Topic 12: Acid Base Equilibria

Question 1

Bronsted-Lowry Acid

Answer 1

Proton Donor

Question 2

Bronsted-Lowry Base

Answer 2

Proton Acceptor

Question 3

Bronsted Lowry Acid-Base Reaction

Answer 3

Reaction involving the transfer of a proton

Question 4

Monoprotic Acid

Answer 4

Acid that releases 1 proton per molecule

Question 5

Diprotic Acid

Answer 5

Acid that releases 2 protons per 1 molecule

Question 6

What is the value of Kw in standard conditions?

Answer 6

10^-14

Question 7

How do you calculate the pH of a strong base?

Answer 7

Kw/[OH] = [H+] then you use -log[H+] to calculate pH

Question 8

How do you calculate the pH of a strong acid ?

Answer 8

-log[H+] = pH

Question 9

How do you calculate the pH of a strong acid base reacting?

Answer 9

Use the XS [OH-] or [H+] to calculate the pH of the final solution

Question 10

Strong acid

Answer 10

All the molecules of acid break apart to form ions

Question 11

Weak Acid

Answer 11

Small fraction of the molecules of acid break to form ions

Question 12

Ka (Acid dissociation constant)

Answer 12

Ka = ([H+][A-])/[HA]

Question 13

What are the assumptions made when weak acid is in just water?

Answer 13

• [A-] = [H+]

- initial [HA] = [HA] at equilibrium

Question 14

What happens to Kw as temperature increases?

Answer 14

• More [H+] & [OH-] formed
• pH increases
• Solution remains neutral as [H+] = [OH-]

Question 15

What does amphoteric mean?

Answer 15

• A substance that can act as a base or an acid

Question 16

When acid solutions are extremely dilute (10^-8) why is the pH not in the alkaline territory?

Answer 16

• The pH is extremely close to 7 as we need to now take into account the [H+] disociation from water

Question 17

What is a buffer solution?

Answer 17

• A solution that resists changes in pH when small amounts of acid or alkali are added

Question 18

Position of the Equivalence point when you react : ( Weak acid + Strong base)

Answer 18

• pH greater than 7

Question 19

Position of the Equivalence point when you react : Strong acid + Weak base

Answer 19

• pH less than 7 (equivalence point)

Question 20

What and Why is the standard enthalpy change of neutralisation almost the same for all Strong acid + Strong base?

Answer 20

• The same reaction H+ + OH- - > H2O for all strong acids and bases
• -57.6 kJ mol^-1

Question 21

Why is the enthalpy change on neutralisation more endothermic for a weak base?

Answer 21

• A weak base is only partially ionised

- Energy must be taken in from he environment to ionise the weak base

Question 22

Why is the enthalpy change of neutralisation more exothermic than -57.6 kJmol^-1 for the weak acid HF ?

Answer 22

• Hydration of HF release more energy than the dissociation

Question 23

Why is the pH at the equivalence point greater than 7?

Answer 23

• The weak base reacts with the H+ from water
• This forms OH-
• Meaning the pH at equivalence is higher

Question 24

How do buffers work?

Answer 24

• Significant Quantities of quantities of the acid and its conjugate base is present
• Therefore the pH doesn’t change as much