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gcse science > Science - Chemistry - Chemical Analysis - C8 > Flashcards

Science - Chemistry - Chemical Analysis - C8 Flashcards

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1
Q

what is purity ?

A

a substance in its natural state which only contains one type of element

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2
Q

what does a chemically pure substance have ?

A

a specific melting point

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3
Q

how can you test a a substances purity ?

A

by measuring its melting/boiling point

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4
Q

what will impurites in substances do ?

A

lower your melting point and increase the melting range of your substance
increase boiling point over a range of temperatures

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5
Q

what are formulations ?

A

useful mixtures with a precise purpose made by a formula

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6
Q

give an example of a formula ?

A

paint

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7
Q

why are formulations important ?

A
  • altering formulations of a pill makes sure that a drug is delivered to the right part of the body
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8
Q

what is chromatography ?

A

separating substances in a mixture

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9
Q

what are the 2 phases of chromatography ?

A

mobile phase
stationary phase

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10
Q

what is the mobile phase ?

A

where molecules can move in a liquid or gas

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11
Q

what is a stationary phase ?

A

molecules can’t move , can be a thick liquid or solid

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12
Q

what happens in chromatography ?

A
  • substances in the sample moves between the 2 stages
  • an equilibrium is formed between the 2 stages
  • the mobile phase moves through the stationary phase and anything dissolved in the mobile phase moves with it
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13
Q

what does how quickly a chemical moves depend on ?

A

it distribution

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14
Q

what is a chemicals distribution ?

A

whether the chemical spends more time in the mobile or stationary phase

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15
Q

what phase to most components in a substance normally separates in ?

A

the stationary phase as long as all components spend different amounts of time in the mobile phase

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16
Q

why, in paper chromatography may the number of spots formed change in different solvents ?

A

the distribution of chemicals is the same in some solvents but different in others

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17
Q

how many spots will a pure substance always form ?

A

1 spot in any solvent

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18
Q

what is the stationary phase in paper chromatography ?

A

the filter paper

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19
Q

what is the the mobile phase in paper chromatography ?

A

the solvent

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20
Q

what does the amount of time spent in each phase in paper chromatography depend on ?

A
  • how soluble they are in the solvent
  • how attracted they are in the paper
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21
Q

what stage do molecules with a higher solubility spend longer in ? (paper chromatography)

A

the mobile phase

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22
Q

what do molecules with higher solubility do in paper chromatography ?

A

travel up the paper higher and are less attracted to the paper

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23
Q

what is a chromatogram ?

A

the result of a chromatography experiment

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24
Q

what is the RF value ?

A

the ratio between the distance travelled by the substance and the distance travelled by the solvent

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25
Q

how do you calculate RF value ?

A

distance travelled by substance / distance travelled by solvent

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26
Q

what is the test for oxygen ?

A

it will relight a glowing splint

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27
Q

what is the test for chlorine ?

A

it bleaches damp litmus paper

28
Q

what is the test for hydrogen ?

A

hold a lit splint at the open end of a test tube you will hear a squeaky pop when you release

29
Q

what is the test for carbon dioxide ?

A

solution of calcium hydroxide (limewater) in a test tube and blow into the test tube, if carbon dioxide is present the solution will turn cloudy

30
Q

what charge ion do flame tests test for ?

A

positive ions

31
Q

why are flame tests used to test for positive ions ?

A

metal compounds burn with colour

32
Q

how do flame tests work ?

A

put sample in flame and observe the colour change

33
Q

what colour does lithium burn ?

A

crimson

34
Q

what colour does sodium burn ?

A

yellow

35
Q

what colour does potassium burn ?

A

lilac

36
Q

what colour does calcium burn ?

A

orange

37
Q

what colour does copper burn ?

A

green

38
Q

describe step by step how to carry out a flame test ?

A
  1. clean nichrome wire loop by dipping it in HCL and holding over blue flame until the flame doesn’t burn another colour
  2. dip wire in sample and record the colour of the flame
39
Q

what is a precipiate reaction ?

A

add drops of sodium hydroxide into the sample and if you get an insoluble coloured metal hydroxide you know what metal your testing

40
Q

what colour does copper turn in precipitate reactions ?

A

blue

41
Q

what is the equation for copper in a precipitate reaction ?

A

Cu2+ + 2OH- - Cu(OH)2

42
Q

what colour does iron turn in precipitate reactions ? ( WITH 2 CHARGE )

A

green

43
Q

what is the reaction for iron 2 charge in a precipitate reaction ?

A

Fe2+ + 2OH- - Fe(OH)2

44
Q

what is the equation for iron 3 chargw in a precipiate reaction ?

A

Fe3+ + 3OH- - Fe(OH)3

45
Q

what colour does iron turn in a precipitate reaction - 3 charge ?

A

brown

46
Q

what colour does magnesium turn in a precipitate reaction ?

A

white

47
Q

what colour does aluminium turn in a precipitate reaction ?

A

white then colourless

48
Q

what is the equation for aluminium in a precipitate reaction ?

A

Al3+ + 3OH- - Al(OH)3

49
Q

what is the equation for magnesium in a precipitate reaction ?

A

Mg2+ + 2OH- - Mg (OH)

50
Q

what are negative ion tests we need to know ?

A

carbonate ions
halide ions
sulfate ion

51
Q

what is the test for carbonate ions?

A

when a carbonate ion reacts with dilute acid you get salt, water and CO2 so use the test for carbon dioxide to test for these ions

52
Q

what is the test for halide ions ?

A

add dilute nitric acid followed by silver nitrate solution

53
Q

what colour does chloride turn when testing for halide ions ?

A

white

54
Q

what is the equation for chloride when testing for halide ions ?

A

Ag+ + Cl- - AgCl

55
Q

what colour does bromide turn when testing for halide ions ?

A

cream

56
Q

what is the equation for bromide when testing for halide ions ?

A

Ag+ + Br- - AgBr

57
Q

what colour does iodide turn when testing for halide ions ?

A

yellow

58
Q

what is the equation for iodide when testing for halide ions ?

A

Ag+ + I- - AgI

59
Q

how do you test for sulfate ions ?

A

add dilute HCL then barium chloride (BaCl2)

60
Q

how do you know the compound was a sulfate when testing for sulfate ions ?

A

white precipiate of barium sulfate is formed

61
Q

what is the equation for a positive sulfate ions ?

A

Ba2+ + SO2- - BaSO

62
Q

why is HCL used when testing for sulfate ions ?

A

to remove any carbonate ions which might be present so it doesn’t confuse results

63
Q

what happens during flame emission spectroscopy ?

A
  1. a sample is placed in a flame as the ions heat up, and electrons get excited
  2. when electrons drop back to get to original energy levels they transfer the energy as light
  3. light passes through the spectroscope which detects different wavelengths of light to produce a line spectrum
  4. combination of wavelengths emitted by an ion depends on its charge and electron arrangement
  5. as no ions have the same charge and electron arrangement each ion produces a different pattern of wavelengths
  6. intensity of a spectrum indicates the concentration of the ion
64
Q

what are the advantages of using flame emission spectroscopy ?

A
  • sensitive, picks up tiniest amounts of things
  • fast
  • accurate
65
Q

what does flame emission spectroscopy identify ?

A

only a single metal not a mixture of ions, but identities a mixture of ions in a solution can be found

gcse science (27 decks)

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