OCR A-Level Chemistry: Chapter 21 - Buffers and Neutralisation
This flashcard set explains the role of buffer solutions in resisting pH changes, identifies their key components, and outlines two preparation methods—using a weak acid with its salt or via partial neutralisation with an alkali.
What is a buffer solution?
A system that minimises pH changes when small amounts of an acid or a base are added.
Key Terms
What is a buffer solution?
A system that minimises pH changes when small amounts of an acid or a base are added.
What two components does a buffer solution contain?
A weak acid and its conjugate base.
How can a weak acid buffer solution be prepared from a weak acid and its salt?
When the weak acid is added to water, it partially dissociates and the number of ions is very small.
When added to wa...
How can a weak acid buffer solution be prepared by partial neutralisation?
Adding an aqueous solution of an alkali to an excess of the weak acid.
The weak acid is partially neutralised by the ...
In a buffer solution, what occurs to increase pH when acid is added?
[H+] increases
H+ ions react with conjugate base A-
Equilibrium shifts to the left removing most H+ ions
In a buffer solution, what occurs to decrease pH when alkali is added?
[OH-] increases
H+ ions react with OH-
HA dissociates, shifting equilibirum to the right to restore H+ ions
Related Flashcard Decks
Study Tips
- Press F to enter focus mode for distraction-free studying
- Review cards regularly to improve retention
- Try to recall the answer before flipping the card
- Share this deck with friends to study together
| Term | Definition |
|---|---|
What is a buffer solution? | A system that minimises pH changes when small amounts of an acid or a base are added. |
What two components does a buffer solution contain? | A weak acid and its conjugate base. |
How can a weak acid buffer solution be prepared from a weak acid and its salt? | When the weak acid is added to water, it partially dissociates and the number of ions is very small. |
How can a weak acid buffer solution be prepared by partial neutralisation? | Adding an aqueous solution of an alkali to an excess of the weak acid. |
In a buffer solution, what occurs to increase pH when acid is added? | [H+] increases |
In a buffer solution, what occurs to decrease pH when alkali is added? | [OH-] increases |
When is a buffer solution most effective? | Equal concentrations of the weak acid and its conjugate base. |
A buffer solution is most effective with equal concentrations of weak acid and its conjugate base | The pH of the buffer solution is the same as the pKa value of HA. |
How can the pH of a buffer solution be calculated? | When Ka, [HA] and [A-] are known: Ka=[H+][A-]/[HA] |
How is pH calculated if [A-]=[HA]? | Ka=[H+] pKa=pH |
What is the Henderson-Hasselbalch equation for calculating pH? | pH=pKa + log([A-]/[HA]) |
Where does blood pH operate between? |
|
What happens if the blood pH falls out of this range? | Below - acidosis causing fatigue, shortness of breath and in extreme, death. |
What is the most important buffer system in blood? |
H2CO3/HCO3- |
What is the equilibrium for the buffer system in blood? | H2CO3(aq) H+(aq) + HCO3-(aq) |
When acid is added to blood, what happens? | [H+] increases |
When alkali is added to blood, what happens? | [OH-] increases |
What are the significant points on a pH titration curve? | At first, excess of acid, pH increases slowly. |
What is the equivalence point? | The volume of one solution that exactly reacts with the volume of the other solution. |
What is an acid-base indicator? | A weak acid, HA, that has a distinctively different colour from its conjugate base, A-. |
When is an indicator suitable for a titration? | The pH indicator range is passed through by the vertical section of the pH titration curve. |