Paper 2 Chemical Analysis

Question 1

What does Pure mean?

Answer 1

A substance containing only one type of element or compound

Question 2

What properties do pure substances have?

Answer 2

• It all melts and solidifies at the same temperature called the melting point
• Boil and condense at the same temperature called the boiling point

Question 3

What are impure substances?

Answer 3

Substances which do not all melt and boil at the same time, they have a range of boiling and melting temperature points

Question 4

What are formulations?

Answer 4

Mixtures which are chemically designed to have specific properties.

Question 5

In chromatography what is the stationary phase and the mobile phase?

Answer 5

Stationary Phase- The absorbent paper

Mobile Phase- The solvent (often water)

Question 6

What does chromatography do?

Answer 6

Separates the mixture into their components by the solvent dissolving the sample and carrying it up the paper.

Question 7

(Chromatography) Why do each components in a mixture move to different distances?

Answer 7

Depending whether it is most attracted to the solvent or paper.

Question 8

Required Practical- Chromatography

Answer 8

1. Draw a pencil line on paper
2. Put samples of known colourings on the line (A B C D…) along with an unknown (X)
3. Dip the paper into a solvent
4. Wait for solvent to travel to the top of the paper
5. Identify X by comparing to the other known substances

Question 9

What is the equation for Rf values?

Answer 9

Rf = distance moved by substance / distance moved by substance

Question 10

Hydrogen gas test

Answer 10

Lit splint should make a squeaky pop when hydrogen is present.

Question 11

Chlorine gas test

Answer 11

Will turn damp indicator paper white

Question 12

Oxygen gas test

Answer 12

Relights a glowing splint

Question 13

Carbon dioxide gas test

Answer 13

When bubbled through limewater it will turn the limewater cloudy

Question 14

Instrumental Methods

Answer 14

Flame emission spectroscopy

Produces a line spectrum which can be used to identify metal ions and measure the concentration of the metal ions

Question 15

What can flame tests be used to identify and what are the examples ?

Answer 15

It can be used to identify metal ions. Lithium, sodium, potassium, calcium and copper compounds can be recognised by their distinctive colour which they give off.

Question 16

Required Practical- Flame Tests

Answer 16

1. Heat a nichrome wire in a Bunsen burner and dip it into a concentrated hydrochloric solution to clean it
2. Dip the wire into the compound
3. Put over Bunsen flame and observe the colour it burns

Question 17

What are the distinctive colours for copper, calcium, lithium, potassium and sodium?

Answer 17

Copper- Green 
Calcium- Brick Red 
Lithium- Crimson Red
Potassium- Lilac 
Sodium- Yellow

Question 18

Why can a flame test be unreliable?

Answer 18

If a sample contains more than one type of ion then the colour can be masked

Question 19

What does carbon dioxide do to limewater?

Answer 19

Turn it cloudy

Question 20

What do solutions of metal compounds contain?

Answer 20

Metal ions

Question 21

What do some metal ions form when sodium hydroxide solution is added to them?

Answer 21

Precipitates

Question 22

What are the precipitates formed when sodium hydroxide is added to them (aluminium calcium magnesium copper iron2 iron3)

Answer 22

Aluminium- white 
Calcium- white 
Magnesium- white 
Copper- blue 
Iron 2- green
Iron 3- brown

Question 23

What happens when a dilute hydrochloric acid and barium chloride are added to a solution containing sulfate ions?

Answer 23

A white precipitate or barium sulfate is produced

Question 24

What precipitates are produced when halide ions react with silver nitrate and dilute nitric solution?

Answer 24

Silver Chloride is white
Silver Bromide is cream
Silver Iodide is yellow