Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chem spec > chemical analysis > Flashcards

chemical analysis Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

define a pure substance in chemistry

A

a single element or compound not mixed with any other substance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

define a pure substance in everyday language

A

a substance that has had nothing added to it; unadulterated and in its natural state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what do pure elements and compounds do

A

they melt and boil at specific temperatures - this data can be used to distinguish pure substances from mixtures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

easiest method to test if a substance is chemically pure

A

heat it and measure boiling and melting point
- pure substance always melts and boils at fixed temp
- impure melt and boil over a range of temps

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

define a formulation

A

a mixture that has been designed as a useful product - many products are complex mixtures in which each chemical has a particular purpose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

how are formulations made

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

examples of formulations

A
  • fuels
  • cleaning agents
  • paints
  • medicines
  • alloys
  • fertilisers
  • foods
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is chromatography

A

a physical separation technique that separates different substances in a mixture based on their solubilities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what does separation in chromatography depend on

A

the distribution of substance between the stationary and mobile phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is an rf value

A

the ratio of the distance moved by a compound to the distance moved by the solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

rf value formula

A

distance moved by substance / distance moved by solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the stationary phase in chromatography

A

the paper

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is the mobile phase in chromatography

A

the solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how does paper chromatography separate mixtures

A

different chemicals have different solubilities so are each attracted to the stationary phase to a different extent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

chromatography method

A
  • draw pencil line at bottom of chromatography paper
  • place two dots of mixture using capillary tube / draw dot of ink if pen used
  • place bottom of paper into solvent; don’t let touch pencil line
  • solvent will travel up paper and ink dissolve in it and carried up paper with solvent
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what can be determined if one spot is formed from chromatography

A

the substance is pure in that solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what can be determined if multiple spots are formed from chromatography

A

there are different solvents with different solubilities within it, so an impure mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what happens to a more soluble substance in chromatography

A

it will travel further up the paper because it is more attracted to the mobile phase and less attracted to the stationary phase
vice versa for less soluble substance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

if only one spot is formed with a solvent, how can we be sure the substance is pure

A

by testing it with a range of solvents, because a pure compound will produce one spot in ALL solvents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what do rf values help with

A

identifying the compounds; look the rf value up in a database and match it to the solvent used to identify the chemical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what happens if an rf value shows several chemicals

A

repeat the experiment using a different solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what happens if a chemical has never been analysed before

A

there will not be an rf value on the database

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

test for hydrogen

A

burning splint held at the open end of a test tube of the gas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

positive test for hydrogen

A

hydrogen burns rapidly with a squeaky pop sound

25
Q

test for oxygen

A

glowing splint inserted into a test tube of the gas

26
Q

positive test for oxygen

A

splint relights in oxygen

27
Q

test for carbon dioxide

A

carbon dioxide shaken with or bubbled through an aqueous solution of calcium hydroxide (limewater)

28
Q

positive test for carbon dioxide

A

limewater turns cloudy

29
Q

test for chlorine

A

damp litmus paper is put into chlorine gas

30
Q

positive test for chlorine

A

litmus paper is bleached and turns white

31
Q

what are flame tests used for

A

identifying metal ions

32
Q

what colour flame do lithium compounds produce

A

Li+ ions produce a crimson flame
LiCk

33
Q

what colour flame do sodium compounds produce

A

Na+ ions produce a yellow flame
SoY

34
Q

what colour flame do potassium compounds produce

A

K+ ions produce a lilac flame
PoLl

35
Q

what colour flame do calcium compounds produce

A

Ca2+ ions produce an orange-red flame
CalOR

36
Q

what colour flame do copper compounds produce

A

Cu2+ ions produce a green flame
CoG

37
Q

what happens if a sample contains a mixture of ions

A

some flame colours can be masked

38
Q

issue with flame tests to identify ions in a compound

A

colour of flame is difficult to distinguish esp if low conc of metal compound

39
Q

what can sodium hydroxide solution be used for

A

identifying positive metal ions (cations)

40
Q

what forms white precipitates when sodium hydroxide solution is added

A

aluminium, calcium and magnesium ions

41
Q

what happens when excess sodium hydroxide solution is added

A

aluminium hydroxide precipitate dissolves and goes clear again

42
Q

what forms coloured precipitates when sodium hydroxide solution is added

A

solutions of copper(II), iron(II) and iron(III)

43
Q

what precipitate is formed when copper(II) ions react with sodium hydroxide

A

blue

44
Q

what precipitate is formed when iron(II) ions react with sodium hydroxide

A

green

45
Q

what precipitate is formed when iron(III) ions react with sodium hydroxide

A

brown

46
Q

what is a positive ion

A

a cation

47
Q

what is a negative ion

A

an anion

48
Q

examples of negative ions (anions)

A
  • carbonate ions
  • halide ions
  • sulfate ions
49
Q

how to test for carbonate ions

A
  • add dilute acid to sample
  • acid reacts with carbonate to make carbon dioxide (as well as salt and water)
  • will effervesce
  • limewater test
50
Q

how to test for halide ions

A
  • add dilute nitric acid
  • add dilute silver nitrate solution
  • halide ions produce a precipitate of silver halide

chloride ions: white precipitate of silver chloride
bromide ions: cream precipitate of silver bromide
iodide ions: yellow precipitate of silver iodide

51
Q

how to test for sulfate ions

A
  • add dilute hydrochloric acid to the sample
  • add barium chloride solution
  • white precipitate of barium sulfate forms if sulfate ions present
52
Q

what are ionic compounds made up of

A

positive ions (cations) and negative ions (anions)

53
Q

advantages of instrumental methods

A
  • highly accurate and sensitive
  • quicker
  • enable very small samples to be analysed
54
Q

disadvantages of instrumental methods

A
  • usually very expensive
  • takes special training to use
  • gives results that can often be interpreted only by comparison with data from known substances
55
Q

what are instrumental methods used for

A

detecting and identifying elements and compounds

56
Q

what is flame emission spectroscopy

A

an example of an instrumental method used to analyse metal ions in solutions

57
Q

how does flame emission spectroscopy work

A

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

58
Q

how do you use the line spectrum from flame emission spectroscopy

A

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

59
Q

as well as identifying a metal ion, what can FES also tell us

A

the conc of the metal ion because the lines become more intense as you increase conc

chem spec (12 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions