Acids, Bases and Buffers

Question 1

ACID

Answer 1

Proton donor.

Question 2

BASE

Answer 2

Proton acceptor.

Question 3

STRONG ACID

Answer 3

A proton donor that completely dissociates in solution.

Question 4

WEAK ACID

Answer 4

A proton donor that partially dissociates in solution.

Question 5

pH

Answer 5

pH = –log[H⁺]
[H⁺] = 10⁻ᵖᴴ;

Question 6

Ionic product of water, Kw

Answer 6

Kw=[H⁺][OH⁻] at 25°C
Kw= 1x10⁻¹⁴ moldm⁻³
pOH +pH = 14
In water [H⁺]=[OH⁻]

Question 7

CONJUGATE ACID-BASE PAIRS

Answer 7

Two species which differ only by a H⁺

Question 8

pKa

Answer 8

pKa = –logKa
Ka = 10⁻ᵖᴷᵃ;
Smaller pKa -> Larger Ka -> Stronger acid

Question 9

Calculating pH of Strong Acid HA

Answer 9

[H⁺] = [HA]
pH = –log[HA]

Question 10

Calculating pH of Weak Acid HA

Answer 10

Ka = [H⁺[A⁻]/[HA]
Since [H⁺]=[A⁻]
[H⁺] = √([HA]xKa)

Question 11

BUFFER SOLUTION

Answer 11

A system that minimises pH changes on addition of small amounts of an acid or a base.

Question 12

How a buffer solution works

Answer 12

HA ⇌ H⁺ + A⁻
• Addition of Acid
[H⁺] increases
Equilibrium shifts to the left, H⁺ + A⁻ → HA
Removing most of the H⁺ added

• Addition of Alkali
[OH⁻aq] increases
Added OH⁻ reacts with H⁺ to form H₂O, H⁺ + OH⁻ → H₂O
Equilibrium shifts to the right
Restoring most of the H⁺ that has been removed

Question 13

Calculate pH in Buffer Solution

Answer 13

Ka= [H⁺][Buffer]/[Acid]

Question 14

Buffer solution in Blood

Answer 14

Carbonic Acid and hydrogen carbonate system

H₂CO₃ ⇌ H⁺ + HCO₃⁻

Question 15

ENTHALPY CHANGE OF NEUTRALISATION, ΔH

Answer 15

Enthalpy change for the formation of one mole of water from the reaction with an acid and alkali, under standard conditions.

Question 16

Important factor when choosing the most suitable indicator to use.

Answer 16

Vertical section matches the pH range of the indicator

Question 17

Calculating the percentage molar dissociation of a weak acid.

Answer 17

[H⁺]/[HA] x 100