C15: Analysis

Question 1

Lithium (Li+)

Answer 1

Crimson

Question 2

Sodium (Na+)

Answer 2

Yellow

Question 3

Potassium (K+)

Answer 3

Lilac

Question 4

Calcium (Ca2+)

Answer 4

Brick Red

Question 5

Barium (Ba2+)

Answer 5

Apple Green

Question 6

What three ions form a white precipitate when reacted with sodium hydroxide solution?

Answer 6

Al3+
Ca2+
Mg2+

Question 7

What substance that forms a white precipitate dissolves in excess sodium hydroxide solution?

Answer 7

Al3+

Question 8

How can you distinguish between the white precipitate formed by Ca2+ and Mg2+?

Answer 8

Flame Test

Question 9

What three ions form a coloured precipitate when reacted with sodium hydroxide?

Answer 9

Cu2+
Fe3+
Fe2+

Question 10

Fe2+

Answer 10

Light green -> brown

Question 11

Light green -> brown

Answer 11

Fe2+

Question 12

Fe3+

Answer 12

Reddish brown

Question 13

Reddish brown

Answer 13

Fe3+

Question 14

Cu2+

Answer 14

Light blue

Question 15

Light blue

Answer 15

Cu2+

Question 16

Crimson

Answer 16

Lithium (Li+)

Question 17

Yellow

Answer 17

Sodium (Na+)

Question 18

Lilac

Answer 18

Potassium (K+)

Question 19

Brick Red

Answer 19

Calcium (2+)

Question 20

Apple Green

Answer 20

Barium (2+)

Question 21

Test for carbonates

Answer 21

Add dilute acid, if it fizzes and produces CO2 it is a Carbonate.

Question 22

Test for halides (Bromine, Chlorine, Iodine)

Answer 22

1. Add dilute nitric acid.
2. Add silver nitrate. If a precipitate forms it is a halide.
   ALWAYS ADD THE ACID FIRST.

Question 23

Chloride

Answer 23

White

Question 24

White

Answer 24

Chlorine

Question 25

Bromine

Answer 25

Cream

Question 26

Cream

Answer 26

Bromine

Question 27

Iodine

Answer 27

Yellow

Question 28

Yellow

Answer 28

Iodine

Question 29

Test for Sulfates

Answer 29

1. Add hydrochloric acid (do this first to remove carbonate ions that would otherwise form a precipitate).
2. Add barium chloride solution.
   If a white precipitate forms it is a sulfate. the precipitate formed is Barium Sulfate.

Question 30

4 techniques for separating mixtures

Answer 30

> Filtration
Crystallisation
Distillation
Chromatography

Question 31

When is filtration used?

Answer 31

Used to separate substances that are insoluble in a particular solvent from those that are soluble.

Question 32

Crystallisation

Answer 32

> Water is evaporated through heating in an evaporating dish on a water bath. (gentler form of heating)
When small crystals begin to form, heat is removed and solution is left to evaporate at room temperature. This last step should take place in a flat bottomed or petri dish to increase surface area for evaporation.

Question 33

Distillation

Answer 33

> Solution is heated until the substance with the lower boiling point evaporates.
Gas gets passed into a condenser and is surrounded with cold water.
A pure, liquid substance will come out.

Question 34

Chromatography

Answer 34

The process whereby small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper.

Question 35

R(f) Retention Factor

Answer 35

Distance a spot has been carried above the baseline/ distance of the solvent front.

Question 36

Benefits of modern chromatography methods

Answer 36

> Highly accurate and sensitive
Quicker
Enable very small samples to be analysed

Question 37

Benefits of classic chromatography methods

Answer 37

> Less expensive
Don’t take the special training required by modern techniques.
Results of modern chromatography can often only be interpreted in comparison with data from known substances.

Question 38

Gas chromatography

Answer 38

> Sample mixture is vaporised.
a ‘carrier gas’ moves the vapour through the coiled column.
Compounds that are more attracted to the material in the column will take longer to come out (have a longer retention time).
Substances can be identified by comparing their retention time to that of known substances.

Question 39

Mass Spectrometry

Answer 39

A machine that can be used to analyse small amounts of a substance to identify it and find its relative molecular mass.

Question 40

Where is the molecular ion peak located on a graph?

Answer 40

The last peak on the right as you look at a mass spectrum.