chemical analysis

Question 1

What is a pure substance?

Answer 1

A single element or compound that is not mixed with another substance

Question 2

How can a boiling and meting point suggest whether a subject is pure?

Answer 2

Pure substances have a fixed boiling point whereas impure substances have unclear boiling points

Question 3

What is a formulation?

Answer 3

A mixture that has been designed as a useful product

Question 4

How do you test for oxygen gas?

Answer 4

A glowing splint will be relit

Question 5

How do you test for hydrogen gas?

Answer 5

A squeaky pop will be produced

Question 6

How do you test for chlorine gas?

Answer 6

Damp blue litmus paper will be bleached

Question 7

How do you test for carbon dioxide gas?

Answer 7

Limewater will turn from colourless to cloudy

Question 8

What is the stationary phase in chromatography?

Answer 8

The paper

Question 9

What is the mobile phase in chromatography?

Answer 9

The solvent

Question 10

What is the Rf value in chromatography?

Answer 10

distance moved by substance
Rf = ————————————–
distance moved by solvent

Question 11

How can chromatography suggest whether a substance is pure?

Answer 11

The compounds in a mixture may separate into different spots depending on the solvent but a pure substance will produce a single spot in all solvents

Question 12

REQUIRED PRACTICAL: CHROMATOGRAPHY

Answer 12

Place spot of mixture on chromatography paper and place in solvent. When the solvent moves up the paper the mixture will separate into spots. Calculate the Rf value of each spot

Question 13

What tests are used for cations?

Answer 13

-Flame tests
-Metal hydroxides

Question 14

What colour does lithium become in a flame test?

Answer 14

Crimson

Question 15

What colour does sodium become in a flame test?

Answer 15

Yellow

Question 16

What colour does potassium become in a flame test?

Answer 16

Lilac

Question 17

What colour does calcium become in a flame test?

Answer 17

Orange-Red

Question 18

What colour does copper become in a flame test?

Answer 18

Green

Question 19

What colour does calcium become in sodium hydroxide?
What is the ionic equation?

Answer 19

White
Ca2+ + 2OH- > Ca(OH)2

Question 20

What colour does copper (II) become in sodium hydroxide?
What is the ionic equation?

Answer 20

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

Question 21

What colour does iron (II) become in sodium hydroxide?
What is the ionic equation?

Answer 21

Green
Fe2+ + 2OH- > Fe(OH)2

Question 22

What colour does iron (III) become in sodium hydroxide?
What is the ionic equation?

Answer 22

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

Question 23

What colour does aluminium become in sodium hydroxide?
What is the ionic equation?

Answer 23

White (but redissolves to become colourless)
Al3+ + 3OH- > Al(OH)3

Question 24

What colour does Magnesium become in sodium hydroxide?
What is the ionic equation?

Answer 24

White
Al3+ + 3OH- > Al(OH)3

Question 25

How do you distinguish between calcium, magnesium, and aluminium?

Answer 25

-Add excess sodium hydroxide -If redissolves then it is aluminium -If not then flame test -If orange-red, then calcium -If not then magnesium!!

Question 26

Which tests are used for anions?

Answer 26

-Carbonates > Carbonates react with dilute acids to form carbon dioxide gas which can then be tested for using limewater -Sulphates > sulphate ions in solution produce a white precipitate with barium chloride and hydrochloric acid -Halides > Adding halides to silver nitrate solution and nitric acid produce precipitates

Question 27

What colour are chlorides (Cl-) in silver nitrate and nitric acid?

Answer 27

White

Question 28

What colour are bromides (Br-) in silver nitrate and nitric acid?

Answer 28

Cream

Question 29

What colour are iodides (I-) in silver nitrate and nitric acid?

Answer 29

Yellow

Question 30

What is flame emission spectroscopy used for?

Answer 30

To analyse metal ions in solution

Question 31

How does flame emission spectroscopy work?

Answer 31

-The sample is put into a flame and the light given out is passed through a spectroscope -The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations

Question 32

What are the advantages of instrumental analysis?

Answer 32

-Fast -Sensitive -Accurate