Chemical Analysis

Question 1

What are pure substances?

Answer 1

Substances containing only one type of element or compound.

Question 2

Pure substances:

Answer 2

• Melt and solidify at one temperature

- Boil and condense at one temperature

Question 3

What are impure substances?

Answer 3

Mixtures- they do not melt or boil at one temperature, the change state over a range of temperatures.

Question 4

What are formulations?

Answer 4

Mixtures that have been carefully designed to have specific properties (e.g. fuels, cleaning agents, paints, medicines).

Question 5

What two phases does chromatography involve?

Answer 5

• A stationary phase (does not move)

- A mobile phase (does move)

Question 6

In paper chromatography what are the stationary and mobile phases?

Answer 6

Stationary: the absorbent paper
Mobile: the solvent (often water)

Question 7

What does chromatography do?

Answer 7

Separates mixtures into their constituent components.

Question 8

How does chromatography work?

Answer 8

• Solvent dissolves the samples and carries them up the paper.
• Each components moves a distance up the paper depending on its attraction for the paper and solvent.
• Can be used to identify artificial colours by comparing the. To the results obtained from known substances.

Question 9

What are the properties of hydrogen?

Answer 9

• Colourless has

- Combines violently with oxygen when ignited.

Question 10

How do you test for hydrogen?

Answer 10

When mixed with air it burns with a squeaky pop.

Question 11

What are the properties of chlorine?

Answer 11

Green poisonous gas that bleached dies.

Question 12

How do you test for chlorine?

Answer 12

Turns damp indicator paper white.

Question 13

What are the properties of oxygen?

Answer 13

Colourless has that helps fuels burn more readily than air.

Question 14

What is the test for oxygen?

Answer 14

Re-lights a glowing splint

Question 15

What are the properties of carbon dioxide?

Answer 15

Colourless gas

Question 16

How do you test for carbon dioxide?

Answer 16

When bubbles through limewater, turns the limewater cloudy.

Question 17

What is a useful instrumental method used to analyse solutions that contain metal ions?

Answer 17

Flame emission spectroscopy

Question 18

Flame emission spectroscopy produces a line spectrum which can be used to:

Answer 18

• Identify metal ions in solutions

- Measure concentration of metal ions

Question 19

What can flame tests be used to?

Answer 19

Identify cations (metal ions)

Question 20

Which elements can be recognised by the distinctive colours they produce in a flame test?

Answer 20

Lithium 
Sodium
Potassium
Calcium
Copper

Question 21

What colour does copper produce in a flame test?

Answer 21

Green

Question 22

What colour does calcium produce in a flame test?

Answer 22

Brick red

Question 23

What colour does lithium produce in a flame test?

Answer 23

Crimson

Question 24

What colour does potassium produce in a flame test?

Answer 24

Lilac

Question 25

What colour does sodium produce in a flame test?

Answer 25

Yellow

Question 26

What happens if a sample in a flame test contains a mixture of ions?

Answer 26

The colours of some ions can be masked.

E.g. if a solution contains sodium and potassium ions, the pale lilac colour from the potassium ions can be hard to detect alongside the intense yellow from the sodium ions.

Question 27

When carbonate react with dilute acids what is formed?

Answer 27

Carbon gas (+ salt and water)

Question 28

What does carbon dioxide do to limewater?

Answer 28

It turns it cloudy

Question 29

What are similar properties of sodium carbonate and potassium carbonate?

Answer 29

They are soluble and dissolve in water to from solutions that contain carbon ions.

Question 30

What do solutions of metal compounds contain?

Answer 30

Metal ions
Some of these form precipitates e.g. insoluble solids that come out of solution when sodium hydroxide solution is added to them.

E.g. when sodium hydroxide is added to calcium chloride solution, a white precipitate of calcium hydroxide is formed.

Question 31

What precipitate does aluminium form and what colour is it?

Answer 31

Aluminium hydroxide

White

Question 32

What precipitate does calcium form and what colour is it?

Answer 32

Calcium hydroxide

White

Question 33

What precipitate does magnesium form and what colour is it?

Answer 33

Magnesium hydroxide

White

Question 34

What precipitate does copper (II) form and what colour is it?

Answer 34

Copper (II) hydroxide

Blue

Question 35

What precipitate does iron (II) form and what colour is it?

Answer 35

Iron (II) hydroxide

Green

Question 36

What precipitate does iron (III) form and what colour is it?

Answer 36

Iron (III) hydroxide

Brown

Question 37

If dilute hydrochloric acid and barium chloride solution are added to a solution containing silicate ions?

Answer 37

A white precipitate of barium sulfate is produced.

Question 38

What happens if solutions of halide ions react with silver nitrate solution in the presence of dilute nitric acid to produce silver halide precipitates:

Answer 38

• Silver chloride is white
• Silver bromide is cream
• Silver iodide is yellow

Question 39

What are the advantages of instrumental methods over manual tests?

Answer 39

Very sensitive
Very fast
Very accurate

Question 40

How does flame emission spectroscopy work?

Answer 40

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 41

In paper chromatography what does the amount of time molecules spend in each phase depend on?

Answer 41

Solubility

How attracted they are to the paper