Biochemistry Exam with Multiple
Choice answers graded A+
Which of following statements about buffers is true?
A) A buffer composed of a weak acid of pKa=5 is stronger at pH4 than at pH6.
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 conjugated base concentrations in a buffer are equal. -
ANS✅✅E) When pH = pKa, the weak acid and conjugated base concentrations in a buffer are
equal.
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 - ANS✅✅D) Hydrogen bonds form
readily in aqueous solutions
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 - ANS✅✅D) 0.1 M HCL
,The Henderson-Hasselbalch equation:
A) Allows the graphic determination of the molecular weight of a weak acid from its pH alone.
B) Does not explain the behavior of di- or tri-basic weak acids
C) Employs the same value for pKa for all weak acids.
D) Is equally useful with solutions of acetic acid and of hydrochloric acid.
E) Relates the pH of a solution to the pKa and the concentrations of acid and conjugate base. -
ANS✅✅E) Relates the pH of a solution to the pKa and the concentrations of acid and conjugate
base.
The four covalent bonds in methane (CH4) are arranged around carbon to give which one of the
following geometries?
A) Linear
B) Tetrahedral
C) Trigonal bipyramidal
D) Trigonal planar
E) Trigonal pyramidal - ANS✅✅B) Tetrahedral
The three-dimensional structure of macromolecules is formed and maintained primarily through non
covalent interactions. Which one of the following is not considered a non-covalent interaction?
A) Carbon-carbon bonds
B) Hydrogen bonds
C) Hydrophobic interactions
D) Ionic interactions
E) Van der Waals interactions - ANS✅✅A) Carbon-carbon bonds
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 - ANS✅✅E) water molecule across a membrane
The equilibrium constant for the ionization of acetic acid [HOAc → OAc− + Η+] is 0.00002. What can
you conclude about this reaction?
A) It is a closed system.
B) At equilibrium, the concentration of HOAc is much higher than the concentrations of OAc− + H+.
C) It never reaches equilibrium.
D) It is spontaneous, starting with CH3COOH.
E) The equilibrium constant increases when the starting concentration of CH3COOH is increased. -
ANS✅✅B) At equilibrium, the concentration of HOAc is much higher than the concentrations of
OAc− + H+.
The pH of a sample of urine is 5.7, while lime juice has a pH 2.0. The urine sample has:
A) approximately a hundred thousand times lower [H+] than the lime juice
B) approximately 5,000 times lower [H+] than the lime juice
C) approximately 3.5 times lower [H+] than the lime juice
D) approximately 0.285 times the [H+] as the lime juice
E) approximately 5 times lower [H+] than the lime juice - ANS✅✅B) approximately 5,000 times
lower [H+] than the lime juice
Physiological pH is 7.4. What is the hydrogen ion concentration of a solution at physiological
pH?
A) -7.4 M
B) 0.6 M
C) 0.6 x 10^-8 M
D) 1 x 10^-8 M
E) 4 x 10^-8 M - ANS✅✅E) 4 x 10^-8 M
Stereoisomers that are nonsuperimposable mirror images of each other are known as:
Choice answers graded A+
Which of following statements about buffers is true?
A) A buffer composed of a weak acid of pKa=5 is stronger at pH4 than at pH6.
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 conjugated base concentrations in a buffer are equal. -
ANS✅✅E) When pH = pKa, the weak acid and conjugated base concentrations in a buffer are
equal.
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 - ANS✅✅D) Hydrogen bonds form
readily in aqueous solutions
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 - ANS✅✅D) 0.1 M HCL
,The Henderson-Hasselbalch equation:
A) Allows the graphic determination of the molecular weight of a weak acid from its pH alone.
B) Does not explain the behavior of di- or tri-basic weak acids
C) Employs the same value for pKa for all weak acids.
D) Is equally useful with solutions of acetic acid and of hydrochloric acid.
E) Relates the pH of a solution to the pKa and the concentrations of acid and conjugate base. -
ANS✅✅E) Relates the pH of a solution to the pKa and the concentrations of acid and conjugate
base.
The four covalent bonds in methane (CH4) are arranged around carbon to give which one of the
following geometries?
A) Linear
B) Tetrahedral
C) Trigonal bipyramidal
D) Trigonal planar
E) Trigonal pyramidal - ANS✅✅B) Tetrahedral
The three-dimensional structure of macromolecules is formed and maintained primarily through non
covalent interactions. Which one of the following is not considered a non-covalent interaction?
A) Carbon-carbon bonds
B) Hydrogen bonds
C) Hydrophobic interactions
D) Ionic interactions
E) Van der Waals interactions - ANS✅✅A) Carbon-carbon bonds
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 - ANS✅✅E) water molecule across a membrane
The equilibrium constant for the ionization of acetic acid [HOAc → OAc− + Η+] is 0.00002. What can
you conclude about this reaction?
A) It is a closed system.
B) At equilibrium, the concentration of HOAc is much higher than the concentrations of OAc− + H+.
C) It never reaches equilibrium.
D) It is spontaneous, starting with CH3COOH.
E) The equilibrium constant increases when the starting concentration of CH3COOH is increased. -
ANS✅✅B) At equilibrium, the concentration of HOAc is much higher than the concentrations of
OAc− + H+.
The pH of a sample of urine is 5.7, while lime juice has a pH 2.0. The urine sample has:
A) approximately a hundred thousand times lower [H+] than the lime juice
B) approximately 5,000 times lower [H+] than the lime juice
C) approximately 3.5 times lower [H+] than the lime juice
D) approximately 0.285 times the [H+] as the lime juice
E) approximately 5 times lower [H+] than the lime juice - ANS✅✅B) approximately 5,000 times
lower [H+] than the lime juice
Physiological pH is 7.4. What is the hydrogen ion concentration of a solution at physiological
pH?
A) -7.4 M
B) 0.6 M
C) 0.6 x 10^-8 M
D) 1 x 10^-8 M
E) 4 x 10^-8 M - ANS✅✅E) 4 x 10^-8 M
Stereoisomers that are nonsuperimposable mirror images of each other are known as:
