Chemical analysis (P2)

Question 1

What is a pure substance?

Answer 1

A substance that only contains one compound or element throughout

Question 2

How do you know how pure a substance is ?

Answer 2

• Will melt or boil at a specific temperature

Question 3

How can you test the purity of a substance?

Answer 3

By measuring the mp or bp and comparing it with the melting or boiling point of the pure substance

Question 4

What is a formulation?

Answer 4

Useful mixtures with a precise purpose that are made by following a ‘formula’
- each component is present in a measured quantity

Question 5

What can formulations be found in in every day life?

Answer 5

• Cleaning products
• fuels
• cosmetics
• fertilisers

Question 6

What is chromatography ?

Answer 6

An analytical method used to separate the substances in a mixture

Question 7

What are the two phases of chromatography?

Answer 7

• Mobile phase - where the molecules can move - always a liquid or gas
• Stationary phase - where the molecules can’t move - this can be a solid or a really thick liquid

Question 8

What are the two phases in paper chromatography?

Answer 8

• The stationary phase is the chromatography paper(offer filter paper)
• The mobile phase is the solvent (e.g. Ethanol or water)

Question 9

What is the calculation for the Rf value?

Answer 9

Distance travelled by substance (baseline to centre of spot) / distance travelled by solvent

Question 10

What is an Rf value?

Answer 10

• The ratio between the distance travelled by the dissolved substance + the distance travelled by the solvent
• The Rf value is dependent on the solvent

Question 11

What is the test for chlorine?

Answer 11

• Bleaches damp litmus paper

Question 12

What is the test for oxygen?

Answer 12

• Glowing splint relit

Question 13

What is the test for carbon dioxide?

Answer 13

Limewater turns cloudy when carbon dioxide is bubbled through it

Question 14

What is the test for hydrogen?

Answer 14

• Squeaky pop test - hold lit splint in test tube

Question 15

How do you test for sulfates? + result?

Answer 15

• With hydrocaloric acid + barium chloride
• • result if sulfate ions are present = a white precipitate formed

Question 16

How do you test for halides + results

Answer 16

And a few drops of nitric acid + silver nitrate
results:
- a chloride gives white precipitate of silver chloride
- a bromide gives a yellow precipitate of silver bromide
- an iodine gives a yellow precipitate of silver iodine

Question 17

How to test for metal ions?

Answer 17

• flame tests

Question 18

When don’t flame tests work?

Answer 18

• If the sample contains a mixture of ions

Question 19

How to test metal hydroxides?

Answer 19

• And a few drops of sodium hydroxide to a solution of your mystery compound in hope it forms a precipitate

Question 20

Acronym for metals that can be tested using flame tests?

Answer 20

Sore (sodium)
Losers (lithium)
Cause (calcium)
Crying (copper)
People ( potassium)

Question 21

Acronym for positive results of flame tests- results in same order as the acronym to remember the metals we use flame tests for.

Answer 21

You (yellow) Sore (sodium)
Can (crimson) Losers (lithium)
Often Read (orange- red) Cause (calcium)
Great (green) Crying (copper)
Letters (lilac) People (potassium)

Question 22

Result of chloride being present when nitric acid + silver nitrate

Answer 22

white precipitate of silver chloride

Question 23

Result of bromide being present when nitric acid + silver nitrate

Answer 23

cream precipitate of silver bromide

Question 24

Result of iodine being present when nitric acid + silver nitrate

Answer 24

yellow precipitate of silver iodine

Question 25

Metal ions tests results

Answer 25

- sodium (Na+) = yellow flame - lithium ( Li+) = crimson flame - calcium (Ca+) = orange-red flame - copper (Cu+) = green flame - potassium (K+) = lilac flame

Question 26

Metal hydroxide test results

Answer 26

- calcium= white precipitate - copper (II)= blue precipitate - iron (II)= green precipitate - iron (III) = brown precipitate - aluminium = white at first but redissolves in excess to form a colourless solution - magnesium= white