Buffers Flashcards
What is a buffer solution?
System that lowers pH changes when small amounts of acid/base added.
Contains weak acid and its conjugate base.
How do you make a buffer from a weak acid and its salt?
Ethanoic acid + salt, when added to water, salt fully dissolves so acts as conjugate base.
How do you make a buffer from the partial neutralisation of a weak acid?
Aq alkali to excess weak acid, some acid left unreacted.
How does position of equilibrium change in a buffer?
Conjugate acid base pair controls pH, base removes increasing acid, equilibrium shifts to left.
Acid removes increasing alkali, equilibrium to right.
When is a buffer most effective?
= conc of weak acid and its base. When HA=A:
- pH of buffer same as Pka of HA
- operating pH over 2 pH units
How do buffers in the body work?
Blood plasma must be 7.35-7.45, so pH is controlled by carbonic acid-hydrogencarbonate.
If too low = acidosis - fatigue, shortness of breath
If too high = alkalosis - muscle spasms, nausea.
Body makes more acidic materials than alkaline, so HCO3- converts to H2CO3-. Prevents build up by convert to CO2.
How do acid-base titrations work?
Use indicators to monitor neutralisation reactions accurately. When base first added, acid is in great excess and pH increases a little. Vertical section, pH increases faster. pH increases rapidly when very little base added.
What is the equivalence point?
The volume of 1 solution that exactly reacts with the volume of the other solution.
Middle of vertical section
Which indicators are used?
Acid base indicator = weak acid with distinctly different colour from its conjugate base. End point = in between.
Must use indicator with colour change along vertical section.
What is the colouring of methyl orange?
Weak acid = red, conjugate base = yellow.
Why is there no indicator for a weak acid-weak base?
No vertical section.
