chapter 5 versi bi

8/10/2019 Chapter 5 Versi Bi

1/66

5.1 Physical And Chemical Changes

Perubahan K im ia Dan Perub ahan Fizik

Topic 5 Energy And Chemical

Changes

ITeach Science Form 4


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Physical And Chemical Changes

Topic 5 Energy And Chemical Changes


Physical changes Chemical changes

Involve changes in physical properties

such as

..

Produce

Normally, change is only

and is

Involve little change of energy.

No change in chemical properties and

composition of substance.

Normally, change is fixed and is

reversible.

Involves a lot of change of energy.

Change in properties

and composition of substance.


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Example Of Physical Changes - Changes

Of Physical State

Ice Water H2o (steam)

No new substance is formed

Processes are reversible.

Composition of substance remain the same.


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Example Of Physical Changes - Dissolving

a solid in water

No new substance is formed.

Glass rod

Beaker

Sugar

Water

Process is reversible.


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Example Of Physical Changes - Crystallisation Of

Sugar/Salt From Its Saturated Solution

Water is evaporated and colourless crystal of sugar/salt are formed.

Evaporating dish Saturated solution of

sugar/salt is cooled at room

temperature.

Composition of substance remains the same


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No new substance is formed.

Composition of substance remain the same.




Example Of Physical Changes - Heating Of Iodine Crystals

In A Closed Container

Iodine crystals sublime and form purple vapour when heated.

The purple vapour sublimes and forms black crystal again.

XXXXXXXXXX

Ice cubes Watch glass

Iodine crystalBeaker


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Products have different chemical properties

New substances are produced.

Process is irreversible.

Example Of Chemical Changes

Sodium React With Water

Water

Heat is released

Sodium + water Sodium hydroxide + hydrogen + heat

.. ..





Product have different chemical properties




...............................................

Charcoal + oxygen Carbon diokside + ash

Fire

Charcoal Ash


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Iron can be attracted by magnet.

Sulphur oxide cannot be attracted by magnet

Product has different chemical properties


................................................

Iron (Black) Iron sulphide (Black)+ Sulphur (Yellow)heat

Pipeclay triangle

Crucible

Mixture of iron filling

and sulphur

Heat


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Iron nail has shining surface.

Iron oxide (rust) is brownish substance.

Iron oxide is new substance with different chemical properties


..........................................

Iron Iron oxide (rust)+ Oxygen Water+

Test tube

Water

Iron nail


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Products have different chemical properties

Products are new substances.


Reaction Between Zinc And Copper (II) Sulphate Solution

Zinc

(shining metal)+ Copper (II)

sulphate

(blue solution)

Zinc

sulphate

(colourless solution)

Test tube

Cooper (II) sulphate solution

Zinc

Copper

(brownish colour)

+


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Products have different chemical composition



.........................................

. + Water +

Co2

..light

d h l h


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Physical

Changes In

Daily Life

Producing sugar

crystal from

sugar cane juice.

Crushing

onion




T i 5 E A d Ch i l Ch





Rusting of iron gate

Cooking rice

Respiration

Chemical

Changes In

Daily Life

Milk turning sour


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5.2 Heat Change In Chemical Reactions

Perubahan Haba Dalam Tindak Balas Kim ia


Changes


T i 5 E A d Ch i l Ch


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Heat energy is ............................... tothe surrounding

Heat energy is.............................fromthe surrounding.

Chemical reaction can be

classified into two groups




Heat Change In Chemical Reactions

Chemical reaction involve heat change either heat is absorbed or release.

Heat energy is .. when bond in the reactants are breaking.

Heat energy is.. when new bonds are formed in the product.

Example :

Sodium hydroxide dissolves in water

(feel hot).

Example :

Ammonium chloride dissolves in

water (feel cold).






Comparison Between Exothermic Reactions And Endothermic Reactions

Exothermic Reactions

Heat energy is released to the surroundings.

Reactant will .

to the surrounding.

As the heat energy is released, the total

energy content in the product is less than the

total energy content of the reactants

Example :

Combustion Neutralisation

Reaction between reactive metal and

water

Energy

level

Heat energy released

Products

Endothermic Reactions

Heat energy is absorbed from thesurroundings.

Reactant will from

the surrounding.

As the heat energy is absorbed, the total

energy content in the product is more than

the total energy content of the reactants

The temperature of the surrounding.. Container and solution

become cold.

Energy

level

Heat energy

absorbedReactants

Example

Photosynthesis

Decomposition by heat

The temperature of the surrounding. Container and solution

become hot.

reactants Products






Chemical Reactions In Industry

Reactions in industry usually occur under optimum conditions so that the time of

reaction is very short and the cost involved is minimal.

The production of ..

The production of .

Example of chemical reactions in industry


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The Production Of Sulphuric Acid (Contact Process)

First Stage

+

Sulphur

dioxide

Second

Stage+

Sulphur

trioxide

(from excess air)

The production of sulphur trioxide is reversible

Forward reaction is an exothermic reaction. Heat is released.

Backward reaction is an endothermic reaction. Heat is absorbed.

Third Stage +

Oleum +

Both steps release heat

energy. Optimum conditions

are maintained.


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5.3 The Reactivity Series Of Metals

Sir i Kereakt i fan Logam


Changes




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Reactivity Series Of Metals


Reactivity Of Metals With Water

Metals React With Water At Different

Rates



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+ hydrogen




Reactive metals react with water and release a lot of heat

The product are hydrogen solution which is alkaline and hidrogen gas is

released.

Potassium + Water + hydrogen

How Reactive Metals React With Water ?

Example

Reactivitydecrease

+ +

Sodium + Water + hydrogen

Calcium + Water + hydrogen

Magnesium + Water



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How Less Reactive Metals React With Water ?

Less reactive metals react with steam / hot water to produce matal

hydroxide + hydrogen

Aluminium + WaterAluminium

hydroxide+ hydrogen

Metal Hot waterMetal

hydroxideHydrogen+ +

Example

Reactivitydecrease

Zinc + WaterZinc

hydroxide+ hydrogen



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p gy g

How Less Reactive Metals React With Water ?

Unreactive metals do not react with either

cold water or hot water / steam.

Example :

..............................................................................



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p gy g


Experiment To Study The Reactivity Of Metal With Water

Variable : _____________________________________

_____________________________________

_____________________________________

Constant : Volume of water / mass of metal

Manipulated : Type of metal.

Responding : Reactivity of metal.

Aim: ____________________________________To Study The Reactivity Of Metal With Water

Conclusion:

Materials _____________________________________

andapparatus : ____________________________________

Magnesium / Aluminium / zinc / Copper reacts with water

Hypothesis: ____________________________________Metals show different reactivity when reacting with water

Observation:



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p gy g

Reactive metals react very..with dilute acids to produce .and ..

Less reaction metal react . vigorously with dilute acids to produce salts and

hydrogen.

Metal + acid salt + hydrogen

Calcium + Dilute Hydrochloride Acid ...+ Hydrogen

Magnesium + Dilute Nitric Acid .+ Hydrogen

Non-reactive metals such as.., and ..

do not react with dilute acids.

Reactivity Of Metals With Dilute Acid

Example

Example



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Experiment To Study The Reactivity Of Metals With Dilute Acid

Variable: _____________________________________

_____________________________________

_____________________________________

Constant : Volume and concentration of acid.



Aim: ____________________________________To study the reactivity of metals with dilute acid.

Observation :

Materials _____________________________________

and apparatus : ____________________________________

Magnesium, aluminium, zinc and copper (All in powder form).

Hypothesis: ____________________________________Metals show different reactivity when reacting with dilute acid.

Conclusion :



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Metals react with oxygen to form oxides of metals when burnt in air


Reactivity Of Metals With Oxygen

Metal + Oxygen Metal oxide

Reactivity of metals with oxygen is determined by the brightness of the flame that

is produced.

Reactive metals burn brightly with different coloured flames when react with oxygen.

Magnesium + Oxygen Magnesium oxide

Less reactive metals glow dimly when react with oxygen.

Zinc + Oxygen Zinc oxide

Non reactive metal do not react when burn in air.

Silver, gold and platinum




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To Study The Reactivity Of Metals With Oxygen

Variable : _____________________________________

_____________________________________

_____________________________________

Constant : Mass / quantity of metal.



Aim: _____________________________________To study the reactivity of metals with oxygen.

Conclusion : ____________________________________

Materials : _____________________________________Magnesium, aluminium, zinc and copper (All in powder form).

Hypothesis: ____________________________________Different metals show different reactivity with oxygen.

Observation:Object Mass (g) Density (gcm3) Ability to sink / float

Iron

Plastic

Rubber

Lead

Wood

Apparatus : _____________________________________



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No reaction


Comparison Of Reactivity Of Metal With Water, Dilute Acid And Oxygen

Reactivity MetalReaction with

water

Reaction with

dilute acids

Reaction with

oxygen

React vigorously

with cold water

React very

violently and

dangerous (may

explode)

Burn very vigorous

and brightly

React with hot

water or steam

React with dilute

acid

Do not react with

cold water or hot

water

React slowly withdilute acid

Burn steadily if

metal are strongly

heated

Glow dimly

Most

reactive

Least

reactive

Do not react with

dilute acid




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The Reactivity Series Of Metals

Potassium

Sodium

Calcium

Magnesium

Aluminium

Zinc

Iron

Tin

Lead

Copper

Silver

Gold

Most reactive

Least reactive


is based on the reactivity of metal with oxygen



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If carbon is .. reactive than other metal, no glow or flame will be seen whenthe mixture of carbon and the metal oxide is heated.


Position Of Carbon In Reactivity Series Of Metals

Carbon is non-metallic element but it can reacts with oxygen to form carbon dioxide.

Position of carbon in the reactivity series can be determined by comparing its reactivity

towards oxygen with other metals.

Carbon + Oxygen Carbon dioxide


If carbon is . reactive than other metal, glow or bright flame will be seen when the

mixture of carbon and the metal oxide is heated. The metal loses its oxygen to carbon.

Carbon is more reactive than zinc

Metal oxide + carbon Metal + carbon dioxideheated

Example : Zinc oxide + carbon Zinc + carbon dioxideheated

Metal oxide + carbon No sign of reactionheated

Example : Aluminium oxide + carbon No sign of reactionheated

Carbon is less reactive than aluminium



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To Determine The Position Of Carbon In The Reactivity

Series

Variable : ___________________________________________

____________________________________________

____________________________________________

Constant : Amount of carbon and metal oxide used.

Manipulated : Type of metal oxide.

Responding : Reactivity of reaction.

Aim: ____________________________________________To study the position of carbon in the reactivity series.

Conclusion : ___________________________________________

Materials : ____________________________________________Copper oxide, iron oxide, zinc oxide, aluminium oxide and carbon (all in powder form).

Hypothesis: ____________________________________________Carbon is placed in between aluminium and zinc in the reactivity series of metals.

Observation: Object Mass (g) Density (gcm3) Ability to sink / floatIron

Plastic

Rubber

Lead

Wood

Apparatus : ____________________________________________Set up

Carbon is placed between zinc and aluminium in the reactivity series of metal.

Hypothesis is accepted.


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5.4 Application Of Reactivity Series Of Metals

Ap l ikasi Sir i Kereakt i fan Logam


Changes




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of metal ore

using carbon for less reactive

metals which are less reactive than

carbon.


Application Of Reactivity Series Of Metals

Most metals in the Earths crust are in compounds form and in ores form

which consist of other impurities.

Metal Ore Composition

Iron Iron oxide

Aluminium Aluminium oxide

Tin Tin oxide

Zinc Zinc sulphide

Ores are separated from impurities by physical separation followed by

extraction of metal from the ores.

Extraction of metals can be carried out by two methods

. of molten ore of

metals for reactive metals which

are more reactive than carbon




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Extraction Of Metals From Their Ores

Reactivity Metal Method Of Extration

Electrolysis of molten ore.

-Carbon

Extraction by heating mixture

of ore and carbon.

Extraction by heating the ore

in air.

Copper

Mercury

Exist as free elements in the

Earthscrust.

Silver

Gold

More reactive

Less reactive




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Extraction Of Tin From Its Ore

Blast Furnace

Tin ore is mined and washed to remove impurities by

floatation process.

Tin ore is heated to remove sulphur and arsenic in it.

Tin ore is then mixed with coke (carbon) and limestone

at 1300C - 1400C in a blast furnace.

Molten tin and molten slag flow to the bottom of the

furnace. Slag float on molten tin and both are removed

through an outlet pipe.

Molten tin is flowed into mould and left harden and

cool as ingots.

Carbon remove oxygen from ore [tin(IV) oxide].

Limestone is to react with impurities in the tin ore

to form slag.

Waste

gas

Tin core

+ coke

+ limestone

Hotair

Slag

Hotair

Molten

tin




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The Importance Of The Reactivity Series

Reactivity series of metal are arranged according to their reactivity with

oxygen.

Importance

To forecast the reactivity of particular metal, and able to

decide the method of storing the metal.

To predict whether reaction will take place between a metal

with an oxide of another metal.

To determine the method of extraction of certain metal from

its ore.



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5.5 Electrolysis

Elektrol is is


Changes




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Electrolysis

Electrolysis is a reaction which uses electrical energy to break down chemical compound

(liquid state) into its elements.

Electricity Chemical reaction

Causes

Apparatus set-up

+ -

A

+ -

Supply electrical energy.

Rheostat

Controls the flow of electriccurrent.

..

Conductor which flow

electrical current into and out

of electrolyte.

.

- Substance in molten or aqueous

form which allow electrical current flows.

- Electrolyte consists of positively charged ion called cation

and negatively charged ion called anion.

.

Positive electrode is connected

to the positive terminal of

battery.

Measure electric current.

Electrolysis

.

Negative electrode is

connected to the terminal of

the battery.



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Electrolysis Of Molten Lead Bromide

During electrolysis :

Positively charged ions (cations) are attracted to the

cathod while negatively charged ion (anions) are attracted

to anode.

At cathode

A shiny silver solid is deposited at the cathode.

Cation (Lead ion) receive electrons from the cathode.

Lead ion + electron Lead atom

Anion (bromide ion) release electrons to the anode.

Bromide ion Bromine atom + electron.

At anode

2 Bromide atoms Bromine molecule (gas).

A brown vapour is given off at the anode.

Ammeter shows current flow by deflecting the pointer.

BatteriesAmmeter

Carbon rod

(Anode)

Molten lead

bromide

(electrolyte)

Carbon rod

(Cathode)

Heat

Electrolysis

A

+ -


l l i


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Oxide ion release electrons

to the anode.

Oxygen gas is released.


Other Examples Of Electrolysis

Electrolyte

Ions

Cathode Anode

Copper (II)

chloride

Copper ion receives

electrons from the

cathode. Brown solid

copper deposited.

Chloride ions release

electrons to the anode.

Greenish vapour chlorine

gas is released.

Cation Anion

Zinc hydroxide

Zinc ion receives electrons

from the cathode.

Shiny solid deposited.

Hydroxide ions release

electrons to the anode.

Oxygen gas is released.

Zinc ionHydroxide

ion

Silver bromide

Silver ion receives

electrons from the

cathode.Shiny silver solid

deposited.

Bromide ions release

electrons to the anode.Bromine gas is released.

Aluminium

Aluminium ion receive

electrons from the

cathode.

Shiny metal deposited.

Aluminium

ionOxide ion

Electrolysis

ElectrolysisTopic 5 Energy And Chemical Changes


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Electrolysis

Uses Of Electrolysis In Industry

Hot air in

Molten iron outSlag out

Raw materials

in

Waste gases

out



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Electrolysis

Electroplating

Example : Electroplating an iron spoon with copper

rheostat

switch

A

+ -

electrical source

ammeter

anode cathode

.

Electrolyte : Solution of a compound which contain

the plating metal ion.

Example :Copper sulphate because iron spoon is going to

plate with copper.

Cathode: Object to be electroplated.

Example : Iron spoon

Copper ions move to iron spoon and receive

electrons from cathode to form copper atom which

deposit on the iron key.

Copper iron + Electron Copper atom

Anode: Plating metal.

Example : Copper

Copper atom dissolves and forms positively charged

copper ions.Copper Copper ion + Electron



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Electrolysis

To prevent metal

from corrosion

Foods cans are made of iron and are

coated with layer of tins.

Iron nails are coated with zinc to prevent

rusting.

To improve the

appearance of the

object

Steel car bumpers are coated with

chromium to prevent rusting as well as

improve its appearance.

Costume jewellery and utensils are mostly

made of steel and coated with silver to

make them more attractive as well as

prevent rusting.



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Electrolysis

Purification Of Metals

Example : Purification of silver

Metals contain impurities can be purified by electrolysis

Electrolyte : Solution of a compound which

contain the metal ions to be purified.

Example :Silver nitrate solution.

Cathode : Pure metal. Example: Pure silver

Silver ion + Electron Silver atom

Anode: Impure silver rod.

Silver atom silver ion + Electron

Silver ions are attracted to the pure silver rod andreceive electrons from cathode to form silver

atoms which deposited on the pure silver rod.

Impure silver atom dissolves and forms positivelycharged silver ion.

Impurities are settled at the base of the

container below anode

rheostat

electrical source

ammeter

anode cathode

A

impurities


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5.6 The Production Of Electrical Energy From Chemical

Reactions

Penghasilan Tenaga Elektr ik Daripada Tindak Balas

Kimia


Changes



Electrical Energy From Chemical Reaction


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Chemicals reaction produce electricity

Electrode: Zinc is more reactive than copper.More reactive metal is made the negative

electrode because it is more likely to release

electron to form ions.

ZincZinc ion + Electron

Negative / :

Cathode

Less reactive metal is made the positive

electrode. Electrons released by zinc electrode

flow to copper plate through connecting wire,

thus produce electrical current. Positively

charged copper ions in electrolyte are

attracted to copper electrode to receive

electron and form copper atoms deposit on

the copper plate. Copper plate becomes

thicker.

Positive / :

Anode

Copper ion + Electron Copper atom

Electrolyte : The blue colour of copper sulphate

solution decrease as copper ion discharged at

electrode and the concentration of copper ions

decrease.

Simple cell consist of two different electrodes

which immersed in an electrolyte.

No electron flow if both electrodes are

the same.


Copper sulphate

solution

V

v

vv

e-

e-

e-

e- e-

e-

e-

v

v

Zn2+

Cu2+

Zinc

Connecting

wire

Voltmeter

Switch

Copper




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Types Of Cells





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Description

Most commonly used chemical cell.

Generates 1.5 volts of electrical energy.

Uses : Advantages and

Disadvantages

Used in radios, toys, remote control

and torch.Advantages :

Portable, cheap, light, small.

Disadvantages:

Non-rechargeable, not lasting

Leakage may occur

(+) Terminal :

Carbon rod

Electrolyte :

Ammonium chloride paste

(-) Terminal :

Zinc case





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Description

Consists of six lead lead-acid cells

connected in series.

Generates 12 volts of electrical energy.


Disadvantages

Usage : in vehicles.

Advantages :

High voltage, rechargeable, long-

lasting.

Disadvantages:

Heavy, expensive, acid may spill.

(+) Terminal :

Lead plate covered with lead

oxide

Electrolyte :

Sulphuric acid





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Description

Uses alkaline solutions as eletrolyte.

Similar to dry cell.


Disadvantages

Usage :

Cameras, portable cassette

players, electronic toys.

Advantages :

Constant voltage, long lasting,

produce large current than dry cell.

Disadvantages:

Non-rechargeable,

more expensive.

(+) Terminal :

Mixture of manganese (IV)

oxide and carbon

Electrolyte :

Potassium hydroxide or sodium hydroxide

Generates 1.5 volts of electrical energy.

(-) Terminal :

Zinc powder





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Description

Known as button.

Generates 1.2 volts.


Disadvantages

Usage :

Watch, cameras, hearing device.

Advantages :

Long-lasting.

Disadvantages:

Non-rechargeable.

(+) Terminal :

Silver oxide or mercury oxideElectrolyte :

Potassium hydroxide

(-) Terminal :

Zinc





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Description

Operates on the same principles as an

accumulator but uses different

material.


Disadvantages

Usage :

Mobile devices such as

mobile phone, camcorder emergencylight system.

Advantages :

Can be recharged, long-lasting.

Disadvantages:

Expensive.

(+) Terminal :

Nickel oxide

Electrolyte :

Potassium hydroxide

(-) Terminal :

Cadmium



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5.7 Chemical Reactions That Occur In The Presence Of

Light

Tindak B alas K imia Yang Berlaku Dengan Kehadiran

Cahaya


Changes



Light and Chemical Reaction


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Photosynthesis process requires sunlight to carry out its reaction.


CO2

O2

ight energy

SUN

Water and mineral salts

are absorbed from the soil

by roots

CO2is absorbed from

the air

+ +

Chemical Reactions Which Require Light

g


Light and Chemical Reaction


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Reaction takes place when photosensitive chemical exposed to light


Effect Of Light On Photosensitive Chemicals And Its Storage

Chemicals which changes when exposed to light is call photosensitive.

Example : Silver chloride, silver bromide, silver iodide and hydrogen peroxide

Photosensitive Chemical is used in making photographic films.

Storage of

photosensitive

chemical

Photosensitive chemicals such as hydrogen peroxide and silver

chloride are stored in dark bottles to avoid exposure to light.

Photographic paper and film are kept in black plastic and container

to avoid exposure to light.

g

Area exposed to light will form a dark area on the photographic film.

black)(greyish

BromideSilverlight

+




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To Study The Effect Of Light On Silver Chloride

Variable: _______________________________________________

________________________________________________

________________________________________________

Manipulated : Closing of the filter paper covered with silver chloride.

Responding : Decomposition of silver chloride / changes of the colour of silver chloride

Constant : Presence of silver chloride

Aim: _______________________________________________To study the effect of light on silver chloride.

Procedure :

Result :

Conclusion : ________________________________________________Silver chloride is photosensitive which will be decomposed by light to form silver atom (grayish

black) and chlorine.________________________________________________
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5.8 Innovative Efforts In The Design Of Equipment Using

Chemical Reactions As Sources Of Energy

Kegunaan Tindak Balas Kim ia Sebagai Sumber Tenaga


Changes

ITeach

Science Form 4


Equipment Using Chemical Reaction As Energy


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Equipment Using Chemical Reactions As Energy Source

Electrical energy comes from combustion of fossil fuels.

Chemical energy (Fuel).

Kinetic energy (Turning

of turbines and

dynamo).

Electrical energy

Fossil fuels are non-renewable and fast depleting, thus energy

should be use efficiently.

q p g gy




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Efficient use of energy

Use energy-saving electrical

appliance.

Set air conditioner

temperature at 25C or

higher and service regularly.

Close the door of

refrigerator immediatelyafter taking things from it.



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Proper Ways Of Disposing Of Electric Cells

Electric cell contain

corrosive and toxicchemical, thus they are

hazardous waste if dispose

together with household

waste.

Electric cell should be

disposed in recycling bins atmobile phone offices,

Department of Environment

offices, shopping malls and

Alam Flora recycling centre.




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New Ways Of Using Chemical Reactions As Sources Of

Energy

Hydrogen fuel cell uses

hydrogen as fuel to work likea battery.

Bro-diesel fuel can bedeveloped from palm oil to

be used in diesel cars,

lorries and buses.

Hydrogen react with oxygen

to produce energy and water

which will not pollute

environment.


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The End

i - Teach

chapter 5 versi bi

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