UNIT 8 PROCESS .3CAUSE AND EFFECT

SECTION. 1ACTIONS AND RESULTS

Rub a match box against the side of a match-box: what is the result?

ACTION RESULT

A match is rubbed against the and as a resultside of a match-box, with the result that it ignites.

The burning match is inverted, the flame becomes bigger.

The match is held pointing upwards, the flame becomes smaller.

The match is shaken, the flame is extinguished.

Make statements

A large object is dropped into a glass

the water overflows.

A match is lighter than water

as a result with the result that

it floats.

A coin is heavier than water

it sinks.

• The process of irrigating(قاية land: water (الِس�is brought( �ْج�َل�ُب� by canal or pipe, and as a (ُيresult the desert changes into farmland.( األرض

and (خصُب)The earth becomes fertile (الزراعيةplants turn green. Another result is that dry valleys are converted into rivers.

• Make statements about the following actions and resulting changes, using with the result that or and as a result, and the words become (+ adjective), turn (+ colour), change into or be converted into (+ noun).

Changes of state

A plant is kept away from

the light, as a result/ with the result that

it becomes pale (etiolated)

A plant is exposed to //////////// ///////////// it turns green.Photographic paper

////////////// ///////////// ///////////// it becomes dark.

Blue litmus paper

is placed in acid, ///////////// it turns red.

Red litmus paper

///////////// in alkali, ///////////// it turns blue.

Iron /////////////// in air and water,

///////////// it changes into iron oxide

Wood is burned ………….. ///////////// it changes into burning gas, ash and charcoal.

A solution of salt and water

is evaporated …………… ///////////// it converts into steam and salt crystals.

3. Change the above descriptions of actions and results in the same way as the example:

Example: If a plant is kept away from the light, it will become etiolated.

• If a plant is exposed to the light, it will turn green.• If a photographic paper is exposed to the light, it will become

dark.• If a blue litmus paper is placed in acid, it will turn red.• If a red litmus paper is placed in alkali, it will turn blue.• If iron is placed in air and water, it will change into iron oxide.• If wood is burned, it will change into burning gases, ash and coal.• If a solution of salt and water is evaporated, it will convert into

steam and salt crystals.

4. Make statements about the following changes of state in the same way as this example:

a) ice heated 0 0C melt water.• If ice is heated to melting point, it will melt,

changing into water.• water 100 0C boil steam. If

water is heated to boiling point, it will boil, changing into steam.

• steam cooled boiling point condense water If steam is cooled to the boiling point, it will condense, changing into water.

• liquid….cooled…..freezing point…..freeze….solid If liquid is cooled to the freezing point it will freeze, changing into solid.

• sulphur……..heated……….vapourise…….vapour. If sulphur is heated, it will vapourise changing into vapour.

• sulphur vapour……..cooled……..sublime……solid If sulphur vapour is cooled, it will sublime, changing into solid.

• salt…put in warm water…….dissolve…..forming a solution. If salt is put in warm water, it will dissolve, forming a solution

• salt in solution…evaporated…crystallise…crystals If salt in solution is evaporated, it will crystallise, forming crystal.

Section 2Other ways of expressing results

ACTION RESULT • Hydrogen combines with oxygen to form water.

2 H2 + O2 2H2O• Gases and solids sometimes dissolve in liquid to form solutions. thus forming solutions. thereby forming solutions.

Make sentences describing chemical reactions from this table:

• Potassium combines with iodine to form potassium iodide, KI.• Calcium combines with oxygen to form calcium oxide, CaO.• Magnesium combines with chlorine to form magnesium chloride,

MgCl2.

• Iron combines with oxygen to form iron (III) oxide, Fe3O4.• Carbon combines with hydrogen to form methane, CH4.

PotassiumCalciumMagnesiumIronCarbon

combines with

hydrogen oxygenchlorineiodine

to form

calcium oxide, Ca O.methane, CH4potassium iodide, KI.Iron (III) oxide, Fe3 O4Magnesium chloride, MgCL2.

6- Read these statements about the action of chemical substances and then complete the examples which follow them:

• Example: Elements combine to make compounds.• For example, sodium combines with chlorine to form sodium chloride. • Many solids burn in gases to form different solids. For instance, calcium burns in Oxygen to form calcium oxide, CaO.• Some substances absorb others, thus producing other substances

For example, chlorophyll absorbs water and carbon dioxide, thus producing oxygen and sugars.• Gases and solids sometimes dissolve in liquids, thereby producing solutions. Thus, sulphur dioxide dissolves in water, thereby producing Sulphurous acid. H2 SO3. Another example is hydrogen chloride, which dissolve in water, thereby producing hydrochloride

acid, HCl.• Radioactive substances disintegrate to from more stable elements

For example, thorium disintegrates to from lead 208.• Metals often react with acids to give metal salts. For example, zinc reacts with Sulphuric acid to give zinc sulphate, ZnSO4.• An acid is neutralized by an alkali to form a salt. For example, hydrochloric acid neutralized by sodium hydroxide solution to form sodium chloride.• Calcium carbonate is decomposed by heating to produce calcium oxide and carbon dioxide. For instance, potassium chlorate is decomposed by heating to produce potassium chloride and

oxygen.

7. Read this passage and look at the diagram.

The carbon cycle The life of plants and

animals depends on chemical substances containing carbon atoms. Plants obtain carbon from the very small amounts of carbon dioxide in the atmosphere.This atmospheric CO2 is continually absorbed and given off (released) in the carbon cycle.

Look at these:

• (A= cause, B= result)• A results in B.• B results from B.• As a result of A, B occurs.• A leads to B (eventually: other events occur

between A and B).

• As a result of eating plants, animals absorb carbon.

• As a result of photosynthesis, carbohydrates are produced by plants.

• As a result of combustion of coal, carbon dioxide is given off.

• As a result of decomposition of dead plants, carbon dioxide is given off.

As a result of

eating plants

photosynthesis,

combustion of coal,

decomposition of dead plants,

carbon dioxide is given off. carbohydrates are produced by plants

animals absorb carbon.

Answer these questions:• Can the liquid flow from left to right?• Why?• Can the liquid from right to left?• Why not?

Look at the diagram of the heart and make two sentences about the function of the valves, using the words given:

• Valve A allows blood to flow from right auricle to right ventricle.

• Valve B allows blood to flow from left auricle to left ventricle.

•

• Sucking air up a tube causes the air pressure to decrease, with the result that it becomes lower than the atmospheric pressure.

Atmospheric pressure consequently makes the water enter the tube.

• Pulling back the piston causes the air pressure decrease, with the result that it becomes lower than the atmospheric pressure.

Atmospheric pressure consequently makes the liquid enter the syringe.

10. Look at this diagram of a lift pump.• Make sentences from this table.•

The result of raising the piston

Atmospheric pressure makes the water

Valve A allows the water

Valve A prevents the water

The result of lowering the piston

Compression makes the water

Valve B allows the water

Valve B prevents the water

from returning to the well.

is that the water is compressed.

to pass the piston.

enter the cylinder.

to enter the cylinder.

from returning past the piston.

is that the air pressure is reduced.

pass the piston.

The effects of heat• These are observable changes produced by heating; some of

them help chemists to identify substances:

. produces

Heating brings about a change of state in ice. [ It causes it to melt ] causes

change in mass

release of gas

change of state

(liquid gas)

change in appearance

change in volume

change in colour

noise

HEATING

Section 4 Explanations

• Why do matches ignite when rubbed?• Matches ignite when rubbed because of / owing to friction. because friction generates heat.• Write explanations in answer to the following questions. The

sentences and phrase on the right will help you. Choose between and because of / owing to / because

• Note: Don’t repeat the noun after because; use a pronoun (it/they).

• Example: Wood floats on water because it is less dense than water.

* NEXT SLIDE

1. Matches ignite when rubbed because friction produces heat.2. Iron objects are attracted or repelled because of magnetism.3. Plants look green because the contain chlorophyll. (4-12 H.W)

Questions Reasons / causes1. Why do matches ignite when rubbed?2. Why are iron objects attracted or repelled?3. Why do plants look green?4. Why does a liquid in a tube look like this?5. Why does wood float on water?6. Why does water enter a pump?7. Why does blood flow only one way in the heart?8. Why do hydrogen balloons rise in the air?9. Why are some rocks use in making cement?10. Why do objects fall to the ground?11. Why do metal objects sink in water?12. Why do plants need CO2?

5. Wood is less dense than water.11. Metal is denser than water.3. Plants contain chlorophyll.1. Friction produces heat.12. Plants use carbon dioxide and water to produce carbohydrates.8. Air is denser than hydrogen. 6. a difference in air pressure.7. valves.2. magnetism.4. surface tension5. gravity9. the calcium carbonate present in some rocks

Section 5 READING

What can you see in these pictures?What are they used for?

Section 5 READING

Read this text. Which paragraph answers each question?

a) How does a thermostat work? (3)

b) How is central heating controlled? (4)

c) What causes expansion and contraction? (1)

d) What is the function of a thermostat? (2)

Thermostats

Heat causes substances to expand. This is because heat causes the atoms and molecules in the substances to move more quickly. As a consequence, they take up more space. This is true for gases, liquids and solids, but gases expand much more than liquids, and liquid much more than solids. When a substance is cooled, the molecules slow down. And as a result the substance contracts.

Thermostats make use of the principle of expansion. The function of a thermostat is to maintain a constant temperature over a period of time. They are used in refrigerators, heating and cooling systems and many industrial processes.

When different materials are heated, some expand more than others. For example, if brass is heated by one degree Celsius, it will expand by one fifty-thousandth of its length. Heating copper, on the other hand, will cause it to expand by about 90% of this. One kind of thermostat contains a strip of brass and a strip of copper which are joined to form a ‘bimetallic strip’. When the strip is heated, the different metals expand by different amounts. As a result, the strip is forced to bed towards the side which expands less. This bending can be used to operate a valve or open and close and electrical circuit.

Such a bimetallic strip is used in central heating systems. It switches off the heaters, when the air reaches a certain temperature, and switches them on when the temperature falls. One end of the strip can move while the other is fixed. The free end completes an electrical circuit which controls the gas or oil burner. The strip bends as it is heated. At a certain temperature the strip bends sufficiently to break the contact, thereby switching off the burner. When the air cools, the strip contracts until it makes contact and switches the burner on again.

15. Match these diagrams with different parts of the passage and discuss them:

a) b) c) d)

heat molecules faster expansion

heat molecules slower contraction

Say whether these statements are true or false and explain your answer:

a) The molecules in gases can move further than the molecules in liquids and solids. (T)

b) Only gases expand when heated. (F)c) If copper is heated by one degree Celsius, it will expand by

about one forty-five thousandth of its length. (F)d) A bimetallic strip made of copper and brass will bend

towards the copper side. (F)e) Substances contract by different amounts when cooled.

(F)f) When a refrigerator gets warmer, its cooling system is

switched on by means of a thermostat. (F)