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Chemistry ⚗ > Chapter 12 - Chemical analysis > Flashcards

Chapter 12 - Chemical analysis Flashcards

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1
Q

what is a pure substance?

A

something made from just one substance

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2
Q

what can a pure substance be?

A

an element or a compound

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3
Q

what are the fixed points of an element or compound?

A

its melting and boiling points

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4
Q

test for water

A

turns white, anhydrous copper sulfate blue

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5
Q

test for PURE water

A

its melting point is exactly 0 degrees and its boiling point is exactly 100

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6
Q

how can the fixed points of a substance be used to identify it?

A

pure substances have specific temperatures at which they boil/melt and these can then be checked in a data base

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7
Q

what will impurities do to the melting point of a substance?

A

it will lower it

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8
Q

what will impurities do to the melting range of a substance?

A

it will increase it

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9
Q

what will impurities do to the boiling point of a substance?

A

it will increase it

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10
Q

how to test a substance’s purity

A

measure its melting and boiling points

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11
Q

what is a formulation?

A

a mixture with a specific purpose

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12
Q

examples of formulations 4

A

paint
tablets
cosmetics
fertilisers

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13
Q

main components of a tablet 4

A

active drug
smooth coatings
colourants
sweeteners

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14
Q

why is the formulation of a tablet so important?

A

it must have a long enough shelf life, be consumable and deliver the drug to the right part of the body

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15
Q

main components and functions of these in paint

A

pigment (for colour)
solvent (alters viscocity for easy painting)
binder (forms a protective film when paint dries)

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16
Q

what is chromatography?

A

an analytical method used to separate substances in a mixture

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17
Q

what are the two phases in chromatography?

A

mobile phase

stationary phase

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18
Q

what is the mobile phase?

A

where the molecules can move. It is a liquid and is what carries molecules up the stationary phase

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19
Q

what is the stationary phase?

A

where the molecules can’t move and are carried by solvent

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20
Q

what is the Rf value?

A

a ratio of the distance travelled by the solute and the solvent

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21
Q

how to calculate Rf value?

A

distance travelled by substance / distance travelled by solvent

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22
Q

why is the Rf value useful?

A

if two Rf values match, the substance may be present It is an easy means of comparison

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23
Q

what does a single spot on a chromatogram show?

A

a pure substance

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24
Q

what does the amount of time molecules spend in each phase depend on?

A

how soluble they are in the solvent

how attracted they are to the paper

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25
Q

what happens to molecules with a higher solubility and lower attraction to paper?

A

they will travel further

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26
Q

how are components of a substance separated?

A

they have different forces of attractions to the paper

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27
Q

what is formed between the mobile and stationary phases during chromatography?

A

an equilibrium

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28
Q

which reaction to do to test for hydrogen?

A

react zinc and sulfuric acid to form zinc sulfate and hydrogen

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29
Q

test for hydrogen

A

hold a lit splint in hydrogen

if hydrogen is present, it will make a squeaky pop

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30
Q

test for oxygen

A

a glowing splint relights

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31
Q

test for carbon dioxide

A

limewater (calcium hydroxide) turns cloudy

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32
Q

test for chlorine

A

damp litmus paper is bleached white

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33
Q

what is a cation?

A

a metal ion

34
Q

process of a flame test

A

a nichrome wire is dipped in hydrochloric acid then heated to clean it
redip wire in acid then into unknown substance
hold loop in blue flame
record colour of flame

35
Q

what colour flame does a lithium ion have?

A

crimson

36
Q

what colour flame does a sodium ion have

A

yellow

37
Q

what colour flame does a potassium ion have

A

lilac

38
Q

what colour flame does a calcium ion have

A

orange-red

39
Q

what colour flame does a copper ion have

A

green

40
Q

problem of flame tests

A

doesn’t work with mixtures - some flame colours may hide others

41
Q

advantages of modern instrumental methods 3

A

more sensitive (only a small amount of sample needed)
faster
very accurate

42
Q

disadvantages of modern instrumental methods 3

A

expensive
special training needed
results can only be interpreted by comparing with known substances

43
Q

what is flame emission spectroscopy used for?

A

analyse samples for metal ions

44
Q

process of flame emission spectroscopy

A

sample placed in a flame
ions heat up
electrons become excited and jump into higher shells
when they drop back, they emit energy as light
light passes through a spectroscope

45
Q

what happens when light emitted passes through a spectroscope?

A

different wavelengths of light are detected to produce a line spectrum

46
Q

what is a substance’s line spectrum?

A

the characteristic pattern of radiation absorbed and emitted

47
Q

why are no two ions’ line spectrums the same?

A

it depends on the ion’s charge and electron arrangement so different ions emit different wavelengths of light, leading to different line spectrums

48
Q

what does the intensity of a spectrum indicate?

A

the concentration of that ion in solution

49
Q

how can flame emission spectroscopy be used to identify different ions in mixtures?

A

the spectras for the different ions are created and then compared to a database

50
Q

how can the machine used for FES indicate the concentration of an unknown?

A

the spectrometer measures the intensity of light with a specific wavelength that is known to be a characteristic of an ion
the machine is calibrated using solutions of the metal ion of known concentrations
it can then give a value for the unknown concentration

51
Q

how to test if a substance is a carbonate?

A

it will fizz and produce carbon dioxide

52
Q

equation and ionic equation for carbonate + acid

A

carbonate + acid -> carbon dioxide + water

CO3 (^2-) + 2H(^+) -> CO2 + H2O

53
Q

which two acids do you have to add to test for sulfate?

A

barium chloride and hydrochloric acid

54
Q

what will form if sulfate ions are present when HCL and Barium chloride are added?

A

a white precipitate (barium sulfate)

55
Q

why must you add HCl before barium chloride when testing for sulfates?

A

the hydrochloric acid gets rid of any carbonate ions, which would also form a precipitate with the barium chloride and confuse results

56
Q

ionic equation for testing for sulfates

A

Ba (^2+) + SO4 (^2-) -> BaSO4

57
Q

what are the three halides we will be testing for?

A

chlorine (Cl-)
bromine (Br-)
Iodine (I-)

58
Q

process/test for halides

A

add a few drops of dilute nitric acid to the unknown
then add a few drops of silver nitrate solution
if a precipitate forms, halide ions are present

59
Q

why is nitric acid added when testing for halides?

A

it dissolves compound and removes any carbonate ions as they would also form a precipitate and confuse results

60
Q

what colour precipitate will a chloride ion form and what is it?

A

white (silver chloride)

61
Q

what colour precipitate will a bromide ion form and what is it?

A

cream (silver bromide)

62
Q

what colour precipitate will a iodide ion form and what is it?

A

yellow (silver iodide)

63
Q

ionic equation for testing for chloride ions

A

Ag+ + Cl- -> AgCl

64
Q

ionic equation for testing for iodide ions

A

Ag+ + I- -> AgI

65
Q

ionic equation for testing for bromide ions

A

Ag+ + Br- -> AgBr

66
Q

general ionic equation when testing for halides

A

Ag+ + X- -> AgX

67
Q

which ions form white precipitates with sodium hydroxide solution?

A

aluminium, calcium and magnesium

68
Q

how to distinguish between calcium, magnesium ad aluminium ions?

A

use a sodium hydroxide test (aluminium precipitate will dissolve eventually)
Use flame test

69
Q

what colour precipitate do calcium ions form in sodium hydroxide solution?

A

white

70
Q

what colour precipitate do copper ions form in sodium hydroxide solution?

A

blue

71
Q

what colour precipitate do iron (II) ions form in sodium hydroxide solution?

A

green

72
Q

what colour precipitate do iron (III) ions form in sodium hydroxide solution?

A

brown

73
Q

what colour precipitate do aluminium ions form in sodium hydroxide solution?

A

white but will eventually dissolve

74
Q

what colour precipitate do magnesium ions form in sodium hydroxide solution?

A

white

75
Q

ionic equation for calcium ion + sodium hydroxide solution

A

Ca2+ + 2OH- -> Ca(OH)2

76
Q

ionic equation for copper (II) ion + sodium hydroxide solution

A

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

77
Q

ionic equation for iron (II) ion + sodium hydroxide solution

A

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

78
Q

ionic equation for iron (III) ion + sodium hydroxide solution

A

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

79
Q

ionic equation for aluminium ion + sodium hydroxide solution

A

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

80
Q

ionic equation for magnesium ion + sodium hydroxide solution

A

Mg2+ +2OH- -> Mg(OH)2

81
Q

why is a precipitate formed?

A

it is insoluble

Chemistry ⚗ (17 decks)

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