12.8 buffer solutions

Question 1

what is a buffer solution?

Answer 1

mixture of molecules in solution which keeps pH more/less constant
- pH doesn’t change significantly if small amounts of acid / alkali are added

Question 2

how is a basic buffer made?

Answer 2

weak base + salt of the weak base
(eg. NH3 + NH4+Cl-)

Question 3

how is an acidic buffer made?

Answer 3

weak acid + salt of weak acid
(eg. CH3COOH + CH3COO-Na+)

Question 4

what is the general equation of a buffer solution?

Answer 4

acid <-> conjugate base + H+

Question 5

how does adding acid affect the equilibrium in a buffer?

Answer 5

• equilibrium shifts towards HA & remove all added H+ ions in the acid
  -> large concentration of A- in buffer makes the ratio of [HA]/[A-] almost constant

Question 6

how does adding alkali affects the equilibrium in a buffer?

Answer 6

equilibrium shifts towards A- + H+ to produce more H+ ions used up by OH- ions
-> some acid molecules (HA) changes to A- but as there is a large concentration of salt ion in the buffer, the ratio [HA]/[A-] stays almost constant

Question 7

what are the 2 assumptions when calculating pH buffers?

Answer 7

• assume [A-] is due to added salt only
• assume initial [HA] is constant since amount of dissociated/reacted is small

Question 8

what is the equation of buffering action in blood?

Answer 8

H2CO3 <-> H+ + HCO3-

Question 9

how does adding alkali affect buffer action in blood?

Answer 9

shifts equilibrium to the right (to H+ + HCO3-) to form more H+

(as alkali reacts with H+)

Question 10

how does adding acid affect buffer action in blood?

Answer 10

shifts equilibrium left (H+ + HCO3- -> H2CO3)