Buffer systems

Question 1

what constitutes a buffer system?

Answer 1

A weak acid and its conjugate base or a weak base and its conjugate acid.

Question 2

Which of the following make a buffer system
a. HCl, NaCl
b. H3PO42-, H2PO4-
c. H2SO4, CH3COOH
d. NH3, NaOH

Answer 2

b.

Question 3

what is the pH of a solution that consists of 0.5M ascorbic acid and 0.75M sodium ascrobate, Ka = 6.8*10^-5

Answer 3

4.34

Question 4

what is the pKa for the acid HA if a solution of 0.65M HA and 0.85M NaH has a pH of 4.75

Answer 4

4.63

Question 5

an acetic acid buffer containing 0.5M CH3COOH and 0.5M CH3COONa has a pH of 4.74, what will the pH be after 0.00200mol of HCl has been added to 100mL of the buffer?

Answer 5

4.71

Question 6

20mL sample of 0.25M HNO3 titrated with 0.15M NaOH. what is the pH of the solution after 30mL of NaOH have been added

Answer 6

2

Question 7

buffer range vs buffer capacity

Answer 7

buffer range is the range of pH values over which the buffer can neutralise effectively maintaining a relatively constant pH. the buffer capacity is the amount of acid or base a buffer can neutralise before the pH changes.

Question 8

can a ch3cooh/ch3coo- buffer can be produced by adding a strong acid to a solution of ch3coo- ions

Answer 8

yes, strong acid reacts with acetic ions, converting them into acetate

Question 9

will increasing the concentrations of the components of a buffer increase the buffer range

Answer 9

no

Question 10

will increasing the concentrations of the components of a buffer increase the buffer capacity

Answer 10

yes

Question 11

f the pH of a buffer solution is greater thn the pKa of the buffer acid, will the buffer have more capacity to neutralise base rather than acid

Answer 11

yes, a buffers capacity to resist changes depends on the strength of the weak acid and its conjugate base.

Question 12

a 35mL sample of 0.2M LiOH is titrated with 0.25M HCl. what is the pH of the solution after 23mL of HCl have been added?

Answer 12

12.3something

Question 13

a 10mL sample of 0.75M CH3CH2COOH is titrated with 0.30M NaOH. what is the pH of the solution after 22mL of NaOH has been added? Ka = 1.3*10^-4

Answer 13

4.76

Question 14

a formic acid buffer containing 0.5M CH3COOH and 0.5M CH3COONa has a pH of 4.74. What will be the pH after 0.0020mol HCl has been added to 100mL of the buffer

Answer 14

1. initial moles
2. reaction produces more of what
3. new concentrations
4. H-H
   = 4.71

Question 15

a 25mL sample of 0.35M HCOOH reacts with 0.2M KOH. What is the pH after 25mL of KOH has reacted

Answer 15

1. initial moles
2. moles of conj base formed with KOH
3. concentrations of A- conj base and HA acid remaining
4. H-H
   = 3.88