Lehninger Biochemistry Chapter 2 – Flashcards

Which of these statements about hydrogen bonds is not true? A) Hydrogen bonds account for the anomalously high boiling point of water. B) In liquid water, the average water molecule forms hydrogen bonds with three to four other water molecules. C) Individual hydrogen bonds are much weaker than covalent bonds. D) Individual hydrogen bonds in liquid water exist for many seconds and sometimes for minutes. E) The strength of a hydrogen bond depends on the linearity of the three atoms involved in the bond.

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.

Hydrophobic interactions make important energetic contributions to: A) binding of a hormone to its receptor protein. B) enzyme-substrate interactions. C) membrane structure. D) three-dimensional folding of a polypeptide chain. E) all of the above are true.

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.

A hydronium ion: A) has the structure H3O+. B) is a hydrated hydrogen ion. C) is a hydrated proton. D) is the usual form of one of the dissociation products of water in solution. E) all of the above are true.

The pH of a solution of 1 M HCl is: A) 0 B) 0.1 C) 1 D) 10 E) -1

The pH of a solution of 0.1 M NaOH is: A) 0.1 B) 1.0 C) 12.8 D) 13 E) 14

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.

The aqueous solution with the highest pH is: A) 1 M HCl. B) 1 M NH3 (pKa = 9.25). C) 0.5 M NaHCO3 (pKa = 3.77). D) 0.1 M NaOH. E) 0.001 M NaOH.

Phosphoric acid is tribasic, with pKa's of 2.14, 6.86, and 12.4. The ionic form that predominates at pH 3.2 is: A) H3PO4. B) H2PO4-. C) HPO42-. D) PO43-. E) none of the above.

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

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.

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

Which of these statements is true of the resulting buffers? A) pH of buffer 1 < pH of buffer 2 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.

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.