Analysis

Question 1

What is an element?

Answer 1

• atoms with the same atomic number

Question 2

What is a compound?

Answer 2

• two or more different elements chemically bonded together in fixed proportions as a result of a chemical reaction

Question 3

What is a mixutre?

Answer 3

• contains 2 or more elements or compounds
• individual substances are not chemically combined
• individual components not in fixed proportions

Question 4

What is a pure substance?

Answer 4

• one element or one compound only

Question 5

What is the difference between melting and boiling points between pure and impure substances?

Answer 5

• pure - specific melting/ boiling point
• impure - range of temperatures

Question 6

What is a formulation?

Answer 6

• mixture that has been designed as a useful product

Question 7

What is the difference between a formulation and a simple mixture?

Answer 7

• many components
• fixed proportion of each component

Question 8

What are some examples of formulations?

Answer 8

• cleaning products
• fertilisers
• fuels
• medicines
• foods

Question 9

How are formulations made?

Answer 9

• mixing components in controlled quantities
• each individual substance has particular purpose
• so that formulation has desired properties

Question 10

What does chromatography do?

Answer 10

• separate a mixture of coloured solutes in a solution
• used to identify substances
• involves a stationary phase and a mobile phase

Question 11

What is a stationary phase?

Answer 11

• does not move
• paper in case of chromatography

Question 12

What is a mobile phase?

Answer 12

• moves through stationary phase
• solvent in case of chromatography

water or ethanol could be the solvent

Question 13

What affects the Rf value of a substance?

Answer 13

• relative strengths of bonds to the mobile or stationary phase
• stronger bond to mobile phase = longer distance up the paper
• stronger bond to stationary phase = shorter distance

Question 14

How do you calculate the Rf value of a substance?

Answer 14

Rf = distance moved by substance/ distance moved by solvent

Question 15

How do you conduct a chromatography?

Answer 15

1) draw baseline with pencil (won’t dissolve)
2) add spot of sample to baseline
3) fill beaker with shallow solvent
4) place in solvent
5) remove and dry

Question 16

How do you identify hydrogen

Answer 16

• hold lit splint near open test tube
• if “pop” is heard then hydrogen is present

Question 17

How do you identify oxygen?

Answer 17

• hold glowing splint in test tube
• if relights then oxygen is present

Question 18

How do you identify carbon dioxide?

Answer 18

• shake gas with limewater
• if limewater turns cloudy/ milky then CO2 is present

Question 19

How do you identify chlorine?

Answer 19

• put damp litmus paper into gas
• if litmus paper turns white then chlorine is present

Question 20

How do you clean the nichrome wire for a flame test?

Answer 20

1) dip loop in dilute hydrochloric acid
2) hold loop in hot part of blue bunsen burner flame
3) repeat 1&2 until there is no extra colour to flame

Question 21

How do you conduct a flame test on a solid sample?

Answer 21

using a damp wooden splint

Question 22

How do you test a sample in the flame test?

Answer 22

1) dip loop in dilute hydrochloric acid then sample
2) hold loop on edge of blue bunsen flame
3) observe + record colour of flame

Question 23

What colour is the flame when the Li+ cation is present?

Answer 23

Crimson

Question 24

What colour is the flame when the Na+ cation is present?

Answer 24

yellow

Question 25

What colour is the flame when the K+ cation is present?

Answer 25

purple

Question 26

What colour is the flame when the Ca2+ cation is present?

Answer 26

orange- red

Question 27

What colour is the flame when the Cu2+ cation is present?

Answer 27

green

Question 28

What compounds are soluble in water?

Answer 28

most potassim, sodium or lithium compounds

Question 29

What happens when insoluble compounds are produced?

Answer 29

- appear as jelly-like/ cloudy precipitates

Question 30

How do you conduct a precipitate test?

Answer 30

1) use clean pipette to transfer 1-2cm^3 of test solution to test tube 2) use another pipette, add few drops of sodium hydroxide solution 3) observe colour of any precipitate 4) if white precipitate forms -> add more sodium hydroxide to see if it dissolves

Question 31

What colour precipitate is produced by the Fe2+ cation?

Answer 31

green

Question 32

What colour precipitate is produced by the Fe 3+ cation?

Answer 32

brown

Question 33

What colour precipitate is produced by the Mg2+ cation?

Answer 33

white

Question 34

What colour precipitate is produced by the Ca+ cation?

Answer 34

white

Question 35

What colour precipitate is produced by the Cu 2+ cation?

Answer 35

blue

Question 36

What colour precipitate is produced by the Al 3+ cation?

Answer 36

white- dissolves in excess sodium hydroxide

Question 37

What is a cation?

Answer 37

a positively charged ion

Question 38

What is an anion?

Answer 38

a negatively charged ion

Question 39

How do you test for carbonate ions?

Answer 39

1) add few drops of dilute hydrochloric acid to solid sample/ solution 2) if carbonate ions are present = bubbles of gas are given off 3) gas may not be carbon dioxide -> limewater test

Question 40

How do you test for halide ions?

Answer 40

1) Add a few drops of dilute nitric acid to sample 2) add a few drops of silver nitrate solution 3) observe colour of precipitate formed

Question 41

What colour precipitate is formed with a Cl- ion?

Answer 41

white

Question 42

What colour precipitate is formed with a Br- ion?

Answer 42

cream

Question 43

What colour precipitate is formed with a I- ion?

Answer 43

yellow

Question 44

What are the advantages of instrumental methods of analysis?

Answer 44

- faster - sensitive (can detect very small quantities of a substance) - accurate (correctly detect & identify substances in sample)

Question 45

What are the disadvantages of flame tests?

Answer 45

- can only detect prescence of metal ions - cannot measure concentration - uncertain if sample is mixture of metal ions

Question 46

How does flame emission spectroscopy work?

Answer 46

- sample heated in flame - thermal energy provided excites electrons in ion -> jump to higher energy levels - fall back to lower shells -> emit energy in form of light - light emitted passed through spectroscope, intensity + wavelengths used to identify metal ions - combination of wavelengths depends of charge of ion + electronic config - output = emission spectrum, different ions produce lines in different parts of spectrum - line spectrum compared against computer database to identify ion

Question 47

How do you test for sulfate ions?

Answer 47

- add hydrochloric acid to sample - add barium chlroide - white precipitate of barium sulfate prodcuted if sulfate ion present