Acids, Bases and Buffers Flashcards
Everything you need to get an A* in AQA Chemistry A level, closely following the AQA specification and textbook
What is an acid?
Proton donor
What is a base?
Proton acceptor
What kind of scale is the pH scale?
A logarithmic scale
Define pH
pH = -log[H+]
Define strong acid
Acids that dissociate completely in aqueous solution
Define weak acid
Acids that dissociate only slightly in aqueous solution
What is Kw
The equilibrium constant for the dissociation of water
Write the equilibrium equation for the dissociation of water
H20 <–> H+ + OH-
What is Kw equal to
Kw = [OH-][H+]
What condition affects Kw?
Kw varies with temperature
What is Ka
The dissociation constant for a weak acid
Write the equation for the dissociation of a weak acid HA
HA <–> H+ + A-
Define pKa
pKa = -log(Ka)
What is pKa a measure of?
How strong a weak acid is - the smaller the value of pKa, the stronger the acid
What is the equivalence point
The point in a titration at which the reaction is just complete
What does the equivalence point look like on a titration curve graph?
It is the straight line region, where there is a rapid change in the pH
What is the end point?
The point in a titration when the volume of reactant added just causes the colour of the indicator to change
What is the half neutralisation point?
The point halfway between 0 and the equivalence point
How can you find pKa using the half neutralisation point?
At the half neutralisation point, pKa = pH
What is a buffer solution?
A buffer solution maintains an approximately constant pH, despite dilution or addition of small amount of acid or base
How are acidic buffers formed?
They contain a weak acid and the salt of that weak acid
How are basic buffers formed?
They contain weak bases and the salt of that weak base
How does the amount of acid and salt in a buffer change when an acid is added, and how does this affect the pH?
The amount of acid increases, and the amount of salt decreases, so the pH decreases
How does the amount of acid and salt in a buffer change when a base is added, and how does this affect the pH?
The amount of acid decreases, and the amount of salt increases, leading to an increase in the pH
