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a2 chem - physical > acids and bases > Flashcards

acids and bases Flashcards

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1
Q

what is a brønsted-lowry acid?

A

a proton donor

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2
Q

what is a brønsted-lowry base?

A

a proton acceptor

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3
Q

what does ‘strong’ mean in terms of acids and bases?

A

completely dissociates in solution

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4
Q

what are some examples of strong acids?

A

HCl, H2SO4 + HNO3

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5
Q

what does monoprotic mean?

A

1mol of acid produces 1mol of H+

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6
Q

what does diprotic mean?

A

1mol of acid produces 2mol of H+

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7
Q

what are strong bases?

A

they produce OH- if the base dissolves in water

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8
Q

what are some examples of strong bases?

A

KOH, NaOH, CuOH

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9
Q

what is meant by ‘weak’ in terms of acids and bases?

A

only slightly dissociate in solution

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10
Q

constituent elements: weak acids are mainly…

A

“carbon containing” (organic)
e.g., ethanoic acid

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11
Q

what is an example of a weak base?

A

ammonia

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12
Q

where does the position of equilibrium lie for weak acids and bases?

A

far to the left

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13
Q

what scale is used to measure pH?

A

the pH scale (logarithmic)
a difference of 1 on the pH scale is a 10x increase/decrease of [H+]

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14
Q

what formula do we use to calculate pH?

A

pH = –log10[H+]

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15
Q

what formula do we use to calculate [H+] using pH?

A

[H+] = 10(-pH)

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16
Q

what is the pH of neutral solutions?

A

pH 7 at room temp.

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17
Q

what is an alkali?

A

a soluble base

alkaline solutions = when bases dissociate in water

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18
Q

what is Ka?

A

the acid dissociation constant - this is only applicable for WEAK ACIDS, due to them only partially dissociating

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19
Q

what is the relationship between Ka and acid dissociation?

A

the higher the value for Ka, the more the acid will dissociate when placed in solution; strong acids have exceptionally high Ka values

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20
Q

what equilibrium do we need to consider when looking at Ka?

A

HA ⇌ H+ + A-

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21
Q

what is the formula for Ka?

A

Ka = [H+][A-]/[HA]

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22
Q

what are the units used for Ka?

A

mol dm-3

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23
Q

how would the formula look for a PURE SOLUTION of a weak acid?

A

Ka = [H+]^2/[HA]

24
Q

what is the formula for calculating pKa?

A

pKa = -log(Ka)

25
Q

what is the formula for calculating Ka from pKa?

A

Ka = 10^(-pKa)

26
Q

what assumption do we make about HA?

A

that the [HA] at equilibrium is the same as the [HA] initially - we assume this as we say that the acid is so weak, barely any of it has dissociated. Again, this is only applicable for pure solutions of the weak acid.

27
Q

what does Kw denote?

A

the ionic product of water

28
Q

what equilibrium are we considering when looking at Kw?

A

H2O ⇌ H+ + OH-

29
Q

what is the formula for calculating Kw?

A

Kw = [H+][OH-]

30
Q

what are the units for Kw?

A

mol2 dm-6

31
Q

what is the value of Kw AT ROOM TEMP?

A

1.00 x10^-14 ; if the value is not given within the question, we assume this value

32
Q

why does pure water remain pure, despite a pH different to 7?

A

for water to be pure, [H+] has to be equal to [OH-]

33
Q

how would the formula look different for Kw of PURE water?

A

Kw = [H+]^2

34
Q

how many types of different titration curves are there?

A

four:
weak acid-weak base
weak acid-strong base
strong acid-weak base
strong acid-strong base

35
Q

what is the definition of equivalence point?

A

the point at which the moles of acid and the moles of base present would neutralise each other

36
Q

what is the definition of end-point?

A

the point at which the indicator changes colour

37
Q

what pH does the inflection occur for strong acid-strong base?

A

between pH2 and pH11

38
Q

what pH does the inflection occur for strong acid-weak base?

A

between pH2 and pH8

39
Q

what pH does the inflection occur for weak acid-strong base?

A

between pH6 and pH11

40
Q

what pH does the inflection occur for weak acid-weak base?

A

there is no major point of inflection

41
Q

what is the choice of indicator dependent on?

A

the pH in which the indicator changes colour must work with the pH at which the equivalence point is - it must be within the inflection pH of the curve

42
Q

what are the two main indicators for titrations?

A

phenolphthalein and methyl orange

43
Q

what is the colour change for phenolphthalein?

A

colourless in acid –> pink in base

44
Q

what is the pH range of the colour change for phenolphthalein?

A

pH8.3 - pH10.

appropriate for titrations including a strong base

45
Q

what is the colour change of methyl orange?

A

red in acid –> yellow in base

46
Q

what is the pH range of the colour change for methyl orange?

A

pH3.1 - pH4.4

47
Q

what does dilution involve?

A

changes in the conc. of H+/OH- in the solution - this is therefore accompanied by a change in the pH of the solution

48
Q

what is the formula for calculating the new conc. of a solution following dilution?

A

new conc. of solution = moles of solute/new total volume.

49
Q

what is the definition of a buffer?

A

buffers are solutions which can resist small changes in pH caused by dilution/addition of small amt. of acid/base.

50
Q

what are the two main types of buffer?

A

acidic buffers and basic buffers

51
Q

buffer action: what happens when a small amt of dilute acid is added?

A
  • addition of extra acid involves addition of extra H+
  • A- (acid) reacts with the H+ and removes them from the solution - this keeps the pH almost constant
52
Q

buffer action: what happens when a small amt of dilute base is added?

A
  • addition of extra base involves addition of extra OH-
  • OH- reacts with the H+ (small amt), removing some H+ from solution - however, position of equilibrium shifts right to restore the H+, which keeps the pH almost constant
53
Q

what does an acidic buffer consist of?

A

an excess of weak acid and its salt
e.g. CH3COONA and CH3COOH can be mixed to form a buffer.
alternatively, the CH3COONA may be formed indirectly from the reaction of NaOH with excess CH3COOH

54
Q

what does a basic buffer consist of?

A

an excess of weak base and its salt

55
Q

what formula do we consider when finding the pH of a buffer solution?

A

Ka = [H+] x ([salt]/[acid])

a2 chem - physical (5 decks)

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