisers and pesticides http://fizik-fizik.blogspot.com

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Industrial waste

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Effect of water pollutants Radioactive wastes and chemical residues will destroy body cells and causes skin cancer

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Ways to control water pollution Enforce the law strictly to prevent the factories from letting harmful chemical residues into the open drain http://fizik-fizik.blogspot.com

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Oil spills

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Effect of water pollutants Kills marine life thus affecting the income of fisherman .

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Ways to control water pollution Impose heavy penalties and fines to the ships which found to pollute the sea http://fizik-fizik.blogspot.com

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Waste water today - Live in a desert tomorrow.

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