Acid-base and pH I

Question 1

Why acids and bases are important?

Answer 1

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

Question 2

3 main definitions of acid/base

Answer 2

-Arrhenius
-bronsted lowry
-lewis theory

Question 3

Arrhenius

Answer 3

• 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)

Question 4

Bronsted-Lowry

Answer 4

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

Question 5

Lewis Theory

Answer 5

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

Question 6

Arrhenius base

Answer 6

KOH

Question 7

Lewis acid

Answer 7

BF3

Question 8

Lewis base

Answer 8

AsH3

Question 9

Bronsted-Lowry conjugate base/ acid

Answer 9

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

Question 10

Bronsted-Lowry strong acid

Answer 10

powerful proton doner

Question 11

Bronsted-Lowry strong base

Answer 11

High tendency to accept protons

Question 12

Bronsted-Lowry weak acid

Answer 12

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

Question 13

Bronsted-Lowry weak base

Answer 13

-conjugated base of strong acids
weak tendency to accept protons

Question 14

acid-base reaction

Answer 14

equilibrium favours the formation of the weaker acid or base

Question 15

Water

Answer 15

-can be acid or base
-AMPHOTERIC SOLVENT

Question 16

ACID? BASE?

Answer 16

“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”

Question 17

Ka

Answer 17

acidity constant

Question 18

K

Answer 18

equilibrium constant

Question 19

Strong acids, ka=

Answer 19

-large Ka
-completely dissociated (ionised)

Question 20

weak acids , Ka?

Answer 20

-small value Ka
-produce less dissociated

Question 21

smaller the pKa..

Answer 21

stronger the acid

Question 22

larger the pKa…

Answer 22

weaker the acid

Question 23

Kw - ionisation constant H2O

Answer 23

10^-14

because

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

Question 24

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

Answer 24

pKw = 14

Question 25

Basicity

Answer 25

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

Question 26

What influence acidity and basicity?

Answer 26

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

Question 27

Stability of the conjugate base...

Answer 27

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

Question 28

Electronegativity

Answer 28

- 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

Question 29

Bond energy

Answer 29

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)

Question 30

Electron DONATING (acidity)

Answer 30

destabilising the acids conjugate base

Question 31

Electron WITHDRAWING (acidity)

Answer 31

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

Question 32

Electron DONATING (basicity)

Answer 32

Increase basicity - stabilises the conjugate acid

Question 33

Electron WITHDRAWING (basicity)

Answer 33

Decrease basicity - destabilise the conjugate acid

Question 34

Hybridisation effect..

Answer 34

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

Question 35

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

Answer 35

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

Question 36

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

Answer 36

INCREASE ACIDITY

Question 37

Delocalisation of the -ive charge into the aromatic ring system

Answer 37

more acidic