(L6) Module 1 L6 - Weak acids and bases

Question 1

What is a weak acid?

Answer 1

An acid that undergoes incomplete dissociation in water into [H3O]

Basically they reach equilibrium

Equilibrium lies to the left (reactant)

Question 2

What is Ka?

Answer 2

Acid dissociation constant.

Question 3

What is acid dissociation constant (Ka) a measure of?

Answer 3

Measure of acid strength. Large vallue of Ka means more extensive dissociation at equilibrium and the stronger the acid

Question 4

how to find pKa?

Answer 4

pKa = -log (Ka)

Question 5

what is Kb?

Answer 5

base dissociation constant

Question 6

What is base dissociation constant (Kb) a measure of?

Answer 6

Measure of base strength. Large value Kb means more formation of OH- at equilibrium and the stronger the base.

Question 7

How to find pKb?

Answer 7

pKb = -log (Kb)

Question 8

What does smaller Kb/Ka mean?

Answer 8

Weaker the acid/base

Question 9

What does larger pKa or pKb mean?

Answer 9

Weaker the acid/base

Question 10

What’s the relationship between Kb and Ka?

Answer 10

Ka * Kb = Kw

Question 11

What’s the relationship between pKb and pKa?

Answer 11

pkA + pKb = 14
This relationship means, stronger the base, weaker the conj acid.

stronger the acid, weaker the conj base.

Question 12

The conjugate base of a strong acid is…

The conjugate acid of a strong base is…

Answer 12

Very weak

Question 13

What is strength of conj acid/base of weak acid/base?

Answer 13

they’ll both be weak.

it’s difficult to generalise. however you can not say that the conj base of a weak acid will be strong.

Question 14

Ka assumptions during calculations:

Answer 14

first put in Ka = products/reactants
1. assume reactant have equal conc. due to 1:1 stochiometry
2.assume products at eqbm approx. equal initial products due to reactants being a weak acid/Ka being small.. so it barely disssociates

Question 15

How can we rearrange Ka equations using the assumptions?

Answer 15

Question 16

Does Kb requires different equations?

Answer 16

No! use the same Ka method and equations for Kb

Question 17

What is a Lewis base?

Answer 17

The proton donator

Question 18

What is a Lewis acid?

Answer 18

Proton acceptor

Question 19

What type of molecule is a lewis base?

Answer 19

Ligands

Question 20

What type of molecule is a lewis acid?

Answer 20

Transition metal cations

Question 21

What are transition metal complexes?

Answer 21

Transition metal complexes are a class of molecules where molecules called ligands (lewis base’s) form bonds to a transition metal cation (lewis acid’s).

When the ligands are water molecules, the resulting complex can act as a weak acid.

Question 22

How does positive charge of metal cation affect pKa?

Answer 22

pKa decreases…
complex becomes more acidic..
as positive charge on
the metal ion increases.

Question 23

What’s the activation of coordinated water molecules importal to?

Answer 23

Activation of coordinated water molecules is central to the function of many enzymes.

Question 24

carboxypeptidase is an enzyme that has zinc in it. it reacts quickly with OH- or slowly with water.
How can this reaction be sped up?

Answer 24

Bond the water to the zinc ion in the enzyme, turning water –> OH-, which speeds up the reaction.