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PMP 102 - Drugs And Medicine > Acid-Base And pH (w4) > Flashcards

Acid-Base And pH (w4) Flashcards

1
Q

pKa shows …

A

How strong an acid is

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2
Q

Strong acid =

A

Completely ionised in water

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3
Q

pH =

A

-log10[H+]

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4
Q

Strong base =

A

Completely dissociated

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5
Q

Kw = 1 x 10^(-14)
Kw =

A

[H+][OH-]

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6
Q

Weak acids =

A

Don’t completely ionise in water.
The amount of ionisation is governed by the equilibrium.

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7
Q

pKa?

A

The pH at which it is exactly half dissociated.

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8
Q

If pH is increased (more basic) ?

A

The acid will become more ionised, pH > pKa dissociated.

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9
Q

If pH is lowered (more acidic) ?

A

The acid becomes less ionised, pH < pKa undissociated.

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10
Q

Ratio of ionised: non-ionised forms …

A

A shift in pH by one unit to either side of the pKa value must change the ration by a factor of 10.

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11
Q

Outline an equation for a neutralisation reaction …

A

ACID + BASE —> SALT + WATER

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12
Q

What does salt hydrolysis usually effect ?

A

The pH of a solution

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13
Q

Strong acid + strong base =

A

Neutral salt
PH = 7

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14
Q

Strong acid + weak base =

A

Acidic salt
pH <7

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15
Q

Weak acid + strong base =

A

Basic salt
pH >7

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16
Q

Weak acid + Weak base =

A

Dependant on which one is stronger

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17
Q

Weak acid + weak base concepts :

A
  • Ka cation > Kb anion = acidic solution
  • Kb anion > Ka cation = basic solution
  • if Ka and Kb are similar the solution is close to neutral.
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18
Q

What is the half equivalence point ?

A

The half point - the half of the total amount of base (added) needed to neutralise the acid it has been added to.
PH = pKa of the weak acid

19
Q

What us the equivalence point ?

A

The end point of the reaction = there are equal stoichiometric amounts.
The reaction has completed as all the acid has been converted to its conjugate Base.

20
Q

What is an acid-base titration (neutralisation) ?

A

The quantitative analysis of the concentration of an unknown acid or base solution.

21
Q

What us a buffer solution ?

A

A solution which is able to resist changes in pH on addition of small amounts of acid or base.

22
Q

Define buffer capacity ….

A

The number of moles per litre of a strong acid or base required to produce an increase or decrease of one pH unit in the solution.

23
Q

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

A

HINT
Use the Henderson-Hasselbalch equitation;
PH = pKa + log10 x ([A-]/[HA-])

Figure out which one is the base [A-]
And which is the acid [HA-]

24
Q

What do we do to move the pH of the buffer solution up by one unit of pH = pKa ? (More basic)

A

We need to insure the ionised form is 10 times higher.

25
Q

Dibasic acid =

A

2 ionisable groups

26
Q

Tribasic acid =

A

3 ionisable groups

27
Q

Ionisable groups ;

A

Some acids have more than one ionisable group this means more than one H+ is released.

28
Q

Is it more difficult to lose a H+ from an anion or uncharged molecule ?

A

It is more difficult to lose a H+ form and anion.

29
Q

What do basic oxides react with ?

30
Q

What to acid oxides react with ?

31
Q

What to amphoteric substances react with ?

A

Both acids and bases

32
Q

What happens when there are more double bonded oxygens in a molecule ?

A

The more acidic it will be

33
Q

Why does acidity increase as number of double bonded oxygens increase ?

A

There is more resonance forming so greater e- delocalisation making a more stable conjugate base.

34
Q

How do you know a reaction is completed ?

A

All the acid has been converted to its conjugate base

35
Q

What does it mean if there is a large pKa difference ?

A

The reaction is irreversible

36
Q

What happens to H20 in an aqueous solution ?

A

The H2O will donate the H+ to any base stronger than OH-

37
Q

What do amphiprotic compounds act as ?

A

They act as a proton donor and as a proton acceptor

38
Q

What do amphoteric compounds function as ?

A

Either an acid or base depending upon conditions it is in.

39
Q

What is an amino acid ?

A

And amphoteric compound, contains separate acidic and basic groups

40
Q

What is the isoelectric point (pI) ?

A

The pH at which concentration of the zwitterion is maximum Or pH at which the concentrations of cationic and anionic forms are equal.

41
Q

When are amino acids positively charged, negatively charged and neutral ?

A
  • positively charged at low acidic pH
  • negatively charged at high basic pH
  • NEUTRAL (zwitterionic) at neutral pH (7)
42
Q

What’s are some properties of an ionised species ?

A
  • very low lipid solubility
  • unable to permeate through membranes
  • only non - ionised drug is usually able to cross membranes
43
Q

Give an example of a compound commonly used to prepare buffers for biochemical experiments …

PMP 102 - Drugs And Medicine (24 decks)

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