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Chromatography

In this worksheet, students will learn about chromatography as a separation technique and its uses in the identification of substances and forensics.

'Chromatography' worksheet

Key stage:  KS 3

Curriculum topic:   Chemistry: Pure and Impure Substances

Curriculum subtopic:   Separating Mixtures

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

Sometimes more than one substance is dissolved in a solution. Chromatography is a technique that is used to separate those substances. For example, if you take a filter paper and put a dot with a marker pen in the centre of it and then add a drop of solvent on the same point as the one you drew the dot on, you will separate the ink into its different colours and the result will look similar to this:

 

Chromatogram

 

Chromatography is used by scientists to analyse samples of water in order to find out how much of certain chemicals are in the water. DNA fingerprinting, which was invented by Professor Sir Alex Jeffreys in 1984 at the University of Leicester, is based on chromatography and is used to identify criminals by their DNA samples. Samples of blood or skin can also be compared by the police using chromatography.

 

Method

 

The sample liquids to be tested are dropped onto special paper. The bottom of the paper is dipped in water or another suitable solvent. The different-sized particles that make up the samples travel through the paper at different speeds, so they separate at different distances. The chromatogram below tested four ink colours in order to separate them into the colours that were mixed to make them up. Study it carefully, because you will be asked questions about it.

 

Chromatogram

Name the technique used to separate different substances dissolved in a solution.

Is this statement true or false?

DNA fingerprinting is based on a technique called distillation.

true

false

Is this statement true or false?

The solvent used in chromatography is water.

true

false

What do you call the paper that shows the results of chromatography?

How does chromatography help in analysing water samples? There are two correct answers.

Water is separated into its different components.

Water may contain chemicals in it and they can be identified with chromatography.

It is determined if a sample of water is safe to drink.

Different ink colours will show up on the chromatogram.

Water will be separated between still and sparkling.

What kind of human tissue evidence from a crime scene may be analysed using chromatography? Tick two options.

paper

blood

shoes

clothes

skin

Here is the chromatogram from the Introduction page:

 

Chromatogram

 

What two colours make up the purple ink?

green

orange

yellow

red

blue

Chromatogram

How do you know that brown ink contains blue ink? 

Purple is separated into red and blue.

There is a blue dot directly above the point labelled as brown.

There is a blue dot directly above the point labelled as green.

Chromatogram

 

What colours make up the yellow ink in the chromatogram?

green

red

yellow

blue

brown

Why do different substances separate at different distances in a chromatogram? Tick two options for a complete answer.

The samples contain different versions of the same substance.

The particles of different chemicals are of different sizes.

Because the water dissolves them.

The different-sized particles travel through the chromatography paper at different speeds.

The results are shown on a computer screen and have different resolution.

  • Question 1

Name the technique used to separate different substances dissolved in a solution.

CORRECT ANSWER
chromatography
EDDIE SAYS
Sometimes there are different substances dissolved in a solution. Chromatography is used to separate them - learn to spell it correctly!
  • Question 2

Is this statement true or false?

DNA fingerprinting is based on a technique called distillation.

CORRECT ANSWER
false
EDDIE SAYS
DNA fingerprinting separates pieces of DNA that are of different sizes. Criminals can be identified if these are compared to known DNA samples. This technique is based on chromatography.
  • Question 3

Is this statement true or false?

The solvent used in chromatography is water.

CORRECT ANSWER
false
EDDIE SAYS
Water is often used in chromatography. However, not all substances are soluble in water, so sometimes other solvents are used, for example ethanol.
  • Question 4

What do you call the paper that shows the results of chromatography?

CORRECT ANSWER
chromatogram
EDDIE SAYS
The piece of paper where the samples are loaded and on which the different substances are separated is called a chromatogram.
  • Question 5

How does chromatography help in analysing water samples? There are two correct answers.

CORRECT ANSWER
Water may contain chemicals in it and they can be identified with chromatography.
It is determined if a sample of water is safe to drink.
EDDIE SAYS
Chromatography is used to analyse samples of water in order to find out if there are chemicals in it. Then it is determined if the water is safe to drink.
  • Question 6

What kind of human tissue evidence from a crime scene may be analysed using chromatography? Tick two options.

CORRECT ANSWER
blood
skin
EDDIE SAYS
Many pieces of evidence from a crime scene can be analysed to match with suspects. From the list above only blood and skin are from human tissue. This is what the question specifies, so blood and skin are the correct answers.
  • Question 7

Here is the chromatogram from the Introduction page:

 

Chromatogram

 

What two colours make up the purple ink?

CORRECT ANSWER
red
blue
EDDIE SAYS
The purple ink dot is separated into two colours directly above the point where the purple dot was drawn; red and blue.
  • Question 8

Chromatogram

How do you know that brown ink contains blue ink? 

CORRECT ANSWER
There is a blue dot directly above the point labelled as brown.
EDDIE SAYS
There is a blue dot directly above the point labelled as brown. This means that this particular brown ink is made of different colours including blue.
  • Question 9

Chromatogram

 

What colours make up the yellow ink in the chromatogram?

CORRECT ANSWER
yellow
EDDIE SAYS
The yellow ink is made of yellow only, as there is only a yellow dot directly above the point labelled as 'yellow'.
  • Question 10

Why do different substances separate at different distances in a chromatogram? Tick two options for a complete answer.

CORRECT ANSWER
The particles of different chemicals are of different sizes.
The different-sized particles travel through the chromatography paper at different speeds.
EDDIE SAYS
Different substances have particles of different sizes. Those travel through the chromatography paper at different speeds.
---- OR ----

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