hw 2 exam 1

Why are the ionic mobilities of H+ and OH- in an aqueous environment much greater than that of other ions?

hydrogen ion can hop from one water molecule to another

Which property of liquid water is also true for solid water?

liquid water has an extensive hydrogen bond network

Which of the following types of bonding interactions is NOT classified as non-covalent? Hydrogen bonding. Electrostatic interactions. Van der Waals. Dipole-Dipole interactions. None of the above.

none

From the pK's in table 2-4, considering all other factors equal, which weak acid/conjugate base pair will give the best buffer for a pH of 4.3?

succinic acid/succinate-

Which statement best explains why nonpolar substances have low solubility in water?

they cannot form h bonds to water

Which best describes the buffering range of phosphoric acid?

pH = 1.15-3.15, 5.82-7.82, 11.38-13.38

In acid dissociation, why is the dissociation constant Ka defined as K[H2O]?

concentration of water is essentially a constant

Which statement best explains why water can solvate both negative and positive ions? It can ionize. It is dipolar. It is very small. It can hydrogen bond.

dipolar

Which statement about the Bronsted-Lowry formulation of acid-base chemistry is false? H3O+ is the conjugate base of the acid H2O. A- is the conjugate base of the acid HA. A base is a substance that can accept a proton. An acid is a substance that can donate a proton

A

Which of the following statements is not true? Acetic acid (pK = 4.76) is an effective buffer against acid at pH 3.76. Ammonium hydroxide (pK = 9.25) is an effective buffer against base at pH 8.25. Ammonium hydroxide (pK = 9.25) is an effective buffer against base at pH 9.75. Acetic acid (pK = 4.76) is an effective buffer against acid at pH 5.76.

Acetic acid (pK = 4.76) is an effective buffer against acid at pH 3.76.

Which of the following statements is not true? Ammonium hydroxide (pK = 9.25) is not an effective buffer against acid or hydroxide at pH 7.75. Ammonium hydroxide (pK = 9.25) is an effective buffer against acid at pH 8.25. Ammonium hydroxide (pK = 9.25) is an effective buffer against acid or hydroxide at pH 9.25. Ammonium hydroxide (pK = 9.25) is an effective buffer against acid at pH 10.25.

Ammonium hydroxide (pK = 9.25) is an effective buffer against acid at pH 8.25.

Which of the following functional groups could NOT act as a hydrogen bond donor?

Both aldehyde and ester.

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<hydrogen bonding<ionic interactions<covalent bonds Hydrogen bonds<ionic interactions<covalent 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

Which of the properties listed is NOT true of liquid water? Liquid water consists of a rapidly fluctuating, three-dimensional network of hydrogen-bonded molecules. Liquid water is only 15% less hydrogen bonded than ice at 0o C. Liquid water is less dense than ice. Liquid water tends to form hydrogen bonded rings of three to seven molecules.

Liquid water is less dense than ice.

Which description best characterizes the length of a hydrogen bond between water molecules?

Longer than a covalent O-H bond, but shorter than the calculated van der Waals distance

Which of the following statements is not accurate when considering water and biological molecules? Non-polar substances associate with water to maximize their exposed surface area. Water can act as a hydrogen bond donor. Water can act as a hydrogen bond acceptor. Polar substances are soluble because of their interaction with water.

Non-polar substances associate with water to maximize their exposed surface area.

An amphiphilic molecule: Has neither polar nor non-polar groups. Has non-polar groups. Has polar groups. Has both polar and non-polar groups.

Has both polar and non-polar groups.

Which statement is NOT a reason for the centrality of water in biochemistry? Water and its ionic components participate in many biochemicalreactions. Water in oceans covers most of the surface of our planet. Water is oxidized to oxygen during photosynthesis. The medium for most biochemical reactions is water.

Water in oceans covers most of the surface of our planet.

Which of the following statements is not accurate when considering water and biological molecules? Polar substances are soluble because of their interaction with water. Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor. The hydrogen bonding pattern of water is disrupted by the presence of hydrophobic molecules

Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor.

Consider the transfer of benzene from water to pure benzene. Which statement is false? A.) The ∆H of transfer is about zero. B.)The ∆G of transfer is negative. C.) T∆S is positive. D.) The process is less favorable at higher temperature.

D Assuming that ∆S and ∆H do not change with temperature, higher temperatures will enhance the positive ∆S, making ∆G=∆H-T∆S even more negative and the process even more favorable at higher temperatures.

bond angle for water

104.5

What is the concentration of hydrogen ions at pH 3?

10^-3 M

What is the concentration of hydroxide ions at pH 10?

10^-4 M

What is the pH of 1 M NaOH?

14

The pK of acetic acid is 4.76. What is the effective buffering range?

3.76- 5.76

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

What is the pH of a solution made by mixing equal volumes of 1 M sodium acetate and 0.1 M acetic acid? (The pK of acetic acid is 4.76.)

5.76

The pK of ammonia is 9.25. What is the effective buffering range?

8.25- 10.25

Which radical (where radical means part of a molecule) shown cannot make a hydrogen bond to water?

CH3

Rank the following bond/interaction distances correctly in order from shortest to longest: Hydrogen bond, van der Waals interactions, covalent bond. Van der Waals interactions, covalent bond, hydrogen bond. Covalent bond, hydrogen bond, van der Waals interactions. Van der Waals interactions, hydrogen bond, covalent bond. Covalent bond, van der Waals interactions, hydrogen bond.

Covalent bond, hydrogen bond, van der Waals interactions.

Which statement is NOT an important aspect of the hydrophobic effect? Hydrophobic molecules have a strong affinity to interact with each other instead of water. The ∆H is near zero or positive when hydrophobic molecules are excluded from water. The larger the surface area of a hydrophobic molecule, the greater the loss of entropy by interacting solvent water. The entropy of water increases when hydrophobic molecules are excluded from water.

Hydrophobic molecules have a strong affinity to interact with each other instead of water.

Consider a solution separated from pure water by a semipermeable membrane that permits the passage of water, but not solutes. Which statement is false? Osmosis is the movement of solvent from a region of high solventconcentration to a solution of lower solvent concentration. 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. Osmotic pressure could be eliminated if enough solute were added to the region of pure water.

Osmotic pressure depends upon the size of the solute molecules.

Which of the following statements about the buffering system in blood in not true? 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. 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 most significant buffering compound in human blood is bicarbonate (HCO3-). 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.

Which of the following statements about water is FALSE? Water will act as a hydrogen bond acceptor with hydroxyl groups. Water carries a dipole because of the geometry of the two oxygen-hydrogen bonds. A network of electrostatic interactions exists between the molecules in water. Substances with polar functional groups are generally soluble in water. The hydrophobic effect is driven largely by the entropy of the non-polar substance.

The hydrophobic effect is driven largely by the entropy of the non-polar substance.

Which of the following statements about water is false? The hydrophobic effect results when solutes are unable to break hydrogen bonds between water molecules. 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. Water is a cohesive substance. Nonpolar substances decrease the entropy of water molecules.

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

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.

Consider a dialysis procedure in which an aqueous solution is separated from pure water by a membrane that is permeable to both water and solutes. Which statement is true?

The tendency of solutes to diffuse from a region of high concentration to a region of lower concentration is thermodynamically favored.

The pK of acetic acid is 4.76. Which statement is true at pH 5.0?

[A-] > [HA]

At the first horizontal inflection point in the titration curve of phosphoric acid, which statement is true?

[H3PO4] = [H2PO4-]

The pK of ammonia is 9.25. Which statement is true at pH 7.0?

[NH4+] > [NH3]