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chemical analysis Flashcards

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1
Q

define pure substance

A

single element / compound not mixed with any other substance

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2
Q

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

A

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

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3
Q

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

A

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.

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4
Q

how can you tell if a substance is a mixture

A

if the substance melts / boils over a range of temperatures

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5
Q

what is a pure substance in everyday language

A

a substance that has nothing else added to it

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6
Q

example of a pure substance in everyday life

A

pure milk

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7
Q

what is a formulation

A

complex mixture , designed to be a useful product

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8
Q

formulations are made by mixing

A

carefully measured components so the product has the properties we need

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9
Q

5 examples of formulations

A

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

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10
Q

all separation techniques are …..

A

physical processes

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11
Q

what does it mean if something is a physical process

A

doesn’t involve physical reactions
no new substances are made

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12
Q

what does paper chromatography do

A

separate substances based in different solubilities

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13
Q

how to carry out chromatography

A

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

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14
Q

what happens in chromatography

A

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

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15
Q

what phase is the paper, why

A

paper- stationary phase, doesn’t move

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16
Q

what phase is the solvent, why

A

solvent- mobile phase, it moves

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17
Q

why does paper chromatography work

A

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

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18
Q

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

A

they wont move very far

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19
Q

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

A

move further up the paper

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20
Q

a pure chemical will produce…..

A

a single spot in all solvents

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21
Q

the chemicals in a mixture may

A

separate into different spots depending on solvent

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22
Q

why do we draw starting line in pencil

A

pen ink would move up paper with solvent

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22
Q

why do we draw starting line in pencil

A

pen ink would move up paper with solvent

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23
Q

why do we draw starting line in pencil

A

pen ink would move up paper with solvent

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24
Q

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

A

**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

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25
Q

how do you calculate rf value

A

distance moved by chemical/ distance moved by solvent

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26
Q

how do you measure distance of chemical

A

pencil line to centre of dot

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27
Q

what is the solvent front

A

distance moved by solvent

28
Q

how would you find out identity of the chemical

A

look up rf value in database

29
Q

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

A

repeat using different solvent to narrow down

30
Q

what is another solvent u can use in chromatography

A

ethanol

31
Q

safety precaution

A

don’t put chemical in eye- irritation

32
Q

3 important points to remember in required practical for chromotography

A

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

33
Q

why is pencil line with ink spots drawn above the water

A

otherwise water will wash off ink

34
Q

why is paper not allowed to touch walls of beaker

A

this will interfere with how water moves

35
Q

why do we use a lid

A

to prevent evaporation

36
Q

what happens once practical is set up

A

water moves up beaker and carries up colours

37
Q

when do we remove paper

A

when water is 3/4 up

38
Q

2 things we do after we remove the paper

A

draw line where water reached
hang up to dry

39
Q

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

A

x rf value on data base

40
Q

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

A

carry out further analysis to identify it

41
Q

how to test for hydrogen

A

hold burning splint at end of open test tube of gas

42
Q

positive test for hydrogen

A

hydrogen burns rapidlt with squeaky pop sound

43
Q

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

A

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.

44
Q

how to test for oxygen

A

glowing splint inserted into test tube of gas

45
Q

positive test for oxygen

A

splint bursts into flames (relights)

46
Q

how to test for co2

A

gas shaken with / bubbled through limewater

47
Q

what is limewater

A

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

48
Q

positive test for co2

A

repeat bubbling/ shaking gas with limewater and turn s cloudy

49
Q

how to test for chlorine

A

insert damp litmus paper into test tube of gas

50
Q

positive test for chlorine

A

chlorine bleaches litmus paper. turns it white

51
Q

what are flame tests used for

A

identifying an unknown compound
which contain a metal ion

52
Q

how to carry out flame test
2 steps

A

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

53
Q

what is the colour of the flame used for

A

to identify the metal ion present

54
Q

what colour flame produced by lithium

A

crimson

55
Q

what colour flame produced by sodium

A

yellow

56
Q

what colour flame produced by potassium

A

lilac

57
Q

what colour produced by calcium

A

orange red flame

58
Q

what colour flame produced by copper

A

green

59
Q

problem with using flame test to identify metal ion

A

colour hard to distinguish
especially if low concentration of metal ion

some samples contain mixture of metal ions, masking colour of flame

60
Q

what can be used instead of flame tests

A

flame emission spectroscopy

61
Q

what happens in flame emission spectroscopy
3 points

A

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

62
Q

what is flame emmision spectroscopy used for.

A

analysing metal ions in a solution

63
Q

the line spectrum can be
analysed to….

A

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

64
Q

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

A

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

65
Q

what does more intense lines mean in flame emission spectroscopy

A

higher concentration

66
Q

hat does instrumental method mean

A

carried out by a machine

67
Q

3 advantages of instrumental methods

A

rapid
sensitive
accurate

Chemistry (18 decks)

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