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chemistry > module 6 > Flashcards

module 6 Flashcards

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1
Q

acids definition

A

compounds which form hydrogen ions in aqueous solution
eg. HNO3, HCl

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2
Q

bases definition

A

compounds which form hydroxide ions in aqueous solutions
eg. NaOH, KOH

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3
Q

alkalis

A

water soluble bases

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4
Q

properties of acids

A
  • pH < 7
  • sour
  • corrosive
  • conductive in solution
  • turn blue litmus red
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5
Q

properties of bases

A
  • pH > 7
  • caustic
  • conductive in solution
  • bitter
  • turn red litmus blue
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6
Q

acid + base

A
  • neutralisation
  • salt + water
    (check solubility)
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7
Q

acid + carbonate

A

salt + carbon dioxide + water

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8
Q

acid + active metal

A

salt + hydrogen gas

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9
Q

indicators

A

substances which change colour based on the pH of environment

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10
Q

antoine lavoiser’s theory
- definition
- advantage
- disadvantage

A

definition: acids were substances which contained oxygen

advantage: worked in many cases
disadvantage: many oxygen containing substances were basic such as CaO
- no proper definition for a base

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11
Q

humphry davy theory
- definition
- advantage
- disadvantage

A

definition: acids were substances which contained replaceable hydrogen

advantage:
disadvantage:
- no proper definition for a base
- some acidic substances did not contain hydrogen eg. CO2

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12
Q

arrhenius’s theory
- definition
- advantage
- disadvantage

A

defintion:
- acids were substances which, in aqueous solution, ionised to form H+ ions
- bases were substances which, in aqueous solution, dissociate to form OH- ions

advantages:
- explained acid-base neutralisation reactions
- works for many acids and bases

disadvantages:
- does not recognise the role of the solvent in determining the relative strength or weakness of an acid
- cannot explain:
- the basic nature of carbonates,
acidic or basic salt
- neutralisation not in aqueous
form

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13
Q

advantages to arrhenius

A
  • explained acid-base neutralisation reactions
  • works for many acids and bases
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14
Q

disadvantages to arrhenius

A
  • does not recognise the role of the solvent in determining the relative strength or weakness of an acid
  • cannot explain:
    - the basic nature of carbonates,
    acidic or basic salt
    - neutralisation not in aqueous
    form
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15
Q

bronsted lowry theory
- definition
- advantages
- disadvantages

A

definition:
- acids are defined as substances which tend to donate protons (H+)
- bases are substances which tend to accept protons (H+)

advantages:
- explains the behaviour for acids and bases and their role in non-aqueous environments
- considers the role of the solvent in determining the strength or weakness of an acid
- explains the acidic and basic behaviour of ions and gases
- explains existence of non-hydroxide bases (NH3)
- shows the amphiprotic nature of substances depending on the environment

disadvantages:
- cannot explain amphoteric substances
- cannot explain acids and bases which do not donate or accept protons

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16
Q

advantages to bronsted lowry

A
  • explains the behaviour for acids and bases and their role in non-aqueous environments
  • considers the role of the solvent in determining the strength or weakness of an acid
  • explains the acidic and basic behaviour of ions and gases
  • explains existence of non-hydroxide bases (NH3)
  • shows the amphiprotic nature of substances depending on the environment
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17
Q

disadvantages to bronsted lowry

A
  • cannot explain amphoteric substances
  • cannot explain acids and bases which do not donate or accept protons
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18
Q

amphoteric

A

substance which can act as either an acid or a base

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19
Q

amphiprotic

A

substance which can act as either an acid or a base specifically due to its ability to either donate or accept a proton in different chemical environments
eg. HCO3-

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20
Q

protic substance

A

has the ability to act as a proton donor
- mono: 1 available eg. HCl
- di: 2 available eg. H2SO4
- tri: 3 protons available eg. H3PO4

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21
Q

why is the proticity important

A
  • affects the final concentration of hydronium ions in aqueous solutions –> final pH
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22
Q

arrows for first second third ionisation

A
  • strong acid: first arrow normal rest bidirectional
  • weak acid: all bidirectional
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23
Q

degree of ionisation

A

[H3O+]eq / [HA] initial
X 100%

[A-] eq / [HA] initial X 100%

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24
Q

unidirectional arrow

A

reaction goes to completion

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25
Q

degree of ionisation of strong acid in water

A

100%
- completely ionises to form hydronium ions

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26
Q

degree of ionisation of weak acids in water

A

< 100%
- does not completely ionise in an aqeous solution to form hydronium ions

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27
Q

an acids strength is defined by

A

its ability to donate a proton

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28
Q

acid –> conjugate

A

base

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29
Q

base –> conjugate

A

acid

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30
Q

strength of conjugate base of weak acid

A

weak

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31
Q

strength of conjugate acid of weak base

A

weak

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32
Q

strength of conjugate base of strong acid

A

extremely week/almost neutral

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33
Q

strength of conjugate base of strong acid

A

extremely week/almost neutral

34
Q

strength of conjugate base of extremely weak/almost neutral acid

A

strong

35
Q

strength of conjugate acid of extremely weak/almost neutral base

A

strong

36
Q

how to demonstrate amphiproticity of a substance

A

react the substance with both a strong acid and a strong base
- show that it can be a bronsted lowry base/acid

37
Q

which types of neutralisation reactions go to completion and how to prove

A

strong acid and/or strong base

LCP:
- weak acid in water forms equilibrium
- when hydroxide is added –> consumes free H3O+
- reduces [H3O+] –» system shifts right –> increase [H3O+]
- more NaOH is added –> more [H3O+] is consumed and equilibrium continues to shift right
- all CH3COOH is consumed

hence a weak monoprotic acid requires the same to completely neutralise a strong base as does a strong monoprotic acid

Bronsted Lowry theory:
- acetic acid is weak base in relation to water but strong base in relation to NaOH –> NaOH is strong base in water and acetic acid is a stronger acid in water
- acetic acid will ionise to completion in th epreence of NaOH –> neutralisation complete

38
Q

degree of ionisation definition

A

ratio of ionised acid molecules to the initial number of acid molecules

39
Q

substances acidity

A

dependent on the concentration of hydronium ions in aqueous solutions

40
Q

pH scale

A

convenient way to compare acidities of different substances

41
Q

pH

A

-log10[H3O+]
- decimal places = number of sig figs in [H3O+]

42
Q

decimal places of pH

A

decimal places = number of sig figs in [H3O+]

43
Q

factors that affect and acids pH

A
  1. concentration
    - more concentrated (higher [H3O+]) lower pH
  2. strength
    - strong acids tend to have lower pH than weaker acids
  3. proticity (strong acids)
    - stronger acids with higher proticity will have lower pH
  4. degree of ionisation (weak acids)
    - weak acids with a higher degree of ionisation will tend to have lower pH
44
Q

concentration of acids affecting pH

A

more concentrated means higher [H3O+] means lower pH

45
Q

strength of acids affecting pH

A

the stronger the acid the lower the pH
- 1.0M HCl completely ionises to form [H3O+] = 1.0M
- Acetic acid does not completely ionise (weak acid) [H3O] < 1.0M

46
Q

proticity affecting pH
is it strong or weak acids

A

strong
- acids with higher proticity tend to have lower pH
- HCl produces 1.0M [H3O+]
- H2SO4 produces [H3O+] > 1.0M as it has two stages of ionisation

47
Q

degree of ionisation affecting pH
is it strong or weak acids

A

weak
- acids with higher degree of ionisation will have a lower pH
- ignore proticity as the subsequent ionisations will have a small k value

48
Q

which has higher degree of ionisation
- acetic acid (CH3COOH)
citric acid (C6H8O7)

A

citric acid

49
Q

pOH

A

-log10[OH-]

50
Q

pH + pOH

A

14

51
Q

Kw

A

[H3O+][OH-] = 1.0 x 10^-14

52
Q

acidic [H3O+] vs [OH-]

pH

A

[H3O+] > [OH-]

pH < 7
pOH >7

53
Q

basic [H3O+] vs [OH-]

A

[H3O+] = [OH-]
pH = 7
pOH = 7

54
Q

neutral [H3O+] vs [OH-]

A

[H3O+] < [OH-]
pH > 7
POH < 7

55
Q

salt produced from strong acid strong base

A

mostly neutral as its conjugates are extremely weak (dont tend to accept protons in solution)

56
Q

salt produced from strong acid weak base

A

mostly acidic salts
- conjugate acid tends to donate protons
- conjugate base is extremely weak (doesn’t accept protons)

57
Q

salt produced from weak acid and strong base

A

mostly basic salts
- conjugate base is weak so tend to donate protons
- conjugate acid is extremely weak so barely accepts protons

58
Q

salt produced from weak acid and weak base

A

mostly neutral - depends on the nature of reactants and conjugates

59
Q

levelling of solvent

A

strength of strong acid is levelled (limited) based of the solvents ability to accept protons
strength of strong base is levelled by ability of solvent to donate protons

60
Q

titration

A

technique which the unknown concentration of a solution is determined by measuring volumes of solutions involved in a reaction
- uses neutralisation rwactions to determine the concentration of an acid or base in a titration

61
Q

what type of reaction does titration use

A

neutralisation

62
Q

equivalence point

A

the point at which equal moles of H3O+ (aq) and OH-(aq) have been reacted together –_> reaction is complete

63
Q

difference between equivalence point and end point

A

equivalence –> trying to measure
end point –> what we observe

64
Q

endpoint

A

point at which a sustained colour change is achieved using an appropriate indicator

65
Q

titration error

A

difference between equivalence point and end point

66
Q

titre

A

minimum volume required to reach the endpoint of the neutralisation reaction in titration

67
Q

titrant

A

the solution which is used to determine the concentration of the unknown solution

68
Q

analyte

A

the solution whose concentration is to be determined

69
Q

standard solution

A

a solution with known concentration

70
Q

steps of titration

A
  1. selection of primary standard
  2. preparation of standard solution
  3. selection of appropriate indicator
  4. rinsing of glassware
  5. performing titration
  6. calculation
71
Q

primary standard + properties

A

substance of sufficiently high purity and stability such that the standard solution can be prepared with a known concentration

  • high purity
  • easy to store
  • inexpensive
  • high molecular weight
  • known chemical formula

eg. hydrated oxalic acid (strong bases suitable) , anhydrous sodium carbonate , sodium hydrogen carbonate (strong acids suitable)

72
Q

how to prepare standard solution

A
  • dry solid powdered primary standard in drying oven/desiccator
  • weight approximate amount required for beaker
  • dissolve the measured mass using demineralised water
  • carefully transfer solution to volumetric flask, previously cleaned with demineralised water
  • rinse beaker three times –> transfer each rinsing to volumetric flask
  • dilute solution by filling up to point where the meniscus on the volumetric flask just touches the gradation line on the neck (hold at eye level to avoid parallax error)
  • stopper the flask
  • invert 20 times to homogenise the solution holding the stopper tight with thumb
73
Q

indicator chosen for titration

A

must change colour over a pH range that closely responds to the pH of the salt produced
- methyl orange (acidic) 3.1 - 4.4
- bromothymol blue (neutral) 6.0 - 7.6
- phenolphthalein (basic) 8.3 - 10.0

74
Q

rinsing glassware

A

pipettes and burettes rinsed with the solution they are to contain
- so concentration can be known accurately
- demin water changes the concentration

volumetric flask and conical flask should be rinsed thoroughly with water –> number of moles of sbtsance they contain can accurately be known

75
Q

volumetric flask + what it should be rinsed with

A

demin water
- must contain accurate number of moles of solute

76
Q

conical flask + what it should be rinsed with

A

demin water
- accurate number of moles of aliquot

77
Q

pipette + what it should be rinsed with

A

solution
- must not dilute the solution it is to deliver
- must faithfully represent concentration

78
Q

burette

A

solution
- dont dilute the concentration it is to deliver
- must faithfully represent the concentration

79
Q

performing titration steps

A

transfer 25ml of standard solution from volumetric flask to conical flask using pipette and bulb filter
(rinsing with demin, the standard solution twice)
- using pipette transfer 25mL of solution into conical flask
- rinse down sides with conical flask to ensure no drops of solution are lost

add few drops of appropriate indicator in the conical flask

fill and position burette appropriately
- rinse with demin water three times
- fill with solution until it is just below the 0mL mark
- read initial value by 2dp to avoid parallax error

perform titration
(rough) then actual

80
Q

back titration

A

used to find the concentration of a substance when the direct titration is impossible or impractical
- titrating a solid (antacid tablets, mineral rock)
- when acid/base is insoluble (carbonate)
- when acid/base is a gas
- direct titration results in a weak - acid-weak base titration with poor indicator colour change
- direct titration is too slow of a reaction

81
Q

neautralisation in real life

A
  • antacid tablest in stomach to stop acid reflux
82
Q
A

chemistry (9 decks)

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