Chemical Analysis

Question 1

what is a pure substance

Answer 1

a pure substance only contains one element or compound

Question 2

what is the link between pure substances and melting and boiling points

Answer 2

pure elements and compounds melt and boil at specific temperatures so their data can be used to distinguish pure substances

Question 3

what is an impure substance

Answer 3

a mixture of elements and compounds

Question 4

examples of pure substances

Answer 4

copper
aluminium
sodium chloride

Question 5

examples of impure substances

Answer 5

milk
beer
water

Question 6

melting and boiling points in impure substances

Answer 6

do not have a specific melting point , they have a range

Question 7

what is a formulation

Answer 7

a mixture that has been designed as a useful product

Question 8

how are formulations made

Answer 8

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

Question 9

examples of formulations

Answer 9

fuels
cleaning agents
paints
medicines
alloys
fertilisers
foods

Question 10

what are many products of formulations

Answer 10

complex mixtures in which each chemical has a particular purpose

Question 11

what is the purpose of chromatography

Answer 11

to separate mixtures and give information to help identify substances

Question 12

what does chromatography involve

Answer 12

a stationary phase and a mobile phase

Question 13

what is the stationary phase in chromotography

Answer 13

chromatography paper

Question 14

what is the mobile phase in chromotography

Answer 14

solvent

Question 15

how does paper chromotography separate compounds

Answer 15

separates compounds by their relative speeds in a solvent as it spreads through paper

Question 16

how does chromatography show how soluble a substance is

Answer 16

it will travel further up the paper

Question 17

what is the solvent front

Answer 17

the distance travelled by the solvent

Question 18

why does the start line have to be in pencil

Answer 18

if it is drawn in ink the ink line will run/smudge up the paper

Question 19

why does the pencil line have to be above the water surface

Answer 19

the colouring spots will dissolve into the water instead of rising up the paper

Question 20

how to structure exam question eg
write a conclusion about the black ink in the experiment (4)

Answer 20

• how many substances are in it
• what substances are in it
• what substances are not in it
• anything else

Question 21

how to calculate rf value

Answer 21

distance moved by the spot / distance moved by the solvent

Question 22

what does it mean if two substances have the same rf value

Answer 22

they are the same substance

Question 23

what is the test for hydrogen

Answer 23

use a burning splint held at the open end of a test tube of the gas
creates a squeaky pop sound as hydrogen burns rapidly

Question 24

what is the test for oxygen

Answer 24

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

Question 25

what is the test for carbon dioxide

Answer 25

bubble the gas through limewater (calcium hydroxide) turns milky/cloudy

Question 26

test for chlorine

Answer 26

damp blue litmus paper into gas bleaches the litmus paper so it turns white

Question 27

method for flame test

Answer 27

1. pour 1cm^3 of each known chloride solution into 5 test tubes 2. clean the nichrome wire by dipping it in dilute hydrochloride acid 3. dip the nichrome wire into solution and hold the tip in a blue bunsen flame 4. record the colour of the flame 5. repeat for the other solutions and clean the wire after each test 6, pour 1cm^3 of the unknown salt solution into test tube 7. dip the nichrome wire into the solution and hold the tip in a blue bunsen flame 8. record the colour of the flame and compare results with known chloride and matching colour flame

Question 28

what colour shows lithium ions are present in the flame test

Answer 28

crimson flame

Question 29

what colour shows that sodium ions are present in the flame test

Answer 29

yellow flame

Question 30

what colour shows potassium ions are present in the flame test

Answer 30

lilac flame

Question 31

what colour flame shows calcium ions are present in the flame test

Answer 31

orange/red flame

Question 32

what colour flame shows copper 11 is present in the flame test

Answer 32

green flame

Question 33

Carbonate ion test method

Answer 33

1. place 2cm^3 of limewater in a clean test tube 2. add a little dilute HCl to the unknown solution 3. if bubbles are present transfer the gas produced to the limewater using a delivery tube 3. repeat this process for the known sodium solutions to identify carbonate ions

Question 34

what is the result for the carbonate ion test

Answer 34

bubbles produced and limewater goes cloudy if present

Question 35

method for sulphate ion test

Answer 35

1. add 10 drops of dilute HCl to the unknown solution in a test tube 2. add 2cm^3 of barium chloride solution 3. pour 1cm^3 of the known sodium solutions into separate test tubes 4. add 5 drops of dilute HCl and then 2cm^3 of barium chloride

Question 36

result of sulphate ion test

Answer 36

white precipitate formed (BaSo4) if sulphate ions present

Question 37

method for halide ion test

Answer 37

1. add 10 drops of dilute nitric acid to unknown solution in a test tube 2 add 1cm^3 silver nitrate soliutuoon to tets tube with the unknown solution 3. pour 1cm^3 of the known sodium solutions into separate test tubes 4. repeat steps 1 and 2 for each solution 5. record colour of precipitate formed in each test tube

Question 38

result of halide ion test

Answer 38

precipitate formed

Question 39

result of chloride ion in halide test

Answer 39

white precipitate

Question 40

result of bromide ion in halide test

Answer 40

cream precipitate

Question 41

result of iodide ion present in halide test

Answer 41

yellow precipitate formed

Question 42

what is the limitation of flame tests

Answer 42

if a sample containing a mixture of ions is used some flame colours can be masked

Question 43

which ions form white precipitates in the sodium hydroxide test

Answer 43

aluminium magnesium calcium

Question 44

what is the white precipitate in the sodium hydroxide test

Answer 44

an insoluble metal hydroxide

Question 45

what happens if you add excess NaOH to the white precipitates formed in the sodium hydroxide test

Answer 45

only aluminiums precipitate will redissolve

Question 46

which metals produce a coloured compound in the sodium hyroxide test

Answer 46

copper II iron II iron III

Question 47

what is formed when copper II is added to sodium hydroxide solution

Answer 47

pale blue precipitate Cu(OH)2

Question 48

what is formed when Fe II is added to sodium hydroxide solution

Answer 48

dirty green precipitate Fe(OH)2

Question 49

what is formed when iron III is added to sodium hydroxide solution

Answer 49

rusty brown precipitate Fe(OH)3

Question 50

acronym for halide test results

Answer 50

cats with brains can ideally yodel

Question 51

what can instrumental methods be used to detect

Answer 51

elements and compounds

Question 52

advantages of instrumental methods compared to chemical tests

Answer 52

accurate sensitive rapid

Question 53

process of flame emission spectroscopy

Answer 53

sample is put into a flame and the light given out is passed through a spectroscope the output it a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations

Question 54

disadvantages of atomic emission spectroscopy

Answer 54

destructive as the sample being tested is burned only identifies the prescence of elements not compounds