Chapter 21 - Buffers and Neutralisation Flashcards
1
Q
what is the equivalence point/ end point of a titration curve
A
- sharp vertical rise in the pH curve
- shows the point where the acid has been fully neutralised
- at this point [H+] = [OH-]
2
Q
how to chose a suitable indicator for a titration
A
- a suitable indicator must change colours entirely within the vertical part of the titration curve to be effective at determining the end point
3
Q
what is a buffer
A
- a chemical that resists the change in pH when small amounts of acid or base are added
- buffers do not stop change in pH they just resist it
4
Q
what is an acidic buffer
A
- resist the change in pH in order to keep the solution bellow pH 7
- they are made of a weak acid and its salt
5
Q
examples of two equilibrium reactions happening in an acidic buffer
A
6
Q
what happened when you add an acid to the acidic buffer
A
- [H+] ions increases
- H+ ions react with the CH3COO- ions in the solution
- there is a high concentration of these from the dissociation of the salt
- increase in [H+] and more CH3COOH being produced means equilibrium shifts to the left
7
Q
what happens when you add a base to the acidic buffer?
A
- OH- ions react with the H+ ions
- low concentration of H+ ions so they are replaced from the high concentration of the acid to counteract the change
- equilibrium shifts to the right to replace the reacted H+ ions
8
Q
calculating the pH of a buffer? assumptions?
A
- you need to know the Ka value, and the concentration of the weak acid and its salt
- assume [salt] = [A-]
- assume [HA start] = [HA equilibrium]
