C8: Chemical Analysis

Question 1

How can we test to see if a substance is pure or not?

Answer 1

Testing to see what the melting/boiling point is
If it is pure it will be very specific

Question 2

What are formulations?

Answer 2

Mixtures of certain substances to fulfil a specific purpose e.g.
-Paints
-Fuels
-Alloys
-Fertilisers

Question 3

What is chromatography?

Answer 3

The separating of a mixture to identify it’s constituent substances e.g. pigments in ink, drugs in urine sample

Question 4

What is the stationary phase?

Answer 4

What the substances move up e.g. chromatography/filter paper

Question 5

What is the mobile phase?

Answer 5

The solvent e.g. water

Question 6

How does the solvent move up the paper?

Answer 6

Due to capillary action
This pulls the substances in the mixture upwards, with lighter particles being moved further up the stationary phase

Question 7

Where is the starting line drawn?

Answer 7

Just above the water line, in pencil (so it won’t move)
All measurements are made from this

Question 8

What is the equation to calculate Rf (retention factor) values?

Answer 8

Rf value = distance substance moved/distance mobile phase moved

Question 9

what can Rf values be compared against?

Answer 9

Known substances to identify them

Question 10

What is the test for hydrogen?

Answer 10

Lit splint produces a squeaky pop

Question 11

What is the test for oxygen?

Answer 11

Will relight glowing splint

Question 12

What is the test for carbon dioxide?

Answer 12

Causes limewater to turn cloudy when bubbled through it

Question 13

What is the test for chlorine?

Answer 13

Bleaches blue litmus paper

Question 14

What do flame tests test for?

Answer 14

Metal ions

Question 15

What colour will the flame turn if lithium is present?

Answer 15

Crimson

Question 16

What colour will the flame turn if sodium is present?

Answer 16

Yellow

Question 17

What colour will the flame turn if potassium is present?

Answer 17

Lilac

Question 18

What colour will the flame turn if calcium is present?

Answer 18

Orange-red

Question 19

What colour will the flame turn if copper is present?

Answer 19

Green/blue

Question 20

How do we test for metal ions in a solution?

Answer 20

Add sodium hydroxide to make metal hydroxide (coloured precipitate)

Question 21

What colour precipitate will aluminium, calcium and magnesium produce?

Answer 21

White

Question 22

What happens when excess sodium hydroxide is added to aluminium?

Answer 22

The white precipitate will dissolve

Question 23

What colour precipitate will copper (II) (Cu2+) produce?

Answer 23

Blue

Question 24

What colour precipitate will iron (II) (Fe2+) produce?

Answer 24

Green

Question 25

What colour precipitate will iron (III) (Fe3+) produce?

Answer 25

Brown

Question 26

What is an example of an ionic equation for metal ions in a solution?

Answer 26

Cu2+ + 2OH- -> Cu(OH)2

Question 27

How do we test for carbonates?

Answer 27

- React with hydrochloric acid to produce carbon dioxide - Set up delivery tube so any gas involved will be collected - Limewater will go cloudy

Question 28

How do we test for halide ions?

Answer 28

Will produce a precipitate when mixed with silver nitrate & nitric acid -Chlorine ions = white -Bromide ions = cream -Iodide ions = yellow

Question 29

What will be produced when sulphate ions are mixed with barium chloride & hydrochloric acid?

Answer 29

A white precipitate

Question 30

What is flame emission spectroscopy?

Answer 30

Involves analysing the wavelengths of light emitted from a flame, which can be used to identify ions accurately

Question 31

What are benefits of flame emission spectroscopy?

Answer 31

It is accurate, sensitive, unbiased & rapid

Question 32

What is a pure substance?

Answer 32

Made up of 1 element or compound

Question 33

What is a mixture?

Answer 33

Lots of different things in it, not chemically bonded together

Question 34

What is the test for pure substances?

Answer 34

- Get crystals of pure solution into a very, very thin tube - Melt in melting point apparatus - See if it melts at one temp, or slowly over a range of temperatures

Question 35

Why is a lid put on the chromatography beaker?

Answer 35

To stop the solvent evaporating

Question 36

What colour will the flame turn if barium is present?

Answer 36

Green