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S1 - Medicinal Chemistry > Acids and Bases > Flashcards

Acids and Bases Flashcards

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1
Q

what is the equation for the self- ionistaion of water ?

A

H20 + H20 ——–> H30+ + OH-

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2
Q

why is water known as an amphoteric ?

A
  • water acts as a base and as an acid
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3
Q

what is the equation for Kw?

A
  • Kw = [H30+] [OH-]
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4
Q

what is the value of Kw at 25c

A
  • 1 x 10-14
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5
Q

why does Kw increase with temperature ?

A
  • ionisation of water is an endothermic process
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6
Q

what is the relationship between PH,Ka and Pka

A
  • high ka = stronger acid = smaller Ph
  • larger ka = smaller pka
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7
Q

how do u calculate pOH ?

A
  • log[OH-]
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8
Q

what equation links pH and pOH ?

A
  • pH +pOH = 14
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9
Q

what is the equation for Ka ?

A

Ka = [H3O+][A-] / [HA]
OR
Ka = [H3O+]^2 / [HA]

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10
Q

what is equation for Kb ?

A

Kb = [HB+][OH-] / [B]

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11
Q

what does a more electronegative atom on the acid mean ?

A

-conjugate base is more stable

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12
Q

how does anion size affect acidity ?

A
  • increasing size = increased acidity
  • as size increases, bond between H and ion is easier to break
  • so H+ is more easily donated
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13
Q

how does strength of the acid affect strength of conjugate base ?

A
  • stronger acid = weak conjugate base / stable
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14
Q

what is delocalization ?

A
  • charge is spread out across a molecule because e- are free to move
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15
Q

how does delocalization stabilize a molecule ?

A
  • delocalization allows for resonance structures and stabilization
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16
Q

which is more stable a weaker or stronger conjugate base ?

A
  • weaker conjugate base
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17
Q

why is acetate ion more stable than ethoxide ion ?

A
  • e - are localised in ethoxide
  • no resonance structures
  • so less stable
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18
Q

How does the inductive effect increase acidity ?

A
  • halogens are more electronegative
  • pulls e- towards itself
  • pulls e- through sigma bonds
  • this decreases electron density
  • base is more stable/ weak
  • acid is stronger
19
Q

How does hybridization affect acid strength ?

A
  • atoms with higher percent of s character are more acidic
  • lone pair is held closer to nucleus
  • more stable / weaker conjugate base
20
Q

what is the s character of a hybrid orbital ?

A
  • percentage of s in it
  • sp = 50
  • sp2 = 33
  • sp3 = 25
21
Q

what is a Bronsted-Lowry acid ?

A
  • proton donor
22
Q

what is a Bronsted-Lowry base ?

A
  • proton acceptor
23
Q

what is a Lewis acid ?

A
  • electron pair acceptor
24
Q

what is a Lewis base ?

A
  • electron pair donor
25
Q

what factors determine the stability of a conjugate base ?

A
  • electronegativity
  • size of anion
  • resonance
  • hybridization
  • inductive effects
    HEIRS
26
Q

how does electrongeativity affect strength of an acid ?

A
  • created a polar bond, H becomes more positive so it is easier to break the bond
27
Q

Are all Bronsted Lowry acids Lewis acids?

A

Yes, but not all Lewis acids, are Bronsted Lowry acids

28
Q

How do you know if salt is more acidic or basic ?

A
  • need ka and kb values whichever is greater dominates
29
Q

What is the common ion effect ?

A
  • shift in equilibrium caused by addition of a compound that has an ion in common with the dissolved substance
30
Q

what effect does a common ion have on ionisation of a weak acid/base ?

A
  • suppresses ionisation
  • because equilibrium shifts to favour reactants so less H+ /OH- conc
31
Q

What is the effect of having a weak acid and its salt in solution ?

A
  • creates a buffer solution
  • ionisation of HA suppressed by presence of A-
  • hydrolysis of A- suppressed due to HA
32
Q

what happens if a strong base is added to a buffer?

A
  • HA+ OH- —> A-+H20
  • pH only changes slightly
33
Q

what happens if a strong acid (HCL) was added to a buffer ?

A
  • HCl—> H+ +Cl-
  • H+ + A- –> HA
  • slight change in pH
34
Q

What is a buffer ?

A
  • minimises change in pH upon addition of a small amount of acid or base
  • made of weak acid + conjugate base
35
Q

what is the halfway point of weak acid / strong base titrations ?

A
  • [HA] = [A-] so pka = pH
36
Q

what is the Henderson-Hasselbalch equation and what is it used for ?

A
  • used to find the pH of a buffer
  • pH = pKa + log [A-]/[HA]
37
Q

what happens to blood pH when you hypo-ventilate ?

A
  • acidosis - pH drops
38
Q

what happens to blood pH when you hyperventilate

A
  • alkalosis - rise in pH
39
Q

What happens when
blood pH drops ?

A
  • increased conc of H2CO3 by protonation of HCO3-
  • H2Co3 looses water to form CO2aq which is coverted to co2 gas
40
Q

What happens when blood ph rises ?

A
  • inc conc of hco3- by deprotination of H2CO3, breathing rate changes
41
Q

Anti-log of Henderson equation

A

[acid] / [base]= 10^(pKa-pH)

42
Q

What is the Henderson Hasselbalch equation ?

A

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

43
Q

What is equation % acid = 100 /1 + 10^(pH - pKa)

A
  • if group is acidic gives % of unionised
  • if basic group gives % ionised

S1 - Medicinal Chemistry (8 decks)

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