Water and pH Exercises
A true statement about hydrophobic interactions is that they:
a) are the driving force in the formation of micelles of amphipathic compounds in water.
b) do not contribute to the structure of water-soluble proteins.
c) have bonding energies of approximately 20–40 Kjoule per mole.
d) involve the ability of water to denature proteins.
e) primarily involve the effect of polar solutes on the entropy of aqueous systems.
Dissolved solutes alter some physical (colligative) properties of the solvent water because they change the:
a) concentration of the water.
b) hydrogen bonding of the water.
c) ionic bonding of the water.
d) pH of the water.
e) temperature of the water.
Osmosis is movement of a:
a) charged solute molecule (ion) across a membrane.
b) gas molecule across a membrane.
c) nonpolar solute molecule across a membrane.
d) polar solute molecule across a membrane.
e) water molecule across a membrane.
The pH of a solution of 1 M HCl is:
a) 0
b) 0.1
c) 1
d) 0.01
e) –1
Which of the following is true about the properties of aqueous solutions?
a) A pH change from 5.0 to 6.0 reflects an increase in the hydroxide ion concentration [OH-] of 20%.
b) A pH change from 8.0 to 6.0 reflects a decrease in the proton concentration [H+] by a factor of 100.
c) Charged molecules are generally insoluble in water.
d) Hydrogen bonds form readily in aqueous solutions.
e) The pH can be calculated by adding 7 to the value of the pOH.
The pH of a sample of blood is 7.4, while gastric juice is pH 1.4. The blood sample has:
a) 0.189 times the [H+] as the gastric juice.
b) 5.29 times lower [H+] than the gastric juice.
c) 6 times lower [H+] than the gastric juice.
d) 6,000 times lower [H+] than the gastric juice.
e) a million times lower [H+] than the gastric juice.
The aqueous solution with the lowest pH is:
a) 0.01 M HCl.
b) 0.1 M acetic acid (pKa = 4.86).
c) 0.1 M formic acid (pKa = 3.75).
d) 0.1 M HCl.
e) 10–12 M NaOH.
In which reaction below does water not participate as a reactant (rather than as a product)?
a) Conversion of an acid anhydride to two acids.
b) Conversion of an ester to an acid and an alcohol.
c) Conversion of ATP to ADP.
d) Photosynthesis
e) Production of gaseous carbon dioxide from bicarbonate.
Which of the following properties of water does not contribute to the fitness of the aqueous environment for living organisms?
a) Cohesion of liquid water due to hydrogen bonding.
b) High heat of vaporization.
c) High specific heat.
d) The density of water is greater than the density of ice.
e) The very low molecular weight of water.
Which of the following statements about buffers is true?
a) A buffer composed of a weak acid of pKa = 5 is stronger at pH 4 than at pH 6.
b) At pH values lower than the pKa, the salt concentration is higher than that of the acid.
c) The pH of a buffered solution remains constant no matter how much acid or base is added to the solution.
d) The strongest buffers are those composed of strong acids and strong bases.
e) When pH = pKa, the weak acid and salt concentrations in a buffer are equal.
A compound has a pKa of 7.4. To 100 mL of a 1.0 M solution of this compound at pH 8.0 is added 30 mL of 1.0 M hydrochloric acid. The resulting solution is pH:
a) 6.5
b) 6.8
c) 7.2
d) 7.4
e) 7.5
a) 0
b) 0.1
c) 1
d) 0.01
e) –1
Which of the following is true about the properties of aqueous solutions?
a) A pH change from 5.0 to 6.0 reflects an increase in the hydroxide ion concentration [OH-] of 20%.
b) A pH change from 8.0 to 6.0 reflects a decrease in the proton concentration [H+] by a factor of 100.
c) Charged molecules are generally insoluble in water.
d) Hydrogen bonds form readily in aqueous solutions.
e) The pH can be calculated by adding 7 to the value of the pOH.
The pH of a sample of blood is 7.4, while gastric juice is pH 1.4. The blood sample has:
a) 0.189 times the [H+] as the gastric juice.
b) 5.29 times lower [H+] than the gastric juice.
c) 6 times lower [H+] than the gastric juice.
d) 6,000 times lower [H+] than the gastric juice.
e) a million times lower [H+] than the gastric juice.
The aqueous solution with the lowest pH is:
a) 0.01 M HCl.
b) 0.1 M acetic acid (pKa = 4.86).
c) 0.1 M formic acid (pKa = 3.75).
d) 0.1 M HCl.
e) 10–12 M NaOH.
In which reaction below does water not participate as a reactant (rather than as a product)?
a) Conversion of an acid anhydride to two acids.
b) Conversion of an ester to an acid and an alcohol.
c) Conversion of ATP to ADP.
d) Photosynthesis
e) Production of gaseous carbon dioxide from bicarbonate.
Which of the following properties of water does not contribute to the fitness of the aqueous environment for living organisms?
a) Cohesion of liquid water due to hydrogen bonding.
b) High heat of vaporization.
c) High specific heat.
d) The density of water is greater than the density of ice.
e) The very low molecular weight of water.
Which of the following statements about buffers is true?
a) A buffer composed of a weak acid of pKa = 5 is stronger at pH 4 than at pH 6.
b) At pH values lower than the pKa, the salt concentration is higher than that of the acid.
c) The pH of a buffered solution remains constant no matter how much acid or base is added to the solution.
d) The strongest buffers are those composed of strong acids and strong bases.
e) When pH = pKa, the weak acid and salt concentrations in a buffer are equal.
A compound has a pKa of 7.4. To 100 mL of a 1.0 M solution of this compound at pH 8.0 is added 30 mL of 1.0 M hydrochloric acid. The resulting solution is pH:
a) 6.5
b) 6.8
c) 7.2
d) 7.4
e) 7.5
Consider an acetate buffer, initially at the
same pH as its pKa (4.76). When sodium hydroxide (NaOH)
is mixed with this buffer, the:
a) pH remains constant.
b) pH rises more than if an equal amount of NaOH is added to an acetate buffer initially at pH 6.76.
c) pH rises more than if an equal amount of NaOH is added to unbuffered water at pH 4.76.
d) ratio of acetic acid to sodium acetate in the buffer falls.
e) sodium acetate formed precipitates because it is less soluble than acetic acid.
A compound is known to have a free amino group with a pKa of 8.8, and one other ionizable group with a pKa between 5 and 7. To 100 mL of a 0.2 M solution of this compound at pH 8.2 was added 40 mL of a solution of 0.2 M hydrochloric acid. The pH changed to 6.2. The pKa of the second ionizable group is:
a) The pH cannot be determined from this information.
b) 5.4
c) 5.6
d) 6.0
e) 6.2
Three buffers are made by combining a 1 M solution of acetic acid with a 1 M solution of sodium acetate in the ratios shown below.
a) pH remains constant.
b) pH rises more than if an equal amount of NaOH is added to an acetate buffer initially at pH 6.76.
c) pH rises more than if an equal amount of NaOH is added to unbuffered water at pH 4.76.
d) ratio of acetic acid to sodium acetate in the buffer falls.
e) sodium acetate formed precipitates because it is less soluble than acetic acid.
A compound is known to have a free amino group with a pKa of 8.8, and one other ionizable group with a pKa between 5 and 7. To 100 mL of a 0.2 M solution of this compound at pH 8.2 was added 40 mL of a solution of 0.2 M hydrochloric acid. The pH changed to 6.2. The pKa of the second ionizable group is:
a) The pH cannot be determined from this information.
b) 5.4
c) 5.6
d) 6.0
e) 6.2
Three buffers are made by combining a 1 M solution of acetic acid with a 1 M solution of sodium acetate in the ratios shown below.
1 M acetic acid 1 M sodium acetate
Buffer
1: 10
mL 90 mL
Buffer 2: 50 mL 50 mL
Buffer 3: 90 mL 10 mL
Buffer 2: 50 mL 50 mL
Buffer 3: 90 mL 10 mL
Which of these statements is true of the
resulting buffers?
a) pH of buffer 1 < pH of buffer 2 < pH of buffer 3
b) pH of buffer 1 = pH of buffer 2 = pH of buffer 3
c) pH of buffer 1 > pH of buffer 2 > pH of buffer 3
d) The problem cannot be solved without knowing the value of pKa.
e) None of the above.
A 1.0 M solution of a compound with 2 ionizable groups (pKa’s = 6.2 and 9.5; 100 mL total) has a pH of 6.8. If a biochemist adds 60 mL of 1.0 M HCl to this solution, the solution will change to pH:
a) 5.60
b) 8.90
c) 9.13
d) 9.32
e) The pH cannot be determined from this information.
a) pH of buffer 1 < pH of buffer 2 < pH of buffer 3
b) pH of buffer 1 = pH of buffer 2 = pH of buffer 3
c) pH of buffer 1 > pH of buffer 2 > pH of buffer 3
d) The problem cannot be solved without knowing the value of pKa.
e) None of the above.
A 1.0 M solution of a compound with 2 ionizable groups (pKa’s = 6.2 and 9.5; 100 mL total) has a pH of 6.8. If a biochemist adds 60 mL of 1.0 M HCl to this solution, the solution will change to pH:
a) 5.60
b) 8.90
c) 9.13
d) 9.32
e) The pH cannot be determined from this information.
The pH of a solution that contains 0.818 M acetic acid (CH3COOH) and 0.172 M sodium acetate is __________.
A) 4.077
B) 5.434
C) 8.571
D) 8.370
E) 9.922
Consider a solution containing 0.100 M fluoride ions and 0.126 M hydrogen
fluoride. The concentration of fluoride ions after the addition of 5.00 mL of
0.0100 M HCl to 25.0 mL of this solution is __________ M.
A) 0.0850
B) 0.00167
C) 0.0980
D) 0.0817
E) 0.00253
Calculate
the pH of a solution prepared by dissolving 0.370 mol of formic acid and 0.230 mol
of sodium formate in water
sufficient to yield 1.00 L of solution. The Ka of formic acid is 1.44 x10-4.
A) 2.099
B) 10.463
C) 3.546
D) 2.307
E) 3.952
A 50.0 mL sample of an aqueous H2SO4 solution is
titrated with a 0.375M NaOH solution.
The equivalence point is reached with 62.5 ml of the base.
The concentration of H2SO4 is __________
M.
A) 0.234
B) 0.469
C) 0.150
D) 0.300
E) 0.938
The pH of a solution prepared by mixing 55.0 mL of 0.183 M KOH and 50.0 mL of
0.145M HC2H3O2 is __________.
A) 1.31
B) 7.00
C) 7.74
D) 9.97
E) 12.43
What change will be caused by addition of a small amount of HCl to a solution
containing fluoride ions and hydrogen fluoride?
A) The concentration of hydronium ions will
increase significantly.
B) The concentration of fluoride ions will
increase as will the concentration of hydronium ions.
C) The concentration of hydrogen fluoride will
decrease and the concentration of fluoride ions will increase.
D) The concentration of fluoride ion will
decrease and the concentration of hydrogen fluoride will increase.
E) The fluoride ions will precipitate out of
solution as its acid salt.
In a solution, when the concentrations of a weak acid and its conjugate base
are equal,
A) the
system is not at equilibrium.
B) the buffering capacity is
significantly decreased.
C) the -log of the [H+] and the -log of the Ka are equal.
D) all of the above are true.
16)
Which of the following could be added to a solution of acetic acid to prepare a
buffer?
A) sodium acetate only
B) sodium acetate or sodium hydroxide
C) nitric acid only
D) hydrofluoric acid or nitric acid
E) sodium hydroxide only
The primary buffer system that controls the pH of the blood is the __________
buffer system.
A) carbon dioxide, carbonate
B) carbonate, bicarbonate
C) carbonic acid, carbon dioxide
D) carbonate, carbonic acid
E) carbonic acid, bicarbonate
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