21 Buffers and Neutralisation Flashcards
Buffer solution
System that minimises pH changes on addition of small amounts of acid or base.
How can you prepare a weak acid buffer solution?
- Preparation from a weak acid and its salt.
- Preparation by partial neutralisation of the weak acid.
Action of a buffer solution when acid is added
Conjugate base reacts with hydrogen ions, so equilibrium shifts to HA (left).
Action of a buffer solution when alkali is added
OH- ions react with H+ ions, so HA dissociates to restore them and equilibrium shifts to the right.
Equivalence point
The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution.
Control of blood pH
CH3COOH/CH3COO– are the conjugate acid-base pair.
When acid is added, equilibrium shifts to left.
When alkali is added, equilibrium shifts to right.
End point
The point in the titration where the indicator changes colours, indicating that the reaction is complete.
For what type of reaction is methyl orange used?
Strong base + strong acid.
Colours of methyl orange for acid and alkali
Acid - red
Alkali - orange
Colour of methyl orange solution at end point
Orange
How do you decide which indicator is suitable for a reaction?
Colour change should coincide with the vertical section of the pH titration curve.
What indicator should be used for a strong acid-weak base reaction?
Methyl orange.
What indication should be used for weak acid-weak base reaction?
Phenolphthalein.
What indicator is used for a weak acid-weak base reaction?
No indicator is suitable as there is no clear vertical section.
