3.9 Acid-Base Equilbiria

Question 1

Describe the Lowry-Bronsted theory

Answer 1

• acid base equilibria involve the transfer of protons between substances
• a Lowry-Bronsted acid is a proton donor
• a Lowry-Bronsted base is a proton acceptor

Question 2

Strong acid vs weak acid

Answer 2

Strong: completely dissociates into its ions
Weak: partially dissociates

Question 3

What is the equilibrium dissociation constant?

Answer 3

Ka

Question 4

Describe the relationship between Ka and acid strength

Answer 4

• stronger acid = higher Ka value
• strong acids dissociate to ions more, meaning the concentration of ions at equilibria is much greater making Ka increase in value

Question 5

When is methyl orange used?

Answer 5

• reactions with a more acidic neutralisation point
• red in acids and turns yellow at neutralisation point

Question 6

When is phenolpthaliein used?

Answer 6

• reactions with more basic neutralisation point
• pink in alkali and turns colourless at neutralisation point

Question 7

pH equation

Answer 7

pH = -log[H+]

Question 8

[H+] conc equation

Answer 8

10^-pH

Question 9

Differentiate between monoprotic, diprotic and triprotic acids

Answer 9

Mono: conc of H+ ions same as conc of acid
Di: conc of H+ ions is double acid conc
Tri: conc of H+ ions is triple acid conc

Question 10

What is Ka?

Answer 10

Acid dissociation constant

Question 11

What does the size of Ka tell you?

Answer 11

Larger = more dissociation
Smaller = less dissociation

Question 12

What is Kw?

Answer 12

The ionic product of water

Question 13

Kw equation at 25°C

Answer 13

Kw = [H+][OH-]

Kw = 1x10^-14

Question 14

Define a buffer

Answer 14

Any system that minimises pH changes by addition of small amounts of acid or base
—> can’t prevent completely but maintained for as long as buffer solution remains

Question 15

Difference between acidic and basic buffer

Answer 15

Acidic: made of weak acid and salt of the acid
Basic: mass of weak base and salt of base

Question 16

Describe how addition of acid and alkali impact an acidic buffer

Answer 16

• if small amounts of acid added to buffer, equilibrium shifts lefts removing nearly all excess H+
• if small amounts of alkali is added to the buffer, the OH- ions will react to the H+ ions to form water
  —> equilibrium right and more H+ ions produced

Question 17

Describe how adding acidic and alkali impacts basic buffed

Answer 17

• adding acid shifts equilibrium to right to remove H+ ions from solution
• adding base shifts equilibrium to left as reacting OH- ions with H+ to form water

Question 18

pH of buffer equations

Answer 18

pKa + log([A-]/[HA])

pKa = -logKa

Ka = 10^-pKa

Question 19

What is meant by the equivalence point?

Answer 19

The point at which the volume of one solution has reacted exactly with the volume of the second solution

Question 20

Indicator for strong acid, strong base

Answer 20

Phenolphathlein or methyl orange

Question 21

Indicator for strong acid, weak base

Answer 21

Methyl orange

Question 22

Indicator for weak acid, strong base

Answer 22

Phenolphthalein

Question 23

Graphs for strong acid and strong base

Question 24

Graphs for weak acid and weak base

Question 25

Graph for strong acid and weak base

Question 26

Graph for weak acid and strong base