Topic 25 - Equilibria

Question 1

Define

Conjugate Acids and Bases

Answer 1

a pair of reactants and products linked to eachother by the transfer of protons

NH3 and NH4+ (base and conjugate acid)

Question 2

Relate strong acids and the concentration of its ions

Answer 2

strong acids fully dissociate in aqueous solution

the [H+] is equal to [A-] in a monoprotic acid

Question 3

Define and Equation

Kw, Ionic Product of water

Answer 3

1x10^-14 mol2 dm-6
Kw - [H+] * [OH-]
equilibrium constant for the dissociation of water

Question 4

Define and Equation

Ka, Acid dissociation constant

Answer 4

eauilibrium constand for the dissociation of a weak acid
Ka = ([] * []) / [HA]

since dissociation is limited [HA] is assumed equal to intitial conc

values are often small so pKa is used = -logKa

Question 5

Define

Buffer Solution

Answer 5

a solution that resists changes in pH when small quantities of an acid or alkali are added to it

Question 6

How are acid buffers made?

Answer 6

1. A weak acid and and its soluble salt
2. Excess of a weak acid and a strong base - some of the weak acid reacts with the base to form the conjugate base of the acid

Question 7

How do acid buffers work?

Answer 7

eqn
Add and acid to an acid buffer
* anions react with the acid contaminant to form ethanoic acid keeping the pH low by trapping them in an undissociated molecule

Add an alkali to an acid buffer
* OH- from alkali reacts with acid to form the ions and water

Question 8

How are alkali buffers made?

Answer 8

a weak base and one of its salts

NH3 and NH4Cl

Question 9

How do alkaline buffers work?

Answer 9

eqn
Add an acid to an alkaline buffer
* base reacts with acid contaminant to form conjugate acid
Add and alkali to the alkaline buffer
* OH- from the alkaline reacts with the conjugate acid of the base keeping the pH low by trapping excess OH in water

Question 10

Define and Equation

Ksp, Solubility Product

Answer 10

sparingly soluble ionic salts establish equilibrium between solid phase and ions in solution
K = ([A] * [B])/[AB]
Ksp = K * constant = [A] * [B]

Question 11

Describe

Common Ion effect

Answer 11

the solubility of an ionic solute will decrease when dissolving in a substance with a commin ion
This is because of Le Chatelier’s Principle

Question 12

Define

Partition coeffcient, Kpc

Answer 12

the ratio of the concentration of a solute in two different immiscible solvents in contact with each other when equilibrium is established
X(aq) –> X(organic)

Kpc = [X org]/[Xaq]

Question 13

How can Ksp values tell you if a precipitate is formed?

Answer 13

If the calculated value of Ksp is more than the given one, ions go into precipitate to reduce ion concentration and maintain equilibrium

Question 14

Factors affecting Partition coeffcient

Answer 14

Solubility - in the two different solvents and the diffrence between the two (depends on the type of intermolecular bond)
Shapes of the molecules - presence of various functional groups