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ib - chemistry > 8. Acids and bases > Flashcards

8. Acids and bases Flashcards

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1
Q

Brønsted–Lowry definitions

A

• an acid is a proton (H+) donor
• a base/alkali is a proton (H+) acceptor

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2
Q

conjugate acid–base pairs always differ by

A

one proton (H+)

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3
Q

amphiprotic refers to

A

the Bronsted-Lowry definition of acids and bases and indicates a species that can donate (acting as an acid) or accept (acting as a base) a proton

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4
Q

amphoteric means that

A

substance can act as an acid and a base

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5
Q

rule for amphiprotic and amphoteric

A

all amphiprotic substances are also amphoteric but not all amphoteric substances are amphiprotic

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6
Q

Lewis definition

A

• an ACid is an electron pair ACceptor
• a base is an electron pair donor

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7
Q

a coordinate (dative) covalent bond is always formed in a … acid–base reaction

A

Lewis

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8
Q

metal+acid →

A

salt+hydrogen

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9
Q

to be a lewis base

A

have a lone pair of electrons

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10
Q

to be a lewis acid

A

have space to accept a pair of electrons in outer shell

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11
Q

acid+carbonate/hydrogencarbonate →

A

salt+carbon dioxide+water

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12
Q

base+acid →

A

salt+water

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13
Q

alkalis are

A

solutions obtained when a metal hydroxide (such as sodium hydroxide) dissolves in water or when certain bases react with water

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14
Q

neutralisation reactions are …thermic and produce … only

A

exo
a salt and water

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15
Q

reactions between acids and bases or acids and alkalis are called

A

neutralisation reactions

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16
Q

pH =

A

−log10[H+(aq)]

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17
Q

a 1 unit change in pH indicates a … change in the H+ ion concentration

A

tenfold

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18
Q

[H+(aq)] =

A

1010−pH

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19
Q

equilibrium constant for the dissociation of water

A

Kw = [H+(aq)][OH-(aq)]

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20
Q

Kw has a value of … at 298K

A

1.0×10-14

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21
Q

strong acids

A

dissociate completely in aqueous solution
ex: hydrochloric (HCl), sulfuric (H2SO4) and nitric (HNO3) acid

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22
Q

the dissociation of a strong acid is represented by

A

HA(aq) → H+(aq) +A-(aq)

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23
Q

weak acids

A

dissociate partially in aqueous solutions

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24
Q

the dissociation of a weak acid is represented by

A

HA(aq) ⇌ H+(aq) +A-(aq)

25
Q

weak bases

A

ionise only partially in aqueous solution

26
Q

strong bases

A

ionise completely in aqueous solution

27
Q

the stronger an acid,

A

the weaker its conjugate base

28
Q

the stronger a base,

A

the weaker its conjugate acid

29
Q

distinguish between strong and weak acid

A
  • conductivity of ⚡️
    strong acid dissociates fully, meaning higher concentration of ions
    strong acids may be described as strong electrolytes
  • strong acids react more violently with metals or carbonates
30
Q

pH can be used to compare acid strength only if

A

equal concentrations of acids are being compared

31
Q

acid deposition

A

any process in which acidic substances (particles, gases and precipitation) leave the atmosphere to be deposited on the surface of the Earth

32
Q

wet deposition

A

acid rain, fog and snow

33
Q

dry deposition

A

acidic gases and particles

34
Q

problems with acid deposition

A
  • effect on vegetation: hydrogen ions displace metal ions from the soil → no more nutrients
  • lakes and rivers: aquatic life is sensitive when pH falls below 6
  • buildings: limestone
  • human health: respiratory illnesses
35
Q

limestone and acid rain equation

A

CaCO3(s) + H2SO4(aq) → CaSO4(s) + H2O(l) + CO2(g)

36
Q

how to deal with acid deposition?

A

• improving the design of vehicle engines
• using catalytic converters
• removing sulfur before burning fuels

37
Q

pre-combustion desulfurisation

A

hydrodesulfurisation (hydrotreating) can
be used – this involves heating crude oil fractions with hydrogen in the presence of a catalyst

this converts the sulfur to hydrogen sulfide (H2S), which can be removed from the reaction mixture by bubbling it through an alkaline solution

38
Q

post-combustion desulfurisation

A

involve passing the exhaust gases from the furnace through a vessel where the sulfur dioxide can react with alkalis/bases such as calcium oxide, calcium carbonate or calcium hydroxide

CaCO3(s) + SO2(g) → CaSO3(s) + CO2(g)

39
Q

acid dissociation constant

A

Ka=Kc × [H2O(l)]

40
Q

expression for the acid dissociation constant is

A
41
Q

Ka =

A

10-pKa

42
Q

the higher the value of Ka, the … the acid

A

stronger

43
Q

the lower the value of pKa the … the acid

A

stronger

44
Q

Ka and pKa are better measures of acid strength than pH because

A

their values do not depend on the concentration of the acid
→ depend only on temperature

45
Q

pKa =

A

−log10 Ka

46
Q

the higher the value of Kb,

A

the more the base ionises and the stronger it is

47
Q

the lower the value of pKb, the … the base

A

stronger

48
Q

pKw =

A

pH+pOH

49
Q

pH+pOH=

A

14

50
Q

Ka ×Kb =

A

Kw

51
Q

pKa+pKb=

A

pKw

52
Q

strong acid + strong base

A
53
Q

weak acid + strong base

A
54
Q

the pKa/b value of the acid/base is equal to the pH/pOH at

A

the half-equivalence point

55
Q

strong acid + weak base

A
56
Q

weak acid + weak base

A
57
Q

an indicator should be chosen so that

A

the equivalence point of the titration occurs within the pH range of the indicator

58
Q

buffer solution

A

a solution that resists changes in pH when small amounts of acid or alkali are added

ib - chemistry (11 decks)

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