Acids and Bases Flashcards
What is the definition of a Brønsted-Lowry acid?
A proton donor (note that it does not need to be in a solution).
What is the definition of a Brønsted-Lowry base?
A proton acceptor (note that it does not need to be in a solution).
What is a conjugate acid?
A species produced when a base gains a proton.
What is a conjugate base?
A species produced when an acid loses a proton.
What is a conjugate acid-base pair?
Two species related to one another by the presence of a hydrogen ion or its absence.
What is the expression for working out pH?
-log₁₀|[H⁺]|
What precision should pH values be quoted to?
2 decimal places.
What is the H⁺ concentration of a diprotic acid relative to the concentration of that acid?
Double.
For a WEAK ACID, what is our expression of Ka simplified to? Why can we do this?
Ka = [H⁺]²/[HA]. We can do this due to HA disassociating into equal amounts of [H⁺] and [A⁻], so [H⁺] = [A⁻].
What indicator would we use for a weak acid-strong base titration?
Phenolphthalein.
What indicator would we use for a strong acid-weak base titration?
Methyl Orange.
What indicator would we use for a strong acid-strong base titration?
Either methyl orange or phenolphthalein.
Why would we not use methyl orange or phenolphthalein for a weak acid-weak base titration?
Because the endpoint for both is far past/before the equivalence point in volume terms, so we would not get any useful approximation of the equivalence point.
What is the difference between the endpoint and the equivalence point when we undergo a titration?
The endpoint is where we stop (when the colour changes), the equivalence point is where the moles of acid equal the moles of the base. We use the endpoint as an estimate for the equivalence point.
Sketch/describe the pH curve [for a weak acid-strong base, strong acid-weak base, strong acid-strong base and weak acid-weak base] (pH against volume), showing on it the colours of methyl orange and phenolphthalein.
