Biochem chpt 2

Which of the following statements about water is false?

-Water molecules make hydrogen bonds readily with each other and with other polar substances.

-Water has a high melting point relative to its molecular mass.

-The hydrophobic effect results when solutes are unable to break
hydrogen bonds between water molecules.

-Nonpolar substances decrease the entropy of water molecules.
Water is a cohesive substance.
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Which of the following statements about water is false?

-Water molecules make hydrogen bonds readily with each other and with other polar substances.

-Water has a high melting point relative to its molecular mass.

-The hydrophobic effect results when solutes are unable to break
hydrogen bonds between water molecules.

-Nonpolar substances decrease the entropy of water molecules.
Water is a cohesive substance.
The hydrophobic effect results when solutes are unable to break hydrogen bonds between water molecules.
What is the pH of a solution made by mixing equal volumes of 1 M sodium acetate and 1 M acetic acid? (The pK of acetic acid is 4.76.)
4.76. It is equal to pK + log(1/1) = pK + 0 = 4.76.
The strongest noncovalent interactions are
ionic interactions.
Consider a solution separated from pure water by a semipermeable membrane that permits the passage of water, but not solutes. Which statement is false?

Osmotic pressure could be eliminated if enough solute were added to the region of pure water.

Osmotic pressure is the pressure that must be applied to the solution to prevent the inflow of water.

Osmotic pressure depends upon the size of the solute molecules.

Osmosis is the movement of solvent from a region of high solvent concentration to a solution of lower solvent concentration.
Osmotic pressure depends upon the size of the solute molecules.
Phosphoric acid is a polyprotic acid, with pK values of 2.14, 6.86, and 12.38. Which ionic form predominates at pH 9.3?
HPO42-
A graduate student at SDSU wants to measure the activity of a particular enzyme at pH 4.0. To buffer her reaction, she will use a buffer system based on one of the acids listed below, which acid is most appropriate for the experiment?
Formic acid (Ka 1.78 × 10-4)
Which of the following correctly lists bonding interactions in terms of their increasing strength:

Covalent bonds<hydrogen bonds<ionic interactions<Van der Waals interactions

Van der Waals interactions<ionic interactions<hydrogen bonding<covalent bonds

Van der Waals interactions<hydrogen bonding<ionic interactions<covalent bonds

Hydrogen bonds<ionic interactions<covalent interactions<Van der Waals interactions
Van der Waals interactions<hydrogen bonding<ionic interactions<covalent bonds
Which of the following functional groups could NOT act as a hydrogen bond donor?

An amino group.
An ester.
An aldehyde.
Both aldehyde and ester.
A hydroxyl group.
Both aldehyde and ester.
An amphiphilic molecule:
Has both polar and non-polar groups
Which radical (where radical means part of a molecule) shown cannot make a hydrogen bond to water?
-CH_3
-NH2
-OH
-COOH
-CH_3
What is the concentration of hydrogen ions at pH 3?10-3 M. pH is equal to -log[H+]Which statement about the pK is not true? The pK is equal to the pH at the midpoint of the titration. The pK is equal to the pH at the maximal buffering capacity. The pK is equal to the pH at the maximum slope of the titration curve. The pK is equal to the pH when [A-] = [HA]The pK is equal to the pH at the maximum slope of the titration curve.The pK is equal to the pH at the minimum slope of the titration curve.The pK of ammonia is 9.25. What is the effective buffering range?pH = 8.25-10.25. The buffering range is pK ± 1.At the first horizontal inflection point in the titration curve of phosphoric acid, which statement is true? [H3PO4] = [H2PO4-] [H2PO4-] = [HPO42-] [H3PO4] > [H2PO4-] [H2PO4-] < [HPO42-][H3PO4] = [H2PO4-]The tendency of water to minimize its contacts with hydrophobic molecules is termed the Enter your answer in accordance with the question statementhydrophobic effect_______ are spheroidal globules of up to several thousand amphiphilic molecules, in which the hydrophobic groups are buried and the polar groups form the surface.micellesT/F Ionic or electrostatic interactions occur between two groups of opposite charge.TWhich statement best explains why water can solvate both negative and positive ions? It can hydrogen bond. It is very small. It can ionize. It is dipolar.It is dipolar.Which statement about the Bronsted-Lowry formulation of acid-base chemistry is false? A- is the conjugate base of the acid HA. An acid is a substance that can donate a proton. A base is a substance that can accept a proton. H3O+ is the conjugate base of the acid H2O.H3O+ is the conjugate base of the acid H2O. H3O+ is the conjugate acid of the base H2O, and OH- is the conjugate base of the acid H2O.Which of the following statements about the buffering system in blood in not true? The most significant buffering compound in human blood is bicarbonate (HCO3-) . Alkalosis is a medical condition where the pH of blood rises above normal. Hyperventilation accelerates the loss of CO2 and causes respiratory alkalosis, which can be ameliorated by breathing in an atmosphere enriched in CO2. The buffering capacity of blood depends primarily on two equilibria: The first, CO2 + H2O H2CO3 and the second, H2CO3 H+ + HCO3-, where the overall pK for these two sequential reactions is 5.35. Blood is buffered so that it maintains a pH of 7.4.The buffering capacity of blood depends primarily on two equilibria: The first, CO2 + H2O H2CO3 and the second, H2CO3 H+ + HCO3-, where the overall pK for these two sequential reactions is 5.35. This last part of this statement is false: Blood is buffered at a pH of 7.4. The buffering range of a buffer is its pK ± 1. Thus a buffer with a pK of 5.35 would not be suitable to buffer blood at a pH of 7.4. The pK of the two equilibria shown - converting CO2 to HCO3- (bicarbonate) - is not 5.35 but rather 6.35. Thus a pH of 7.4 falls approximately within the buffering range of such a buffer (albeit at its higher limitThe pK of ammonia is 9.25. Which statement is true at pH 7.0? [NH4+] = [NH3] [NH4+] < [NH3] Ammonia is an effective buffer at this pH. [NH4+] > [NH3][NH4+] > [NH3]In a hydrogen bond between a water molecule and another biomoleculethe hydrogen bond will typically form between a hydrogen atom of the water molecule and either a nitrogen, sulfur, or oxygen atom of the other molecule.