Buffers

Question 1

Buffers Def’n:

Answer 1

A weak acid plus its conjugate
base that cause a solution to resist changes
in pH when an acid or base are added

Question 2

Effectiveness of a buffer is determined by

Answer 2

– 1) the pH of the solution, buffers work best
within 1 pH unit above and 1 pH unit below
their pKa
(ie. within a 2 pH unit range)

– 2) the concentration of the buffer; the more
present, the greater the buffering capacity

Question 3

A buffer is effective over a range of…

Answer 3

about
2 pH units, centered around the pKa of the
weak acid

– That is, pH = pKa ± 1

Question 4

Buffer capacity is related to the
concentrations of

Answer 4

the weak acid and its
conjugate base.

– the greater the concentration of the weak acid
and its conugate base, the greater the buffer
capacity

Question 5

Buffers are composed of…

Answer 5

a weak conjugate
acid-base pair.

• Resist large changes in pH when strong
  acids or bases are added to them.
• Ex: HC2H3O2 and NaC2H3O2
• Ex: NH3 and NH4Cl

Question 6

How Do Buffers Work?

Answer 6

• Buffer = HX and X^(-)
• If strong acid is added to a buffer, the base
  component (X-) neutralizes it.

X- (aq) + H3O+
(aq) → HX (aq) + H2O (l)

• This reaction goes to completion.

-If strong base is added to a buffer, the acid
component (HX) neutralizes it.

HX (aq) + OH- (aq) → X- (aq) + H2O (l)

• This reaction goes to completion.

Question 7

Adding a strong base to
a weak acid solution will…

Answer 7

progressively convert
more and more HA to A-

• Notice that the pH
  doesn’t change
  significantly near the pKa: the solution is said
  to be buffered.

Question 8

The shape of a titration curve is…

Answer 8

sigmoidal.

• Most of the base is
  consumed in a range of
  about one pH unit on
  either side of the pKa.
• In this range, the change
  in pH with moles of base
  added is minimal; thus,
  this is the best buffering
  range.

Question 9

pKa can be related to

Answer 9

pH

Question 10

Buffer capacity:

Answer 10

the ability of a solution to resist
changes in pH

Question 11

Most effective buffering occurs where:

Answer 11

solution pH = buffer pKa

• At this point: [weak acid] = [conjugate base]

Question 12

Effective buffering range

Answer 12

is usually at pH values
equal to the pKa ± 1 pH unit

Question 13

One ionizable group
can be titrated with

Answer 13

one equivalent of
strong base

Question 14

The greatest
buffering capacity of
an ionizable group is

Answer 14

at its pKa

Question 15

Each
ionizable
group has…

Answer 15

a
unique pKa

Question 16

Buffered
solutions
resist…

Answer 16

changes in pH

Question 17

Most biochemical processes depend heavily…

Answer 17

on the pH of
the solution. Thus various compartments of the body and its
cells are maintained at optimum pH values for the relevant
processes that occur there

Question 18

Most important buffer systems
in humans:

Answer 18

• Bicarbonate/CO2 pKa=6.1
• Phosphate pKa=6.8
• Proteins pKa=Variety

Blood Plasma pH is 7.4