C17 - Chemical Analysis (PAPER 2)

Question 1

What is a pure substance

Answer 1

a substance containing only one type of element or compound

Question 2

What is an impure substance

Answer 2

a mixture

Question 3

Do pure or impure substances have specific melting and boiling points

Answer 3

Pure substances

Question 4

What are formulations
- what are some examples

Answer 4

Mixtures of many components in specific proportions to make useful products
- fuels, cleaning agents, paints, alloys, fertilisers, foods

Question 5

What is chromatography

Answer 5

a method to separate different components in a mixture

Question 6

What is the Rf value
- What is the formula for it
- What does it stand for

Answer 6

a ratio of how far up the paper a certain spot moves compared to how far the solvent has
- distance moved by substance / distance moved by solvent
- retention factor

Question 7

What is the link between Rf value and solubility

Answer 7

The higher the Rf value, the more soluble a substance is

Question 8

How can you tell if a substance is pure from its chromatogram

Answer 8

It will only have one spot

Question 9

What numbers are all Rf values between

Answer 9

0 and 1

Question 10

What is the stationary phase in a chromatogram

Answer 10

the paper

Question 11

What is the mobile phase in a chromatogram

Answer 11

the solvent

Question 12

What is the solvent front

Answer 12

the top of where the solvent travels up the paper

Question 13

What is the test for hydrogen gas
- What is the observation

Answer 13

hold a lighted splint near the gas
- hear a squeaky pop

Question 14

What is the test for oxygen gas
- What is the observation

Answer 14

hold a glowing splint near the gas
- splint relights

Question 15

What is the test for carbon dioxide gas
- What is the observation

Answer 15

bubble the gas through limewater
- the limewater turns milky (cloudy white)

Question 16

What is the test for chlorine gas
- What is the observation

Answer 16

hold a piece of damp litmus near the gas
- bleaches the litmus white

Question 17

What is the test for Aluminium cations ( Al [3+] )

Answer 17

• on slow addition of excess sodium hydroxide solution, white precipitate forms that eventually dissolves again with excess sodium hydroxide

Question 18

What is the test for calcium cations ( Ca [2+] )

Answer 18

on addition of excess sodium hydroxide solution, white precipitate that doesn’t dissolve

Question 19

What is the test for magnesium cations ( Mg [2+] )

Answer 19

on addition of excess sodium hydroxide solution, white precipitate that doesn’t dissolve

Question 20

What is the test for copper (II) cations ( Cu [2+] )

Answer 20

forms a blue precipitate when NaOH is added

Question 21

What is the test for iron (II) cations ( Fe [2+] )

Answer 21

forms a green precipitate when NaOH is added

Question 22

What is the test for iron (III) cations ( Fe [3+] )

Answer 22

forms a brown precipitate when NaOH is added

Question 23

What is a cation

Answer 23

a positively charged ion

Question 24

What is an anion

Answer 24

a negatively charged ion

Question 25

What is the test for a carbonate anion ( CO3 [2-] )
- What is the observation for a positive result

Answer 25

add dilute acid
- carbon dioxide gas formed which can be tested for with limewater

Question 26

What is the test for a chloride anion ( Cl [-] )
- What is the observation for a positive result

Answer 26

add silver nitrate solution in the presence of nitric acid
- white precipitate formed

Question 27

What is the test for a bromide anion ( Br [-] )
- What is the observation for a positive result

Answer 27

add silver nitrate solution in the presence of nitric acid
- cream precipitate formed

Question 28

What is the test for a iodide anion ( I [-] )
- What is the observation for a positive result

Answer 28

add silver nitrate solution in the presence of nitric acid
- yellow precipitate formed

Question 29

What is the test for a sulphate anion ( SO4 [2-] )
- What is the observation for a positive result

Answer 29

add barium chloride solution in the presence of hydrochloric acid
- white precipitate formed

Question 30

What coloured flame does lithium produce whilst burning

Answer 30

crimson

Question 31

What coloured flame does sodium produce whilst burning

Answer 31

yellow

Question 32

What coloured flame does potassium produce whilst burning

Answer 32

lilac

Question 33

What coloured flame does calcium produce whilst burning

Answer 33

orange - red

Question 34

What coloured flame does copper produce whilst burning

Answer 34

green

Question 35

What are the benefits of using instrumental analysis

Answer 35

they are rapid, accurate and sensitive

Question 36

What are the drawbacks of using instrumental analysis

Answer 36

require training to use, comparing to records

Question 37

What is flame emission spectroscopy
- how does it work

Answer 37

a type of instrumental analysis similar to a flame test
- the solution is put into a flame
- electrons move to outer shells
- When heating is stopped, energy is given off as the electrons move back to their original shells
- energy is given off as light
- This is passed through a spectroscope
- the instrument provides the exact wavelength of the light
- the wavelength can be compared to a reference to establish the identity of the sample

Question 38

What is a flame test

Answer 38

a way of identifying metals by seeing what colour flame it produces whilst burning