Test Bank for Biochemistry 6th Edition Reginald Garrett +A

$35.00
Test Bank for Biochemistry 6th Edition Reginald Garrett +A

Test Bank for Biochemistry 6th Edition Reginald Garrett +A

$35.00
Test Bank for Biochemistry 6th Edition Reginald Garrett +A

1. All are distinctive properties of living systems EXCEPT:

a.Living organisms are relatively simple.
b.Biological structures play a role in the organism’s existence.
c.The living state is characterized by the flow of energy through the organism.
d.Living organisms are highly organized.
e.Living organisms are actively engaged in energy transformation.

ANSWER: a

2. Even though the building blocks have fairly simple structures, macromolecules are exquisitely organized in their intricate three-dimensional architecture known as:

a.configuration.
b.conformation.
c.sequence.
d.Lewis structure.
e.structural maturation.

ANSWER: b

3. All of the following activities require the presence of ATP or NADPH EXCEPT:

a.osmoregulation.
b.biosynthesis.
c.movement of muscles.
d.light emission.
e.none, they are all energy-requiring activities.

ANSWER: e

4. Which are the four most common elements in the human body?

a.hydrogen, calcium, oxygen and sodium
b.hydrogen, oxygen, iron and carbon
c.hydrogen, oxygen, carbon and nitrogen
d.oxygen, carbon, iron and nitrogen
e.oxygen, silicon, calcium and nitrogen

ANSWER: c

5. What makes carbon such an abundant element in biomolecules?

a.It can form up to five bonds by sharing its electrons.
b.It forms only single bonds.
c.It provides low bond energy.
d.It forms stable covalent bonds by electron pair sharing.
e.It does not usually bond to other carbons, allowing a more diverse combination of elements.

ANSWER: d

6. The major precursors for the formation of biomolecules include all EXCEPT:

a.nitrate and dinitrogen.
b.water.
c.carbon dioxide.
d.ammonium ion.
e.none, all are major precursors.

ANSWER: e

7. From the major precursors, the complex biomolecules are made in which sequence?

a.metabolites, building blocks, macromolecules, supramolecular complexes
b.macromolecules, building blocks, metabolites, supramolecular complexes
c.building blocks, macromolecules, supramolecular complexes, metabolites
d.metabolites, macromolecules, building blocks, supramolecular complexes
e.metabolites, building blocks, supramolecular complexes, macromolecules

ANSWER: a

8. The structural integrity of supramolecular complexes (assemblies) of multiple components are bonded to each other by all of the following forces EXCEPT:

a.covalent bonds
b.van der Waals forces
c.hydrogen bonds
d.hydrophobic interactions
e.ionic interactions

ANSWER: a

9. Organelles have what three attributes?

a.Only in prokaryotic cells, membrane bound, have a dedicated set of tasks.
b.Only in eukaryotic cells, membrane bound, have a dedicated set of tasks.
c.Only in eukaryotic cells, seldom membrane bound, have a dedicated set of tasks.
d.Only in prokaryotic cells, membrane bound, multi-functional.
e.In both prokaryotic cells and eukaryotic cells, membrane bound, have a dedicated set of tasks.

ANSWER: b

10. Membrane structures are maintained primarily by:

a.hydrophobic interactions.
b.covalent bonds.
c.hydrogen bonds.
d.non-spontaneous assembly.
e.ionic interactions.

ANSWER: a

11. All of the following are properties of membranes EXCEPT:

a.supramolecular assemblies.
b.define boundaries of cellular components.
c.spontaneous assemblies resulting from hydrophobic interactions.
d.identical protein and lipid composition in the major organelles.
e.none, all are true.

ANSWER: d

12. Which of the following properly ranks the non-covalent interactions in order of increasing strength?

a.ionic, hydrogen bond, van der Waals
b.van der Waals, hydrogen bond, ionic
c.van der Waals, ionic, hydrogen bond
d.hydrogen bond, van der Waals, ionic
e.cannot be determined since ionic interactions and hydrogen bonds often vary in strength

ANSWER: e

13. Weak forces that create constantly forming and breaking interactions at physiological temperatures, but cumulatively impart stability to biological structures generated by their collective activity include all EXCEPT:

a.hydrogen bonds
b.van der Waals forces
c.covalent bonds
d.ionic interactions
e.hydrophobic interactions

ANSWER: c

14. Which of the following is a true statement about non-covalent bonds?

a.They are all the result of electron sharing.
b.Hydrogen bonds, ionic bond and hydrophobic interactions all carry a degree of specificity while van der Waals interactions are induced.
c.All noncovalent bonds are formed between oppositely charged polar functions.
d.Van der Waals interactions are not affected by structural complementarity, while hydrogen bonds, ionic bonds and hydrophobic interaction are affected by structural complementarity.
e.Hydrogen, van der Waals, and hydrophobic interactions do not form linear bonds.

ANSWER: b

15. Electrostatic forces

a.include ionic interactions between negatively charged carboxyl groups and positively charged amino groups.
b.average about 2 kJ/mol in aqueous solutions.
c.typically are directional like hydrogen bonds.
d.require a precise fit like van der Waals interactions.
e.include ionic, induced dipole and permanent dipole interactions.

ANSWER: a

16. All are true about hydrophobic interactions EXCEPT:

a.Hydrophobic interactions result from the strong tendency of water to exclude nonpolar groups or molecules.
b.Hydrophobic interactions result because water molecules prefer the stronger interactions that they share with one another, compared to their interactions with nonpolar molecules.
c.Hydrophobic interactions result from hydrogen bonds between water and the hydrophobic molecules.
d.The preferential interactions between water molecules “exclude” hydrophobic substances from aqueous solution and drive the tendency of nonpolar molecules to cluster together.
e.Hydrophobic interactions result in nonpolar regions of biological molecules being buried in the molecule’s interior to exclude them from the aqueous milieu.

ANSWER: c

17. Which of the following molecular recognition mechanisms is based upon structural complementarity?

a.interaction of a protein with a metabolite.
b.the association of a strand of DNA with its complementary strand.
c.the ability for a sperm cell to bind to an egg.
d.the binding of a hormone to its receptor.
e.all of the above

ANSWER: e

18. All of the statements about structural complementarity are true EXCEPT:

a.Weak chemical forces mediate it.
b.It produces strong irreversible interactions.
c.It is the interaction of a biological macromolecule and its ligand.
d.It is the basis of many biological functions.
e.It is the means of recognition in bimolecular interactions.

ANSWER: b

19. Which of the following statements regarding molecular recognition is correct?

a.Covalent bonds are a common interaction used in molecular recognition.
b.Molecular recognition takes place only between protein molecules.
c.For molecular recognition to occur, complementarity of the molecules is required.
d.Hydrogen bonds are not effective mediators of molecular recognition due to their low strength.
e.None of the above are correct.

ANSWER: c

20. Biological molecules are functionally active only within a narrow range of environmental conditions with denaturation occurring in all EXCEPT:

a.dramatic increase in temperature.
b.change in ionic strength.
c.refrigeration.
d.addition of strong acid or base.
e.none, all will denature biological macromolecules.

ANSWER: c

21. All of the following functions of an enzyme are true EXCEPT:

a.Enzymes help to catalyze virtually every metabolic reaction.
b.Enzymes mediate the rates of cellular reaction in proportion to cellular requirements.
c.Enzymes are sensitive to temperature, pH, and concentration changes.
d.An increased activity of an enzyme increases the amount of energy produced.
e.Enzymes are used as a catalyst to increase reaction rates many orders of magnitude.

ANSWER: d

22. All are true for prokaryotic cells EXCEPT:

a.Some have flagella.
b.They have a simple plasma or cell membrane.
c.They posses a distinct nuclear area, but no nucleus.
d.They have ribosomes, but no mitochondria.
e.All are true.

ANSWER: e

23. Composed of peptidoglycan, a rigid framework of polysaccharide cross-linked by short peptide chains, describes what structural feature of a prokaryotic cell?

a.cytosol
b.ribosome
c.nuclear area
d.cell membrane
e.cell wall

ANSWER: e

24. All are internal membrane specialized structures of animal cells EXCEPT:

a.lysosome.
b.nucleus.
c.endoplasmic reticulum.
d.mitochondria.
e.chloroplast.

ANSWER: e

25. Arrays of filaments in eukaryotic cells that give the cell its shape and its capacity to move are called the:

a.plasma membrane.
b.smooth endoplasmic reticulum.
c.cytoskeleton.
d.lysosome.
e.Golgi body.

ANSWER: c

26. Supramolecular complexes of nucleic acid encapsulated in a protein coat, and in some instances, surrounded by a membrane envelope are called:

a.viruses.
b.plasmids.
c.nucleosomes.
d.ribosomes.
e.all are true.

ANSWER: a

27. Viruses are acellular, but they act as cellular parasites in order to:

a.reproduce.
b.protect themselves.
c.grow in size.
d.gain genetic information.
e.all are true.

ANSWER: a

28. Rough ER are “studded” with:

a.lysosomes.
b.ribosomes.
c.peroxisomes.
d.nucleosomes.
e.all are true.

ANSWER: b

29. When viral genetic elements are integrated into the host chromosome and become quiescent, it is referred to as:

a.cytolytic.
b.lysogeny.
c.hemolytic.
d.propagational.
e.autonomy.

ANSWER: b

30. Which organelle is responsible for the bulk of energy production in the form of ATP?

a.chloroplast
b.mitochondria
c.golgi apparatus
d.lysosome
e.endoplasmic reticulum

ANSWER: b

31. Which of the following molecules is not generally incorporated into macromolecules?

a.amino acids
b.monosaccharides
c.nucleotides
d.fatty acids
e.all of the above are incorporated into macromolecules

ANSWER: d

32. ​Discuss the distinctive properties of living organisms.

ANSWER: First, living systems are highly organized. For example, large animals are composed of many different types of cells that in turn have subcellular structures called organelles—complex assemblies of very large polymeric molecules called macromolecules. Second, every biological structure in a living system—from parts of organisms, such as limbs and organs, down to the chemical agents of metabolism, such as enzymes and metabolic intermediates—has a particular function. Third, living systems perform energy transformations by means of special energized biomolecules such as ATP and NADPH. Fourth, living systems are capable of self-replication—the ability to reproduce virtually identical copies of themselves.
TOPICS: 1.1 What Are the Distinctive Properties of Living Systems?

33. Briefly explain the different organelles.​

ANSWER:

Organelles, found only in eukaryotic cells, are cellular inclusions that are usually membrane bounded and are dedicated to important cellular tasks. Organelles include the nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, and vacuoles, as well as other relatively small cellular inclusions, such as peroxisomes, lysosomes, and chromoplasts. The nucleus is the repository of genetic information as contained within the linear sequences of nucleotides in the DNA of chromosomes. Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. They carry out the energy-releasing aerobic metabolism of carbohydrates and fatty acids, capturing the energy in metabolically useful forms such as ATP. Chloroplasts endow cells with the ability to carry out photosynthesis. The endoplasmic reticulum is a labyrinthine organelle where both membrane proteins and lipids are synthesized. The Golgi is an asymmetrical system of flattened membrane-bounded vesicles often stacked into a complex. The vacuole is usually the most obvious compartment in plant cells. It is a very large vesicle enclosed by a single membrane called the tonoplast.

TOPICS: 1.3 What Is the Structural Organization of Complex Biomolecules?

34. Discuss the properties of a hydrogen bond.​

ANSWER: Hydrogen bonds form between a hydrogen atom covalently bonded to an electronegative atom (such as oxygen or nitrogen) and a second electronegative atom that serves as the hydrogen bond acceptor. Hydrogen bonds, at a strength of 12 to 30 kJ/mol, are stronger than van der Waals forces and have an additional property: H bonds are cylindrically symmetrical and tend to be highly directional, forming straight bonds between donor, hydrogen, and acceptor atoms. Hydrogen bonds are also more specific than van der Waals interactions because they require the presence of complementary hydrogen donor and acceptor groups.​
TOPICS: 1.4 How Do the Properties of Biomolecules Reflect Their Fitness to the Living Condition?

35. ​Briefly explain the structural organization of bacteria.

ANSWER: Bacteria, which are prokaryotes, are very small, on the order of several microns in length, and are usually surrounded by a rigid cell wall that protects the cell and gives it its shape. Prokaryotic cells have only a single membrane, the plasma membrane or cell membrane. They contain no nucleus but possess a distinct nuclear area called the nucleoid where a single circular chromosome is localized. Reactions of cellular respiration are localized on internal membranous structures derived from and continuous with the cell membrane. In cyanobacteria, flat, sheetlike membranous structures called lamellae—formed from cell membrane infoldings—are the sites of photosynthetic activity. Some bacteria have flagella, single, long filaments used for motility.​
TOPICS: 1.5 What Are the Organization and Structure of Cells?

36. Describe the structure of viruses.​

ANSWER: Viruses are supramolecular complexes of nucleic acid, either DNA or RNA, encapsulated in a protein coat and, in some instances, surrounded by a membrane envelope. Viruses are acellular, but they act as cellular parasites in order to reproduce. The bits of nucleic acid in viruses are, in reality, mobile elements of genetic information. The protein coat serves to protect the nucleic acid and allows it to gain entry to the cells that are its specific hosts. Mature virus particles in host cells arise by encapsulating the nucleic acid within a protein coat called the capsid.​
TOPICS: 1.6 What Are Viruses?

Chapter 02 – Water: The Medium of Life

1. Properties of water that render it so suited to its role as a medium of life include all EXCEPT:

a.Unrivaled ability to form hydrogen bonds.
b.Unusually high dielectric constant of water explains water’s ability to surround ions and increase the ions’ attraction for one another.
c.Unparalleled ability to orient around nonpolar solutes to promote hydrophobic interactions.
d.The small, but significant, tendency to form H+ and OH− ions.
e.None, all are true.

ANSWER: b

2. All are true for water for a substance of its molecular weight that is neither metallic nor ionic EXCEPT:

a.a high surface tension.
b.a chemically inert solvent, which has a great capacity to dissolve a diverse spectrum of molecules and ions.
c.a positive volume of melting.
d.a high dielectric constant.
e.a high capacity to form hydrogen bonds

ANSWER: c

3. The unrivaled ability to form ____ hydrogen bonds per liquid water molecule is the source of the strong intermolecular attractions unique to water.

a.1
b.2
c.3
d.4
e.5

ANSWER: d

4. Because of its highly polar nature, water is an excellent solvent for polar substances, but NOT for:

a.salts.
b.sugars.
c.aldehydes and ketones.
d.hydrocarbons.
e.alcohols and amines.

ANSWER: d

5. The solvent with the highest dielectric constant in this group is:

a.water.
b.acetic acid.
c.ethanol.
d.hexane.
e.benzene.

ANSWER: a

6. Hydrogen bonds in ice are all EXCEPT:

a.directional.
b.straight.
c.weak.
d.responsible for the lower density of ice over liquid water.
e.holding water molecules in ice apart.

ANSWER: c

7. Pure liquid water consists of H2O molecules:

a.held in a rigid three-dimentional network.
b.with local preference for linear geometry.
c.with large numbers of strained or broken hydrogen bonds.
d.which do not switch H-bonds readily.
e.all are true.

ANSWER: c

8. The average lifetime of a hydrogen bond connection in water is on the order of 10:

a.picoseconds.
b.microseconds.
c.milliseconds.
d.seconds.
e.nanoseconds.

ANSWER: a

9. The ____ bonding of water with the polar functional groups on nonionic polar solutes such as sugars are ____ than the intermolecular attractions between solute molecules allowing solute molecules to readily dissolve in water.

a.ionic, stronger
b.hydrogen, weaker
c.hydrophobic, stronger
d.hydrogen, stronger
e.ionic, weaker

ANSWER: d

10. The H-bonded water around an ionic substance tends to ____; and the H-bonded water around nonpolar solutes tends to ____.

a.inhibit ionization, promote hydrophobic interactions
b.inhibit ionization, inhibit hydrophobic interactions
c.not impact ionization, inhibit hydrophobic interactions
d.promote ionization, not impact hydrophobic interactions
e.promote ionization, promote hydrophobic interactions

ANSWER: e

11. Amphiphilic (amphipathic) molecules include:

a.sugars.
b.acidic amino acids.
c.inorganic salts.
d.water.
e.salts of fatty acids.

ANSWER: e

12. In micelles:

a.polar ends form hydrophobic interactions with water.
b.nonpolar ends form hydrophilic interactions with water.
c.hydrocarbon tails form hydrophobic interactions with water.
d.polar ends are hydrophobic and nonpolar ends are hydrophilic.
e.hydrocarbon tails are excluded from the water into hydrophobic domains.

ANSWER: e

13. By limiting the orientation that neighboring water molecules can assume, solutes give ____ to the solvent and ____ the dynamic interplay among H2O molecules that occurs in pure water.

a.pressure, disrupt
b.disorder, increase
c.disorder, decrease
d.order, diminish
e.order, increase

ANSWER: d

14. To ____ the osmotic pressure created by the contents of their cytosol, cells tend to store substances such as amino acids and sugars in ____ form.

a.increase, monomeric
b.minimize, polymeric
c.minimize, monomeric
d.maximize, polymeric
e.increase, polymeric

ANSWER: b

15. Water ionizes because:

a.the smaller electronegative oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
b.the larger electronegative oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
c.the smaller electropositive oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
d.the larger electropositive oxygen atom strips the electron from one of its hydrogen atoms, leaving the proton to dissociate.
e.None of the above

ANSWER: b

16. Grapefruit juice at pH 3.2 contains about ____ times as much H+ as orange juice at pH 4.3.

a.0.9
b.10−7.5
c.10−2
d.12
e.101

ANSWER: d

17. All are examples of weak electrolytes EXCEPT:

a.hydrochloric acid.
b.acetic acid.
c.lactic acid.
d.phosphoric acid.
e.carbonic acid.

ANSWER: a

18. If 0.1 moles of Na2HPO4 and 0.1 moles of NaH2PO4 are mixed in water, what is the resulting pH? The pKa values for phosphoric acid are 2.1, 7.2, 12.4.

a.2.1
b.4.65
c.7.2
d.9.8
e.12.4

ANSWER: c

19. Estimate the pH of the resulting solution prepared by mixing 1.0 mole of solid disodium phosphate (Na2HPO4) and 1.25 mole of hydrochloric acid. The pKa values for phosphoric acid are 2.1, 7.2, 12.4.

a.pH < 2.1
b.pH = 2.1
c.2.1 < pH < 7.2
d.pH = 7.2
e.7.2 < pH < 12.4

ANSWER: c

20. Which of the following pairs would be the best buffer at pH 10.0?

a.Acetic acid and sodium acetate (pKa = 4.76)
b.H2CO3 and NaHCO3 (pKa values are 3.77 and 10.4)
c.Lactic acid and sodium lactate (pKa = 3.86)
d.NaH2PO4 and Na2HPO4 (pKa values are 2.1, 7.2, 12.4)
e.Sodium succinate and succinic acid (pKa = 4.21)

ANSWER: b

21. What ionic form(s) is/are most prevalent at pH 7.0? The pKa values of phosphoric acid are 2.1, 7.2, and 12.4.

a.HPO42
b.H2PO4
c.HPO42 and PO43
d.H2PO4− and HPO42
e.All are correct

ANSWER: b

22. A plasma pH of 6.8 doesn’t seem too far away from a normal pH of 7.4, but at pH 6.8 the H+ concentration is ____ times greater than at pH 7.4 and results in severe acidosis.

a.0.1
b.0.6
c.4
d.10
e.20

ANSWER: c

23. pH = pKa when:

a.[A−]/[HA] = 0
b.log ([A−]/[HA]) = 1
c.[A−] >> [HA]
d.[A−] = [HA]
e.log ([HA]/[A−]) = 1

ANSWER: d

24. Buffers have all of the following characteristics EXCEPT:

a.they have relatively flat titration curves at the pH(s) where they buffer.
b.they resist changes in their pH as acid or base is added.
c.they are typically composed of a weak acid and its conjugate base.
d.they buffer best for polyprotic acids half-way between the two pKa values.
e.buffer where the amounts of conjugate base are nearly equivalent to the amounts of weak acid.

ANSWER: d

25. Buffer systems are effective when the pH values are within ____ pH unit(s) of the pKa value.

a.1
b.2
c.3
d.4
e.5

ANSWER: a

26. Intracellular pH is maintained primarily by the ____ and ____ buffer systems, and the extracellular pH by the ____ buffer system.

a.HPO42/H2PO4−; HCO3−/H2CO3; histidine
b.H3PO4/H2PO4−; histidine; HCO3−/H2CO3
c.HCO3−/H2CO3; H3PO4/H2PO4−; histidine
d.HPO42/H2PO4−; histidine; HCO3−/H2CO3
e.HCO3−/H2CO3; histidine; H3PO4/H2PO4

ANSWER: d

27. Hyperventilation is a physiological mechanism to:

a.lower [CO2 (g)] in the blood and increase blood pH.
b.raise [CO2 (g)] in the blood and increase blood pH.
c.lower [CO2 (g)] in the blood and decrease blood pH.
d.raise [CO2 (g)] in the blood and decrease blood pH.
e.lower [CO2 (g)] in the blood and increase [HCO3−].

ANSWER: a

28. Water is particularly suited as a solvent for biosystems because it has all of the following characteristics EXCEPT:

a.Water is a medium for ionization enhancing the variety of chemical species.
b.Water is innocuous, yet a powerful solvent.
c.Water is an excellent solvent for nonpolar substances.
d.Water is relatively chemically inert, yet dissolves a variety of solutes.
e.Through hydrophobic interactions, lipids coalesce into membranes in water.

ANSWER: c

29. Which of the following weak acids would make the best buffer at pH = 5.0?

a.acetic acid (Ka = 1.74 × 10−5, pKa = 4.76)
b.H2PO4− (Ka = 1.38 × 10−7, pKa = 7.20)
c.bicarbonate (Ka = 6.3 × 10−11, pKa = 10.24)
d.tris-hydroxymethyl aminomethane (Ka = 8.32 × 10−9, pKa = 8.07)
e.lactic acid (Ka = 1.38 × 10−4, pKa = 3.86)

ANSWER: a

30. The enzyme fumarase has a pH optimum of about 7.6. What would be the buffer of choice to study this enzyme?

a.lactic acid (Ka = 1.38 × 10−4, pKa = 3.86)
b.bicarbonate (Ka = 6.3 × 10−11, pKa = 10.24)
c.acetic acid (Ka = 1.74 × 10−5, pKa = 4.76)
d.succinate (Ka = 2.34 × 10−6, pKa = 5.63)
e.tris-hydroxymethyl aminomethane (Ka = 8.32 × 10−9, pKa = 8.07)

ANSWER: e

31. When preparing an acetate buffer at pH 4.5 with 0.01 M solutions of acetic acid (pKa = 4.8) and sodium acetate, the volume of acetic acid needed would be ____ the volume of sodium acetate solution.

a.equal to
b.less than half of
c.more than half of
d.about six times
e.about twice

ANSWER: e

32. Hypoventilation is characterized by inability to excrete CO2 rapidly enough and can be caused by all EXCEPT:

a.anesthetics.
b.depressant drugs.
c.narcotics.
d.lung diseases.
e.encephalitis.

ANSWER: e

33. Aspirin contains a carboxylic acid with a pKa of 3.5. Which of the following is true?

a.Aspirin will be mostly protonated in the stomach
b.Aspirin will be mostly protonated in the bloodstream
c.Aspirin will be easily absorbed in the stomach due to its negative charge
d.Aspirin will be easily transported in the bloodstream due to its negative charge
e.both a and d are correct

ANSWER: e

34. If a weak acid is 25% deprotonated at pH 4, what would the pKa be?

a.3.40
b.3.52
c.4.48
d.4.60
e.cannot determine from given information

ANSWER: c

35. Which of the following would be the conjugate acid of hydrogen phosphate, HPO4-2?

a.H2PO4
b.H3PO4
c.H2PO4-2
d.H2PO4
e.none of the above

ANSWER: a

36. Formic acid is the active agent in an ant bite. What is the ratio of base/acid for formic acid (pKa = 3.9) in the blood stream at pH 7.4?

a.3.16 × 10-4
b.3.16 × 103
c.0.54
d.1.90
e.cannot be determined based upon the provided information

ANSWER: b

37. Which of the following statements is INCORRECT about the nature of the hydrogen bond

a.The donor is a hydrogen atom bonded to an atom that is less electronegative than hydrogen.
b.The more linear the bond, the stronger the interaction.
c.The acceptor is a fairly electronegative atom containing a nonbonding pair of electrons.
d.It is a type of noncovalent bond.
e.All of the above statements are true about the nature of the hydrogen bond.

ANSWER: a

38. A weak acid is 33% dissociated at pH 5.0. What is the pKa for this acid?

a.4.5
b.4.7
c.5.3
d.5.5
e.cannot be determined from the information provided

ANSWER: c

39. ​Discuss the dielectric constant of water. Write the equation used to calculate the dielectric constant.

ANSWER: The attractions between the water molecules interacting with, or hydrating, ions in solution are much stronger than the attractions between oppositely charged ions. Water’s ability to surround ions in dipole interactions and diminish their attraction for each other is a measure of its dielectric constant, D. Indeed, ionization in solution depends on the dielectric constant of the solvent; otherwise, the strongly attracted positive and negative ions would unite to form neutral molecules. The strength of the dielectric constant is related to the force, F, experienced between two ions of opposite charge separated by a distance, r, as given in the relationship

F = e1e2/Dr2

where e1 and e2 are the charges on the two ions.​

TOPICS: 2.1 What Are the Properties of Water?

40. Calculate the equilibrium constant, Keq, for 1 L of pure water.​

ANSWER: The dissociation of water into hydrogen ions and hydroxyl ions occurs to the extent that 10−7 mol of H+ and 10−7 mol of OH are present at equilibrium in 1 L of water at 25°C.

The equilibrium constant for this process is​

where brackets denote concentrations in moles per liter. Because the concentration of H2O in 1 L of pure water is equal to the number of grams in a liter divided by the gram molecular weight of H2O, or 1000/18, the molar concentration of H2O in pure water is 55.5 M (molar). The decrease in H2O concentration as a result of ion formation ([H+], [OH] = 10−7M) is negligible in comparison; thus, its influence on the overall concentration of H2O can be ignored. Therefore,

TOPICS: 2.1 What Are the Properties of Water?

41. Explain weak electrolytes with an example.​

ANSWER: Substances with only a slight tendency to dissociate to form ions in solution are called weak electrolytes. Acetic acid, CH3COOH, is a good example:

The acid dissociation constant is represented as Ka. Ka is also termed an ionization constant because it states the extent to which a substance forms ions in water. The relatively low value of Ka for acetic acid reveals that the un-ionized form, CH3COOH, predominates over H+ and CH3COOin aqueous solutions of acetic acid. Viewed another way, CH3COO, the acetate ion, has a high affinity for H+.

TOPICS: 2.2 What Is pH?

42. Discuss the Phosphate Buffer System in living systems.​

ANSWER: The intracellular pH of most cells is maintained in the range between 6.9 and 7.4. Phosphate is an abundant anion in cells, both in inorganic form and as an important functional group on organic molecules that serve as metabolites or macromolecular precursors. Phosphate has a characteristic pK2 of 7.2. At physiological pH, phosphate can donate or accept hydrogen ions to buffer any changes in pH. For example, if the total cellular concentration of phosphate is 15 mM (millimolar) and the pH is 7.3, the distribution of the major phosphate species is given by

Thus, if [HPO42 –] + [H2PO4] = 15mM, then

[HPO42 –] = 8.33 mM and [H2PO4] = 6.67 mM

TOPICS: 2.3 What Are Buffers, and What Do They Do?

43. Explain the role that water plays in living systems.​

ANSWER: Water is a “poor” solvent for nonpolar substances. Thus, through hydrophobic interactions, lipids coalesce, membranes form, boundaries are created delimiting compartments, and the cellular nature of life is established. Because of its very high dielectric constant, water is a medium for ionization. Ions enrich the living environment in that they enhance the variety of chemical species and introduce an important class of chemical reactions. They provide electrical properties to solutions and therefore to organisms. The thermal properties of water allow effective temperature regulation in living organisms. The heat generated within an organism as a result of metabolism can be efficiently eliminated through evaporation or conduction of water.

TOPICS: 2.4 What Properties of Water Give It a Unique Role in the Environment?
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