C2 - Analysing Substances

Question 1

How does chromatography purify substances?

Answer 1

The substance that needs to be purified will be separated from other substances which makes it pure

Question 2

How does chromatography find out which substances are present?

Answer 2

The substances are separated from each other meaning that they are pure so we can analyse which substances are present

Question 3

What is paper chromatography?

Answer 3

A type of chromatography where colours present in a substance travel up the paper at different rates

Question 4

Give the 2 uses of chromatography

Answer 4

Chemical analysis that finds out what the substances present are
Synthesis (purifying substances)

Question 5

What is chromatography?

Answer 5

A chemical process that separates mixtures of dissolved substances

Question 5

What is the stationary phase?

Answer 5

The part of the chromatography equipment that does not move and is usually solid

Question 6

What is the stationary phase in paper chromatography?

Answer 6

Filter paper

Question 7

What is the mobile phase?

Answer 7

The part of the chromatography that pushes the substances across the stationary phase

Question 8

What is the mobile phase in paper chromotography?

Answer 8

Solvent

Question 9

What is a chromatogram?

Answer 9

The filter paper in paper chromatography with the spots at different heights after the chromatography has taken place

Question 11

Why do we use reference substances?

Answer 11

So that we can see if some of the unknown substances are actually the reference substances

Question 12

How do we know if an unknown substance and a reference substance are the same?

Answer 12

They will be level in height on the chromatogram

Question 13

Why can’t some substances be detected by colour on the chromatogram?

Answer 13

They are colourless substances

Question 14

What do we do to distinguish invisible spots?

Answer 14

Dip the filter paper in locating agent

Question 15

What is a locating agent?

Answer 15

A chemical that reacts with a substance to form a coloured compound

Question 16

What is thin layer chromatography?

Answer 16

A variant of paper chromatography that uses silica plates instead of filter paper as a stationary phase

Question 17

What is the advantage of using thin layer chromatography instead of paper chromatography?

Answer 17

Small quantities of the substances can be used

Question 18

Why do some substances move across the mobile phase at different speeds than each other?

Answer 18

Some substances have an equilibrium position that favours the mobile phase more or less than others

Question 21

What is chemical analysis?

Answer 21

Analysing substances to find out their chemical composition and structure

Question 22

What is gas chromatography?

Answer 22

A form of chromatography that uses a carrier gas as a mobile phase and is very accurate

Question 23

Which substances are used as carrier gases and why?

Answer 23

Argon and nitrogen

They are inert (don’t react)

Question 24

Describe gas chromatography

Answer 24

The substances are heated until they become gases
The carrier gas brings the substances along a tube and they pass a sensor
The fact that they travel at different speeds means that they will go through the sensor at different times

Question 25

What is retention?

Answer 25

How much a substance holds back (favours the stationary phase)

Question 26

What is a mass spectrometer?

Answer 26

An instrument that weighs molecules and tells us the molecular mass of substances

Question 27

What do substances need to be so that mass spectrometry works?

Answer 27

They need to be ionised to be detected

Question 28

What is a mass spectrum?

Answer 28

The graph output of a mass spectrometer

Question 29

What does the height of a peak on the mass spectrum mean?

Answer 29

Represents an ion

Tells you the relative atomic mass

Question 30

Describe the process of paper chromatography

Answer 30

A pencil line is drawn 1 cm above the base of the filter paper with a ruler
The different substances are spotted onto the line at different points
Reference substances are also spotted onto the line
The bottom of the filter paper is dipped in solvent
The substances travel up the filter paper with the solvent and stop at different points forming a chromatogram

Question 30

What is the retention time?

Answer 30

The time a substance takes to reach the detector

Question 31

What is the retardation factor?

Answer 31

How much a substance favours the mobile phase or stationary phase
1 for mobile and 0 for stationary

Question 31

What are the 3 advantages of using machines for chemical analysis?

Answer 31

Can detect even the tiniest amounts of substances

Very fast and tests can be automated

Very accurate

Question 32

How do you calculate the retardation factor?

Answer 32

Distance between spot and pencil line / distance between top of mobile phase and pencil line