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Chemistry > Topic 12 Acid Base Equilibria > Flashcards

Topic 12 Acid Base Equilibria Flashcards

1
Q

What are brønsted Lowry acids and bases

A

Proton donators and acceptors

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2
Q

What is transferred in acid base reactions

A

Protons

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3
Q

What is pH

A

-log[H+]

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4
Q

What do acids actually form in water

A

H3O+ / hydroxonium ions

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5
Q

What’s the difference between weak and strong acids

A

Strong acids fully dissociate in water but weak acids dissociate poorly

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6
Q

What behaves as a base when acid is added to water

A

The water

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7
Q

What do acids and bases react to form

A

Salts

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8
Q

Is the enthalpy change of neutralisation always exo or endothermic

A

Exothermic

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9
Q

What are the 2 enthalpys involved in neutralisation of a weak acid

A
  1. Enthalpy of dissociation
  2. Enthalpy for the reaction of OH- and H+
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10
Q

What enthalpy is involved in neutralisation of a strong acid

A

Enthalpy when OH- and H+ react

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11
Q

What is Ka

A

Acid dissociation constant

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12
Q

When working with Ka for a weak acid what 2 assumptions do you have to make

A
  1. [HA] at equilibrium = initial conc
  2. [H+]=[A-] at equilibrium
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13
Q

What is the simplified Ka expression

A

Ka = [H+]^2/HA

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14
Q

Does water exist in equilibrium or not

A

Yes

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15
Q

Water dissociation equation non simplified

A

2H2O <—> H3O+ + OH-

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16
Q

Water dissociation equation simplified

A

H2O <—> H+ + OH-

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17
Q

Kc expression for water

A

Kc = [H+][OH-]/[H2O]

18
Q

Formula of Kw

A

Kw =[OH-] x [H+]

19
Q

What is the value of Kw

A

1.00 x 10^-14

20
Q

Does Kw change with temp and why

A

Yes - dissociation of water increases with temperature so there is more OH- and H+

21
Q

What is special about pure water

A

[OH-] = [H+]

22
Q

What is the simplified definition of Kw when working with pure water

A

Kw = [H+]^2

23
Q

Define pKw and pKa

A

pKw = -logKw
pKa = -logKa

24
Q

What do you use to measure pH

A

pH meter

25
Q

Qualities of strong base into strong acid titration curve

A

Equivalence point at 7, starts at pH 1 ends at pH 13

26
Q

Qualities of weak base into strong acid titration curve

A

Equivalence point < 7 , start at pH 1 end at pH 9

27
Q

Qualities of strong base into weak acid titration curve

A

Equivalence point > 7 , starts at pH 5 ends at pH 13

28
Q

What is the half neutralisation point and what can it be used to calculate

A

Half way between start and equivalence points, pH at this point can be used to calculate pKa as [HA] = [A-]. Cancels out in the Ka equation so Ka = [H+] which can be found from the pH (pKa = pH)

29
Q

What makes an indicator “suitable”

A

Change colour completely within the vertical section of a titration curve

30
Q

Methyl orange colour change

A

Red-Orange acid - base

31
Q

Phenolphthalein colour change

A

Clear - pink
Acid - base

32
Q

Why are no indicators suitable for weak acid/base titrations

A

There is no sharp pH change

33
Q

What is a buffer

A

A solution that resists changes in pH when a small amount of acid or base is added

34
Q

What makes up an acidic buffer

A

A weak acid and a salt of its conjugate base

35
Q

What happens when you add an acid to an acidic buffer (2 steps)

A
  1. H+ ions react with A- (high conc from salt)
  2. More HA is produced as equilibrium has shifted left
36
Q

What happens when you add a base to an acidic buffer (2 steps)

A
  1. OH- ions react with H+ ions in solution
  2. Equilibrium shifts right so HA dissociates to H+ and A- to restore the concentration of H+ ions
37
Q

What other way can a buffer be formed and where does this happen.
Give 2 steps to explain this process

A

Excess weak acid + strong base - in a titration.
1. All of the base reacts HA + OH-—-> A- + H2O
2.A- and excess HA left in solution which forms a buffer solution

38
Q

What are basic buffers made of

A

Weak base and its salt

39
Q

What weak acid and ion form the buffer in blood. Give two equilibrium equations for this buffer

A

Carbonic acid and hydrogencarbonate ions
1. H2CO3 <—> H+ + HCO3-
2. H2CO3 <—-> H2O + CO2

40
Q

What do you have to remember when calculating pH of buffers

A

[H+] ≠ [A-]

41
Q

What is the Henderson Hasselbalch equation and what is it used for

A

pH = pKa + log [A-]/[HA]
Used to work out how to make a buffer of a specific pH

Chemistry (14 decks)

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