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PMP-102 > Acid-base and pH I > Flashcards

Acid-base and pH I Flashcards

1
Q

Why acids and bases are important?

A
  • acid /base reactions in our body
  • food contains different acids/bases
  • most drugs are weak acid or bases
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2
Q

3 main definitions of acid/base

A

-Arrhenius
-bronsted lowry
-lewis theory

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3
Q

Arrhenius

A
  • acid : produces H+ and an anion in water
  • base : produce HO- and a cation in water
  • Neutralisation : produces a salt (ionic compound, anion of an acid + cation of a base)
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4
Q

Bronsted-Lowry

A

Acid : a H+ donor
Base : a H+ acceptor
Acid-base reaction : H+ is transferred from an acid to a base

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5
Q

Lewis Theory

A

Lewis acid : accepts e- (electrophile), e- deficient
Lewis base : donates e- (nucleophile) to a nucleus with an empty orbital, e-rich
Form covalent bond

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6
Q

Arrhenius base

A

KOH

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7
Q

Lewis acid

A

BF3

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8
Q

Lewis base

A

AsH3

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9
Q

Bronsted-Lowry conjugate base/ acid

A
  • HNO2 (acid) / H3O+ (conj. acid)
  • H2O (base) / H3O+ (conj. base)
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10
Q

Bronsted-Lowry strong acid

A

powerful proton doner

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11
Q

Bronsted-Lowry strong base

A

High tendency to accept protons

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12
Q

Bronsted-Lowry weak acid

A

-conjucated acid of strong base.
-weak tendence to donate protons

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13
Q

Bronsted-Lowry weak base

A

-conjugated base of strong acids
weak tendency to accept protons

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14
Q

acid-base reaction

A

equilibrium favours the formation of the weaker acid or base

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15
Q

Water

A

-can be acid or base
-AMPHOTERIC SOLVENT

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16
Q

ACID? BASE?

A

“Any species that contains hydrogen can potentially act as an acid, and any
compound that contains a lone pair of electrons can act as a base”

17
Q

Ka

A

acidity constant

18
Q

K

A

equilibrium constant

19
Q

Strong acids, ka=

A

-large Ka
-completely dissociated (ionised)

20
Q

weak acids , Ka?

A

-small value Ka
-produce less dissociated

21
Q

smaller the pKa..

A

stronger the acid

22
Q

larger the pKa…

A

weaker the acid

23
Q

Kw - ionisation constant H2O

A

10^-14

because

Kw = (H3O+)(HO-)
( 10^-7 )^2
= 10^-14

24
Q

pKa (acid) + pKb (conjugated base of acid)

A

pKw = 14

25
Q

Basicity

A

Basicity relates to the ability of a compound to use its nonbonding electrons
to combine with a proton

26
Q

What influence acidity and basicity?

A
  1. Stability of the conjugate base
  2. Electronegativity
  3. Bond energy
  4. Electron donating and withdrawing
  5. Hybridisation
  6. Resonance/ delocalisation
27
Q

Stability of the conjugate base…

A
  • To assess acidity = stabilisation of conjugate base
  • To asses basicity = ability to use its nonbonding e- to combine with a proton
28
Q

Electronegativity

A
  • ACIDITY increase = More electronegative elements Help to stabilise the -ive charge of conjugate base (bigger Ka, lower pKa)

-BASICITY decrease = E- more electronegative elements are less likely to be donated to a proton

29
Q

Bond energy

A

Acidity INCREASE= descending group

Increasing size of the atom and the corresponding improved ability to disperse the -ive charge over the atom. Weakening in bond strengths (with H)

30
Q

Electron DONATING (acidity)

A

destabilising the acids conjugate base

31
Q

Electron WITHDRAWING (acidity)

A

stabilising the acids conjugate base

-“attract the e- from the negatively charged atom of the conjugate base, which are then shared with all the atoms of the molecule

32
Q

Electron DONATING (basicity)

A

Increase basicity - stabilises the conjugate acid

33
Q

Electron WITHDRAWING (basicity)

A

Decrease basicity - destabilise the conjugate acid

34
Q

Hybridisation effect..

A

Acidity C-H bond = C sp e- held closer, conjugated base MORE stable, more acidic compound

Hybridisation state of the C - sp3, sp2 or sp

35
Q

Why is lone pair of e- in an sp2 or sp orbital more difficult to protonate (weak base) than e- in sp3 orbital?

A

The e- is held closer to the nucleus so therefore the attraction is greater

36
Q

Delocalisation of charge in the conjugate base anion through resonance is a stabilising factor which…

A

INCREASE ACIDITY

37
Q

Delocalisation of the -ive charge into the aromatic ring system

A

more acidic

PMP-102 (49 decks)

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