C3.1 Qualitative analysis

Question 1

What are two reasons chemical analysis is used on food and other products?

Answer 1

Purity and safety

Question 2

What are the two main types of chemical analysis?

Answer 2

Qualitative and quantitative analysis

Question 3

What is qualitative analysis used for?

Answer 3

Investigating what kind of substances are present in a sample

Question 4

What is quantitative analysis used for?

Answer 4

Measuring the amount of each substance present in a sample

Question 5

What two things must an analyst identify to identify the ionic compound?

Answer 5

The anion and cation

Question 6

How can you be sure that the answer is correct when using an ion test?

Answer 6

The ion test must give a positive result to only one type of ion

Question 7

What can flame tests be used for?

Answer 7

Detecting some metal cations

Question 8

What colour flame does the flame test for calcium produce?

Answer 8

Brick red

Question 9

What colour flame does the flame test for sodium produce?

Answer 9

Yellow

Question 10

What colour flame does the flame test for potassium produce?

Answer 10

Lilac

Question 11

What colour flame does the flame test for copper produce?

Answer 11

Green/blue

Question 12

How are cations that can’t be detected with a flame test identified?

Answer 12

By adding a few drops of sodium hydroxide solution

Question 13

Why does adding a few drops of sodium hydroxide solution to an unknown substance help identify a cation?

Answer 13

Because many metal hydroxides are insoluble, so a precipitation reaction can occur. The precipitate formed can then be used to identify the ion present

Question 14

What colour precipitate does a cation of aluminium form when sodium hydroxide solution is added to it?

Answer 14

White

Question 15

What colour precipitate does a cation of calcium form when sodium hydroxide solution is added to it?

Answer 15

White

Question 16

What colour precipitate does a cation of copper(||) form when sodium hydroxide solution is added to it?

Answer 16

Pale blue

Question 17

What colour precipitate does a cation of iron(||) form when sodium hydroxide is added to it?

Answer 17

Green

Question 18

What colour precipitate does a cation of iron(|||) form when sodium hydroxide solution is added to it?

Answer 18

Brown (rust)

Question 19

How can you distinguish calcium and aluminium ions when they both form a white precipitate when a few drops of sodium hydroxide solution is added to them?

Answer 19

You add sodium hydroxide in excess

Question 20

What happens to the white calcium ion precipitate when sodium hydroxide solution is added in excess?

Answer 20

It remains unchanged

Question 21

What happens to the white aluminium ion precipitate when sodium hydroxide solution is added in excess?

Answer 21

The precipitate redissolves to form a colourless solution

Question 22

What is the precipitate when adding sodium hydroxide solution to an unknown substance?

Answer 22

A solid hydroxide of the cation

Question 23

What would the precipitate formed from the reaction of copper(||) sulphate and sodium hydroxide be?

Answer 23

Copper(||) hydroxide

Question 24

Why must an ion test only give a positive result for one type of ion?

Answer 24

If a positive result was produced for two or more different ions you wouldn’t be sure which of these ions was present in the compound

Question 25

What are the three ways the water supply in Britain is cleaned?

Answer 25

- filtered to remove solid particles - chlorinated to kill bacteria - chemically treated to remove other impurities

Question 26

What group is chlorine found in?

Answer 26

Group 7 (halogens)

Question 27

How can halide ions be identified?

Answer 27

By acidifying the solution with dilute nitric acid, then adding silver nitrate

Question 28

What precipitate is produced when dilute nitric acid and silver nitrate are added to a solution containing halides?

Answer 28

A silver halide precipitate

Question 29

What colour precipitate is formed when silver nitrate is added to an acidified solution containing chloride ions?

Answer 29

White

Question 30

What colour precipitate is formed when silver nitrate is added to an acidified solution containing bromide ions?

Answer 30

Cream

Question 31

What colour precipitate is formed when silver nitrate is added to an acidified solution containing iodide ions?

Answer 31

Yellow

Question 32

Why can ions in solution move about independently?

Answer 32

Because they are separated

Question 33

What ions do many types of fertiliser contain?

Answer 33

Ammonium ions

Question 34

Why can fertilisers be dangerous?

Answer 34

They can get into rivers and lakes and harm water life

Question 35

How do you test for ammonium ions?

Answer 35

The substance is warmed with sodium hydroxide solution. If a smelly alkaline gas is given off that turns damp red litmus paper blue it is ammonia gas

Question 36

How is a carbonate identified?

Answer 36

You add a dilute acid to the substance. If the gas given off turns limewater milky it is carbon dioxide gas and so the substance was a carbonate

Question 37

How does water get dissolved substances inside it?

Answer 37

- from the rocks over which it flows | - from the chemicals used in water treatment

Question 38

Why are maximum limits for the amounts of chemicals and microorganism found in water set?

Answer 38

- so that it looks and tastes good | - so that it's safe to drink

Question 39

What are three chemicals used in water treatment?

Answer 39

- chlorine - aluminium salts - sodium fluoride

Question 40

Why is sodium fluoride added during water treatment?

Answer 40

It has been shown to reduce tooth decay

Question 41

Why are aluminium salts added during water treatment?

Answer 41

To remove small particles of solids

Question 42

Why are some scientists concerned about the use aluminium fluoride within water treatment?

Answer 42

High levels of aluminium have been linked to Alzheimer's disease and damage to the digestive system

Question 43

How do aluminium salts remove small particles of solids from water?

Answer 43

They stick to small dirt particles to form clumps so that they can be removed more easily

Question 44

What is a pure liquid?

Answer 44

A liquid that only contains one substance

Question 45

What does an acid + a metal produce?

Answer 45

A salt + hydrogen

Question 45

What does an acid + a base produce?

Answer 45

A salt + water

Question 45

What does an acid + a metal oxide produce?

Answer 45

A salt + water

Question 45

What does an acid + a metal carbonate produce?

Answer 45

A salt + water + carbon dioxide