grade8 science
TRANSCRIPT
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Environmental Science Grade 8 Module 1
WaterWelcome to Unit 1 of Grade 8 Environmental Science. In this unit we
are going to look at water. Our world is full of water. Water is a
useful substance in our lives. Imagine a world without water, can
there be life? We use water for bathing and we all drink water. Canyou think of other ways in which we use water? In this unit we will
look at the properties of water.
What is in this Unit?In this unit you have 6 sections. These are:
Section 1 What is Matter?
Section 2 Change of State
Section 3 Physical and Chemical Change
Section 4 Reaction of Water with Some Metals
Section 5 Effects of Electricity on WaterSection 6 Solutions and Crystals
Read through the learning outcomes carefully, to know what you are
expected to learn at the end of this unit.
Learning OutcomesBy the end of this unit you should be able to:
Fstate the properties of water
Fstate the uses of water
Fstate that water is matter and exists in liquid, solid andgaseous form
Fidentify the changes in states
Fto explain the difference between physical and chemicalchange
Fexplain the reaction of water with some metals and
Fexplain the effect of electricity on water
UNIT
1
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Environmental Science Grade 8 Module 1
&Learning ResourcesThere are many things you would need if you were going to carry
out all the practical activities in this unit.
We have listed them where we explain the practical activity to you.
Study TimeIn this unit you will probably need to spend at least 6-10 hours to
study the materials. This is only a guideline. You might even spend
more or less hours. If you spend more hours dont worry. What is
important is to complete all the sections and do all the activities
correctly.
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! Activity 1(a)List 10 examples of matter.
Your list is expected to have at least 10 examples.
1.......................................
2...........................................
3....................................
4.......................................
5...........................................
6.......................................................................................
7...................
8.......................................................
9...........................................................................
10.................................................................................................................................
3
Key Ideas
Matter: Anythingthat has mass and
occupies space.
Mass: Is theamount of matterfound in asubstance.
Environmental Science Grade 8 Module 1
Section 1: What is Matter?You are welcome to Section 1. In the introduction to Unit 1, we talked
about water. Can you remember some of the ways in which we use
water? Take sometime to think. In this section we consider matter,
its nature and its different states. We are surrounded by many forms
of matter. At every moment of our life we are making use of matter.We breathe oxygen from the air. We drink water. Oxygen, air and
water are forms of matter. Iron or wood we use for construction are
examples of matter. Please enjoy studying this section.
Learning ResourcesBefore you start the lesson you need to have the following
a stone
some ice
water a spirit lamp or source of heat
MatterConsider oxygen, air, water, iron and wood which we discussed
earlier. What do you think they have in common? You might have
discovered that all these things can occupy space and have mass. We
can therefore say that matter is anything that occupies space and has
weight.
Before proceeding further, do the following activity to check yourunderstanding of matter.
Check your answer with mine provided at the end of this unit.
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Environmental Science Grade 8 Module 1
Please note that all things on earth are examples of matter. If you
have not written some of the items suggested in the answer at the
end of this unit, do not worry because, as I said, all things on earth
are examples of matter.
States of MatterMatter exists in three different states. We normally talk about 3 states
of matter:
Solid state
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Key IdeasSolid state: Astate of matterwere particles areclosely packed.
Liquid state: Astate of matterwere particles arenot closelypacked.
Gas state: A stateof matter in whichparticles arefurther apart and
move randomly.
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Environmental Science Grade 8 Module 1
Liquid state
Gaseous state
Now lets discuss each of these states of matter in more detail.
SolidsOne of the states of matter is a solid. Think of something solid. A
stone is a solid, a chair is a solid. Most solids are hard or stiff.
Solids
Solid things do not change their shape to fill boxes or glasses. If you
put a book in your bag, does it spread out to fill your bag?
...........................................................................
.............................................................................................
The answer is no, the book does not spread out to fill your bag.
Solids are made of tiny particles. The particles of a solid pull on one
another and they are very close to each other. The particles do not
move so much, they only move back and forth. When they move this
way they are said to vibrate.
LiquidsThe particles of a liquid are not as close to each other as particles of a
solid. The particles of a liquid move faster than the particles of asolid. They are also not held tightly together. There is empty space
between the particles. A liquid does not have a shape of its own. It
flows until it fits the shape of the container that holds it. Can you
name some things which are usually in a liquid state?
......................................................................................
..........................................................................
Water, milk, petrol, ink, paint.
Look at the diagram below showing some examples of liquids.
LiquidsGases
Chair
Stone
WoodRail
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You can not see a gas, but it is there. You cannot hold a gas in your
hands.
A gas has no colour or shape, but it is there.
A gas is not a solid or liquid but it is there.
A gas is also a state of matter. Look closely at the picture of a bicycle
tyre and a balloon. They are filled with gases. Can you think of
things that contain gases? There are different types of gases. You cansmell some gases but some gases do not smell at all.
Gases
Particles in a gas are not so close to one another. The particles of a
gas move faster than the particles of either a solid or a liquid. There
is a lot of empty space between the particles of a gas. We can
summarize the characteristics of solids, liquids and gases as follows:
Solids Keep the same shape.
They stay where they are put.
It is not easy to move through a solid.
Cannot be compressed (make small).
Liquids Can take the shape of the container.
Liquids can be poured.
It is easy to move through a liquid.
Gases
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!Activity 1(b)1. Given below are some examples of matter:
Book, stone, oxygen, pencil, orange juice, steam, water, hydrogen, tree, coco-cola.
Write down each item in the correct column. The first one is done for you.
Solid Liquid Gas
Book
Can fill the whole container.
Spread out quickly.
It is easy to move through a gas.
Gases are very easy to compress.
The things mentioned above are used to describe differences betweensolids, liquids and gases. Please note that there are more ways we
can describe solids, liquids and gases.
Before proceeding, complete the following activity to check your
understanding of states of matter.
How did you find the activity? Was it difficult to do? Check your
answer with the answers provided at the end of the unit.
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Environmental Science Grade 8 Module 1
Mukuka
Section 2: Change of StateIn Section 1 you learnt what matter is and its three states. In this
section, you will learn about how matter changes from one state to
another. What happens when you heat candle wax? What happens to
ice when it is heated? What happens when you put water in a freezer
over night? In this section we will find answers to all these
questions.
Change of StateYou know from Section 1 that matter exists in three states:
Solid state
Liquid state
Gaseous /vapour state
In this section you are going to observe some changes that happen tomatter when it is heated or cooled. You know that water is matter in
liquid form. Water can also exist in other states such as solid (ice) and
gas (vapour).
You will also observe from the experiments in this section that water
can change from one state to another when we heat or cool it. Now
let us find out from this experiment how water or candle wax can
change from one state to another. Our two friends Sibeso and
Mukuka will join you in doing this experiment.
Practical Activity 1:What happens when you heat wax?
I will need the following materials: a beaker a stirring rod
a thermometer a source of heat - stove or Bunsen
burner
candle wax
Sibeso: What will you do next?
Mukuka:I will put some candle wax in a beaker over asource of heat. I am going to use the stove.Here is a picture showing the beaker on a tripodstand over a Bunsen burner. This is what you woulduse in a science laboratory.
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Figure 1.2
Mukuka:Now I am going to heat the wax gently on the stove.
Sibeso: Be careful not to burn yourself!
Mukuka I will put some candle wax in a beaker over asource of heat. I am going to use the stove.Here is a picture showing the beaker on atripod stand over a Bunsen burner. This is whatyou would use in a science laboratory.
Now here is a question for you:
What do you think happens to the wax in the beaker
as Mukuka heats it? Write your idea in this space..........................................................................1. The solid wax slowlydisappearsand turns into
liquid. it has changed state from solid to liquid.
Now Sibeso is going to do another practical activity.
This time you are going to find out what happenswhen we heat ice.
Practical Activity 2:
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Environmental Science Grade 8 Module 1
Source of heat
Wax
Beaker
Thermometer
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What happens when you heat ice?
I am going to use the following materials: a beaker a stirring rod
a thermometer a source of heat some ice
Mukuka:Tell us what you are going to do.
Sibeso: I will put some ice in a beaker on the tripodstand. You can see a drawing in Figure 1.3
below. I will also put the thermometer in the
beaker. Figure 1.3
Sibeso: Next I will heat the ice in the beaker gently but I
am using a stove. I am going to leave thethermometer in the beaker for 10 minutes.
Mukuka:What did you discover Sibeso?
Sibeso: The temperature reading before heating was about0C or below. As I heat the ice it slowly disappearedand turns to water.
When I continued heating, the temperature of thewater rises and the water turns to water vapour andrises out of the beaker as steam.
So now you have seen that when you heat ice it first changes state
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Environmental Science Grade 8 Module 1
Sibeso
Source of heat
Ice
Beaker
Thermometer
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from solid to liquid. As you continue heating the liquid changes to
water vapour or steam.
Now let us do another practical activity. This time you are going to
observe what happens when ice is left in the beaker at room
temperature. In this case we are not going to heat the ice.
Practical Activity 3:What happens when you leave ice in an openspace at room temperature?
I will need the following materials:
A beaker, a thermometer and ice
This is what I am going to do:
I will put some ice in a beaker place it on thetripod stand as shown in figure 1.4 below.
Figure 1.4
I will then place the thermometer in the beaker.
I will leave the ice and thermometer in thebeaker for some time.
Sibeso: Now mukuka answer the following questions:
1. What happens to the ice after some time?.................................................................................
2. Is there any change in the thermometer
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Environmental Science Grade 8 Module 1
Mukuka
Tripod stand
Ice
Beaker
Thermometer
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Sibeso
reading?....................
3. What did you observe on the outside of thebeaker?....
Mukuka : Here are the answers:
1. Solid ice is slowly turning into water.
2. There is no change in the thermometerreading.
3. Some water droplets have formed outsidethe beaker.
Now you can read the information below to help you understand
what happened to wax and ice in experiments 1, 2 and 3 this Section.
FMelting and Melting PointYou may have noticed that as you heat wax and ice they change, to
form a liquid. This change of wax or ice is called melting. When
the temperature of ice is raised above 0C, it melts to form water. All
solids turn to liquids when they reach their melting points. Now lets
see what happens to temperature of a solid as it melts.
FWhat Happens to the TemperatureDuring Melting?
You may have observed from the practical activity that we need to
keep heating until all the solid melts. The temperature stops rising
and stays at the same point.
Now let us find out what happens when you heat water. To do this
we are going to do the practical activity below:
Practical Activity 4:What happens when you heat water?
I will need the following materials :
a beaker a tripod water
a source of heat.Sibeso: This is what Iam going to do:
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Environmental Science Grade 8 Module 1
Source of heat
Beaker
Steam
Water
Tripod stand
I will fill half of the beaker with water. ThenI will mark the level of water in the beaker. Iwill then place the beaker on the tripod stand
as shown in figure 1.5.Figure 1.5
I will heat the water in the beaker.
I will Continue heating it until it starts boiling. I will let the water boil for at least 10 minutes
and then stop heating.
Mukuka:Sibeso, have you finished doing the practicalactivity?
Sibeso :Oh, yes. I have !
Mukuka:That's good. Now answer the followingquestions:
1. What happens to the water as you heat it?
......................
2. What do you see on the surface of the water inthe beaker as the water boils?................
3. Now look at the level of water, does it
change?
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..................
4. Give a reason for the change in the water level..........
.........Sibeso: Here are the answers:
1. As I started heating the water small bubblesstarted forming in the beaker.
2. As the water boils more bubbles are formedand steam starts coming out of the beaker.
3. The level of water starts dropping as the wateris boiled for some time.
4. The level drops because evaporation has takenplace.
We now discuss in more detail what happens to particles of water
when we heat it.
FWhat happens when water isboiled?
When we heat water the particles move about more quickly. Some of
the particles move very fast and they break out of the surface of the
water in the form of water vapour or steam, which spreads in the air.
This process is called evaporation. Particles of water vapour (gas)
arenot close to each other. They are free to move about. These
particles can spread to fill any container. They are separated from
each other by a lot of space.
What happens to the temperature
When water is boiled?Can you remember what happens to the temperature when it reaches
its melting point? Write your answer in the space below:
..............................................................
..................................................
The temperature stops rising and stays at the melting point. The
same thing happens when you heat water. When water reaches its
boiling point the temperature stops rising and stays at the boiling
point.
Do you know the boiling point of pure water?
......................................
..................................................
F
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Environmental Science Grade 8 Module 1
Mukuka
The boiling point is 100C.
FExplaining EvaporationWe saw from the activity that when water reaches its boiling pointthe particles break free from each other and mix with other particles.
The particles get a lot of energy and they move about very fast. The
particles then move away from the surface of the water in form of
water vapour which spreads in the air.
In the practical activity you saw that the level of water dropping as
you continued boiling it. Where did this water disappear to? Of
course it evaporated. After washing our clothes we hang them in the
sun to dry. Do you know what happens to the water in the wet
clothes?Figure 1.6
Clothes drying in the sun
The water evaporates leaving the clothes dry. Let us now find out
what happens when we cool water. We will now try the practical
activity below. Our two friends will do the activity for you. Read and
follow what they do.
Practical Activity 5:What is the effect of cooling water?
I will need the following materials:
A refrigerator or deep freezer
A beaker with cold water
Sibeso: Mukuka, what are you going to do now?Mukuka:I will do the following:
Half fill the beaker with water put the beaker in thefreezer of the refrigerator. Leave the beaker in the
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Environmental Science Grade 8 Module 1
Sibeso
freezer until the following day.
Sibeso: Mukuka answer the following questions now:1. What happens to the water in the beaker?
.......
.....2. How does the beaker feel like when you
touch it?......
......
Sibeso 1. I noticed that the water in the beaker hasturned into ice.
2. The beaker feels very cold as I touch it.
FExplaining FreezingWhen you cool water it turns into a solid (ice). This process is called
freezing or solidification. Freezing or solidification happens when a
liquid loses heat. The temperature at which a liquid changes to a solid
is called its freezing point. The freezing point of pure water is 0C.
FCondensationNow let us look at what happens when you cool steam. Our two
friends Sibeso and Mukuka will work with you in the followingpractical activity.
Practical Activity 6:Effect of cooling steam
I will need the following materials:
A source of heat (a brazier)
A kettle
A bottle
A beaker Water
Sibeso: I am going to set up the apparatus as shown infigure 1.6 below. Then will do the following :
Fill half of the kettle with water.
Place the kettle with water on a brazier.
Heat the water gently until it starts to boil.
Hold the bottle close to the kettle sprout
(Mouth of the kettle)as shown in figure 1.7.
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Environmental Science Grade 8 Module 1
Brazier
Drops of water
Cold water bottle
Steam
Sprout
Kettle
Beaker
Place a beaker below the bottle.
figure 1.7Condensation
Mukuka:Sibeso, now answer the following questions :1. As the water boils, what do you see
coming out of the mouth of the kettle?....
2. What do you see on the surface of thebottle?
..
Hold the bottle in the same position for
sometime.
3. What is dropping into the beaker belowthe bottle?
Sibeso :This is what I saw:1. As the water started boiling steam or
water vapour started coming out of the
mouth of the kettle.2. Small drops of water started forming on the
surface of the bottle with cold water.3. Drops of water collected in the beaker below
the cold water bottle.
FWhat have you learnt from this
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practical activity?We have seen that water can change from one state to another. When
you boil it changes to gas in the form of water vapour or steam. If
you cool the steam (water vapour) it changes back to liquid water.
This change of water from gas to liquid is called condensation. The
processes we have discussed above can be summarised as shown in
Figure 1.7. Is it possible for a solid to change straight to a gas? Yes, it
is. Let us find out from this practical activity. Our two friends will
again do the activity for you.
Practical Activity 7:
I will need the following materials: A test tube
A test tube holder
Crystals of iodine
A source of heatFigure 1.8
Sublimation
Mukuka:I am going to set up the apparatus as shown infigure 1.8. Then I will do the following:
18
Ice WaterWaterSteam
SteamIce WaterHeat heat
Cool
Heat heat cool
Figure 1.7
Environmental Science Grade 8 Module 1
Mukuka
Purple smoke
Test tube holder
Source of heat
Iodine crystals
Test tube
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Environmental Science Grade 8 Module 1
Place a small quantity of iodine crystals in a
test tube. Hold the test tube in a holder Heat the bottom of the test tube gently for a
few minutes.Sibeso: Mukuka, have you finished doing the practical
activity?
Mukuka:I have finished. It was very interesting !Sibeso: Good ! then answer the following questions:
1. What happens to iodine in the testtube?
2. What do you see in the upper part of
the test tube?..
3. What happens to the quantity of iodineat the bottom of the test tube?..
What happens when you heat iodine?
These are the results I got:
1. There was only small amount of iodine remainingat the bottom of the test tube.
2. We have seen that the iodine changed from solid
to gas without becoming a liquid.3. There was only a very small amount remaining at
the bottom of the test tube.
This change in which a solid turns directly into a gaswhen heated is called sublimation. Sublimation is alsoused to describe the change of state from gas to
solid when a gas is cooled.
1. The iodine crystal at the bottom sublimes andchanged its colour to purple.
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2. A purple smoke is seen coming out the test tube.
FWhat can you learn from thepractical activity?
After heating the iodine crystals the shiny and bright crystals gave a
purple smoke. The upper part of the test tube had some crystals of
iodine when the test tube was cooled. Examples of substances that
sublime include Iodine, Solid Carbon dioxide and Ammonium
Chloride. The change of state of matter can be summarised as shown
below.
Figure 1.9
Change of state of matter
Now try this activity to see how much you have learned
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Environmental Science Grade 8 Module 1
Sublimation
SolidificationMelting
Solid
Liquid
EvaporationHeat
Gas
CoolCondensation
Sublimation
Condensation
Heat Cool
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!Activity 21. Name the three states of matter.
........
2. Distinguish between the three states of matter in terms of their particles.
.....
.............................
.....
3. In your own words explain the following processes:
(A) Melting ....................................
(b) Evaporation .....
(c) Condensation .
(d) Sublimation
4. Give two examples of substances that undergo sublimation.
(a) ...........
(b) ......
Environmental Science Grade 8 Module 1
Check your answer with the answers provided at the end of thisunit.
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Key Ideas
Irreversible :means hat asubstance cannotbe changed backto its originalform.
Environmental Science Grade 8 Module 1
Section 3: Physical and ChemicalChange
Welcome to Section 3. In the last two sections you learnt about the
changes in the states of matter. You now know that matter can
change from one state to the other. These changes can either bephysical or chemical. In this section we are going to learn more
about physical and chemical changes.
FPhysical ChangeA physical change is one which does not produce any new substance
and the change can be reversed.
I am sure you have all seen ice. Ice is one of the common substances
found in your area. Now, when you heat ice as a solid, what
happens? Of course ice will change state from being solid to liquid.
This changeof state is called melting. When ice melts into a liquid,
is there any new substance formed? No new substance is formed.
Suppose, we put water in a freezing compartment of the refrigerator
for at least 24hours, what will happen to it? The water turns to ice,
no new substance is formed as the water can be turned back to ice on
cooling it in the refrigerator. Therefore the melting of ice and the
freezing of water are examples of a physical change. Another
example of a physical change is dissolving. You are familiar with
sugar or salt dissolving when stirred in water. Here again no new
substance is produced. Can you think of any physical change that
commonly takes place around your home? Now lets look at another
type of change.
FChemical ChangeThis is just the opposite of physical change. A chemical change is a
change which always produces new substances. A chemical change
is irreversible. By irreversible we mean that this substance cannot be
changed back to its original form.
Now let us proceed with the following investigation. Sibeso and
Mukuka will do this demonstration for you. Please follow what they
do, carefully.
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Mukuka
Practical Activity1: Showing a ChemicalChange
I will need the following materials: Match box
Matches
A white plain sheet of paper
Mukuka:This is what I am going to do :Strike a match and light a piece of paper. I will
then let it burn for a while and blow it off.
Sibeso: Mukuka, you can now answer the following questions :1. What happens to the colour of the
paper?2. Does it represent a physical change or a
chemical change?
...............3. Justify your answer in (2)?
..
This is what I observed:
1. When the paper was burnt, it turned black, theblack substance is called ash.
2. This represents a chemical change because ash isa new substance.
3. This ash cannot be reversed to paper.
Other examples of a chemical change include burning of wood,
reaction between magnesium and oxygen, reaction of water and
calcium.
At this stage we can say that in a chemical change, new substancesare formed but in a physical change, no new substances are formed.
I hope you have now understood the difference between physical
and chemical changes.
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!Activity 31. Below are some statements describing physical and chemical changes. Write
either P (for physical change) and C (for chemical change) next to thestatements.
(a) Boiling water
(b) Boiling an egg ..
(c) Melting of ice
(d) Chewing a bubble gum
(e) Burning a piece of wood .
2. List three (3) other physical changes.
(a) ...
(b) ...
(c) ...
3. Explain the difference between chemical and physical change.
........
Environmental Science Grade 8 Module 1
Now do the following activity to check your progress.
I hope you have now understood the difference between chemical
and physical changes. Now compare your answers with mine at the
end of this unit.
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Sibeso
Section 4: Reaction of Water withSome Metals
Welcome to Section 4, I hope you have now understood the
difference between physical and chemical changes in section 3. Now
you are going to move a step forward and study more on how somemetals react with water. Where you live are there any metals
around? What about in your house, are there any objects made of
metal? What happens when water comes in contact with metal?
What about when you go to collect water from the well or river or
tap, do you use a plastic or metal bucket? If you use a metal bucket
does the water react with the metal bucket? If so how can you know
that the metal bucket is reacting with water? Well, this section will
look at what types of metals react with water.
Learning Resources Calcium metal
Magnesium ribbon
Iron fillings
Copper fillings
Pair of tongs
Clamp stand
Six test tubes
Test tube rack
Beaker
Burner Match stick
To find out if some metals react with water. Join Sibeso and Mukuka
as you carry out several practical activities. We will start by looking
at how at what happens when calcium reacts with water.
Practical Activity 1:Reaction of calcium and water
I will need the following materials:
Water
Test tube
Burner
Calcium Pair of tongs/spatula
Mukuka:You will need to be very careful when pickingthe metals. Use a spatula for the calcium; donot use your fingers because it is corrosive to
the skin. Please be careful. If it comes in
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Beaker
Water
Calcium
contact with your skin, wash your hands carefully.
Sibeso: Thank you Mukuka for the warning, To carry out this
practical activity iwill set up the materials as shownin figure 1.10. I will then do the following :
Get a test tube and half fill with water.
Using a pair of tongs or spatula get a piece of
calcium and drop it into the cold water.
After 3 minutes get the same beaker and heat
the water with the burner.
Figure 1.10
Reaction of calcium and water
Mukuka:Sibeso, you can now answer the followingquestions:
1. What happens to the calcium metal whenit is in cold water?
2. (a) What can you say about the speed of thereaction when you heat water?(b) What is the difference in the two reactions?
These are the results I got:
1. Bubbles are produced; this shows that a
reaction is taking place.
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Mukuka
2. (a) More bubbles are produced at a faster rate.
(b) Reaction of Calcium in warm water is fasterthan the reaction of calcium with cold water.There are more bubbles produced in warm water
than cold water.
FWhat can you learn from thispractical activity?
You have learned that calcium can react in both cold and warm water.
The difference in the reaction is that Calcium reacts faster in warm
water than cold water. Now lets try another investigation, this time
we want to see what happens when a metal: magnesium is mixed
with water. Now let us move to practical activity 2. Sibeso andMukuka will again do the practical activity with you.
Practical Activity 2:Reaction of Water with Magnesium
I will need the following materials:
Test tube
A pair of tongs Water
Source of heat
Mukuka:I am going to set up the apparatus as shown infigure 1.11a. Then I will do the following :
Get a test tube and half fill the test tube withwater.
Using a pair of tongs carefully get the magnesium
ribbon and gently put in the test tube of water.Look at the diagram below. Make sure you havearranged your apparatus accordingly.
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Figure 1.11(a)Reaction of water with magnesium
Observe the reaction.
After 3 minutes get the same test tube withmagnesium ribbon then heat gently till it boils.
Figure 1.11(b)
Reaction of water with magnesium
Sibeso: Mukuka, you can now answer the followingquestions :1. What is happening to the magnesium ribbon
in the test tube of cold water?............
2. What is happening to the reaction ofmagnesium in warm water?.......
3. What can you say about the reaction ofmagnesium in cold and warm water?
This is what I observed:
1. No reaction is taking place.2. Few bubbles are seen hence reaction is taking
place.3. Well magnesium does not react in cold water but
it reacts in warm water.
Let us now look at another practical activity.
Test tubeWater
Test tube holder
Magnesium ribbon
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Environmental Science Grade 8 Module 1
Test tubeWater
Source of heat
Test tube holder
Magnesium ribbon
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Practical Activity 3:Reaction of Water and Iron
I will need the following materials:
1 test tube water
iron fillings
Spatula
burner
Figure 1.12Reaction of water and iron
Sibeso: I am going to set up the apparatus as shown
in figure 1.12. Then I will do the following :
Get a test tube and half fill it with water.
Using a spatula collect the iron pieces
and put then gently into the test tube. Observe thereaction carefully.
After 3 minutes, gently heat the test tube till thewater starts boiling.
Mukuka:Sibeso, you can now answer the following questions :
1. What reaction can you see when you put piecesof iron in cold water?....
2. What reaction can you see when you put iron inwarm water?
3. What can you say about the reaction of iron incold or warm water?
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Environmental Science Grade 8 Module 1
Test tube
Test tube holder
Water
Iron fillings
Sibeso
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Mukuka
Sibeso: This is what I observed:
1. No reaction is taking place when I placed ironpieces in a test tube of cold water.
2. No reaction is taking place when I placed ironpieces a test tube of warm water.
3. There is no reaction with either cold water orwarm water.
FReaction of iron with waterWe have learnt that iron does not react in either cold water or warm
water.
Let us now look at another activity. This time we will find out what
happens when water mixes with copper.
Practical Activity 4:Reaction of Copper with Water
I will need the following materials:
1 Test tube
Water
Burner
Copper
Pair of tongs or spatula
Mukuka:I am going to do the following :
Get a test tube and half fill it with water, Using a pair of tongs collect pieces of the copper
metal and put them in the test tube of cold water asshown in Figure 1.13 (a).
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Figure 1.13 (a)
Set up the apparatus as shown in figure 1.13 (b).
Figure 1.13 (b)
Now heat the test tube for 3 minutes till it starts boiling.
Sibeso: Mukuka, you can now answer the followingquestions:
1. What happens to the copper in cold water?.
2. What happens to the copper in warm water?....
3. What can you say about the reaction of copperin cold or warm water?
..
This is what I observed:1. There was no reaction when you mixed cold water
with copper in the test tube.
2. There was no reaction when you mixed warmwater with copper in the test tube.
3. Copper does not react in either cold water orwarm water.
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Environmental Science Grade 8 Module 1
Test tube
Test tube holder
Copper metal
pieces
Water
Test tube holder
Test tube
Source of heat
Water
Copper metal pieces
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FWhat can you learn from theseactivities?
Let us see what was actually happening in these practical activities
and the conclusions we are going to draw from them.
Firstly you noticed that some metals can react in both cold and hot
water. Can you list which metal reacted in cold and hot water?
.. ............ calcium reacted in both cold and hot water.
Some metals could not react in cold water but only hot water, which
metal is this? It is magnesium.
On the other hand some metal could neither react in cold water or
hot water. Which metals are these? .................. and Yes the two metals are iron and copper. But there
is some thing about iron you must know, it does react with water if
there is oxygen in the water. When you look at some metal buckets
or cups or dishes you use for collecting water you will notice a
brownish substance on them. This is called rust. That is a reaction
between iron and water in the presence of oxygen.
Calcium reacts faster in cold and hot water than these other metals,
what can you conclude? Well you can say Calcium is more reactive
metal than magnesium, iron and copper. Magnesium is also morereactive than iron and copper. Copper is the least reactive metal.
Another metal which reacts with water at a faster rate is potassium.
Its the most reactive of all metals.
Because of the way these metals react they are put in what is referred
to as a reactivity series. A series is a sequence or line up in which
metals are arranged according to how fast the react with water. Look
at the reactivity series below and study it carefully. The list starts
with the most reactive and ends with the least reactive metal.
Potassium most reactive
Calcium
Magnesium
Aluminium
Zinc
Iron
Lead
Copper
Gold - least reactive
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Mukuka
Clamp stand
Test tube
Beaker
Water
Calcium
Now that you have studied how metals react with water and how
they are arranged in the reactivity series from the most reactive to the
least reactive, we are going to identify what is produced at the end of
the reaction.
Well first you will need to carry out another practical activity.
Practical Activity 5:Reaction of Calcium with Water
I will need the following materials:
A beaker
Test tube
Clamp stand Calcium
Figure 1.14a
Reaction of calcium with water
Mukuka:Iam going to do the following :
Set up the apparatus as shown in figure 1.14a
Using pair of tongs I will collect enough some pieces
of calcium and put it in the beaker.
Quickly cover the calcium with a test tube as shownin the figure 1.14a.
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Environmental Science Grade 8 Module 1
Clamp stand
Beaker
Water
Calcium
Gas
Figure 1.14b
If the reaction is slow I will heat the water, I willalso make sure I have enough calcium.
When all the water has been displaced or removed bythe gas collected in the test tube,1 will remove thetest tube while its mouth is still in water trough thenclose the mouth immediately with my finger before Iremove it from the water.
Light a wood splint or match stick, and thenintroduce the burning splint to the gas inside the testtube quickly.
Figure 1.14c
Sibeso: Mukuka, its now time for you to answer the followingquestions:
1. What happens to the water as bubbles arecollected in the test tube?
.........
2. What happens when the burning splint ormatch stick is introduced to the gas collected?........................
Mukuka:1. Gas displaces the water in the test tube andwater turns milky
2. Flame of the burning splint is put off with apop sound.
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FWhat can you learn from thispractical activity?
You have already learnt how calcium reacts with water. Well when it
reacts a gas is produced. The gas produced is hydrogen. Since anew product is produced this is a chemical change. But how can you
know that it is hydrogen gas that was produced? Think about it.
Well can you remember what happened when you introduced a
burning splint to the gas? What happened?
.................
.................................................
The flame was put off with a pop sound. The test identity of
hydrogen is shown by putting off a burning splint with a pop sound.
How can you show the reaction between water and the metals we
have studied? Study the word equation below.
Metal + Water Metal hydroxide + hydrogen
e. g. Calcium + Water Calcium hydroxide + Hydrogen
You notice that another substance is produced apart from hydrogen.
This is calcium hydroxide.
Well calcium hydroxide is a solution that is formed when calcium
and water reacts. Calcium hydroxide is an alkaline solution. How
can you identify an alkaline solution? Well you use a special red
paper called red litmus paper. When you dip a red litmus paper in
this solution it will turn blue. This will always happen to any
solution that is an alkaline.
Remember that when most metals react with water hydrogen gas is
given off plus the hydroxide of that metal. For example in the aboveexperiment the hydroxide of calcium is calcium hydroxide, in fact
the water turns milky because of the presence of calcium hydroxide.
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Environmental Science Grade 8 Module 1
!Activity 41. (a) Arrange the following metals in the reactivity series starting with the least.
Zinc ....Iron ....
Magnesium ...
Lead ...
Aluminium ...
(b) Write a word equation of the reaction of magnesium and water?
........
(c) What gas is produced in the equation you have written above?
............
(d) What test is used to identify this gas?
........................................................
Now do the activity below to check your progress so far.
How did you find this activity? Check for the answers to this
exercise at the end of this unit. If you found any part difficult go back
and re-read the parts you did not understand well.
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Section 5: Effects of Electricity onWater
Welcome to section 5. I hope you enjoyed studying the previous
sections. In this section you will learn about the effect of electricity
on water. In the previous section you learnt that water reacts withmetals such as calcium and magnesium. Now what do you think
could be the effect of electricity on water? You will learn more about
this in this section. In order to find out the effect of electricity we will
start by doing the practical activity below. Our two friends Sibeso
and mukuka will join us as we do the activity. Please read and follow
all the very carefully.
Practical Activity1:To Find Out the Effects of Electricity on Water
I will need the following Materials:
Two carbon rods
Medium sized test tubes
Connecting wires
A switch
Wood splint
Two beehive shelves
One 6 volt battery
Water and dilute hydrochloric acid
Mukuka:This is what I am going to do :1. I will arrange the apparatus as shown in the
diagram below.
Figure 1.15Effects of electricity in water
I will close the switch and carefully observewhat happens
I will now add a few drops of the dilutehydrochloric acid and carefully stir the water.
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Environmental Science Grade 8 Module 1Key Ideas
Electrolyte: Is asolution that canconductelectricity.
Mukuka
Bulb
Gas collecting
Gas bubbles
Trough
Test tube
Electrode (anode)
Battery
6V
Electrode (cathode)
Beehive shelf
Switch
Gas collecting
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Environmental Science Grade 8 Module 1
Leave the set up for some time in order forthe gases to collect.
Now carefully remove one of the test tubesoff its electrode making sure that the gas doesnot escape. Introduce a burning splint to the
mouth of the test tube. Remove the other test tube as before.
Quickly introduce a glowing splint.
Sibeso: Be careful as you handle dilute hydrochloric acid asit can burn your skin. Mukuka now answer thefollowing questions :
1. What do you observe at the two electrodes whenthe switch is closed?....
2. What do you observe at the electrodes afterdilute hydrochloric acid was added?.......
3. After some time (15 minutes) what do youobserve with amount of gases collected atthe electrodes?
....4. What do you observe when you put the burning
splinter in the first test tube?
........
5. What do you observe when the burning splint isintroduced in the second test tube?............
6. What can you say about the nature of gasescollected?
............
Mukuka:I observed that:
1. When the circuit was closed before adding thedilute hydrochloric acid, there were no bubblesare produced at the electrodes.
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Environmental Science Grade 8 Module 1
2. After adding the acid bubbles started beingforming around the electrodes.
3. After about 15 minutes quite a lot of gashad collected in each tube. There was more
gas produced in one tube than the other.
4. When a burning splint was introduced in the testtube with more gas it was put off with a popsound.
5. When I introduced a glowing splint in the testtube it was re-lighted and burnt more brightly.
FWhat can you learn from this practicalactivity?
When electricity is passed through acidified water, gases are
produced. Electricity can not pass through pure water because it is a
bad conductor of electricity. Dilute hydrochloric acid is added to the
water to make it conduct electricity.
When a dilute acid is added to water, it becomes an electrolyte. An
electrolyte is a solution which will conduct an electric current and be
decomposed by it. To decompose is to break down into smaller
parts. Electricity decomposes (splits) water into simpler particles.Therefore this decomposition of an electrolyte is known as
electrolysis. How are you coping with this new information? This
splitting of water into simpler particles, is it a chemical or physical
change?
......................
It is a chemical change. The gases are produced at the electrodes. An
electrode is a plate or rod which conducts electricity in and out of an
electrolyte. These electrodes can be made of metals like platinum,
zinc,copper etc or a non metal like carbon.
In your experiment you connected one of the electrodes to the
positive terminal and the other to the negative terminal. These
terminals are made of metal rods or plates. The one that was
connected to the positive terminal is called the Anode. The one
connected to the negative terminal is called the Cathode.
One of the gases put off a burning splint with a pop sound, it is
hydrogen. The other gas relit a glowing splint, it is oxygen. These
two observations are the identity test of the gases respectively.
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Now try this activity to check your progress.
How did you find the activity? Was it easy? Now compare your
answers with mine at end of the unit.
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Environmental Science Grade 8 Module 1
!Activity 51. The diagram below shows an experiment used to produce two gases by
passing an electric current through an electrolyte.
Electrolysis
Figure 1.16
a. Suggest the electrolyte used in this experiment.
...........
b. What is the name of the process of decomposing a substance using an
electric current?........................................
............................................................................................................................
c. Name the gas that would be collected in test tube A.
..............
d. What is the identity test for the gas that would be collected in test tube B?
..........
e. Which test tube would contain a larger amount of gas at the end ofthe experiment?
..............
f. What is the use of the gas collected in test tube A?
...............
Electrode (cathode)
Trough
Test tube
Electrode (anode)
Battery
6V
Test tube
Electrolyte
Switch
BAMore gas
Gas
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Environmental Science Grade 8 Module 1
Key Ideas
Solution: this isformed when asolid dissolves ina solvent.
Crystals: solidswith a definiteshape formedfrom a solution ofits solute.
Mukuka
Section 6: Solutions and CrystalsWhen you add small amount of sugar to water the sugar disappears.
When the sugar disappears, it becomes a sugar solution. In this case
sugar is soluble in water because it forms a solution which is a sugar
solution. Is this a chemical or physical change?
In science we use some general words to describe the sugar and
water. The sugar is called the solute and the water is called solvent.
In this section we are going to look at solutions and crystals in
general.
FSolutionsRemember that when you add small amount of sugar to water, thesugar disappears. The disappearing of the sugar is called dissolving.
When sugar dissolves in water it forms a solution. In science the
sugar is referred to as a solute and the water as a solvent.
Note that sugar dissolves faster in hot water than cold water. When
we add more sugar to very little water, the sugar will not dissolve
any more. In science we say the sugar has been saturated. The
solution is now called saturated solution. Let us find out more about
this in the following investigation.
Practical Activity 1:What Materials Dissolve in Water?
I will need the following materials:
Salt
Sugar
Mealie meal
Sand 4 beakers with water
Stirring rod or spoon
Mukuka:I am going to do the following :
Add a teaspoon of sugar to the water in thefirst glass and label it sugar.
Add a teaspoon of salt to another glass withwater label the beaker salt.
Add a teaspoon of mealie meal to the thirdglass and label it mealie meal.
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Environmental Science Grade 8 Module 1
Add a teaspoon of sand to the fourth glassand label it sand.
Sugar salt mealie meal sand
Figure 1.17
Sibeso: Mukuka, now answer the following questions:
1. Which of the solids seem to disappear?............
2. Which solids can you still see?
..........
Mukuka:These are the results I got:
1. Sugar and salt disappeared after stirring it in
water for a few minutes.
2. Solids like sand and mealie meal did notdisappear instead they collected at the bottomof the glass of water.
FExplaining SolutionsYou saw from the practical activity that sugar and salt, disappeared
or dissolved when it was stirred in water. We can say sugar or saltare soluble in water (they are able to disolve). The mixture of water
and salt or sugar is called a solution.
FA saturated SolutionIf you keep adding sugar to a glass of water at first it will dissolve.
What do you think can happen if you keep adding more and more
sugar? The sugar will reach a point where it will no longer dissolve
in water. The more sugar you add you will observe that there will betoo much sugar for the water to dissolve, when this happens we can
say you have made a saturated solution of the sugar.
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Mukuka
FSeparating MixturesWe have discussed that salt can easily dissolve in water. What about
Sand can it easily dissolve in water?
................................................
Sand cannot easily dissolve in water. We have see that we can mix
salt and sand with water, yet they cannot be separated the same way.
How can you separate a mixture of bean and maize seeds?
...........................
...............................................
You can separate these two by sorting them by hand, you can do this
by placing bean seeds in one pile and maize seeds in another pile.This is a fairly easy way of separating mixtures. Is it easy to separate
salt from water?................................
No, it is not easy to separate salt and water using our hands. These
mixtures are called solutions, they have to be separated using other
methods. Now do the practical activity below in which we will
investigate how to separate a mixture of sand and salt in water.
Practical Activity2:
Separating a Mixture of Salt, Sand in Water
I will need the following materials:
Two beakers A stirring rod Clamp and stand Bunsen burner An evaporating dish Sand Water Filter funnel Filter paper
Mukuka: I am going to do the following : Place 2 teaspoons of sand and 2 teaspoon salt
in a beaker. Mix the sand and salt well using a stirring rod.
Add about 50ml of water to the mixture of
sand and salt. Stir the mixture of sand, salt and water in
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the beaker with a stirring rod,
Sibeso: Mukuka, now answer the following questions:
1. What happens to the sugar and salt afterstirring?
Figure 1.18
Set up the apparatus as shown in figure 1.19below.
Figure 1.19
Filtration
...
.
Mukuka: I will continue with the practical activity by doingthe following:
Place the beaker with the mixture on the burnerstand and heat it gently while stirring themixture with a stirring rod.Fold a piece of filter paper as shown below in
figure 1.19 below and place it in a funnel.
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Environmental Science Grade 8 Module 1
First fold
Second fold
Funnel
Filter paper
Third fold
Beaker
Salt solution
and sand
Residue
Beaker
Liquid
Filter paper
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Now pour the hot liquid onto the funnel.
Please make sure that any liquid that passes
through the filter paper is collected in the beaker asshown in the diagram.
Pour the liquid that has collected in beaker below thefunnel onto the evaporating dish as shown in figure1.20 below:
Figure 1.20
Put the dish on a burner and heat theliquid until all the water evaporates.
Sibeso :Mukuka, you can now answer the following questions
1. What remained on the filter paper?....
2. Describe the liquid that collected in thebeaker after filtering.
..
What is left on the evaporating dish as all thewater evaporates?......................
3. When you stirred the white salt and brown sandin water, the white salt dissolved in water leavinga brownish substance which later settled at thebottom of beaker.
4. After pouring the mixture of sand and salt a
brownish substance (sand) remained on the filterpaper.
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Environmental Science Grade 8 Module 1
Steam
Filtrate
Stand
Source of heat
Evaporating dish
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Environmental Science Grade 8 Module 1
5. A clear liquid collected in the beaker at thebottom of the funnel.
6. Salt crystals were left on the evaporating dishas the water evaporates.
FExplaining FiltrationWhen a mixture of salt, sand and water is poured on the filter paper
placed in a funnel, sand is separated from salt using a process called
filtration. The salt solution is able to pass through the small holes in
the filter paper because salt particles are very small. The sand
particles cannot pass through the holes because they are too big.
Filtration is usually used to separate the solid and liquid parts of a
suspension. A suspension consists of solids that cannot dissolve in
water for example sand. The liquid part is called the filtrate. Thesolid that remains on the filter paper is called a residue.
FSoluble and Insoluble MaterialsThe practical activity shows that not all substances can dissolve in
water. Those that dissolve in water like salt are said to be soluble in
water, those that do not dissolve are referred to as insoluble. Can
you write 2 examples of solids that are soluble in water?
1..
2..................
Did your answer include salt and sugar? There many substances that
is soluble in water. Salt and sugar are some of the common
examples. Now write 2 examples of solids that cannot dissolve in
water.
1....................
2........................
Did your answer include sand, stones or mealie meal? Any way
there are more substances that cannot dissolve (not soluble) in water
in addition to the ones I have suggested above.
FCrystalsWhen saturated solution is cooled, some of the solute comes out of
solution as a solid called a crystal. This process is called
crystallisation.
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Sibeso
Now let us do the practical activity below.
Practical Activity 3:Making Crystals of Copper II Sulphate
I will need the following materials:
Copper II sulphate
Water Spoon Trough Filter paper Stirring rod Two beakers
Thermometer
Sibeso: Iam going to do the following:
Put 50ml of water in a beaker. Add a little amount of copper II sulphate using a
spoon.
Stir the mixture well until all the copper II sulphatedissolves.
Keep adding a little copper II sulphate at a time
until no more will dissolve. Using a filter paper filter the solution into another
beaker. Leave the saturated solution over night.
Mukuka:Sibeso, now answer the following questions:
1. What do you see in the beaker the next day?...
2. Now pick the largest crystal and suspend it by athread as shown in figure 1.23 below.
Look at the crystal each morning for 3 days.
3. Record what you see after 3 days as shown infigure 1.23 below...
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Copper sulphate
solution
Crystal
!Activity 61. What is a solution?
...............................
.......
2. What do you call a solid that dissolves in liquid?
...
...
3. What name is given to the process by which crystals are formed?......
.......
4. What do you call a solution that can not dissolve any more solute at a giventemperature?
.......
......
Figure 1.23Growing a copper sulphate crystal
1. Next day I saw that the crystal is growing.
2. The crystal grew bigger and had definite shapeor pattern.
What can you learn from this activity?When the saturated copper sulphate solution was left for a few days,
particles came out of the solution. The crystal grew slowly over the
five days. The crystal despite its growing bigger kept the same shape
or pattern. When a saturated solution is cooled solid crystals are
formed this process is called crystallization. Some of the common
crystals include
Salt
Sugar
Now try this activity to see how much you have learned.
How did you find this self marked activity? Was it easy? If not,
please do not panic just re-read the section and make sure you
understand the subject matter before proceeding to the next part.You will find the answers at the end of this unit.
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Unit Summary
Matter is defined as anything that occupies space and
has mass.
Matter exists in three different states namely solid,liquid and gas.
In a physical change, no new substances produced and its
reversible.
In a chemical change a new substance is formed and it not
reversible.
Matter changes state when it is heated or cooled.
The processes that take place with during the change of
state are melting, boiling, solidification, evaporation andsublimation.
The tiny particles in solids are closely packed together.
The tiny particles in liquids are further apart.
In gases, the tiny particles are still further apart.
Dilute acid is added to water to make it a good electrolyte.
RAnswers to Activities in this Unit
Activity 1(a)
Solid Liquid Gas
1. Book 5. Water 8. Oxygen
2. Stone 6. Soft drink 9. Nitrogen
3. Metal
4. Brick 7. Orange juice 10. Hydrogen
Activity 1 (b)
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Environmental Science Grade 8 Module 1
Solid Liquid Gas
Book Water Oxygen
StoneSoft drink Nitrogen
Metal Orange juice Hydrogen
Brick
Activity 1 (b)
Figure 1.24
Activity 2
1. Solid, liquid, and gas
2. In solids particles are closer to each other.
In liquids particles are a little further apart.
In gases particles are free to move about since they are
further apart.
3. (a) Melting is when a solid changes to liquid
(b) Evaporation is when a liquid changes to vapour
(c ) Condensation is when a vapour (steam) changes to liquid.
(d) Sublimation is when a gas changes directly into solid or a
solid changes directly into gas.
4. (a) Iodine
(b) Ammonium chloride
(c ) Solid carbon dioxide
Activity 3
1. (a) P
(b) C
(c) P
(d) C
(e) C
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Environmental Science Grade 8 Module 1
2. (a) Condensing of water vapour ( or steam) to water as a liquid
(b) Drying or evaporation of water from a salt solution
subsequently collecting back the salt again.
(c ) Freezing of water to ice
3. (a) In a physical change no new substance is formed while in a
chemical change a new substance is formed.
(b) A physical change is reversible while a chemical
change is not.
Activity 4
1. Magnesium
2. Aluminium
3. Zinc
4. Iron
5. Lead
6. Copper
(b) Magnesium + water Magnesium hydroxide +
hydrogen
(c) Hydrogen gas
(d) It puts off a burning split with a pop sound.
Activity 5
1. (a) Acidified water or dilute hydrochloric acid dissolves in
water.
(b) Electrolysis
(c) Oxygen
(d) It puts off a burning splint with a pop sound
(e) Test tube B
(f) Production of strong flame for welding metals or
respiration or for use in incubators in hospitals and deep
water divers
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Environmental Science Grade 8 Module 1
Activity 6
1. A mixture of solute and solvent
2. Solute
3. Crystallisation4. Saturated solution
Glossary
Alkaline solution: A solution that turns a red litmus paper blue.
Anode: Positive electrode.
Boiling point: The temperature at which a liquid changes to
gas state.
Cathode: Negative electrode.
Chemical change: A change which is not reversible and in which
a new substance is formed.
Chemical reaction: A change in which one or more new
substances are formed.
Electrode: Any conducting material where current
enters or leaves an electrolyte during
electrolysis.
Filtrate: The liquid that passes through a filter.
Mass: Amount of matter contained in a substance.
Physical change: A change in which no new substance is
formed and it is also easily reversed.
Residue: The solid left on a filter paper after filtration.
Temperature: How hot or cold a substance is.
Thermometer: An instrument used to measure temperature.