C8

Question 1

Define pure substance

Answer 1

a single element or compound, not mixed with any other
substance

Question 2

State properties of a pure substance

Answer 2

They melt and boil at specific temperatures

Question 3

Define a formulation

Answer 3

mixture that has been designed as a useful product

Question 4

State examples of formulations

Answer 4

fuels, cleaning agents, paints, medicines, alloys, fertilisers and
foods

Question 5

How to calculation rF value?

Answer 5

distance moved by substance ÷ distance moved by solvent

Question 6

State the method for chromatography

Answer 6

• Draw a starting line on the paper with a pencil and placed spots of the samples on the line.
• Hang the paper in a beaker of ethanol, with the ethanol being below the height of the samples of the line.
• Wait 15 minutes, or until the ethanol has soaked the paper till the top, remove the paper and allow it to dry.
• Once removed from the beaker the solvent front should be marked on the paper.

Question 7

Why is the starting line drawn in pencil

Answer 7

Graphite in pencil is insoluble in the solvent.

Question 8

Why is the level of the solvent in the beaker below the sample line?

Answer 8

The substance may dissolve into the substance rather than travelling up.

Question 9

What is the stationary phase in chromatography?

Answer 9

paper

Question 10

What is the mobile phase in chromatography?

Answer 10

solvent

Question 11

Explain, by referring to the stationary and mobile phases, why the samples move at different speeds during the experiment.

Answer 11

If the sample travels further up the paper, the sample has a stronger affinity to the mobile phase. If the sample doesn’t travel far up the paper, it has a strong affinity for the stationary phase (or weaker affinity to the mobile phase).

Question 12

What is the test and result for the gas hydrogen?

Answer 12

Test: Lit splint
Result: Squeaky pop

Question 13

What is the test and result for the gas oxygen?

Answer 13

Test: Glowing splint
Result: Relit splint

Question 14

What is the test and result for the gas carbon dioxide?

Answer 14

Test: Bubble the gas through limewater
Result: Limewater turns cloudy

Question 15

What is the test and result for the gas chlorine?

Answer 15

Test: Damp blue litmus paper
Result: Litmus turns red and then bleaches

Question 16

What colour will the flame turn if Lithium is present?

Answer 16

Crimson

Question 17

What colour will the flame turn if Sodium is present?

Answer 17

Yellow

Question 18

What colour will the flame turn if Potassium is present?

Answer 18

Lilac

Question 19

What colour will the flame turn if Calcium is present?

Answer 19

Orange-red

Question 20

What colour precipitate does an aluminium ion form with NaOH?

Answer 20

White

Question 21

What colour will the flame turn if Copper is present?

Answer 21

Green

Question 22

What colour precipitate does a calcium ion form with NaOH?

Answer 22

White

Question 23

What colour precipitate does a magnesium ion form with NaOH?

Answer 23

White

Question 24

What happens when NaOH is added in excess to aluminium?

Answer 24

the aluminium precipitate dissolves

Question 25

What colour precipitate does copper (II) ion form with NaOH?

Answer 25

blue

Question 26

What colour precipitate does iron (II) ion form with NaOH?

Answer 26

green

Question 27

What colour precipitate does iron (III) ion form with NaOH?

Answer 27

brown

Question 28

Carbonates react with ... to create ...

Answer 28

Carbonates react with dilute acids to create carbon dioxide.

Question 29

How to test for halide ions?

Answer 29

First add dilute nitric acid, followed by silver nitrate solution.

Question 30

What colour precipitate does chloride give?

Answer 30

white

Question 31

what colour precipitate does bromide give?

Answer 31

cream

Question 32

What colour precipitate does iodide give?

Answer 32

yellow

Question 33

How to test for sulfate ions?

Answer 33

- First add dilute hydrochloric acid, followed by barium chloride solution. - A white precipitate will form when sulfate ions are in this solution.

Question 34

How are instrumental methods better than chemical tests?

Answer 34

- Accurate - Sensitive - Rapid

Question 35

What is flame emission spectroscopy? How does it work?

Answer 35

- Example of an instrumental method used to analyse metal ions in solutions - Sample is put into a flame and the light given out is passed through a spectroscope - Output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations - high-tech flame test measures wavelength of light given out in flame - can identify each ion in mixture

Question 36

Why is the Rf value of a dye not affected by how far the solvent front is allowed to travel?

Answer 36

the ratio of the spot distance moved to solvent distance moved is constant.

Question 37

What other change to the investigation could result in a different Rf value?

Answer 37

Use different solvent

Question 38

Sewage is waste water. Sewage contains organic matter. Describe how sewage is treated to remove organic matter (4)

Answer 38

- screening - sedimentation (to produce sewage sludge and effluent) - anaerobic digestion of (solid sewage) sludge - aerobic biological treatment of (liquid) effluent

Question 39

Explain why the concentrations of sodium ions and of chloride ions in the ground water in the table above are unchanged by filtration. (2)

Answer 39

- the ions pass through the filter - because the ions are in the solution

Question 40

Explain why the ground water in the table above requires "expose to ultraviolet light" before the water is safe to drink. (2)

Answer 40

- (the ground water) contains microbes which are harmful (to health) - (so) the water is sterilised

Question 41

After treatment the ground water in the table above is sold by a company as pure water. The ground water in above table is not chemically pure because the water contains sodium ions and chloride ions. Suggest what the company means by ‘pure’.

Answer 41

the water is in its natural state

Question 42

Explain why the yellow dye and red dye travel different distances in Experiment 1. Refer to forces of attraction between the dyes and the chromatography paper in your answer (explain why the yellow pigment travelled further) (2)

Answer 42

- the yellow dye travels further - because the yellow dye has a weaker attraction to the chromatography paper

Question 43

If you are testing for multiple anions, what acid do you use?

Answer 43

Nitric acid - won't affect the result.

Question 44

What if there is only one sample to analyse (anion tests)? (what is the correct order to carry out these tests?) (6)

Answer 44

1. Carbonate: adding acid will only react with the carbonate, therefore if we get bubbles it will be due to to carbonate. This will not react with sulfate and halides. 2. Sulfate - we then add Ba2+ second, as it if was added first it would react with the carbonate as well. A white ppt would be produced. Be sure not to use BaCl2, if you intend to use halide test afterwards. 3. Halide - you could then add silver nitrate to carry out your halide test. This has to be carried out last otherwise the silver will react with carbonates and sulfates, and produces insoluble products.