1.12 Acids and bases
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What is an acid?
A proton donor
What is a base?
A proton acceptor
What is an alkali?
A soluble base
How do you find the pH of a solution? (equation)
-log₁₀[H⁺]
What is [H⁺]?
The concentration of hydrogen ions in the solution.
What is a strong acid?
When H⁺ fully dissociates from the acid.
What is a weak acid?
When H⁺ only partially dissociates from the acid.
What is a monoprotic acid?
Releases one H⁺ per molecule of acid.
What is a diprotic acid?
Releases two H⁺ per molecule of acid.
What is the equation used to find concentration or volume post-dilution?
C₁V₁ = C₂V₂
What is the ionic product of water, based on?
The fact that water only dissociates partly.
What is the dissociation of water equation?
H₂O ⇌ H⁺ + OH¯ H₂O + H₂O ⇌ H₃O⁺ + OH¯
What is the ionic product of water formula?
Kw = [H⁺][OH¯]
Why is the concentration of water not in the ionic product of water?
It is in so much excess, that the water concentration is pretty much constant.
What is Ka?
The weak acid dissociation constant.
What is the weak acid dissociation formula?
[HA]
What is pKa?
The pH of a weak acid solution.
How do you find pKa?
-log₁₀Ka
When does pKa = pH?
When the weak acid is at the half neutralisation point where [A¯] = [HA]
What is Ka when the concentration of [H⁺] = [A¯]?
[HA]
Why does Kw vary with temperature?
• The forward’s reaction is endothermic. • So increasing temperature shifts the equilibrium in favour of the forward’s reaction. • This, therefore, increases the Kw.
How do you find the pH of a reaction between a weak acid & strong base? (when acid is in excess)
• Find acid (HA) moles and OH¯ (base) moles. • Find out how much HA is in excess? • Find A¯ moles and concentration. • Find the excess HA concentration. • Use Ka to find [H⁺] and then pH.
How do you find the pH of a reaction between a weak acid & strong base? (when the base is in excess)
• Find acid (HA) moles and OH¯ (base) moles. • Find out how much OH¯ is in excess. • Use Kw to find [H⁺] and then find the pH.
Outline what a titration reaction is?
• Used to find the concentration of a solution by gradually adding a second solution to react with. • You need to know the equation of the reaction. • You need to know the concentration of the second solution. • It is all based on neutralisation between the two solutions.