Chemistry

SeparationTechniques

When scientists investigate samples of chemicals collected in the environment there's often more than one substance present in the sample and the different substances must be sorted out before an effective analysis can even begin.

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details about the lesson go to

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Introduction: Separation Techniques

It’s not often that scientists have to go to the front line of a war zone, but that’s what happened recently in Syria.

The government there, which is �ghting in a civil war, had used poisonous gas against the rebels. But before the United

Nations could demand that Syria give up its chemical weapons it had to prove what was in them. That’s where the scientists

came in.

Travelling in very dangerous areas where they could be shot at any time, the chemists moved through the war zone

collecting samples from where the gas had been used. Fortunately they did so safely and got the samples back to the lab.

The next job was to analyse the samples to see exactly what gas had been used.

They used a two-step technique called gas chromatography–mass spectrometry. The �rst step separates the sample into

its components. The second step identi�es the components by identifying signature chemical properties.

The scientists proved that the poisonous gas sarin had been used and so the United Nations was able to force Syria to

destroy its chemical weapons. 

Read the full Cosmos Magazine article here.

Question 1

List: Have you ever noticed that you're surrounded by both pure substances and mixtures? List three things from around

your home or school that you think might be pure substances and another three things that you think might be mixtures.

Pure substances Mixtures

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Gather: Separation Techniques

Already today, your body has processed matter in the form of solids, liquids and gases: your breakfast, a drink and the air

around you. Understanding what all these types of matter are composed of helps scientists to solve real problems, such as

investigating the presence of the deadly toxin, sarin. This requires knowing whether any sample of matter is pure or

mixed – and if it is mixed, how to separate out the di�erent components.

All matter is made up of extremely tiny particles. These particles can be atoms of one type of element or two or more

di�erent elements that are chemically combined into a compound.

A pure substance can be either an element or a compound.

For example, gold is a pure substance composed of only gold atoms while distilled water is a pure substance composed of

hydrogen and oxygen atoms chemically bonded together to form water molecules.

A mixture is a combination of two or more pure substances that can be physically separated.

For example, a soft drink is a mixture of water, sugar, carbon dioxide gas and other chemicals. Air is also a mixture,

composed of nitrogen, oxygen, carbon dioxide and other gases.

Classifying matter

Question 1

Recall: Only elements are pure substances.

True

False

I'm not sure

Question 2

De�ne: What is a mixture?

A pure substance

A combination of two or more substances that

can be physically separated

A compound of two or more elements

I'm not sure

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Question 3

Label: Each sphere below represents an atom and each colour represents a di�erent element. Some of the atoms are

joined together to form molecules. There's no matter in between the particles – just empty space!

Identify each sample of matter as either a mixture or a pure substance by dragging and dropping the labels. Two have been

done for you.

We can group mixtures further by classifying them into those that are heterogeneous and those that are homogeneous.

Homogeneous and heterogeneous mixtures

Credit: ADLC – Elementary Science: Mixtures by ADLC Educational Media (YouTube).

0:00 / 4:54

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Question 4

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional, but we recommend taking notes – they will help you remember the main points of the

video and also help if you need to come back to answer a question or review the lesson.

Question 5

De�ne: After watching the video, de�ne the terms homogeneous mixture and heterogeneous mixture.

Question 6

Summarize: Based on information in the video, complete the following table.

Mixture Homogeneous Heterogeneous

e.g. corn starch and water yes

vinegar and water

pepper and salt

sand and water

salt and water

A solution is a homogeneous mixture in which one or

more substances (the solutes) are dissolved in another

substance (the solvent).

Solutions are made up of elements or compounds mixed

together at the molecular level.

Apple juice is a solution. The juice looks and tastes the

same whether it comes from the top, middle, or bottom of

the glass.

Solutions

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Question 7

Discuss: Do you agree or disagree with the statement "All solutions are mixtures, but not all mixtures are solutions"? Give a

reason for your choice.

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Question 8

Review: Before we look at how various mixtures can be separated, it's important that you're comfortable with how

mixtures are classi�ed and how they're distinguished from pure substances. Consider the following terms relating to

matter that you've encountered in this lesson: 

pure substance   |   mixture   |   homogeneous mixture   |   heterogeneous mixture

atom   |   element   |   compound   |   solute   |   solvent   |   solution

Revisit these concepts and then construct a detailed mind map that shows your understanding of how these terms are

related.

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Process: Separation Techniques

Gas masks contain sophisticated �lters to separate out toxic particles from the air to protect the wearer. Combustion engines,

such as those in cars and buses, also contain �lters. These �lters separate out tiny carbon particles from the exhaust.

It's often important for human and environmental health that the components of a mixture are separated away from each

other. As reported in the Introduction, scientists investigated mixtures suspected of containing microscopic particles of a

lethal substance called sarin.

The combustion engines in cars and buses have been designed to separate out very tiny carbon particles and prevent them

from polluting the atmosphere. A similar, more sophisticated, separation system can be found in the gas masks worn by

the scientists in Syria.

Mixtures can be separated into their di�erent pure substance components based on the physical properties of the

components.

Pure substances have unique physical properties such as di�erent density, state of matter, melting point, boiling point and

solubility. Scientists need an understanding of these di�erent physical properties to be able to distinguish one type of

particle from another.

Techniques used to separate mixtures rely on these di�erences in the physical properties of the components.

Separating mixtures

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Credit: Separating Mixtures by Anthea Barbara (YouTube).

0:00 / 2:29

Question 1

Notes: Use this space to take notes for the video.

Note: This is not a question and is optional.

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Filtration can be used to separate insoluble solids from a

liquid. It uses a �lter. The holes in a �lter are usually too

small to see, but solid pieces get trapped whereas the

liquid and anything soluble pass through.

Example: When a mixture of sand and water is poured

through �lter paper in a funnel, the sand particles remain

as a solid residue in the �lter paper, while the water is

collected in the beaker below as a liquid �ltrate. 

If the water has salt dissolved in it, the salt passes through

the �lter paper into the �ltrate.

Filtration separates on the basis of di�erences in particle

size and solubility.

Filtration

Evaporation is a method that recovers solid substances

dissolved in a liquid. It recovers the solute from the

solution by evaporating away the solvent, but not the

solute.

Example: Salt can be collected from a salt water mixture by

evaporation. The liquid water evaporates to leave the salt

behind, since water has a much lower boiling point than

salt.

Evaporation separates on the basis of di�erences in boiling

point.

Evaporation

Question 2

Explain: What happens to the particles in a solution during the process of evaporation.

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Simple distillation is an extension of evaporation. It's

used to recover a pure liquid substance from a solution.

The solution is heated to evaporate the solvent. But unlike

simple evaporation this solvent, which is now in gaseous

form (a vapour) is collected. It is cooled to condense it back

into liquid in a separate container.

Example: A mixture of salt and water is heated to just over

100°C in a special distillation �ask. 100°C is over the boiling

point of water so the water turns into vapour. 100°C is well

below the boiling point of salt, so it stays in the �ask. The

water vapour passes into a cooling tube which condenses

it back into liquid water so it can be collected as distillate.

The salt has been left behind.

Simple distillation separates on the basis of di�erences in

boiling point.

Simple distillation

Question 3

Sort: Sequence the following processes into their correct order as they occur during the distillation of pure water from salty

sea water.

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Flotation can be used to recover a solid or a liquid from

another liquid depending on which components sink or

�oat.

Example: If sawdust and sand are stirred into water, the

sawdust �oats and the sand sinks, because the sawdust is

less dense than the water and the sand is more dense

than the water.

Another example of this is if oil and water are stirred

together. The oil will �oat on top of the water as it is less

dense than the water.

Flotation separates on the basis of di�erences in density. A

less dense component will �oat to the top of a liquid

where it can be skimmed or poured o� and a more dense

component will sink to the bottom.

Flotation

Oil �oating on water.

Question 4

Categorize: Identify the separation technique represented by the following images.

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Question 5

Analyse: Identify the separation techniques you would likely need to use to separate a mixture of styrofoam beads,

sand and magnesium sulfate solution given the information in the table below. Explain your choices.

Step 1: Styrofoam beads Step 2: Sand Step 3: Magnesium sulfate

Water soluble no no yes

State of matter at 25oC solid solid solid

Less dense than water yes no no

Separation technique

required – including

explanation

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Experiment: Separation Techniques

Separation of a mixture by simple paper chromatography

The Cosmos Magazine article identi�es a sophisticated separation technique known as gas chromatography.

Chromatography is a separation technique based on how the components of a mixture interact with their surroundings.

There are many di�erent types of chromatography but in each case the sample mixture needs to be dissolved, carried

along by a solvent and dropped. Some components of the sample mixture interact more strongly with the surroundings

and so travel at di�erent speeds from other components in the mixture.

The inks in non-permanent black felt-tip pens are often made from a mixture of di�erent coloured pigments that can all

dissolve in water. However, due to their di�erent structures, these pigments are soluble by di�erent amounts and so travel

at di�erent speeds.

Water acts as a solvent to dissolve the inks. The water carries the pigments along as it wets the �lter paper and then drops

them onto the paper at di�erent places to create a uniquely coloured pattern for each felt-tip pen.

Did you know?

Did you know that the water wets the paper because of a phenomenon called capillary action? It's essentially the same

action that a tree uses to soak water up its trunk from its roots and into its branches.

To separate the mixture of coloured pigments present in black inks using paper chromatography.

Background

Aim

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1 �lter paper disc

4 di�erent brands of water-soluble black felt-tip pens (labelled A, B, C, D)

Pencil

Plastic dropper

10 mL distilled water

Optional extension – 10 mL salt water solution (10%)

Students should wear a lab coat and goggles at all times.

1. Using clean hands, fold the �lter paper in half, then in half again, to make quarters.

2. Unfold the �lter paper onto a clean, dry and �at surface – this will give you 4 fold lines on your paper.

3. Using the black coloured felt-tip pens place a small dot (about 2 mm diameter each) on each of the four fold lines

approximately 2 cm from the centre

4. Write the letter corresponding to each black felt-tip pen at the edge of the �lter paper using the pencil

5. Very carefully, use the plastic dropper to place one drop of water onto the centre of the �lter paper and watch

what happens. Record your initial observations in the project space below.

6. Once the water has stopped spreading, add another drop and record your next set of observations.

7. Add further drops of water, one drop at a time, waiting in between each drop for the spreading to stop. Record

your �nal observations.

If you have time, you could repeat the experiment in exactly the same way but using salty water instead of distilled water. 

Independent variable – di�erent brand of black felt-tip pen ink.

Dependent variable – distance travelled by each pigment in the ink mixture.

Materials

Safety information

Procedure

Variables

Question 1

List: Identify all of the controlled variables in this experiment.

Note: The independent variable is what is being changed each time, the dependent variable is what you are measuring or testing

and the controlled variables are all of the factors that remain constant throughout the experiment.

HypothesisIt's possible that di�erent brands of black felt-tip pen inks will contain di�erent mixtures of pigments that travel at di�erent

speeds during the separation process.

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Collect: Use the project space below to present your results. You should construct a table of results which best suits the

data but you may also include photos, video or other representations.

Discussion

Question 3

Justify: Explain why you used a pencil to write the letter

corresponding to each black felt-tip pen at the edge of the

�lter paper (rather than a pen).

Question 4

Assess: Explain whether or not you think separation of the

mixture is taking place to the same extent for each brand

of black felt-tip pen. Use your results to support your

answer.

Question 5

Propose: Suggest what you might observe if the experiment was repeated to include a permanent black felt-tip pen.

Explain your reasoning.

Question 6

Evaluate: Identify some limitations to the experimental

design that prevent you from collecting more reliable and

accurate data. 

Question 7

Evaluate: Suggest changes that you could make if you

were to repeat this experiment, which address the

limitations you identi�ed.

Results

Question 2

Question 8

Conclude: Write a concluding statement that addresses both the aim of the experiment and the hypothesis.

Conclusion

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Career: Separation Techniques

As the only child of a cleaner and a builder, young Martin Boland never gave much thought to going to university.

Martin had his sights set on becoming a �ghter pilot in the Royal Australian Air Force.

So he studied chemistry and physics in high school in the

hope that they would help get him into the air force. But

Martin's dreams were dashed when he was told he was

too tall to �t into the ejector seats of a �ghter jet.

Nevertheless, inspired by the science o�cers he had seen

on Star Trek, he decided to study chemistry at university.

Martin now calls chemistry “the great love of his life.” He is

a lecturer of pharmaceutical and medicinal chemistry at

Charles Darwin University in the Northern Territory. He

also runs his own research lab, where he tries to �gure out

how to use native plants as medical treatments and how to

make drugs last longer in the unforgiving hot climate of

Northern Australia. Martin has even had the opportunity

to work with Australia's only nuclear reactor in Sydney.

But what Martin loves most is talking about science. He

relishes every opportunity to share his scienti�c

knowledge with the public and constantly takes part in

various science outreach activities.

His background in chemistry also gives him a deep

understanding of chemical weapons. Organic chemistry is

the basis for most poisons and explosives, such as those

used in Syria, Iraq, and Boston, says Martin. He hates to

see chemistry being put to use in chemical warfare, and

hopes it will one day be a thing of the past.

Outside the lab, Martin is a certi�ed mountain bike and ski

instructor, and stand-up comedian. He is also trying to

ful�l his childhood dream of joining the air force by

applying for the Australian Army Reserves.

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Question 1

Research:  Chemical agents can cause damage to humans either immediately, like mustard gas in World War I and II, or

over a longer term, such as prolonged exposure to arsenic poison. However, for many years, researchers around the world

have been working to develop therapeutic uses of such chemicals. Speci�c forms of both mustard gas and arsenic have

useful anti-cancer properties. 

Find out about one naturally occurring chemical agent that can also be used as a medical treatment. Examples include:

snake venom, cone snail toxin, ricin from castor oil plants and scorpion toxin. Identify the source organism of the chemical,

how the chemical is used by the organism (e.g. defence or attack) and in general terms how it might be used as a medical

treatment.

Image credits

Introduction: iStock; Gather: Apple juice, iStock; Process:

Reuters / Mohamed Abdullah and iStock, coloured lollies,

iStock; Oil �oating on water, Martin Leigh/Getty Images.

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Test: Separation Techniques

Note: There may be more than one correct answer to the multiple-choice questions below.

Question 1 (1 mark)

Which of the following are pure substances?

Elements

Mixtures

Compounds

I’m not sure

Question 2 (1 mark)

A mixture is a combination of two or more substances that

cannot be physically separated.

True

False

I'm not sure

Question 3 (1 mark)

If you can see the di�erent parts of a mixture then it is

classi�ed as:

homogeneous

heterogeneous

I’m not sure

Question 4 (1 mark)

A solution is a special type of heterogeneous mixture.

True

False, a solution is a homogeneous mixture

I'm not sure

Question 5 (1 mark)

Brine is a mixture in which salt is dissolved in water. Which

statements are true?

Brine is a solution

Brine can be separated into its components by

evaporation

Salt is the solvent and water is the solute

Salt is the solute and water is the solvent

I'm not sure

Question 6 (1 mark)

Substances can be separated by di�erences in their

physical properties. These include:

boiling point

cost

density

solubility

particle size

I'm not sure

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Question 7 (1 mark)

Which of the following separation techniques could be

used to separate a mixture of two substances based on

their solubility?

Filtration

Evaporation

Distillation

Flotation

I'm not sure

Question 8 (1 mark)

Which description below most accurately describes the

di�erence between evaporation and distillation?

Distillation involves evaporation, but the

solvent is collected as well as the solute

Evaporation involves distillation, but the

solvent is collected as well as the solute

Distillation involves evaporation, but only the

solute is collected

Evaporation and distillation are unrelated

methods of separation

I'm not sure

The diagram to to the right shows �ltration. Use this to

answer Questions 9 and 10.

Question 9 (1 mark)

In the diagram, A is the:

�ltrate

residue

solute

distillate

I'm not sure

Question 10 (1 mark)

In the diagram, B is the:

�ltrate

residue

solute

distillate

I'm not sure

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Question 11 (1 mark)

Oil and water can be separated using �otation because:

oil is more dense than water so �oats on top

oil is more dense than water so sinks to the

bottom

oil is less dense than water so �oats on top

oil is less dense than water so sinks to the

bottom

I'm not sure

A mixture, pictured below, contains the substances in the table. Your task is to separate them all. Use the substances'

properties to work out which separation techniques to use to answer Questions 12 to 16.

SubstanceMore/less dense than

waterSoluble in water Magnetic

sand more no no

plastic beads less no no

sugar more yes no

paper clips (metal) more no yes

Question 12 (1 mark)

Which separation technique could be used to separate the

paper clips from the rest of the mixture?

Distillation

Magnetism

Flotation in water

Filtration

Evaporation

I'm not sure

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Question 13 (1 mark)

If you add water to the mixture – say, double the volume of

the mixture – then stir it well and leave to settle, what will

be some of the e�ects?

The plastic beads will settle to the bottom

The sand will settle to the bottom

The sand will dissolve

The sugar will dissolve

I'm not sure

Question 14 (1 mark)

Which separation technique could be used next to

separate the beads from the rest of the mixture?

Distillation

Magnetism

Flotation in water

Filtration

Evaporation

I'm not sure

Question 15 (1 mark)

Assuming that, as per the previous question, you added

water to the mixture, and the paper clips and plastic beads

have been removed, which method would be best to

separate the sand and sugar?

Distillation

Magnetism

Flotation in water

Filtration

Evaporation

I'm not sure

Question 16 (1 mark)

With paper clips, plastic beads and sand removed, this

leaves the sugar and water.

Which �nal separation technique is required to isolate the

sugar?

Distillation

Magnetism

Flotation in water

Filtration

Evaporation

I'm not sure

No, no further separation

Question 17 (1 mark)

Learning goal 1: Pure water is a pure substance but sea water is a mixture. Explain this di�erence in terms of the types of

particles that each substance contains and whether or not they can be physically separated.

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Total available marks: 19

Question 19 (1 mark)

Learning goal 3: There are many ways of separating mixtures, including �ltration, evaporation, distillation and �otation.

Choose one of these techniques and describe how it works. Make sure you identify which physical property it relies on to

separate the di�erent components.

Question 18 (1 mark)

Learning goal 2: Explain the di�erence between homogeneous and heterogeneous mixtures in your own words.

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