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PMP-102 > Acid-Base and pH II > Flashcards

Acid-Base and pH II Flashcards

1
Q

What does pKa show?

A

How strong an acid is

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2
Q

pH

A

-log10 [ ]

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3
Q

[ ]

A

concentration of an acid

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4
Q

pH

A

is completely dissociated / ionised in water

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5
Q

How to calculate concentration of an acid (strong acid)?

A

Ka = [A-] [H30+] / [HA]

base is the same as the salt and acid

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6
Q

RECAP Kw

A

[10^-7]^2

= 10^-14

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7
Q

Calculate concentration of strong base use Kw

A

pH = -log10 [H3O+]

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8
Q

Acid molarity

A

m/Mr

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9
Q

Calculate moles:

A

m/Mr
unit: g/mol or M

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10
Q

Conc [] = n/v

A

c=n/v
dm3 for volume

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11
Q

Weak acid and weak base:

A

equilibrium / not completely dissosiated

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12
Q

Weak ACID always has…

A

Conjugated BASE

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13
Q

Weak BASE always has…

A

Conjugated ACID

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14
Q

How to calculate pH or weak acids

A

pH 1/2 pKa - 1/2 log [HA]

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15
Q

Calculate the pH of a 0.010 M solution of aspirin at 25C
Ka of aspirin is 3.2 x 10^-4 at this temp

A

pKa = -log10 Ka

(Ka of weak acid)

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16
Q

pH of weak acid

A

1/2 pKa - 1/2log [HA]

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17
Q

In a weak acid, not completely dissociated in water [HA] can be considered the same as…

A

original weak acid

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18
Q

Define equilibrium:

A

A state in which opposing forces or influences are balanced.

“the task is the maintenance of social equilibrium”

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19
Q

Calculate weak base: NH3

A

pH = pKw -1/2 pKb = 1/2 log [B]
pKb -log10 Kb =
pH

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20
Q

Henderson-Hasselbalch equation:

A

e.g acid conc of 2 = acid has been transformed to one of conc of base
acid = 1
conj base = 1
pH = pKa

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21
Q

pKa

A

the Ph at which it is exactly half dissociated

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22
Q

If we increase the pH (more basic)?

A

acid becomes more ionised pH > pKa dissociated

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23
Q

If we lower pH (more acidic)?

A

acid becomes less ionised pH< pKa UNdissociated

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24
Q

if pH is SMALLER than pKa

A

The acid will be in an undissociated form

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25
Q

If pH is 4

A

4 = 5 + log

26
Q

Ionised form = conjugated base

A

When talking about the WEAK acid

27
Q

When in ionised form use which equation?

A

H-H equation

28
Q

pH = pKa + [A-] / [HA] at pH 4

A

log [A-] / [HA] = pH - pKa =

29
Q

Original acid

A

1 - conjugated base

[HA] = 1 - X

30
Q

Acid-base reactions:

31
Q

strong acid + strong base

A

Neutral base

32
Q

strong acid + weak base

A

Acidic salt

33
Q

Weak acid + strong base

A

basic salt

34
Q

Weak acid + weak base

A

depends which one is stronger

35
Q

NaCl + H2O&raquo_space;> Na+ + Cl-

A

Neutral solution - cannot react further with water

36
Q

Cl- + H2O <> HCl = HO-

A

Cl- = very weak conjugate base of HCl
Reaction with water can be neglected

37
Q

HCl (strong acid) = NH3 (weak base <> NH4Cl {acid salt}

A

No H2O = weak bases tend not to have a hydroxide

38
Q

Weak acid + weak base = depends on which one is stronger

A

Ka cation > Kb anion = solution acidic

39
Q

kb anion > ka cation =

A

solution basic

40
Q

Ka & Kb similar =

A

solution is close to neutral (pH approx. 7)

41
Q

Acid-base titration (neutralisation)

A

quantitive analysis of the concentration of an unknown acid or base solution

42
Q

Strong base added to weak acid =

A

solution containing the weak acid and its conjugate base until the initial weak acid is completely neutralised by the base

43
Q

H-H equation

A

pH = pKa = log [base] / [acid]

This is the conjugate base [A-]

44
Q

equivalence point:

A

acid-base (added&raquo_space;> equal stoichiometric amounts

45
Q

When is reaction completed??

A

all acid has been converted to its conjugated base

46
Q

Half equivalence point: half of the total amount of base (added) needed to neutralise the acid has been added

A

pH = pKa of weak acid

47
Q

[H3O+] =

A

(initial amount moles of acid) = (amount of moles of base added) / (volume of acid) + (volume of base added)

48
Q

After neutralisation:

49
Q

Acid-base graph:

A

1) pH low at start
2) rises sharply
3) rises very slowly

50
Q

Equivalence point

A

the point on the graph where the curve is steep (straight up)

51
Q

What would be equivalence point in string acid or base?

52
Q

what is the equivalence point with weak acid or base?

53
Q

Indicator

A

The best one is in the range of the equivalence point

54
Q

Buffer

A

A solution usually containing an acid and a base, or a salt, that tends to maintain a constant hydrogen ion concentration

55
Q

Buffer is made of

A

HIGH concentration of weak acid
CH3CO2H <> CH3CO2- + H+

56
Q

And a completely ionised strong base

A

CH3Co2-Na+ > CH3CO2- + Na+

57
Q

The H+ in the buffer will react with…

A

the Na+ from the strong acid

58
Q

Preparing a buffer:

59
Q

Which pKa is the most relevant for biological systems and why?
To which dissociation does it correspond?

A

pKa = 7.21 /
pKa = 2.21 X
pKa = 12.67 X

60
Q

Which relative concentrations do we need to have the maximum buffering power??

A

Function as a buffer and control the pH to 7.0

61
Q

IN CLASS TEST:
What is the pH of a buffer solution containing 0.042M NaH2PO4 and 0.058M Na2HPO4?

A

Use H-H equation

62
Q

How much does pH change if we add 1mL of 10M NaOh to 1L of this buffer solution?

A

M = mol / vol, mol = M x V

0.01 mol NaOH titrate (neutralise) 0.01 mol NaH2PO4 and form 0.01 mol Na2HPO4&raquo_space;> new conc: 0.032 M NaH2PO4, 0.068M Na2HPO4

PMP-102 (49 decks)

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