What equilibrium is established in an acidic buffer solution?
HA ⇌ H⁺ + A⁻
Weak acid partially dissociates; conjugate base comes from the salt.
Why does adding a strong acid to a buffer cause only a small pH change?
A⁻ reacts with H⁺
Conjugate base removes added H⁺, shifting equilibrium to the left.
Why does adding a strong base to a buffer cause only a small pH change?
HA reacts with OH⁻
Weak acid donates H⁺ to neutralise OH⁻, forming A⁻.
True or False:
The effectiveness of a buffer depends on having similar concentrations of acid and conjugate base.
True
Maximum buffering occurs when [HA] ≈ [A⁻].
What happens to the equilibrium position when H⁺ is added to a buffer?
Shifts left
Added H⁺ is removed by reacting with A⁻ to form HA.
What happens to the equilibrium position when OH⁻ is added to a buffer?
Shifts right
OH⁻ removes H⁺, so HA dissociates to replace it.
True or False:
A buffer works by preventing any equilibrium shift when acid is added.
False
Buffer action relies on equilibrium shifting to oppose changes.
What equation is used to calculate the pH of an acidic buffer?
pH = pKa + log([A⁻]/[HA])
Derived from rearranging Ka expression.
How does increasing the ratio [A⁻]/[HA] affect the pH of a buffer?
Increases
Higher proportion of conjugate base lowers [H⁺].
True or False:
If [A⁻] equals [HA], the pH of the buffer equals the pKa.
True
log(1) = 0 so pH = pKa
What is the effect on pH if a buffer is diluted but the ratio [A⁻]/[HA] stays constant?
No change
pH depends on ratio, not absolute concentrations.
Why is a buffer most effective within one pH unit of its pKa?
Ratio of [A⁻] to [HA] is near 1.
Both acid and conjugate base are present in similar amounts.
True or False:
A buffer becomes ineffective if one component is nearly used up.
True
System can no longer neutralise added acid/base effectively.
What happens to buffer capacity when concentrations of both components increase?
Increases
More substance available to react with added acid/base.
Why are strong acids unsuitable for making buffer solutions?
No equilibrium
Strong acids fully dissociate, so no reversible system exists.
-
2.1 Atoms, Compounds, Molecules & Equations50
-
2.2 Amount of Substance47
-
2.3 Acid–Base69
-
2.4 Electrons, Bonding and Structure90
-
3.1 Periodicity22
-
3.2 Group 2 and Halogens55
-
3.3 Qualitative Analysis39
-
3.4 Enthalpy Changes62
-
3.5 Reaction Rates (Qualitative)55
-
3.6 Equilibrium (Qualitative)24
-
4.1 Basic Organic Chemistry Concepts42
-
4.2 Hydrocarbons85
-
4.3 Alcohols and Haloalkanes79
-
4.4 Organic Synthesis12
-
4.5 Analytical Techniques (IR & MS)36
-
5.1 Reaction Rates (Quantitative)24
-
5.2 Equilibrium (Quantitative)12
-
5.3 pH and Buffers15
-
5.4 Enthalpy, Entropy & Free Energy27
-
5.5 Redox & Electrode Potentials63
-
5.6 Transition Elements95
-
6.1 Aromatic Compounds29
-
6.2 Carbonyl Compounds20
-
6.3 Carboxylic Acids & Esters25
-
6.4 Nitrogen Compounds102
-
6.5 Polymers24
-
6.6 Organic Synthesis (Advanced)20
-
6.7 Chromatography & Spectroscopy (NMR)26
