chapter 2

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Translational and thermal motion causes liquid water molecules to reorient approximately every 10–12 seconds. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

B

The 104.5° bond angle in the water molecule is the result of the of electron orbitals around oxygen. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

K

The polarity of the O–H bond is caused by the of oxygen relative to that of hydrogen. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

I

For the represented by D–H....A, the donor D is weakly acidic and the acceptor A is weakly basic. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

A Signup and view all the answers

Octane molecules dispersed in water tend to aggregate because that allows water molecules to be more . A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

F Signup and view all the answers

The insolubility of nonpolar molecules in water is due to the large , which is the result of water molecules forming an ordered network surrounding nonpolar molecules. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

H Signup and view all the answers

A strong acid is completely ionized in water, whereas a weak acid is A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

N Signup and view all the answers

Phosphate (pK = 2.15, pK = 6.82, and pK3 = 12.38) will be mostly in the HPO42– form at pH 1 7.2. At pH 5.82 it is mostly in the form. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

D Signup and view all the answers

A solution containing a weak acid (pK = 7.5) and its conjugate base at pH of 8.5 has a good capacity to buffer the addition of A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

L Signup and view all the answers

A phosphate buffer solution at pH = pK = 2.15 would have equal amounts of phosphate in 1 the form and the H PO 2 – form.4 A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

C Signup and view all the answers

Rank the following interactions in order of increasing strength (start with the weakest interaction).

London dispersion forces, hydrogen bonds, ionic interactions, covalent bonds Signup and view all the answers

The strongest noncovalent interactions are

ionic interactions. Signup and view all the answers

Hydrogen bonds within liquid water

are dipole-dipole attractions. Signup and view all the answers

Urea is a water-soluble product of nitrogen metabolism. How many hydrogen bonds can one urea molecule donate to surrounding water molecules?

4 Signup and view all the answers

Methanol can act both as a H-bond donor and as a H-bond acceptor. What is the maximal number of H-bonds a single molecule of methanol can form with surrounding water molecules.

3 Signup and view all the answers

In a hydrogen bond between a water molecule and another biomolecule

the 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. Signup and view all the answers

Which of the following statements about water is not true?

It can form two hydrogen bonds per water molecule. Signup and view all the answers

Which of the following statements about water is not true?

Water is a nonpolar molecule that with a bent molecular geometry. Signup and view all the answers

Which of the following statements about water is incorrect?

Cations are solvated by shells of water molecules oriented with their hydrogen atoms pointed toward the ions. Signup and view all the answers

Which of the following statements about water is incorrect?

It is a small, polar molecule with a low dielectric constant. Signup and view all the answers

Ice

All of the statements above are true. Signup and view all the answers

Covalent C─C and C─H bonds have bond strengths that are approximately times higher than those of H-bonds.

20 Signup and view all the answers

The boiling point of water is 264°C higher than the boiling point of methane because

water molecules are connected to each other by H-bonds. Signup and view all the answers

is exceptionally soluble in water due to the formation of hydrogen bonds.

Ethanol Signup and view all the answers

Molecules such as methanol and ethanol are very soluble in water because

they contain O─H groups that can form multiple H-bonds with water. Signup and view all the answers

Hydrophobic interactions between nonpolar molecules

require the presence of surrounding water molecules. Signup and view all the answers

Fatty acids such as palmitate and oleate are usually characterized as

amphiphilic. Signup and view all the answers

Amphiphilic molecules

have both hydrophilic and hydrophobic groups. Signup and view all the answers

Which of the following statements about hydrophobic interactions is not true?

They are caused by hydrophobic molecules interacting strongly with each other. Signup and view all the answers

Which of the following is the best explanation for the hydrophobic effect?

It is an entropic effect, caused by the desire of water molecules to increase their entropy by excluding hydrophobic groups, which they must otherwise surround with highly ordered structures. Signup and view all the answers

In the energetics of transferring hydrocarbons from water to nonpolar solvents, the factor TS is commonly

positive. Signup and view all the answers

Globules of up to several thousand amphiphilic molecules arranged with the hydrophilic groups on the surface and the hydrophobic groups buried in the center that form in water are called

micelles. Signup and view all the answers

Sheets composed of two layers of amphipathic molecules arranged with the hydrophilic groups on the surface and the hydrophobic groups buried in the center that form in water are called

bilayer membranes. Signup and view all the answers

Physical properties that depend on the amounts of various species, rather than the identities of those species, are called

colligative properties. Signup and view all the answers

Osmotic pressure is a function of

solute concentration. Signup and view all the answers

K , the ionization constant of water, is. at

10–14; 25°C Signup and view all the answers

Weak acids

are only partially ionized in an aqueous solution. Signup and view all the answers

A solution is made by mixing 0.05 mL of 1.0 M HCl with 999.95 mL of pure water. Calculate the pH of the resulting solution (assume the total volume is 1.0 L).

4.3 Signup and view all the answers

The pH of coffee is 5.6. The pH of grapefruit juice is 2.6. This means that the proton concentration in coffee is

a thousand times lower than in grapefruit juice. Signup and view all the answers

A solution is made by mixing 1.0 mL of 1.0 M acetic acid (pK = 4.76, K = 1.74 x 10–5 ) a with one 999 mL of pure water. Calculate the pH of the resulting solution (assume the total volume is 1.0 L).

3.9 Signup and view all the answers

You mix 999 mL pure water and 1 mL of 2.0 M NaOH. Calculate the pH of the resulting solution. (assume the total volume is 1.0 L).

11.3 Signup and view all the answers

The pH of a 0.1 M solution of sodium acetate would be

basic, because of the acetate ion reacts with water to form acetic acid and OH . Signup and view all the answers

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?

HPO4 Signup and view all the answers

To make a phosphate buffer at pH 6.82 starting with one liter of 10 mM phosphoric acid (pKs are 2.15, 6.82, and 12.38), you could add

You can't make a buffer by adding HCl or KOH. Signup and view all the answers

You mix equal volumes of 0.05 M NaH PO and 0.05 M Na HPO (pK's for phosphoric acid 24 are 2.15, 6.82 and 12.38). Which of the following best describes the resulting solution?

pH 6.82 and well buffered Signup and view all the answers

To make an acetate buffer at pH 4.76 starting with 500 mL of 0.1 M sodium acetate (pK acetic acid = 4.76), you could add

0.025 mol of HCl. Signup and view all the answers

The pK of citric acid is 3.09. What is the citric acid : monosodium citrate ratio in a 1.0 M 1 citric acid solution with a pH of 2.09?

10:1 Signup and view all the answers

The pKs of succinic acid are 4.21 and 5.64. How many grams of monosodium succinate (FW = 140 g/mol) and disodium succinate (FW = 162 g/mol) must be added to 1 L of water to produce a solution with a pH 5.28 and a total solute concentration of 100 mM? (Assume the total volume remains 1 liter, answer in grams monosodium succinate, grams disodium succinate, respectively.)

9.7 g, 4.9 g Signup and view all the answers

What is the approximate pK of a weak acid HA if a solution 0.1 M HA and 0.3 M A– has a a pH of 6.5?

6.0 Signup and view all the answers

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 (K 1.78 × 10−4) Signup and view all the answers

The pH at the midpoint in the titration of an acid with a base is

equal to the pK of the corresponding acid. Signup and view all the answers

The capacity of a buffer to resist changes in pH upon addition of protons or hydroxide ions depends on

all of the above Signup and view all the answers

The pH of blood is affected by

all of the above Signup and view all the answers

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Questions and Answers

The polarity of the O–H bond is caused by the of oxygen relative to that of hydrogen. A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

A strong acid is completely ionized in water, whereas a weak acid is A)hydrogen bond B)rotational C)H3PO4 D)H2PO4 E)HPO4 F)disordered G)positive entropy H)negative entropy I)higher electronegativity J)insoluble K)tetrahedral arrangement L)acid M)base N) only partially ionized

Rank the following interactions in order of increasing strength (start with the weakest interaction).

The strongest noncovalent interactions are

Hydrogen bonds within liquid water

Urea is a water-soluble product of nitrogen metabolism. How many hydrogen bonds can one urea molecule donate to surrounding water molecules?

Methanol can act both as a H-bond donor and as a H-bond acceptor. What is the maximal number of H-bonds a single molecule of methanol can form with surrounding water molecules.

In a hydrogen bond between a water molecule and another biomolecule

Which of the following statements about water is not true?

Which of the following statements about water is not true?

Which of the following statements about water is incorrect?

Which of the following statements about water is incorrect?

Ice

Covalent C─C and C─H bonds have bond strengths that are approximately times higher than those of H-bonds.

The boiling point of water is 264°C higher than the boiling point of methane because

is exceptionally soluble in water due to the formation of hydrogen bonds.

Molecules such as methanol and ethanol are very soluble in water because

Hydrophobic interactions between nonpolar molecules

Fatty acids such as palmitate and oleate are usually characterized as

Amphiphilic molecules

Which of the following statements about hydrophobic interactions is not true?

Which of the following is the best explanation for the hydrophobic effect?

In the energetics of transferring hydrocarbons from water to nonpolar solvents, the factor TS is commonly

Globules of up to several thousand amphiphilic molecules arranged with the hydrophilic groups on the surface and the hydrophobic groups buried in the center that form in water are called

Sheets composed of two layers of amphipathic molecules arranged with the hydrophilic groups on the surface and the hydrophobic groups buried in the center that form in water are called

Physical properties that depend on the amounts of various species, rather than the identities of those species, are called

Osmotic pressure is a function of

K , the ionization constant of water, is. at

Weak acids

A solution is made by mixing 0.05 mL of 1.0 M HCl with 999.95 mL of pure water. Calculate the pH of the resulting solution (assume the total volume is 1.0 L).

The pH of coffee is 5.6. The pH of grapefruit juice is 2.6. This means that the proton concentration in coffee is

A solution is made by mixing 1.0 mL of 1.0 M acetic acid (pK = 4.76, K = 1.74 x 10–5 ) a with one 999 mL of pure water. Calculate the pH of the resulting solution (assume the total volume is 1.0 L).

You mix 999 mL pure water and 1 mL of 2.0 M NaOH. Calculate the pH of the resulting solution. (assume the total volume is 1.0 L).

The pH of a 0.1 M solution of sodium acetate would be

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?

To make a phosphate buffer at pH 6.82 starting with one liter of 10 mM phosphoric acid (pKs are 2.15, 6.82, and 12.38), you could add

You mix equal volumes of 0.05 M NaH PO and 0.05 M Na HPO (pK's for phosphoric acid 24 are 2.15, 6.82 and 12.38). Which of the following best describes the resulting solution?

To make an acetate buffer at pH 4.76 starting with 500 mL of 0.1 M sodium acetate (pK acetic acid = 4.76), you could add

The pK of citric acid is 3.09. What is the citric acid : monosodium citrate ratio in a 1.0 M 1 citric acid solution with a pH of 2.09?

What is the approximate pK of a weak acid HA if a solution 0.1 M HA and 0.3 M A– has a a pH of 6.5?

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?

The pH at the midpoint in the titration of an acid with a base is

The capacity of a buffer to resist changes in pH upon addition of protons or hydroxide ions depends on

The pH of blood is affected by

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