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CHEM 2.0 > Chemical Analysis > Flashcards

Chemical Analysis Flashcards

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1
Q

what is a pure substance?

A

a single substance (element or compound) that is not mixed with anything else

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2
Q

what kind of MP and BP do pure substances have?

A

a fixed one

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3
Q

a mixture will melt or boil…?

A

over a range of temperatures

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4
Q

what is a formulation?

A

a mixture of different compounds in fixed proportions

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5
Q

what is the stationary phase in chromatography?

A

the paper

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6
Q

what is the mobile phase in chromatography?

A

the solvent

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7
Q

what does the separation in chromatography depend on?

A

the distribution of substances between the phases

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8
Q

what does Rf stand for?

A

retention factor

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9
Q

how do you calculate Rf?

A

distance travelled by dye / distance travelled by solvent

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10
Q

how does an Rf value change across solvents?

A

different compounds have different Rf values in different solvents

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11
Q

how many spots will a pure substance produce in chromatography?

A

one spot in all solvents

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12
Q

why is the baseline in chromatography drawn in pencil?

A

so that the pen ink doesn’t dissolve and move up the paper

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13
Q

why is the level of solvent in chromatography below the sample line?

A

if it wasn’t, it would spread out rather than going up

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14
Q

why do samples move at different speeds during chromatography?

A

the more soluble a substance is in the mobile phase, the further it will travel up the stationary phase

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15
Q

more soluble means what?

A

substance has a stronger attraction to the mobile phase and will move further up the stationary phase

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16
Q

what is the gas test for oxygen?

A

Glowing splint held in a test tube. if oxygen is present, splint relights

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17
Q

what is the gas test for hydrogen?

A

lighted splint held in a test tube. if hydrogen is present, a pop sound is heard

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18
Q

what is the gas test for carbon dioxide?

A

gas bubbled through limewater. if carbon dioxide is present, Limewater turns milky or cloudy white

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19
Q

what is the gas test for chlorine?

A

Damp litmus paper held in a test tube. if chlorine is present, Paper turns white

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20
Q

describe the process of flame test to identify metal ions in ionic substances

A
  • dip nichrome wire in acid and then water to remove contaminants
  • dry wire in roaring bunsen burner flame
  • dip wire into ionic solution to be tested
  • place wire into hottest part of flame and record any change in colour of the flame
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21
Q

what is the positive result for lithium in the flame test?

A

flame turns crimson red

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22
Q

what is the positive result for potassium in the flame test?

A

flame turns lilac

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23
Q

what is the positive result for calcium in the flame test?

A

flame turns orange-red

24
Q

what is the positive result for sodium in the flame test?

A

flame turns yellow

25
Q

what is the positive result for copper in the flame test?

A

flame turns green

26
Q

give 2 limitations of the flame test to identify metal ions in ionic substances

A
  • difficult to distinguish colours as they may be very similar
  • in a mixture, only the dominant colour will be seen - a bold colour will mask a weaker one
27
Q

describe the process of the precipitate test

A
  • place 1-2cm^3 of ionic solution into test tube
  • use pipette to drop 10 drops of NaOH into test tube
  • observe and record result
  • add a further 2-3cm^3 of NaOH to test tube and note any further changes
28
Q

what is the positive result for aluminium in the precipitate test?

A

white precipitate forms, and after adding more NaOH it dissolves

29
Q

what is the positive result for calcium in the precipitate test?

A

white precipitate forms, and after adding more NaOH it remains

30
Q

what is the positive result for magnesium in the precipitate test?

A

white precipitate forms, and after adding more NaOH it remains

31
Q

what is the positive result for Copper (II) in the precipitate test?

A

blue precipitate forms, and after adding more NaOH it remains

32
Q

what is the positive result for iron (II) in the precipitate test?

A

green precipitate forms, and after adding more NaOH it remains

33
Q

what is the positive result for iron (III) in the precipitate test?

A

brown precipitate forms, and after adding more NaOH it remains

34
Q

describe the method of the carbonate test

A
  • pour ~1cm depth of sample into test tubes
  • place ~2cm depth of limewater into another test tube
  • add ~1cm depth of dilute hydrochloric acid to test tube, and quickly place the bung into the neck of the test tube and the delivery tube into the limewater
35
Q

what is the positive result for carbonate in carbonate test using dilute acid (HCl)?

A

bubbles turn limewater cloudy

36
Q

what are the conclusions of carbonate test?

A
  • carbonate ion (CO3^2-) is identified by producing CO2 gas when reacted with any acid
  • CO2 gas will turn limewater cloudy when bubbled through it
37
Q

describe the method of the sulfate test

A
  • pour ~1cm depth of each of labelled sulfate solutions into 2 test tubes in the rack and a similar amount of tapwater into another test tube and distilled water in another
  • add a few drops of dilute hydrochloric acid to each solution
  • add ~1cm depth of barium chloride solution
38
Q

what would carbonate ions in sulfate test produce?

A

bubbles of gas when acid was added

39
Q

what is the positive result for sulfate ions in sulfate test?

A

white precipitate

40
Q

what is the conclusion of the sulfate test?

A

sulfate ion (SO4^2-) produces a white precipitate when reacted with acidified (to remove false positives) barium chloride solution

41
Q

describe the method of the halide test

A
  • pour ~1cm depth of sample into test tube
  • add a dew drops of nitric acid into test tube
  • add ~1cm depth of silver nitrate solution
  • record observations
42
Q

why is nitric acid used in the halide test?

A

an acid is needed to remove any false positives, but HCl can’t be used as it contains chloride ions which will give a positive result

43
Q

what is the positive result of chloride ion in halide test?

A

white ppt

44
Q

positive result of bromide ion in halide test?

A

cream ppt

45
Q

positive result of iodide ion in halide test?

A

yellow ppt

46
Q

what is the conclusion of halide test?

A

halide ions produce a precipitate when reacted with acidified silver nitrate solution, and the colour of precipitate deepens going down group 7

47
Q

what would carbonate ions in halide test produce?

A

bubbles of gas when acid was added

48
Q

how is chemical vs instrumental analysis done?

A
  • chemical analysis is performed by scientists who analyse chemical reactions and make conclusions from their observations
  • instrumental analysis is performed by machines and instruments
49
Q

give some examples of chemical analysis

A
  • flame tests
  • precipitate tests
  • identifying gases
  • titrations
50
Q

give some examples of instrumental analysis

A
  • flame emission spectroscopy
  • mass spectroscopy
  • infra-red spectroscopy
51
Q

what are some advantages of chemical analysis?

A
  • often simple to perform
  • no expensive equipment required
52
Q

what are some disadvantages of chemical analysis?

A
  • Time-consuming (slow)
  • requires a large sample size
53
Q

what are some advantages of instrumental analysis?

A
  • Highly accurate
  • uses a small sample size
  • can analyze complex mixtures quickly (fast) and provides a lot of information
54
Q

what are some disadvantages of instrumental analysis?

A
  • expensive equipment
  • requires frequent calibration
55
Q

how does flame emission spectroscopy work?

A
  • every element has its own distinctive spectrum with specific wavelengths of light on it
  • instead of using flame colour to help identify an element a spectrum of light of the flame is detected instead
56
Q

what is flame emission spectroscopy used for?

A
  • elements to be identified in distant stars and planets
  • kidney dialysis
57
Q

how is flame emission spectroscopy used in kidney dialysis?

A
  • determining the concentration of sodium ions
  • calibration curve will be produced using known concentrations of sodium ions and light intensity will be measured for those concentrations
  • calibration curve used to determine ion concentration from the sample’s light intensity

CHEM 2.0 (14 decks)

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