Acids, Bases and Buffers Flashcards
ACID
Proton donor.
BASE
Proton acceptor.
STRONG ACID
A proton donor that completely dissociates in solution.
WEAK ACID
A proton donor that partially dissociates in solution.
pH
pH = –log[H⁺] [H⁺] = 10⁻ᵖᴴ;
Ionic product of water, Kw
Kw=[H⁺][OH⁻] at 25°C
Kw= 1x10⁻¹⁴ moldm⁻³
pOH +pH = 14
In water [H⁺]=[OH⁻]
CONJUGATE ACID-BASE PAIRS
Two species which differ only by a H⁺
pKa
pKa = –logKa
Ka = 10⁻ᵖᴷᵃ;
Smaller pKa -> Larger Ka -> Stronger acid
Calculating pH of Strong Acid HA
[H⁺] = [HA] pH = –log[HA]
Calculating pH of Weak Acid HA
Ka = [H⁺[A⁻]/[HA]
Since [H⁺]=[A⁻]
[H⁺] = √([HA]xKa)
BUFFER SOLUTION
A system that minimises pH changes on addition of small amounts of an acid or a base.
How a buffer solution works
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
Calculate pH in Buffer Solution
Ka= [H⁺][Buffer]/[Acid]
Buffer solution in Blood
Carbonic Acid and hydrogen carbonate system
H₂CO₃ ⇌ H⁺ + HCO₃⁻
ENTHALPY CHANGE OF NEUTRALISATION, ΔH
Enthalpy change for the formation of one mole of water from the reaction with an acid and alkali, under standard conditions.
