27. A buffer solution a. is used to control the pH of a solution b. contains at
ID: 575021 • Letter: 2
Question
27. A buffer solution
a.
is used to control the pH of a solution
b.
contains at least 100 times more of a weak acid than its conjugate base
c.
contains at least 100 times less of a weak acid than its conjugate base
d.
always has a pH of 7
28. The main intracellular buffer system is
a.
H3PO4/H2PO4
b.
H2PO4/ HPO42
c.
HPO42/PO43
d.
H3PO4/PO43
Exhibit 2B
Contains information on the pK's of some common buffers.
Buffer
pK1
pK2
pK3
Acetate
4.75
Ammonia
9.25
Carbonic acid
6.37
10.20
Citric acid
3.09
4.75
5.41
Formic Acid
3.75
Phosphoric acid
2.14
7.20
12.4
Pyruvic acid
2.50
Tris
8.3
29. Refer to Exhibit 2B. The enzyme lysozyme has an optimum pH close to 5. A suitable buffer would be:
a.
Acetate
b.
Carbonate
c.
Phosphate
d.
Pyruvate
e.
None of these is a suitable buffer for this reaction.
30. Nonphysiological buffers such as HEPES and PIPES have come into common use because
a.
they are inexpensive
b.
they can be prepared much more easily than other buffers
c.
they have less tendency to interfere with reactions
d.
they contain nitrogen
31. Which of the following is not true?
a.
A buffer is a solution which maintains a solution at a neutral pH
b.
Buffer solutions are made to resist change in pH
c.
Zwitterion buffers are less likely to interfere with biological reactions than non-zwitterions
d.
HEPES is a zwitterion buffer
32. The main blood buffer system is
a.
H2CO3/HCO3
b.
HCO3/CO32
c.
H2CO3/CO32
d.
none of the above
33. Buffers work to maintain pH because
a.
they obey LeChatlier’s principle
b.
weak acids cannot change the pH of a solution
c.
weak bases added to strong bases neutralize each other
d.
they destroy the hydrogen ion that is added
27. A buffer solution
a.
is used to control the pH of a solution
b.
contains at least 100 times more of a weak acid than its conjugate base
c.
contains at least 100 times less of a weak acid than its conjugate base
d.
always has a pH of 7
Explanation / Answer
27. The purpose of a buffer is to keep the pH from fluctuating too much. Thus answer is option a)is used to control the pH of a solution.
28.Answer is option b)H2PO4-/HPO42-.
29. The buffer whose pKa is closest to 5 will be suitable which is for Acetate among the given options.So answer is a).Acetate.
30. Right answer is c) they have less tendency to interfere with reactions.
31 Buffers resist change in pH and are not to maintain neutral pH.So answer is b)A buffer is a solution which maintains a solution at a neutral pH.
32.Answer is a) H2CO3/HCO3
33.According to Le Châtelier's principle if a system in equilibrium is disturbed then the sytem's response is an attempt to restore the equilibrium. Similarly a buffer tries to maintain pH when a acid or base is added and tries to maintain a pH near an equilibrium position, which can be found using Henderson Hasselbalch equation. Hence answer is a) they obey LeChatlier’s principle.
Comment in case of any doubt.
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