Biochemistry – 2nd Edition
ST
SOLUTION
UV
MANUAL
IA
_A
Raymond S. Ochs
PP
Complete Solution Manual for Instructors and
RO
Students
VE
© Raymond S. Ochs
D?
All rights reserved. Reproduction or distribution without permission is prohibited.
??
©MEDGEEK
, Solutions Manual for Biochemistry, 2e by
Raymond S. Ochs (All Chapters)
End of chapter answers
Chapter 2
ST
1. a) The properties are similar because both gas and liquid are fluids.
b) All phase transitions of water are unusual. The liquid to gas because it occurs at a high
temperature, due to hydrogen bonding. The liquid-solid transition is unusual because the
UV
maximal density of water occurs at 4oC, due to closer approach of water molecules in the liquid.
c) Most of the unusual properties are due to the extensive hydrogen bonding possible
because of the OH bond and the geometry of the molecule, forming extensive three dimensional
lattices.
2. It is possible. Using the density (1 g/ml) and molecular weight (18 g/mol) of water, the
IA
concentration is 1/18 mol/l or 55.5 M.
3. Electronegativities are calculated from molecules in which the bonds occur. They are
different in different molecules due to other forces (through bond and through space electrical
_A
effects), so the values are averaged. The scale for each atom is thus a relative one; the difference
between atoms can be easily estimated by subtracting the electronegativity values of each. The
1-4 scale was arbitrarily chosen.
4. Sulfur is larger, the electrons more diffuse, and as a result is unable to form a hydrogen bond.
PP
5. They are in adjacent columns in the periodic table, so we can expect some properties to be
shared, but have distinct valences. The nitrogen atom has five electrons, 1s22p3. The p orbital
has 6 potential electrons; the 3 in nitrogen atom are thus half-filled. Once bound to other atoms,
the electrons are hybrids, such as the common hydride, NH3. The extra electron pair in this
RO
molecule makes it a Lewis base (electron pair donor). However, N can occur in acids too, such
as in nitric acid. As amines, the reason for the tendency to positive charge is that when amines
accept a proton (Bronstead base) they become positively charged.
The oxygen atom as six electrons, 1s22p4. It also hybridizes in forming compounds; in
this case many of its compounds become acids such as R-COOH. When this loses a proton, it
becomes negatively charged. However, the oxygen hydride analogous to NH3 – H2O – can be
VE
considered both basic and acidic.
6. CO2 has polar bonds, but is not a polar molecule because the polarity vectors cancel out. The
geometry of the molecule is linear.
D?
7. NH4+ dissolves in water because it has a full charge, which attracts the partial negative
charges of water even more powerfully than another polar molecule does.
??
1
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, 8. The terminology was applied before the true nature of the effect was known. Thus is
appears that water and oil repel each other, but the underlying reason is because of affinity of
water molecules towards each other, not of chemical repulsive forces.
9. For polar molecules, the attraction is due to the ability of partial negative and partial positive
portions to attract one another. For nonpolar molecules, relatively weak interactions such as
dipole-induced dipole charges provides only very modest charge attraction. Nonpolar molecules
are forced together largely due to the self-attracting water molecules in a water-oil system.
ST
10. Saturation in water solutions occur once all of the hydrogen bonds are formed. As there is
no longer an ability to separate the ions (hydrate them), they form a separate solid phase. This
utilization of all hydrogen bonds is apparent also in biological molecules, such as cellulose, and
UV
the interiors of many proteins, and of DNA.
11. Water buffers temperature because the vibrational forces of the OH bond are stabilized by
hydrogen bonding. These forces must be overcome to make the molecules more mobile, and
thereby raise the temperature.
IA
12. Because the equilibrium constant changes, temperature must affect the forward rate of water
dissociation more than the reverse rate. That is likely because forming two products with
increased translation is favored with increasing kinetic energy, due to the increased temperature.
_A
13. The protons don’t actually move long distances, but exchange their hydrogen bonds for
covalent bonds in concert with neighboring water molecules. Thus, the movement of protons is
virtual, just like the movement of electrons along wires across the country; the same electron
does not actually move coast to coast.
PP
14. Using the Bronsted definition is more awkward when the species does not have a proton to
donate. As a work around, you have to say that the ability of CO2 to react with water means that
the species H2CO3 is the “hydrated equivalent” that participates in acid dissociation.
15. The log transformation means that linear changes in value for pH are actually power
RO
changes; a doubling of pH means a 10-fold change in hydrogen ion concentration. Taking the
negative of the log value means that the changes are in the opposite direction to the changes in
the value of pH. Thus, an increase in pH means a decrease in hydrogen ion concentration.
Together, they make thinking about acidity changes nonintuitive. As the notion is embedded in
all of science, however, it must be maintained. While it becomes familiar, it is always valuable
VE
to be vigilant against misinterpretation.
16. Increasing the concentration of [A] means that the rate of the forward reaction – kf[A][B] –
must increase. Notice that making this increase disturbs the initial equilibrium, so that some B
must react with A to form some C and D. A new equilibrium will form once the rate of the
D?
reverse reaction adjusts to match the forward one; this is the definition of equilibrium. At this
point, there will be an increase in [C] and in [D] compared with the initial equilibrium. This is
what is behind the Le Chatelier principle.
??
2
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, 17. The salt, say NaCl, when dissolved in water is hydrated. This hydration will tie up water in
shells around each ion. Thus, those water molecules are immobilized in terms of lining up with
the electric field. Thus, the dielectric of a salt water solution must be less than pure water.
18. The solution would be basic. NaHCO3 is the conjugate base of H2CO3. When added to a
solution, it will react in the reverse direction from the CO2 hydration reaction, thereby
consuming protons, and lowering the [H+] of the solution.
ST
19. (a) Arrehnius: the dissociation reaction increases the [H+] of water, and thus water is an
acid by this definition
(b) Bronsted: water donates a proton to the solution, and is thus an acid by this definition.
(c) Lewis: The newly formed H of H3O+ in the product has accepted an electron pair from
UV
the O-H of the other reacting water molecule. This is a rather tortured view to enable a Lewis
acid view, but it is possible to show acid-base reactions of any type as Lewis acids or bases.
20. NaCl in solution ties up water molecules as shells around each of the two ions. As a result,
concentrated salt solutions have fewer water molecules available for the survival of bacterial.
Additionally the high ionic strength is a stressor for cell integrity.
IA
21. A- + H+ ⇌ HA. This lowers the concentration of protons in solution, and is thus basic.
22. The conjugate form of an acid or a base is charged.
_A
23. At a pH value much lower than the pK, ammonia is +1; at a pH value much higher than
the pK, ammonia is 0.
PP
RO
VE
D?
??
3
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ST
SOLUTION
UV
MANUAL
IA
_A
Raymond S. Ochs
PP
Complete Solution Manual for Instructors and
RO
Students
VE
© Raymond S. Ochs
D?
All rights reserved. Reproduction or distribution without permission is prohibited.
??
©MEDGEEK
, Solutions Manual for Biochemistry, 2e by
Raymond S. Ochs (All Chapters)
End of chapter answers
Chapter 2
ST
1. a) The properties are similar because both gas and liquid are fluids.
b) All phase transitions of water are unusual. The liquid to gas because it occurs at a high
temperature, due to hydrogen bonding. The liquid-solid transition is unusual because the
UV
maximal density of water occurs at 4oC, due to closer approach of water molecules in the liquid.
c) Most of the unusual properties are due to the extensive hydrogen bonding possible
because of the OH bond and the geometry of the molecule, forming extensive three dimensional
lattices.
2. It is possible. Using the density (1 g/ml) and molecular weight (18 g/mol) of water, the
IA
concentration is 1/18 mol/l or 55.5 M.
3. Electronegativities are calculated from molecules in which the bonds occur. They are
different in different molecules due to other forces (through bond and through space electrical
_A
effects), so the values are averaged. The scale for each atom is thus a relative one; the difference
between atoms can be easily estimated by subtracting the electronegativity values of each. The
1-4 scale was arbitrarily chosen.
4. Sulfur is larger, the electrons more diffuse, and as a result is unable to form a hydrogen bond.
PP
5. They are in adjacent columns in the periodic table, so we can expect some properties to be
shared, but have distinct valences. The nitrogen atom has five electrons, 1s22p3. The p orbital
has 6 potential electrons; the 3 in nitrogen atom are thus half-filled. Once bound to other atoms,
the electrons are hybrids, such as the common hydride, NH3. The extra electron pair in this
RO
molecule makes it a Lewis base (electron pair donor). However, N can occur in acids too, such
as in nitric acid. As amines, the reason for the tendency to positive charge is that when amines
accept a proton (Bronstead base) they become positively charged.
The oxygen atom as six electrons, 1s22p4. It also hybridizes in forming compounds; in
this case many of its compounds become acids such as R-COOH. When this loses a proton, it
becomes negatively charged. However, the oxygen hydride analogous to NH3 – H2O – can be
VE
considered both basic and acidic.
6. CO2 has polar bonds, but is not a polar molecule because the polarity vectors cancel out. The
geometry of the molecule is linear.
D?
7. NH4+ dissolves in water because it has a full charge, which attracts the partial negative
charges of water even more powerfully than another polar molecule does.
??
1
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, 8. The terminology was applied before the true nature of the effect was known. Thus is
appears that water and oil repel each other, but the underlying reason is because of affinity of
water molecules towards each other, not of chemical repulsive forces.
9. For polar molecules, the attraction is due to the ability of partial negative and partial positive
portions to attract one another. For nonpolar molecules, relatively weak interactions such as
dipole-induced dipole charges provides only very modest charge attraction. Nonpolar molecules
are forced together largely due to the self-attracting water molecules in a water-oil system.
ST
10. Saturation in water solutions occur once all of the hydrogen bonds are formed. As there is
no longer an ability to separate the ions (hydrate them), they form a separate solid phase. This
utilization of all hydrogen bonds is apparent also in biological molecules, such as cellulose, and
UV
the interiors of many proteins, and of DNA.
11. Water buffers temperature because the vibrational forces of the OH bond are stabilized by
hydrogen bonding. These forces must be overcome to make the molecules more mobile, and
thereby raise the temperature.
IA
12. Because the equilibrium constant changes, temperature must affect the forward rate of water
dissociation more than the reverse rate. That is likely because forming two products with
increased translation is favored with increasing kinetic energy, due to the increased temperature.
_A
13. The protons don’t actually move long distances, but exchange their hydrogen bonds for
covalent bonds in concert with neighboring water molecules. Thus, the movement of protons is
virtual, just like the movement of electrons along wires across the country; the same electron
does not actually move coast to coast.
PP
14. Using the Bronsted definition is more awkward when the species does not have a proton to
donate. As a work around, you have to say that the ability of CO2 to react with water means that
the species H2CO3 is the “hydrated equivalent” that participates in acid dissociation.
15. The log transformation means that linear changes in value for pH are actually power
RO
changes; a doubling of pH means a 10-fold change in hydrogen ion concentration. Taking the
negative of the log value means that the changes are in the opposite direction to the changes in
the value of pH. Thus, an increase in pH means a decrease in hydrogen ion concentration.
Together, they make thinking about acidity changes nonintuitive. As the notion is embedded in
all of science, however, it must be maintained. While it becomes familiar, it is always valuable
VE
to be vigilant against misinterpretation.
16. Increasing the concentration of [A] means that the rate of the forward reaction – kf[A][B] –
must increase. Notice that making this increase disturbs the initial equilibrium, so that some B
must react with A to form some C and D. A new equilibrium will form once the rate of the
D?
reverse reaction adjusts to match the forward one; this is the definition of equilibrium. At this
point, there will be an increase in [C] and in [D] compared with the initial equilibrium. This is
what is behind the Le Chatelier principle.
??
2
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, 17. The salt, say NaCl, when dissolved in water is hydrated. This hydration will tie up water in
shells around each ion. Thus, those water molecules are immobilized in terms of lining up with
the electric field. Thus, the dielectric of a salt water solution must be less than pure water.
18. The solution would be basic. NaHCO3 is the conjugate base of H2CO3. When added to a
solution, it will react in the reverse direction from the CO2 hydration reaction, thereby
consuming protons, and lowering the [H+] of the solution.
ST
19. (a) Arrehnius: the dissociation reaction increases the [H+] of water, and thus water is an
acid by this definition
(b) Bronsted: water donates a proton to the solution, and is thus an acid by this definition.
(c) Lewis: The newly formed H of H3O+ in the product has accepted an electron pair from
UV
the O-H of the other reacting water molecule. This is a rather tortured view to enable a Lewis
acid view, but it is possible to show acid-base reactions of any type as Lewis acids or bases.
20. NaCl in solution ties up water molecules as shells around each of the two ions. As a result,
concentrated salt solutions have fewer water molecules available for the survival of bacterial.
Additionally the high ionic strength is a stressor for cell integrity.
IA
21. A- + H+ ⇌ HA. This lowers the concentration of protons in solution, and is thus basic.
22. The conjugate form of an acid or a base is charged.
_A
23. At a pH value much lower than the pK, ammonia is +1; at a pH value much higher than
the pK, ammonia is 0.
PP
RO
VE
D?
??
3
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