Topic 8 - Chemical Analysis

Question 1

What is a pure substance?

Answer 1

A single element or compound, not mixed with any other substance

Question 2

What is significant about the melting and boiling point of pure elements?

Answer 2

They melt and boil at specific temperatures so can be distinguished by this data

Question 3

What is a formulation?

Answer 3

A mixture that has been designed as a useful product

Question 4

How are formulations made?

Answer 4

By mixing the components in carefully measured quantities to insure that the product has its required properties

Question 5

Give examples of formulations

Answer 5

Fuel, cleaning agents, paint, medicines, alloys, fertilisers, foods

Question 6

What are complex mixtures?

Answer 6

Many products are complex mixtures in which each chemical has a particular purpose

Question 7

What is chromatography used for?

Answer 7

To separate mixtures and give information to help identify substances

Question 8

What are the phases involved in chromatography?

Answer 8

The stationary phase and a mobile phase

Question 9

What does separation by chromatography depend on?

Answer 9

The distribution of substances between the phases

Question 10

What is a compounds Rf value?

Answer 10

The ratio of the distance moved by a compound to the distance moved by the solvent

Question 11

Why can you identify a compound from its RF value?

Answer 11

Different compounds have different Rf values in different solvents

Question 12

What happens to the compounds in a mixture during chromatography?

Answer 12

They may separate into different spots depending on the solvent

Question 13

What happens to a pure compound during chromatography?

Answer 13

It will produce a single spot in all solvents

Question 14

What is the test for hydrogen?

Answer 14

Hold a burning splint at the end of an open test tube - hydrogen burns rapidly with a pop sound

Question 15

What is the test for oxygen?

Answer 15

Insert a glowing splint into a test tube – the splint relights in oxygen

Question 16

What is the test for carbon dioxide?

Answer 16

Use an aqueous solution of calcium hydroxide (lime water) – when carbon dioxide is shaken with or bubbled through limewater it turns cloudy

Question 17

What is the test for chlorine?

Answer 17

When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white

Question 18

What can flame tests be used for?

Answer 18

To identify some metal ions (Cations)

Question 19

What colour does lithium compounds go during a flame test?

Answer 19

Crimson

Question 20

What colour does sodium compounds go in a flame test?

Answer 20

Yellow flame

Question 21

What colour do potassium compounds go in flame tests?

Answer 21

Lilac

Question 22

What colour do calcium compounds go in flame tests?

Answer 22

Orange – red flame

Question 23

What colour do copper compounds go in a flame test?

Answer 23

Green

Question 24

What happens if a sample containing a mixture of ions is used for a flame test?

Answer 24

Some flame colours can be masked

Question 25

What can sodium hydroxide solution be used for?

Answer 25

To identify some metal ions (cations)

Question 26

What solutions form white precipitate when sodium is hydroxide solution is added?

Answer 26

Aluminium, calcium and magnesium

Question 27

What happens to the aluminium hydroxide precipitate in excess sodium hydroxide solution?

Answer 27

It dissolves

Question 28

What solutions from coloured precipitate when sodium hydroxide solution is added?

Answer 28

Copper II, iron II, iron III

Question 29

What colour does copper II form when added to sodium hydroxide solution?

Answer 29

Blue

Question 30

What colour does iron II form when added to sodium hydroxide solution?

Answer 30

Green

Question 31

What colour does iron III form when added to sodium hydroxide solution?

Answer 31

Brown

Question 32

What is formed when carbonates react with dilutes acid?

Answer 32

Carbon dioxide gas

Question 33

How can Carbon dioxide gas be identified?

Answer 33

With lime water

Question 34

What do halide ions and silver nitrate solution form in the presence of dilute nitric acid?

Answer 34

Precipitates

Question 35

What colour does silver chloride go when reacted with silver nitrate solution in the presence of dilute nitric acid?

Answer 35

White

Question 36

What colour does silver bromide go when reacted with silver nitrate solution in the presence of dilute nitric acid?

Answer 36

Cream

Question 37

What colour does silver iodide go when reacted with silver nitrate solution in the presence of dilute nitric acid?

Answer 37

Yellow

Question 38

How do you test for sulphate?

Answer 38

React sulphate ions with barium chloride solution in the presence of dilutes hydrochloric acid to produce a white precipitate

Question 39

How else can elements and compounds be detected?

Answer 39

Using instrumental methods

Question 40

What are the advantages for instrumental methods?

Answer 40

Accurate, sensitive and rapid

Question 41

What is flame emission spectroscopy?

Answer 41

And instrumental methods used to analyse metal ions in solutions

Question 42

How do you do flame emission spectroscopy?

Answer 42

The sample is put into a flame and the light given out is passed through a spectroscope

Question 43

What is the output of a flame emission spectroscope?

Answer 43

A line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations