Exam 3

Question 1

The fraction of dissociation for the reaction of a base (B) with H2O is defined as: a= [BH+] / [B] + [BH+]
a. True
b. False

Answer 1

b. False

Question 2

The chemical species C4H3O4- is amphiprotic (can act both as an acid or base in a reaction)
a. True
b. False

Answer 2

a. True

Question 3

The pH at which the average charges of a polyprotic species equals to 0, is called the isoionic point.
a. True
b. False

Answer 3

b. False

Question 4

In a solution of a polyprotic acid, the concentration of the second ionization is always greater than that of the first ionization.
a. True
b. False

Answer 4

b. False

Question 5

The value of Kw increases with an increase in temperature.
a. True
b. False

Answer 5

a. True

Question 6

The pH of a solution remains constant if a strong acid is added to a buffer solution until the buffer capacity is exceeded.
a. True
b. False

Answer 6

a. True

Question 7

In a chemical equilibrium, the rate of the forward reaction is always equal to the rate of the reverse reaction.
a. True
b. False

Answer 7

a. True

Question 8

A diprotic base can accept two protons per molecule, resulting in the formation of two conjugate acids.
a. True
b. False

Answer 8

a. True

Question 9

The bicarbonate buffering system in human blood, which consists of carbonic acid (H2CO3) and its conjugate base bicarbonate (HCO3-), is effective in maintaining blood pH because the pKa of carbonic acid is close to the physiological pH of blood, which is approximately 7.4.
a. True
b. False

Answer 9

a. True

Question 10

The Henderson-Hasselbalch equation can be used to determine the pH of a biological buffer solution by knowing the pKa of the acid component and the ratio of the concentration of the conjugate base to the acid.
a. True
b. False

Answer 10

a. True

Question 11

An application of the common ion effect is the titration of a mixture. When salt AX with a Ksp= 8.3x10^-17 and salt BX with Ksp= 1.8x10^-10 are titrated, which salt will precipitate first?
a. AX will precipitate first because it has a lower Ksp
b. BX will precipitate first because it has a higher Ksp.
c. AX will precipitated last because it has a lower Ksp
d. AX and BX will precipitate at the same time
e. None of the above.

Answer 11

a. AX will precipitate first because it has a lower Ksp.

Question 12

Which of the following pairs of compounds and ions could be used to make a buffer solution?
a. HCI and NaCI
b. C6H8O7 and C6H7O7Na
c. H3PO4 and KH2PO4
d. Options a and b are correct
e. Options b and c are correct

Answer 12

e. Options b and c are correct

Question 13

A measure of the ability of a buffer to resist changes in pH.
a. Buffer capacity
b. Equilibrium constant
c. Solubility constant
d. Isoelectric point
e. Isoionic point

Answer 13

a. Buffer capacity

Question 14

At what pH would the average charge of a polyprotic acid be zero?
a. Isoelectric pH
b. Isoionic pH
c. At maximum [H+]
d. At maximum [OH-]
e. None of the above

Answer 14

a. Isoelectric pH

Question 15

Which weak acid would be best to use when preparing a buffer solution with a pH of 9.10?
a. An acid with Ka= 5.0x10^-11
b. An acid with Ka= 8.3x10^-10
c. An acid with Ka= 1.0x10^-5
d. An acid with Ka= 8.3x10^-6
e. An acid with Ka= 2.0x10^-2

Answer 15

b. An acid with Ka= 8.3x10^-10

Question 16

There are seven common strong acids. Which of the following statements is NOT true for strong acids?
a. Strong acids in solution are completely ionized.
b. HNO2 is a strong acid.
c. For strong acid solutions with a concentration between 10^-6 and 10^-8 M, the pH is determined using systematic equilibrium.
d. For strong acid solutions with concentrations > 10^-6 M, the pH is calculated from the concentration of the strong acid.
e. For strong acid solutions with concentrations , 10^-8 M, the pH is always close to 7.

Answer 16

b. HNO2 is a strong acid.

Question 17

Which is NOT a property of buffers?
a. Buffers resist changes in pH when acids or bases are added or when dilution occurs.
b. Buffers are a mixture of weak acid and conjugate base.
c. The pH of a buffer is independent of ionic strength.
d. The pH of a buffer is dependent on temperature.
e. Buffers are a mixture of weak bases and conjugate acid.

Answer 17

d. The pH of a buffer is dependent on temperature.

Question 18

For the polyprotic acid H3A, which of the equilibria below is INCORRECT?
a. A3- <–> HA2- + OH-
b. H2A- <–> HA2- + H+
c. HA2- <–> A3- + H+
d. H3A <–> H2A- + H+
e. HA2- <–> H2A- + OH-

Answer 18

a. A3- <–> HA2- + OH-

Question 19

What is the conjugate base of sulfuric acid?
a. HSO4-
b. H3O+
c. OH-
d. SO42-
e. H3SO4+

Answer 19

a. HSO4-

Question 20

H2L is a diprotic amino acid with a pKa1= 2.344 and a pKa2= 9.868. At pH= 6.32, what is the principal species in solution? (Hint: write out the equilibrium)
a. H2L+
b. L-
c. HL
d. H3L+
e. L2-

Answer 20

c. HL

Question 21

Calculate the pH of a 0.010 M CH3CO3H (acetic acid) solution. Ka = 1.8 x 10^-5
a. 9.26
b. 3.39
c. 2.02
d. 10.61
e. 4.74

Answer 21

a. 9.26

Question 22

One of the most popular questions ever created for chemistry exams involved calculating the pH of a 1.0x10^-8 M solution of hydrochloric acid. So here it is for you. Based on your knowledge about analytical chemistry, what is the closes to the correct answer?
a. 8.0
b. 6.0
c. 6.99
d. 10.0
e. 4.5

Answer 22

c. 6.99

Question 23

Which of the following is the correct Kb expression for the reaction below?
B(aq) + H2O(l) <–> HB+(aq) + OH-(aq)

Answer 23

d. Kb= [HB+] [OH-] / [B]

Question 24

The Ka value for an acid is 1.0x10^-2. What is the Kb value for its conjugate base?
a. 1.0 x 10^-2
b. 1.0 x 10^-6
c. 1.0 x 10^-12
d. 1.0 x 10^6
e. 1.0 x 10^2

Answer 24

c. 1.0 x 10^-12

Question 25

Calculate the pOH of a 0.010 M HCI solution.
a. 2.00
b. 6.00
c. 10.00
d. 12.00
e. 14.00

Answer 25

d. 12.00