C8 Chemical analysis

Question 1

In chemistry what is a “pure” substance?

Answer 1

A substance made of a single element or compound

Question 2

How can pure substances be distinguished from impure ones?

Answer 2

By their melting/boiling points

Question 3

Describe the melting and boiling points of pure substances

Answer 3

One very specific temperature

Question 4

Describe the melting and boiling points of impure substances

Answer 4

They change state over a temperature range

Question 5

How does adding an impurity affect the melting an boiling point of a substance?

Answer 5

It lowers the melting point and increases the boiling point

Question 6

What is a formulation?

Answer 6

A mixture designed as a useful product

Question 7

Give three examples of formulations

Answer 7

fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

Question 8

What is chromatography?

Answer 8

A process to separate the constituents of a mixture

Question 9

In paper chromatography, what is the stationary phase and what is the mobile phase

Answer 9

Paper is stationary, solvent (usually water or ethanol) is mobile

Question 10

What does the number of spots on a chromatogram tell you about the chemical tested?

Answer 10

The number of spots is the number of compounds in the mixture

Question 11

How can chromatography show the difference between pure and impure substances?

Answer 11

Pure ones will not separate into a number of spots

Question 12

How is the Rf value calculated?

Answer 12

distance moved by spot/distance moved by solvent

Question 13

What does a substance’s Rf value depend on?

Answer 13

How soluble it is in the solvent

Question 14

In chromatography, why must the substances be placed on a pencil line?

Answer 14

Pencil will not dissolve in the solvent

Question 15

In chromatography why must the solvent height be lower than the pencil line?

Answer 15

So that the substances do not dissolve into the solvent off the paper

Question 16

How can hydrogen be tested for?

Answer 16

Makes a squeaky pop when a splint is placed in it

Question 17

How can oxygen be tested for?

Answer 17

Relights a glowing splint

Question 18

How can carbon dioxide be tested for?

Answer 18

Bubble through limewater, turns it milky (cloudy)

Question 19

Why does carbon dioxide turn limewater cloudy?

Answer 19

Solid calcium oxide forms

Question 20

How can chlorine be tested for?

Answer 20

Bleaches damp litmus paper white

Question 21

What is a flame test?

Answer 21

A test to identify metal ions (cations)

Question 22

What is the colour of the flame produced from a lithium containing compound?

Answer 22

Crimson

Question 23

What is the colour of the flame produced from a copper containing compound?

Answer 23

Green

Question 24

What is the colour of the flame produced from a sodium containing compound?

Answer 24

Yellow

Question 25

What is the colour of the flame produced from a potassium containing compound?

Answer 25

Lilac

Question 26

What is the colour of the flame produced from a calcium containing compound?

Answer 26

Orange-red

Question 27

Other than flame tests, how can metal ions be identified?

Answer 27

Use of sodium hydroxide

Question 28

Which solutions produce white precipitates on addition of sodium hydroxide?

Answer 28

Solutions containing aluminium, magnesium, calcium ions

Question 29

How can a solution of aluminium ions be distinguished from calcium and magnesium ones?

Answer 29

Its precipitate will dissolve in excess sodium hydroxide

Question 30

How can compounds of calcium and magnesium be distinguished from each other?

Answer 30

Using flame tests calcium compounds produce an orange - red flame

Question 31

What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing copper (II) ions?

Answer 31

Blue

Question 32

What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing iron(II) ions?

Answer 32

Green

Question 33

What is the colour of the precipitate formed from the addition of sodium hydroxide to a solution containing iron(III) ions?

Answer 33

Brown

Question 34

What is the reaction that occurs when iron (III) reacts with sodium hydroxide?

Answer 34

Fe3+ + 3OH- --> Fe(OH)3

Question 35

What is the test for carbonates?

Answer 35

Add an acid to generate carbon dioxide gas

Question 36

What is the test for halides?

Answer 36

Add silver nitrate and nitric acid to generate a solid silver halide precipitate

Question 37

What are the colours of the silver halides?

Answer 37

Silver chloride white, silver bromide cream, silver iodide yellow

Question 38

What is the test for sulphate ions?

Answer 38

Add barium chloride and hydrochloric acid, forms white precipitate

Question 39

What is an instrumental method?

Answer 39

Use of scientific technology to perform chemical analysis

Question 40

What are the disadvantages of instrumental methods?

Answer 40

They are accurate (gives correct results), sensitive (only needs a small sample to work), rapid (a lot faster than other tests)

Question 41

What are the three advantages of instrumental methods?

Answer 41

A trained person is needed to operate the technology, the technology can be very expensive

Question 42

What is flame emission spectroscopy?

Answer 42

An instrumental analysis tool for identifying metal ions

Question 43

How is flame emissions spectroscopy carried out?

Answer 43

Sample placed in a flame, light emitted is passed through a spectroscope to give a spectrum which can be compared to a reference