chemical analysis

Question 1

define pure substance

Answer 1

single element / compound not mixed with any other substance

Question 2

how to check if a substance is pure or a mixture(impure)

Answer 2

heat substance
measure heating point
measure boiling point
if its fixed, the substance is pure

Question 3

Pure ……… and ……. melt and boil at ……. temperatures. Melting point and boiling point …. can be used to
distinguish ….. substances from mixtures.

Answer 3

Pure elements and compounds melt and boil at specific
temperatures. Melting point and boiling point data can be used to
distinguish pure substances from mixtures.

Question 4

how can you tell if a substance is a mixture

Answer 4

if the substance melts / boils over a range of temperatures

Question 5

what is a pure substance in everyday language

Answer 5

a substance that has nothing else added to it

Question 6

example of a pure substance in everyday life

Answer 6

pure milk

Question 7

what is a formulation

Answer 7

complex mixture , designed to be a useful product

Question 8

formulations are made by mixing

Answer 8

carefully measured components so the product has the properties we need

Question 9

5 examples of formulations

Answer 9

fuels,
cleaning agents,
paints,
medicines,
alloys,
fertilisers
foods.

Question 10

all separation techniques are …..

Answer 10

physical processes

Question 11

what does it mean if something is a physical process

Answer 11

doesn’t involve physical reactions
no new substances are made

Question 12

what does paper chromatography do

Answer 12

separate substances based in different solubilities

Question 13

how to carry out chromatography

Answer 13

pencil line along bottom of chromatography paper
dot of #1 colour on line
#2 dot next to it
bottom of paper in solvent

Question 14

what happens in chromatography

Answer 14

solvent makes way up paper and
dissolves ink in 2 coloured dots

Question 15

what phase is the paper, why

Answer 15

paper- stationary phase, doesn’t move

Question 16

what phase is the solvent, why

Answer 16

solvent- mobile phase, it moves

Question 17

why does paper chromatography work

Answer 17

each chemical in mixture is attracted to paper to a different extent

Question 18

what will happen to chemicals that are strongly attracted to stationary phase (paper)

Answer 18

they wont move very far

Question 19

what will happen to chemicals that are weakly attracted to stationary phase (paper)

Answer 19

move further up the paper

Question 20

a pure chemical will produce…..

Answer 20

a single spot in all solvents

Question 21

the chemicals in a mixture may

Answer 21

separate into different spots depending on solvent

Question 22

why do we draw starting line in pencil

Answer 22

pen ink would move up paper with solvent

Question 22

why do we draw starting line in pencil

Answer 22

pen ink would move up paper with solvent

Question 23

why do we draw starting line in pencil

Answer 23

pen ink would move up paper with solvent

Question 24

RP- paper chromatography describe in depth 6 key points 4 add on points

Answer 24

***use ruler- draw horizontal pencil line 2 cm from edge of paper -X no. of pencil spots, equal intervals, minimum 1 cm away from sides of paper ***glass capillary tube- put small spot of colouring on each pencil spot. -small spots- stop colours running into eachother -label spots in pencil ***pour 1cm squared water in beaker ***tape paper to glass rod so bottom of paper dips into water ***remove paper when water is around 3/4 up it -use pencil, mark point where water reached ***hang paper to dry ***calculate RF value

Question 25

how do you calculate rf value

Answer 25

distance moved by chemical/ distance moved by solvent

Question 26

how do you measure distance of chemical

Answer 26

pencil line to centre of dot

Question 27

what is the solvent front

Answer 27

distance moved by solvent

Question 28

how would you find out identity of the chemical

Answer 28

look up rf value in database

Question 29

you want to identify chemical but several other chemicals have same rf value. what do u do

Answer 29

repeat using different solvent to narrow down

Question 30

what is another solvent u can use in chromatography

Answer 30

ethanol

Question 31

safety precaution

Answer 31

don't put chemical in eye- irritation

Question 32

3 important points to remember in required practical for chromotography

Answer 32

pencil line with ink above water paper x touch side of beaker use lid

Question 33

why is pencil line with ink spots drawn above the water

Answer 33

otherwise water will wash off ink

Question 34

why is paper not allowed to touch walls of beaker

Answer 34

this will interfere with how water moves

Question 35

why do we use a lid

Answer 35

to prevent evaporation

Question 36

what happens once practical is set up

Answer 36

water moves up beaker and carries up colours

Question 37

when do we remove paper

Answer 37

when water is 3/4 up

Question 38

2 things we do after we remove the paper

Answer 38

draw line where water reached hang up to dry

Question 39

how do you know if chemical hasn't been analysed before

Answer 39

x rf value on data base

Question 40

what would you do if chemical hasn't been analysed before

Answer 40

carry out further analysis to identify it

Question 41

how to test for hydrogen

Answer 41

hold burning splint at end of open test tube of gas

Question 42

positive test for hydrogen

Answer 42

hydrogen burns rapidlt with squeaky pop sound

Question 43

The test for ...... uses a burning ..... held at the open end of a test tube of the gas. Hydrogen burns ..... with ... sound.

Answer 43

The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.

Question 44

how to test for oxygen

Answer 44

glowing splint inserted into test tube of gas

Question 45

positive test for oxygen

Answer 45

splint bursts into flames (relights)

Question 46

how to test for co2

Answer 46

gas shaken with / bubbled through limewater

Question 47

what is limewater

Answer 47

aqueous solution of calcium hydroxide (calcium hydroxide dissolved in water)

Question 48

positive test for co2

Answer 48

repeat bubbling/ shaking gas with limewater and turn s cloudy

Question 49

how to test for chlorine

Answer 49

insert damp litmus paper into test tube of gas

Question 50

positive test for chlorine

Answer 50

chlorine bleaches litmus paper. turns it white

Question 51

what are flame tests used for

Answer 51

identifying an unknown compound which contain a metal ion

Question 52

how to carry out flame test 2 steps

Answer 52

small amount of chemical onto wire on a handle. put end in blue bunsen burner flame

Question 53

what is the colour of the flame used for

Answer 53

to identify the metal ion present

Question 54

what colour flame produced by lithium

Answer 54

crimson

Question 55

what colour flame produced by sodium

Answer 55

yellow

Question 56

what colour flame produced by potassium

Answer 56

lilac

Question 57

what colour produced by calcium

Answer 57

orange red flame

Question 58

what colour flame produced by copper

Answer 58

green

Question 59

problem with using flame test to identify metal ion

Answer 59

colour hard to distinguish especially if low concentration of metal ion some samples contain mixture of metal ions, masking colour of flame

Question 60

what can be used instead of flame tests

Answer 60

flame emission spectroscopy

Question 61

what happens in flame emission spectroscopy 3 points

Answer 61

. sample of metal ion put into a flame . light given out passed into spectroscope . spectroscope converts light into line spectrum

Question 62

what is flame emmision spectroscopy used for.

Answer 62

analysing metal ions in a solution

Question 63

the line spectrum can be analysed to....

Answer 63

identify the metal ions in the solution + measure concentration of metal ions

Question 64

what is important to know about the positions of the lines in the spectrum

Answer 64

the position of the lines are specific for a given metal ion

Question 65

what does more intense lines mean in flame emission spectroscopy

Answer 65

higher concentration

Question 66

hat does instrumental method mean

Answer 66

carried out by a machine

Question 67

3 advantages of instrumental methods

Answer 67

rapid sensitive accurate