Buffer Solutions Flashcards
What is a buffer solution?
A system that minimises pH changes when small amounts of an acid or base are added by using conjugative acid-base pairs
Describe how to prepare a weak acid buffer solution.
- needs a weak acid and its conjugate base
- eg. Mix together a solution of a weak acid with a solution of one of its salts, which provides the conjugate base when dissolved into solution
Describe how to prepare a buffer solution from the partial neutralisation of a weak acid.
- add an aqueous solution of an alkali to an excess of a weak acid
- the weak acid is partially neutralised by the alkali, forming the conjugate base
How does the addition of an acid shift the position of equilibrium to restore pH?
- The [ H+ ] increases
- The H+ ions react with the conjugate base
- The position of equilibrium shifts left to remove the H+ ions
How does the addition of an alkali shift the position of equilibrium to restore pH?
- The [ OH- ] increases
- OH- reacts with the smaller concentration of H+ so [ H+ ] decreases
- The position of equilibrium shifts right as the weak acid dissociates more to increase [ H+ ]
What is the equation for calculating the pH of a buffer solution?
[ H+ ] = Ka x [ HA ] / [ A- ]
What buffer system controls blood pH?
Carbonic acid - hydrogencarbonate buffer system
What pH range should blood fall between?
7.35 -7.45
What happens as a result of blood pH falling below 7.35?
- people can develop acidosis which can cause fatigue, shortness of breath, shock or death
What can happen as a result of blood pH rising above 7.45?
- people can develop alkalosis, which can cause muscle spasms, light-headedness and nausea
What is the equilibrium for the carbonic acid - hydrogencarbonate buffer system?
H2CO3 (aq) <—> H+ (aq) + HCO3- (aq)
