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Chemistry A-Level OCR > 5.1.3 Acids, Bases and Buffers > Flashcards

5.1.3 Acids, Bases and Buffers Flashcards

1
Q

what is an acid

A

proton donors

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2
Q

what is a base

A

proton acceptors

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3
Q

what is a conjugate base

A

the base formed after the acid loses its proton

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4
Q

what is a conjugate acid

A

the acid formed after a proton is gained

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5
Q

what is a strong acid

A

when the H+ ions completely dissociate

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6
Q

what is a weak acid

A

when the H+ ions slightly dissociate

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7
Q

what is amphoteric

A

when a substance can act as both an acid and a base

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8
Q

why is water an ampholyte

A

it can accept or donate a proton

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9
Q

give examples of a strong acid

A

HCl, H2SO4, HNO3

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10
Q

give examples of a weak acid

A

CH3COOH, H2CO3

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11
Q

give examples of a strong base

A

NaOH, KOH

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12
Q

give examples of a weak base

A

NH3

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13
Q

describe equilibrium in strong acids and bases

A

equilibrium lies to the right as most of the acid molecules have dissociated the solution is a strong electrical conductor

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14
Q

describe equilibrium in weak acids and bases

A

equilibrium lies to the left hand side as most of the acid molecules do not dissociate and the solution is a weak electrical conductor

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15
Q

pH=

A

-log[H+]

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16
Q

[H+]=

A

10^-pH

17
Q

what is a strong monobasic acid

A

only one proton is donated per acid molecule e.g HCl

18
Q

what is a strong dibasic acid

A

two protons are donated per acid molecule e.g H2SO4

19
Q

what equation is associated with neutral

A

[H+]=[OH-]

20
Q

what equation is used with water and what is the Kw constant

A

Kw=[H+][OH-] so Kw=[H+]^2 because [H+]=[OH-] Kw=1x10^-14 at 298k and 1atm

21
Q

give the calculation for weak acid

A

[H+]=square root of Kax[HA]
ka=H+^2/HA
H+=A-

22
Q

give the calculation for bases

A

[H+]=Kw/[OH-]

23
Q

give the calculation for water

A

Kw=[H+]^2

24
Q

give the calculation for buffers with a salt

A

[H+]=Ka x (HA/A-)

25
Q

give the calculation for buffers with a strong base

A

nHA new = nHA initial - nOH-

[H+]=Ka x (HA/A-)

26
Q

describe the dissociation of water

A

-endothermic so increasing temperature shifts equilibrium to the right increasing H+ so pH decreases

27
Q

give the basic reaction for a weak acid

A

HA H+ + A-

28
Q

give the basic reaction for ionic product of water

A

H2O H+ + OH-

29
Q

give the calculation of working out pH of a diluted

A

[H+]=old volume/new volume x old [H+]

pH=-log[H+]

30
Q

how do you construct a pH curve

A
  • measure initial pH of the acid
  • add alkali in small amounts
  • record pH
  • when approaching end point add smaller amount
31
Q

describe equilibrium in indicators and give the equation

A
  • HA H+ + A-
  • in acid there is a lot of H+ so equilibrium favours the left hand side
  • in alkali the H+ is used up so equilibrium shifts to the right
32
Q

what is the endpoint in indicators

A

when there are equal amounts of both colours HA=A-

33
Q

what is the equivalence point in indicators

A
  • when the number of moles of acid exactly match the number of moles of alkali
  • [H+]=[OH-]
34
Q

what is a buffer

A

solutions that resist changes in pH upon addition of small amounts of acid or alkali

35
Q

what does a buffer contain

A
  • a solution of a weak acid and high concentration of its conjugate base and excess HA
  • HA=A- + H+
36
Q

describe what happens to equilibrium when a acid is added to a buffer

A
  • acid provides more H+ that react with A-

- equilibrium shifts to the left hand side and pH is raised and restored

37
Q

describe what happens to equilibrium when an alkali is added to a buffer

A
  • provides OH- that react with H+ tp form water

- equilibrium shifts to the right hand side and pH is lowered and restored

38
Q

give the equation for the buffer system in the blood and explain it

A
  • H2CO3 H+ + HCO3-
  • this carbonic acid-hydrogen carbonate equilibrium acts as a buffer to control the pH of the blood
  • present in blood plasma to maintain a pH of 7.35-7.45

Chemistry A-Level OCR (28 decks)

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