Natural Sciences3rd YearTerm 2

Mixtures

Solutions & Dissolving The Water Cycle

Name and Surname: ________________________________________Year group: ____________________MIXTURES OF MATERIALS

KEY WORDS

1.mixture two or more substances that are mixed together

Fruit Salad

2. separate to break up a mixture into the substances mixed

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3. physically to use hands or tools to separate a mixture

4. sieving to use a tool with holes that allows pieces of a certain size to pass

5. filtering to separate a liquid and a solid by pouring it through a material like filter paper

a mesh fabric

6. hand sorting to separate a mixture of solids by hand

7. settling allow a solid mixed with a liquid to settle at the bottom

8. decanting to carefully tilt the container and pour off the top layer of a mixture

Introduction: MixturesDate:___________________

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The first question that we need to answer before we can go any further is probably,

what is a mixture? A mixture is two or more different materials that have been mixed

together. Mixtures are absolutely everywhere you look. Most things in nature are

mixtures. Look at rocks, the ocean, or even the atmosphere. In some materials, the

different materials are still clearly visible after mixing. A mixture of peanuts and

raisins would be an example of such a mixture. How would we separate the peanuts

and raisins? Well, we could simply pick the raisins out of the peanuts!

A mixture of peanuts & raisins.

Can you think of other mixtures in which the different materials are still clearly visible

after mixing? Look at the pictures below for some ideas.

A mixture of different coloured jelly beans. A mixture of different fruits in a fruit salad.

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A mixture of swans and ducks on a lake. A mixture of red, green and yellow peppers.

A mixture of different flowers. A mixture of different shells from the beach.

In other mixtures, the materials are mixed so thoroughly that it seems one material

has ‘disappeared’ into the other. Such mixtures are called solutions. We will learn

more about solutions later in the term.

Let us look at the following concepts first:

MixtureWe’ve seen that mixtures are all around us. In short it is something that could be

separated into two or more substances.

SolutionA solution is when two or more substances dissolves (disappear) into each other.

The substance that dissolves is called the solute. The substance that does not

dissolve is called the solvent. E.g. salt water = water (solvent) + salt (solute)

SolidSolids are objects that are firm and stable. They hold their shape and it could be

hard, soft, big or small. E.g. a jelly bean.

Liquid

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Liquids flow and take on the shape of the container they are in. Therefore we can

say that it has no fixed shape. E.g. water.

SolubleThis means a substance is able to dissolve in a solvent. E.g. sugar is soluble

because it is able to dissolve (disappear) in water.

InsolubleThis means the substance is unable to dissolve in a solvent. E.g. sugar is

not soluble in oil.

Pure substanceA pure substance is made up of only one kind of molecules. It is a substance that

cannot be separated by physical means such as filtration, evaporation or distillation.

E.g. iron, wood, copper, water, gold, oxygen, sugar etc.

Activity 1Answer the following questions.

1. What exactly is a ‘mixture’?

______________________________________________________________

______________________________________________________________

2. What do we call a mixture that seems to disappear into one another?

___________________________

3. A substance that dissolves is called the ______________________.

4. A substance that does not dissolve is called the ____________________.

5. In a solution of water and salt; water would be the __________________ and

salt would be the _____________________.

6. Draw a picture of any mixture that you can think of. (Tip: Look at the

examples on p.2&3 for some guidance and use colour.)

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Separating mixturesDate:___________________

In this next section we will be studying all of the different ways of separating

mixtures. It is possible to mix materials in many different combinations. In a mixture,

the materials that have been mixed do not change. They keep their individual

properties (appearance). Sometimes it is possible to separate a mixture into the

original individual materials it stared out with.

Let’s look at a few methods used to separate mixtures into a pure substance:

A magnetA magnet is used to separate a metal from non-metal. E.g. it could be used to

separate iron from sand.

FiltrationFiltration is a method used to separate a solid from a liquid. The liquid passes

through the holes of the filter paper. The solid particles are too big and get stuck,

which means that it stays behind.

A mixture of solids and liquid.

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EvaporationEvaporation is used to separate a dissolved solute from a solution. When

we heat salt water, the water will evaporate, leaving the crystals of salt

behind.

SievingA sieve is a tool with many holes and that is used to separate smaller particles from

larger ones, or liquids from solids. A simple strainer that your mother uses in the

kitchen is a great example. Once she pours the spaghetti and water mixture through

the strainer the water is sieved from the cooked spaghetti.

Spaghetti in a strainer.

Hand sortingWhen there are physical differences between the materials that you want to

separate, they can easily be identified and materials could be sorted by hand. E.g.

sorting smarties from jelly tots.

DistillationThis is a very complicated method. It takes place when a liquid is purified by boiling

and condensing the vapours (gas). E.g. salt water is turned into fresh water through

distillation. Various forms of fuel, such as gasoline, are separated from crude oil by

distillation. Alcoholic beverages are made through distillation; the alcohol is boiled

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off from the rest of the mixture and collected in a concentrated (removed water)

format.

The Process of Distillation.

Activity 2Look at the table below. It contains pictures of mixtures.

1. For each of the mixtures in the table write what materials it is made up of in

the middle column.

2. In the last column, write how you would separate the mixture.

Picture of mixture Materials in the mixture How would you separate?

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SolutionsDate:___________________

Have you ever mixed things in the kitchen just to see what you could make? Maybe

you’ve sprinkled some cinnamon or salt into a cup of water or poured in a splash of

vinegar or oil. Maybe you called it your ‘secret potion’! Did you know that

you were making a solution?!

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We’ve already seen that a solution is when two or more substances dissolve into

each other. If you mix sugar and water, for instance, you can make a solution. If

you are still wondering what the difference between a mixture and a solution is, the

answer is simple; a mixture cannot completely be mixed, it can easily be separated.

Think of a mixture of sand and water, the sand would sink to the bottom of the glass

of water. And a solution dissolves completely into each other.

Do you still remember?

The substance that looks as if it has disappeared is called the solute, e.g.

salt, sugar etc.

The substance that we can still see is called the solvent, e.g. water.

The solvent and solute together are called the solution.

Look at the following experiment. (Your teacher can demonstrate in class.)

Experiment: Dissolving sugar at different temperatures

Learn about solutions as you add more and more sugar cubes to different

temperature water. This easy experiment shows that you can only dissolve a certain

amount and that this changes as the water gets hotter.

What you'll need:

Sugar cubes

Cold water in a clear glass

Hot water in a clear glass (be careful with the hot water)

Spoon for stirring

Instructions:

1. Make sure the glasses have an equal amount of water.

2. Put a sugar cube into the cold water and stir with the spoon until the sugar disappears.

Repeat this process (remembering to count the amount of sugar cubes you put into the water)

until the sugar stops dissolving, at this stage sugar starts to gather on the bottom of the glass

rather than dissolving.

3. Write down how many sugar cubes you could dissolve in the cold water.

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4. Repeat the same process for the hot water; compare the number of sugar cubes dissolved in

each liquid, which dissolved more?

What's happening?

The cold water isn't able to dissolve as much sugar as the hot water, but why? Another name for the

liquids inside the cups is a 'solution', when this solution can no longer dissolve sugar it becomes a

'saturated solution’; this means that sugar starts forming on the bottom of the cup.

The reason the hot water dissolves more is because it has faster moving molecules which are spread

further apart than the molecules in the cold water. With bigger gaps between the molecules in the hot

water, more sugar molecules can fit in between.

Activity 3In this activity we are going to mix substances with water to see which ones make

solutions.

How do you think will we know when a substance has made a solution with the

water?

___________________________________________________________________

___________________________________________________________________

MATERIALS:

Small quantities (amounts) of the following substances:

- Sugar

- Salt

- Sand

- Oil

- Vinegar

- Flour

Tap water

Transparent containers

Plastic spoons for scooping

INSTRUCTIONS:

1. Fill the containers halfway with water.

2. Place one small scoop of sugar in it and stir well.

3. Look at the mixture and discuss what it looks like.

4. Complete the table on the next page. What did you see happening? Make a cross in the

correct column.

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5. Once you have recorded your observation, you can empty the container.

6. Repeat steps 1 – 4 until you have tested all of the substances on the list.

Substance It looks as though none of the

substance has disappeared.

It looks as if all or most of the

substance has disappeared.Sugar

Salt

Sand

Oil

Vinegar

Flour

Which of the substances seemed to disappear when they were mixed with the

water?

___________________________________________________________________

Which of the substances did NOT form solutions with water? (Hint: which ones did

not look as if they ‘disappeared’ into the water?)

___________________________________________________________________

DissolvingDate:___________________

What does it mean if we say that a substance dissolved into another substance?

The answer is simple, think of it this way, when a solute (salt) disappears into solvent

(water), we say that it has dissolved.

Surely the question on everyone’s lips is: “Is melting and dissolving the same?” The

answer to that question is NO, because in order for a solid to melt it needs either

heat or energy and for a substance to dissolve it just needs water.

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“Tom, do you think all substances dissolve in water?

“Good question, Kim. But I don’t think so, take oil and water for instance or

even sand and water.”

Examples of substances that dissolve:

Cup of coffee

Cup of tea

Cup of soup (instand mix)

Cup of hot chocolate

Salt water

Sugar water

Water and liquid soap (washing hands)

Milk and milkshake powder

_______________________________

_______________________________

_______________________________

Can you think of any other substances that will be able to dissolve? Add them to the

above list.

Activity 4Answer the following questions. You might have to read through the previous

lessons to find the answers.

1. What is the difference between a ‘mixture’ and a ‘solution’?

Mixture -_______________________________________________________

______________________________________________________________

Solution -______________________________________________________

______________________________________________________________

2. Name one example of a mixture.

_______________________________________

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3. Name one example of a solution.

_______________________________________

4. Name one example of a solute.

_________________________

5. Name one example of a solvent.

_________________________

6. What does it mean if we say that a substance dissolved into another

substance?

______________________________________________________________

7. Melting is not the same as dissolving. How do they differ from each other?

______________________________________________________________

______________________________________________________________

The Rate of DissolvingDate:___________________

We’ve spoken about substances that dissolve but next we will be concentrating on

the ‘rate of dissolving’. This means we are going to determine how fast or slow a

solute, e.g. sugar will dissolve into a solvent, e.g. water.

Factors to investigate for the rate of dissolving are:

Temperature

Agitation

Surface-area

Grain size

Temperature

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The temperature tells us how hot or cold a solution is. Temperature is measured

with a thermometer. The hotter the solvent (water), the quicker the rate of dissolving

will be.

AgitationWhen a solution is shaken or stirred it will also speed up the rate of dissolving.

Surface-area (Quantity)In this context the surface area refers to the solvent (water) area. The quantity

(amount) of the solute (sugar) will also influence the rate of dissolving. E.g. the more

sugar a person adds to the solvent (water) the longer it will take to dissolve.

Grain sizeThe size of the particles that form the solute will influence the rate of dissolving. The

bigger the solute (sugar), the slower the rate of dissolving will take place. E.g. sugar

particles are bigger than powder particles, which mean that sugar will take longer to

dissolve than powder.

Let’s look at the next few experiments:

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“Tom likes his coffee sweet, with 3 teaspoons of sugar. For the coffee to taste

sweet, the sugar must be dissolved.”

“Indeed I do, Kim!”

In the experiment above we have three transparent containers. Each filled with

100ml of water. The temperature of the water differs. The first container is filled with

hot water, the second container with tap water and the third container is filled with ice

water. Each container then receives one table spoon of salt. After the salt is added

the solutions are stirred by moving a teaspoon back and forth through the water.

(Note that stirring of the three solutions must occur at the same time for comparisons

to be drawn, so assistance from friends is needed.) The main aim of this experiment

is to determine whether salt will dissolve faster in hot water, water at room

temperature or cold water. The amount of water used remained the same in all three

containers as well as the amount of salt added and the time spent stirring. The only

difference in each of these situations was the temperature of the water. Not only did

we measure the temperature of the water but also the time it took for the salt to

dissolve. Obviously the salt dissolved quicker in the hot water because energy

(heat) was added to the solvent (water).

Second experiment:

In the experiment above we have two transparent containers. Each filled with 100ml

of tap water. Two table spoons of salt were added to both containers. The solution

in the second container was stirred but NOT the first container. The main aim of this

experiment is to determine whether salt will dissolve faster when the solution is

stirred or when the solution is NOT stirred. The amount of water used remained the

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same in both of the containers as well as the amount of salt added and the

temperature of the water. The only difference between these two solutions was that

the one solution was stirred and the other was left untouched. Obviously the salt in

the stirred container dissolved faster than the one that was left untouched because

particles dissolve faster when they are stirred.

Third experiment:

In the experiment above we have two transparent containers. Each filled with 100ml

of tap water. In the first container only one table spoon of salt was added and in the

second container eight table spoons of salt were added. Both of the solutions were

stirred with the same intensity. The main aim of this experiment is to determine

whether the quantity of salt will influence the rate of dissolving. The amount of water

used remained the same in both of the containers as well as the temperature; and

both solutions were stirred. The only difference between these two solutions was

that the one solution contained one table spoon of salt and the other solution eight

table spoons of salt. Obviously the salt in the container with one table spoon of salt

dissolved faster than the one with the eight table spoons because the amount of

particles that had to dissolve was less.

Fourth and final experiment:

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In the experiment above we have two transparent containers. Each filled with 100ml

of tap water. In the first container fine table salt was added and in the second

container coarse rock salt was added. Both of the solutions were stirred with the

same intensity. The main aim of this experiment is to determine whether fine table

salt or coarse rock salt will dissolve faster in water. The amount of water used

remained the same in both of the containers as well as the temperature; and both

solutions were stirred. The only difference between these two solutions was that the

one solution contained fine table salt and the other solution contained coarse rock

salt. Obviously the solution with the fine table salt dissolved faster than the solution

with the coarse rock salt because the particles are much smaller.

Activity 5

1. What does the ‘rate of dissolving’ mean?

_____________________________________________________________

2. List four factors that influence the rate of dissolving.

____________________________

____________________________

____________________________

____________________________

3. Which instrument is used to measure temperature?

____________________________

4. What does the word ‘agitation’ mean?

_____________________________________________________________

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5. What happens to sugar and coffee powder once it is added to hot water?

______________________________________________________________

6. What taste does sugar give to coffee, tea or hot chocolate?

__________________________

7. a. Label the following sketch.

________________ _________________ ________________

b. What is the main aim of this experiment?

____________________________________________________________

____________________________________________________________

c. List three things that remained the same in these three situations.

______________________________

______________________________

______________________________

d. What did not remain the same in these three situations?

______________________________

e. In which solution did the salt dissolve faster? Why?

____________________________________________________________

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____________________________________________________________

*(Learners should pay attention to question seven; similar questions could be asked

about any of the three remaining experiments.)

The Water CycleDate:___________________

Run and get a glass of water and put it on the table next to you.  Take

a good long look at the water.  Now…can you guess how old it is?

The water in your glass may have fallen from the sky as rain just last

week, but the water itself has been around pretty much as long as the

Earth has! And you thought your parents were old. In other words the

water on the Earth is a constant; that is, the same water is here now as

was here when the Earth was first created. The Earth has a limited amount of water

that moves around from dams, rivers, the ocean, swimming pools, clouds etc. But

how does the water move around? The answer lies in nature’s greatest recycling

effort – the water cycle. It is the water cycle that ensures we have continuing source

of clean, fresh water. But before we discuss the water cycle there are a few terms

we need to understand.

Evaporation:   Evaporation is when the sun heats up water in rivers or lakes or the ocean and turns

it into water vapour or steam. The water vapour or steam leaves the river, lake or

ocean and goes into the air.

Transpiration:Transpiration is the process by which plants lose water out of their leaves. 

Transpiration gives evaporation a bit of a hand in getting the water vapour back up

into the air. (Kind of the same way that humans perspire).

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Condensation: Water vapour in the air gets cold and changes back into liquid, forming clouds. This

is called condensation. You can see the same sort of thing at home...  Pour a glass

of cold water on a hot day and watch what happens.  Water forms on the outside of

the glass.  That water didn't somehow leak through the glass!  It actually came from

the air.  Water vapour in the warm air turns back into liquid when it touches the cold

glass.

Precipitation: Precipitation occurs when so much water has condensed that the air or the clouds

cannot hold it anymore.  The clouds get heavy and water falls back to the earth in

the form of rain, hail, sleet or snow.

Collection: When water falls back to earth as precipitation, it may fall back into the oceans, lakes

or rivers or it may end up on land.  When it ends up on land, it will either soak into

the earth or become part of the “ground water” that plants and animals use to drink

or it may run over the soil and collect in the oceans, lakes or rivers where the cycle

starts all over again.

Do you still remember that we learned about the phases of matter during your

second year? Do the words solid, liquid and gas ring a bell? During the water cycle

process the water changes phase. During the evaporation and transpiration stage

the water in a dam, river, ocean etc. changes from being a liquid to a gas (water

vapour). During the condensation stage the water vapour gets cold and changes

into a liquid forming the clouds that you can see in the sky. During the precipitation

stage the liquid falls to the ground in the form of rain (liquid) or snow, sleet or hail

(solids). When collection takes place; the snow, hail or sleet (solids) changes back

into liquid and ends up in dams, rivers, the ocean, swimming pools etc.

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Snow is a solid. Hail is a solid. Sleet is a solid.

Rain is a liquid. Rivers are liquids. The ocean is a liquid.

Steam is a gas.

Activity 6Match column A with column B. Only write down the correct letter next to the

corresponding question number. E.g. 1.1 B

Column A Answers Column B

1.1 Evaporation

1.2 Transpiration

________

________

A. Water vapour in the air gets cold and

changes back into liquid.

B. Water falling back on Earth into rivers,

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1.3 Condensation

1.4 Precipitation

1.5 Collection

________

________

________

lakes and the ocean.

C. Water vapour leaving rivers, lakes or

the ocean and goes into the air.

D. Too much water has condensed and

the clouds or the air cannot hold it

anymore.

E. Plants losing water from their leaves.

The Water Cycle (continues)Date: __________________

When water is heated by the sun, it evaporates, or is turned into water vapour,

leaving any impurities behind. This heated water vapour rises in the air. It is joined

by water vapour from plant transpiration or that which is drawn from the soil. This

vapour may be pushed hundreds of kilometers or more by the upper winds. When

the water vapour cools enough, it condenses, or turns back into tiny water droplets,

which usually form around dust or salt particles in the air. These tiny droplets may

join together into larger drops, which then fall as precipitation. Depending on

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temperature and other factors, this precipitation can take the form of hail, rain, snow

or even sleet.

When it rains, the drops may land back in the water or, on a tree leaf and be

evaporated again, or they may be soaked up by the ground. This underground water

will travel through spaces in the rocks called aquifers. In places where surface water

isn’t always available, wells or bore holes can be drilled into an aquifer and the water

pumped out. Some underground water will travel on a downhill journey in aquifers

for thousands of years before making its way out of the ground.

This water may join run-off from the land’s surface and enter a river, lake or ocean.

The sun heats this water, and the cycle begins again.

Activity 7Draw the water cycle in the block provided below. Label the processes involved.

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*****

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