Chemial analysis

Question 1

What is chemical analysis?

Answer 1

The process of establishing what chemicals are present in a substance

Question 2

In everyday language what is a “pure” substance?

Answer 2

A substance that has had nothing added to it and is in its “natural” state

Question 3

In chemistry what is a “pure” substance?

Answer 3

A substance made of a single element or compound

Question 4

How can pure substances be distinguished from impure ones?

Answer 4

By their melting/boiling points

Question 5

Describe the melting and boiling points of pure substances

Answer 5

One very specific temperature

Question 6

Describe the melting and boiling points of impure substances

Answer 6

They change state at a range of temperatures

Question 7

What is a formulation?

Answer 7

A complex mixture designed as a useful product

Question 8

Give three examples of formulations

Answer 8

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

Question 9

What is chromatography?

Answer 9

A process to separate the constituents of a mixture

Question 10

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

Answer 10

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

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

How can chlorine be tested for?

Answer 19

Bleaches damp litmus paper white

Question 20

What is a flame test?

Answer 20

A test to identify metal ions (cations)

Question 21

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

Answer 21

Crimson

Question 22

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

Answer 22

Green

Question 23

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

Answer 23

Yellow

Question 24

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

Answer 24

lilac

Question 25

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

Answer 25

Orange-red

Question 26

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

Answer 26

Use of sodium hydroxide

Question 27

Which solutions produce white precipitates on addition of sodium hydroxide?

Answer 27

Solutions containing aluminium, magnesium, calcium ions

Question 28

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

Answer 28

Its precipitate will dissolve in excess sodium hydroxide

Question 29

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

Answer 29

Blue

Question 30

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

Answer 30

Green

Question 31

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

Answer 31

Brown

Question 32

What is the test for carbonates?

Answer 32

Add an acid to generate carbon dioxide gas

Question 33

What is the test for halides?

Answer 33

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

Question 34

What are the colours of the silver halides?

Answer 34

Silver chloride white, silver bromide cream, silver iodide yellow

Question 35

What is the test for sulfate ions?

Answer 35

Add barium chloride and hydrochloric acid, forms white precipitate

Question 36

What is an instrumental method?

Answer 36

Use of scientific technology to perform chemical analysis

Question 37

What are the three advantages of instrumental methods?

Answer 37

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

Question 38

What is flame emission spectroscopy?

Answer 38

An instrumental analysis tool for identifying metal ions

Question 39

How is flame emissions spectroscopy carried out?

Answer 39

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