Chemical Analysis

Question 1

A green flame is produced by the presence of ..

Answer 1

copper ions

Question 2

What is the positive test for the presence of iodide ions?

Answer 2

dilute nitric acid followed by silver nitrate solution will form a yellow precipitate

Question 3

Which ion gives an orange-red flame test?

Answer 3

Calcium ions

Question 4

What forms a brown precipitate when sodium hydroxide solution is added?

Answer 4

Iron (III)

Question 5

When you add dilute hydrochloric acid then barium chloride solution and a white precipitate is formed, what is it called?

Answer 5

Barium carbonate

Question 6

What is the ionic equation for the formation of aluminium hydroxide?

Answer 6

Al³⁺(aq) + 3OH⁻(aq) → Al(OH)₃(s)

Question 7

What is a pure substance?

Answer 7

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

Question 8

How can you test the purity of a sample?

Answer 8

by measuring its melting or boiling point

Question 9

What will impurities do?

Answer 9

• lower the melting point and increase the melting range of your substance
• increase the boiling point and may result in a sample boiling over a range of temperatures

Question 10

What is a formulation?

Answer 10

a mixture that has been designed as a useful product

Question 11

How are formulations made?

Answer 11

by mixing the components in carefully measured quantities to ensure that the product has the required properties

Question 12

What are examples of formulations?

Answer 12

• fuels
• cleaning agents
• paints
• medicines
• alloys
• fertilisers
• foods

Question 13

What is the test for hydrogen?

Answer 13

• a lit splint held at the open end of a test tube of the gas
• hydrogen burns rapidly with a pop sound.

Question 14

What is the test for oxygen?

Answer 14

• a glowing splint inserted into a test tube of the gas
• the splint relights in oxygen

Question 15

What is the test for carbon dioxide?

Answer 15

• an aqueous solution of calcium hydroxide (lime water)
• when carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)

Question 16

What is the test for chlorine?

Answer 16

• uses litmus paper
• when damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.

Question 17

What compound results in a crimson flame?

Answer 17

lithium ions

Question 18

What ion results in a yellow flame?

Answer 18

sodium ions

Question 19

What ion results in a lilac flame?

Answer 19

potassium ions

Question 20

What solution can be used to identify some metal ions (cations)?

Answer 20

sodium hydroxide

Question 21

What solutions of ions form white precipitates when sodium hydroxide solution is added?

Answer 21

aluminium, calcium and magnesium

Question 22

What dissolves in excess sodium hydroxide solution?

Answer 22

aluminium hydroxide precipitate

Question 23

What forms a blue precipitate when sodium hydroxide solution is added?

Answer 23

Copper (II)

Question 24

What forms a green precipitate when sodium hydroxide solution is added?

Answer 24

Iron (II)

Question 25

What do carbonates react with to form carbon dioxide gas?

Answer 25

- dilute acids - carbon dioxide can be identified with limewater

Question 26

How do you test for halide ions?

Answer 26

- add dilute nitric acid - followed by silver nitrate solution

Question 27

What colour precipitate does silver chloride give?

Answer 27

white

Question 28

What colour precipitate does silver bromide give?

Answer 28

cream

Question 29

What colour precipitate does silver iodide give?

Answer 29

yellow

Question 30

How do you test for sulfate ions?

Answer 30

- add dilute hydrochloric acid - following by barium chloride solution

Question 31

What precipitate forms in testing for sulfate ions?

Answer 31

white precipitate

Question 32

What is chromatography used for?

Answer 32

to separate mixtures and can give information to help identify substances

Question 33

What is the mobile phase?

Answer 33

- where the molecules can move - liquid or gas

Question 34

What is the stationary phase?

Answer 34

- where the molecules can't move and can be a solid or a really thick liquid - paper

Question 35

What is the Rf value?

Answer 35

distance travelled by substance B/distances travelled by solvent A

Question 36

In chromatography, the amount of time the molecules spend in each phase depends on?

Answer 36

1. how soluble they are in the solvent 2. how attracted they are to the paper

Question 37

How does paper chromatography separate mixtures?

Answer 37

- the substances in the sample constantly move between the mobile and the stationary phase - an equilibrium is formed between the two phases - the mobile phase moves through the stationary phase and anything dissolved in the mobile phase moves with it

Question 38

How does chromatography tell you if a substance is pure?

Answer 38

it will only ever form one spot in any solvent as there is only one substance in the sample

Question 39

What are the advantages of instrumental methods?

Answer 39

- very sensitive - very fast - very accurate

Question 40

Compare flame emission spectroscopy with flame tests?

Answer 40

- flame tests can't be used to identify a mixture of ions in a solution - only a single metal - in flame emission spectroscopy, the identities of a mixture of ions in solutions can be found

Question 41

What is flame emission spectroscopy?

Answer 41

an example of an instrumental method used to analyse metal ions in solutions

Question 42

How does flame emission spectroscopy work?

Answer 42

- 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