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Chemistry IB HL > Topic 8 - Acids & Bases > Flashcards

Topic 8 - Acids & Bases Flashcards

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1
Q

Arrhenius’ theory

A

Acid: substance that ionises in water to produce H+

Alkali: soluble base that ionises in water to produce OH-

All alkalis are bases but not all bases are alkali.

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2
Q

Limitation of Arrhenius’ concept

A

the rxn between NH3 and HCl gas can’t be explained, as NH3 doesn’t contain OH-

NH3 (g) + HCl (g) -> NH4Cl (s)

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3
Q

Bronsted-Lowry theory

A

Acid: proton (H+) donor

Base: proton (H+) acceptor

In an aq soln, a proton can be represented as either hydrogen (H+) or hydronium (H3O+)

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4
Q

in what conditions will H3O+ form?

A

when a water molecule forms a coordinate bond with a proton

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5
Q

common acids are referred to as:

A
  • monoprotic: donates 1 proton
    eg. HCl
  • diprotic: donates 2 protons
    eg. H2SO4
  • triprotic: donates 3 protons
    eg. H3PO4
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6
Q

What can be concluded in a reversible rxn involving an acid/base? Give an example.

A
  • the acid/base is weak as they don’t fully dissociate

e.g. CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq)
CH3COOH: BL acid
H3O+: conjugate acid

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7
Q

conjugate

A

if it’s a backwards rxn instead of forwards, the conjugate base will act as a base

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8
Q

conjugate acid-base pair

A
  • conjugate acids and bases will differ from one another by a single proton
  • they are called conjugate acid-base pairs
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9
Q

Amphiprotic species

A

species that can act as either BL acid or BL base depending on the rxn

e.g. HCO3 - (aq) + H2O (l) CO3 2- (aq) + H3O+ (l)
HCO3 - (aq) + H2O (l) H2CO3 (aq) + OH- (aq)

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10
Q

zwitter ion

A

acts as an acid in the presence of a strong base by donating a proton, and vice versa for strong acids
eg. H2O

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11
Q

Requirements for BL

A

Acid: must be able to dissociate and release H+

Base: must be able to accept H+ (have lone e- pair)

Amphiprotic: must possess both a lone e- pair and a H+ ion

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12
Q

difference between amphiprotic and amphoteric

A
  • amphiprotic specifically related to BL theory (where emphasis is on proton transfer)
  • amphoteric has a broader meaning, describing a substance that can act as both acid & base even in rxns that don’t involve proton transfer
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13
Q

types of bases

A
  • metal oxides/hydroxides
  • ammonia
  • soluble carbonates
  • hydrogen carbonates
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14
Q

why doesn’t HNO3 release H2 gas?

A

because of its oxidising properties

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15
Q

ACID + METAL -> ?

A

Acid + metal -> salt + H2

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16
Q

ACID + BASE -> ?

A

acid + base -> salt + water

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17
Q

ΔH(neut)

A

enthalpy change occurring when an acid and base react together to form 1 mol of water

for all strong acids & bases, enthalpy change is very similar: ΔH = -57 kJ/mol

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18
Q

ACID + CARBONATE -> ?

A

acid + carbonate -> salt + H2O + CO2

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19
Q

acid turns phenolphthalein…

A

colourless

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20
Q

acid turns methyl orange…

A

red

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21
Q

acid turns litmus paper…

A

red

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22
Q

acid tastes…

A

sour

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23
Q

bases taste…

A

bitter

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24
Q

bases turn litmus paper…

A

blue

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25
Q

bases turn methyl orange…

A

yellow

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26
Q

bases turn phenolphthalein…

A

pink

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27
Q

uses of titration in acid-base titrations

A
  • to calculate the conc of ethanoic acid in vinegar with a standard soln of aq NaOH, using phenolphthalein
  • to calculate the conc of NaOH with a standard soln of HCl, using methyl orange
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28
Q

pH scale

A
  • the negative log of the conc of H3O+ or H2

- expressed in moles/litre

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29
Q

Kw

A
  • the autoionisation constant
  • expressed as Kw = [H3O][OH]
  • expression doesn’t include H2O as its a pure liquid
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30
Q

ionisation of water

A
  • water is a weak electrolyte
  • in pure state it doesn’t ionise much
  • contains a few H3O+ and OH- ions
  • in pure state, it will undergo self-ionisation
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31
Q

differences between strong and weak acids

A
  • strong acids exist entirely as ions in a solution
  • weak acids produce an equilibrium mixture in which an undissociated form dominates
  • strong acids are good proton donors
  • weak acids are bad proton donors

as their dissociation rxn is completed:

  • strong acids’ conjugate bases aren’t ready to accept a proton
  • weak acids’ conjugate bases are ready to accept a proton
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32
Q

difference between strong and weak bases

A
  • strong bases are good proton acceptors
  • weak bases are poor proton acceptors
  • strong bases react to form conjugates that don’t show acidic properties
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33
Q

Distinguishing between strong acids & bases and weak acids & bases

A
  • electrical conductivity: strong acids and bases have higher electrical conductivity
  • rate of rxn: strong acids and bases react faster
    higher no. of H+/OH- ions = higher rate of rxn
  • pH: the stronger the acid/base, the more polar the pH
34
Q

acid deposition

A

the process by which acid-forming pollutants are deposited on the Earth’s surface

35
Q

acid rain

A
  • most prevalent form of acid deposition

- refers to solns with pH

36
Q

Sulphur oxides

A
  • forms from combustion of fossil fuels
    S (s) + O2 (g) -> SO2 (g)

SO2 (g) + H2O (l) -> H2SO3 (aq)
H2SO3 is sulphurous acid.

37
Q

nitrogen oxides

A
  • forms at high temps in IC engines or during lightning

N2 (g) + O2(g) -> 2NO (g)

N2 (g) + 2O2 (g) -> 2NO2 (g)

38
Q

how does dry acid deposition affect plants?

A
  • blocks their stomata

- without Mg2+, plants can’t synthesise chlorophyll

39
Q

types of acid deposition

A
  • wet acid deposition
    eg. rain, snow, etc falls to the ground as aq ppt
  • dry acid deposition
    eg. acidifying particles, gases, etc fall to ground as dust and smoke; later dissolves in water to form acids
40
Q

Impact of acid deposition on water

A
  • increased acidity of water bodies, causing harm to aquatic life
    Al(OH)3 (s) + 3H+ (aq) -> AL3+ (aq) + 3H2O (l)
    Al3+ ions interfere with fish gills and reduce oxygen-carrying ability
  • acid rain also causes eutrophification
41
Q

effect of SO2 on metals

A
  • accelerates corrosion
    Fe (s) + SO2 (g) + O2 (g) -> FeSO4 (s)
    Fe (s) + H2SO4 (aq) -> FeSO4 (aq) + H2
  • removes protective Al2O3 coating from Al
    Al2O3 + 6HNO3 (aq) -> 2Al(NO3)3 (aq) + 3H2O (l)
42
Q

Impact of SO2 on plant life

A
  • slower growth/healing
  • leaching (washing away important minerals) in soil, such as Mg2+ or Ca2+
  • can release Al3+, damaging plant roots
43
Q

pre-combustion method of reducing SO2 emission

A
  • sulphur present as metal sulphides can be removed by crushing coal and washing with water, so metal sulphides (being high density) will sink and separate from coal
  • HDS (hydrodesulphurisation)
44
Q

HDS (hydrodesulphurisation)

A
  • catalytic removal of sulphur from refined petroleum products
  • by reacting it with hydrogen to produce H2S
  • then can be captured and converted to pure sulphur
45
Q

post-combination method of reducing SO2 emissions

A

flue gas desulphurisation

46
Q

flue gas desulphurisation

A

CaO (s) + SO2 (g) -> CaSO3 (s)

CaCO3 (s) + SO2 (g) -> CaSO3 (s) + CO2

47
Q

group trends of hydrogen halides

A
  • relative acidic strength of hydrogen halides increase down the group
  • despite decreasing polarity down the group
  • due to decreasing bond strength of hydrogen-halogen bonds as halogen ion increases in size
48
Q

Lewis acid

A

lone pair acceptor

49
Q

Lewis base

A

lone pair donor

50
Q

difference between Lewis base and Brønsted-Lowry base

A
  • actually still the same group of compounds

- because by both definitions they are species with a lone pair of e-s

51
Q

difference between Lewis acid and Brønsted-Lowry acid

A
  • Brønsted-Lowry definition of acids is narrower (only includes H+)
  • all Brønsted-Lowry acids are Lewis acids but not vice versa
  • Lewis acids include any species able to accept a lone pair of e-s
  • this means Lewis acids include molecules with incomplete valence shells (which Brønsted-Lowry doesn’t include)
52
Q

what is the bond formed from a Lewis acid-base reaction

A
  • covalent coordinate bond

- because both electrons will come from the Lewis base

53
Q

nucleophile

A
  • likes nucleus
  • e-rich species
  • donates a lone pair to form a new covalent bond in a rxn
  • basically a Lewis base
54
Q

electrophile

A
  • likes electrons
  • electron-deficient species
  • accepts a lone pair from another reactant to form a covalent bond
  • basically a Lewis acid
55
Q

autoionisation of water

A

when 2 H2O molecules turn into a hydronium and hydroxide ion

  • the hydronium ion takes the proton from the H of the other H2O molecule
  • the hydroxide ion got its proton (H atom) stolen but retains the 2 e-s from the bond
56
Q

quantity of H3O to OH- in an acidic soln

A

H3O > OH

57
Q

quantity of H3O to OH in a basic soln

A

H3O

58
Q

quantity of H3O to OH in a neutral soln

A

H3O = OH

59
Q

when does ionisation of water become significant

A

in extremely dilute acids/bases

60
Q

chemical method of distinguishing between strong and weak acids

A
  • rxn with reactive metal/carbonate
  • the stronger acid reacts faster

OR

  • rxn with alkali
  • stronger acid will induce higher temp change
61
Q

physical method of distinguishing between strong and weak acid

A
  • conductivity test

- strong acid will conduct more

62
Q

weak acids in environment

A
  • sulfurous acid, H2SO3
  • nitrous acid, HNO2
  • carbonic acid, H2CO3
63
Q

effect of H2SO3 on environment

A
  • leaching of soil
  • corrosion of limestone buildings/statues/marble
  • harms/kills plants
64
Q

effect of HNO2 on environment

A
  • leaching of soil
  • corrodes marble/limestone buildings/statues
  • harms/kills plants
65
Q

effect of H2CO3 on environment

A
  • acidification of lakes

- corrosion of marble/limestone buildings/marble

66
Q

Example of weak base

A

NH3

67
Q

example of strong base

A

NaOH

68
Q

example of strong acid

A

HCl, H2SO4

69
Q

weak acid

A

CH3COOH

70
Q

differing properties between stronger and weaker acids

A
  • stronger = better conductor
  • stronger = more vigorous rxn with carbonates and metals
  • stronger = lower pH
71
Q

explain how water can act as both a BL acid and BL base

A
  • BL base: water can accept a proton to form H3O+

- BL acid: water can donate a proton o form OH-

72
Q

reagents and conditions to prepare ethanoic acid from ethanol

A

H2SO4 (sulphuric acid) and Cr2O7 2- (chromium dichromate)

heat under reflux.

73
Q

why would a very acidic aq solution contain OH- ions?

A
  • in v acidic solns, [H+] increases and [OH-] decreases but there are still some present

[OH-] = Kw / [H+] therefore [OH-] cannot be zero.

74
Q

what is the effect of increasing temp on the equilibrium constant of water dissociation equation (given that dissociation of water is endothermic)?

A
  • forward rxn favoured as it is endothermic
  • Kw increases as [OH-] and [H+] increase
  • endothermic favoured as it will use up some of the heat supplied
75
Q

A piece of metal is added to a strong acid and a weak acid. Describe observations that would allow one to distinguish between them:

A

Strong acid:

  • greater temp change
  • faster rate of Hydrogen production
  • faster rate of Mg dissolving
76
Q

Ka

A
  • acid dissociation constant

- larger Ka = stronger acid

77
Q

Kb

A
  • base dissociation constant

- larger Kb = stronger base

78
Q

pH

A

calculated as pH = - log [H+]

79
Q

pOH

A

calculated as pOH = - log [OH-]

80
Q

relationship between pH and pOH

A

pH + pOH = 14

81
Q

pKw

A
  • the negative log of Kw
  • pKw = 14 if condition is room temp

pH + pOH = pKw

Chemistry IB HL (11 decks)

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