Proton transfer reactions (Acids and Bases)
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What is a Bronsted-Lowry acid?
A proton donor
What is a Bronsted-Lowry base?
A proton acceptor
Monoprotic
An acid that can donate only one proton (H+ ion).
Diprotic
An acid that can donate two protons (H+ ions).
Where does the loss of this proton come from?
Hydroxyl (OH) group
What are conjugate acid-base pairs?
Members of a conjugate pair differ from each other by one transferable hydrogen ion.
What does amphiprotic mean?
A species that can accept and donate protons.
pH is defined as:
pH = -log10 [H+]
H+ ions units are
mol dm–3
The concentration of H+ of a solution is shown as:
[H+] = 10-pH
What is neutral
7
What is a neutralisation reaction?
Between acid and base
what does an acid and a base form?
salt and water
What does an acid and a carbonate form?
water and carbon dioxide and salt
pH of acids
Acidic solutions (strong or weak) always have more H+ than OH- ions Since the concentration of H+ is always greater than the concentration of OH- ions, [H+] is always greater than 10-7 mol dm-3 Using the pH formula, this means that the pH of acidic solutions is always below 7 The higher the [H+] of the acid, the lower the pH
pH of bases
Basic solutions (strong or weak) always have more OH- than H+ ions Since the concentration of OH- is always greater than the concentration of H+ ions, [H+] is always smaller than 10-7 mol dm-3 Using the pH formula, this means that the pH of basic solutions is always above 7 The higher the [OH-] of the base, the higher the pH
pH of water
Water at 298K has equal amounts of OH- and H+ ions with concentrations of 10-7 mol dm-3 To calculate the pH of water, the following formula should be used: pH = – log10[H+ (aq)] [H+ (aq)] = concentration of H+/H3O+ ions pH = -log (10-7) = 7 Thus, water has a pH of 7 at 298 K
How does increasing temperature affect Kw?
Kw increases.
What is the equilibrium constant expression (Kc) for the ionisation of water?
Kc = [H⁺][OH⁻] / [H₂O]
Why is the concentration of water considered constant?
Because only a very small fraction of water molecules ionise.
What is the expression for the ion product of water (Kw)?
Kw = [H⁺][OH⁻]
What is the value of Kw at 298 K?
1.00 × 10⁻¹⁴
What does Kw represent?
The product of the concentrations of H⁺ and OH⁻ ions in water.
What are the concentrations of H⁺ and OH⁻ in neutral water at 298 K
[H⁺] = 1.0 × 10⁻⁷ mol dm⁻³ and [OH⁻] = 1.0 × 10⁻⁷ mol dm⁻³