Final exam

Question 1

How strong are hydrogen bonds? How do they compare to covalent bonds?

Answer 1

They are strong intermolecular forces but weak in comparison to covalent bonds

Question 2

Are hydrogen bonds actually bonds?

Answer 2

No, they are intermolecular forces

Question 3

How does the distance between donor and acceptor (in a hydrogen bond) affect the energies associated with the force of attraction?

Answer 3

As the distance increases, the force of attraction decreases

Question 4

Based on Coulomb’s Law, why are ion-dipole forces of attraction stronger than dipole-dipole forces?

Answer 4

The charge is greater in ion-dipole interactions: a true charge interacts with a partial charge, yielding a greater force

Question 5

When thinking about forces of attraction, does the solvent matter? Why or why not?

Answer 5

Yes, because the solvent can influence the force of attraction

Question 6

The influence of the solvent on the forces of attraction/repulsion between charges is corrected for by the _______________ ____________.

Answer 6

Dielectric constant

Question 7

What does water having a dielectric constant of around 80 really mean?

Answer 7

As the dielectric constant increases, the force of attraction decreases between charged species; water will sheild the positive and negative charges from each other; this means that water shields charges from one another 80 times more than does a vacuum

Question 8

What trends are noticeable regarding dielectric constants?

Answer 8

Polar substances have higher dielectric constants; nonpolar substances have lower dielectric constants

Question 9

Considering the overall trend regarding dielectric constants, is the force of attraction between potassium ions and chloride ions greater in water or benzene?

Answer 9

Benzene

Question 10

How does the dielectric constant relate to solublity?

Answer 10

Charged species are less soluble in solvents with low dielectric constants; charged species are more soluble in solvents with high dielectric constants

Question 11

How many hydrogen bonds can water form with itself in liquid form? Solid form?

Answer 11

4 hydrogen bonds

3 - 4 hydrogen bonds

Question 12

How would you describe the behavior of pure liquid water?

Answer 12

Rapidly fluctuating hydrogen-bonded network that reorients on the order of picoseconds with approximately 3.4 bonds hydrogen bonds per water molecule and three to five water-member rings

Question 13

What is different about the water molecules that surround a solute (i.e., waters of hydration)?

Answer 13

Waters around a solute are more constrained; they form a cage-like structure around the solute in an attempt to maximize hydrogen bonding; this means that waters farther away from the solute are freer

Question 14

What thermodynamic quantitiy determines if a process or reaction is spontaneous?

Answer 14

Gibbs Free Energy

A negative G means a reaction is spontaneous

Question 15

What do H and S mean in thermodynamics?

Answer 15

H refers to enthalpy change

S refers to entropy

Question 16

Enthalpy is the driving force of a reaction when its value is _______________; entropy is the driving force of a reaction when its value is ________________.

Answer 16

Negative

Positive

Question 17

The enthalpy change for placing a nonpolar solute in water is often positive (endothermic) and the entropy change is negative. What can you say about the energetics of placing a nonpolar solute in water? What happens when many nonpolar particles are placed in water?

Answer 17

Nonpolar solutes aggregate with one another in a process called the hydrophobic effect; however, this is not the driving force for aggregation. As solutes are added, the surface area of the aggregation increases, which decreases the number of water molecules in the caged-like network around the aggregation. This means that water molecules are released into the bulk and increase in entropy as they are less constrained. Entropy of water molecules is the driving force for the hydrophobic effect.

Question 18

What happens when a substance like sodium dodecyl sulfate is placed in water?

Answer 18

A water cage will form around the nonpolar, hydrophobic tail

Water will solvate the polar, hydrophilic tail

Question 19

When a collection of sodium dodecyl sulfate particles are placed in water, what happens (e.g., polar head, nonpolar tail)?

Answer 19

The particles aggregate into a micelle, a spherical aggregate

Question 20

What is the driving force for the formation of micelles?

Answer 20

Increased entropy

Question 21

What structure would form if SDS was placed in a nonpolar solvent?

Answer 21

A reverse micelle

Question 22

What if you consider a collection of molecules like the one shown below places in aqueous solution?

Answer 22

A bilayer or vesicle/liposome will form

Question 23

What factors dictate when a micelle or vesicle will form?

Answer 23

The number of nonpolar tails present:

When one hydrophobic tail is present, a micelle will form

When two hydrophobic tails are present, a bilayer or vesicle will form

Question 24

Calculate the amount of H⁺ in blood if the pH is 7.4.

Answer 24

[H⁺] = 10^-pH

pH = - log [H⁺]

[H⁺] = 10^-7.4

= 4.0 x 10^-8 H⁺ ions

Question 25

A 10-fold change in the concentration of H+ inside the cell results in a change of _________ pH unit.

Answer 25

1

Question 26

Stronger acids have higher ______ but lower _____.

Answer 26

Ka

pKa

Question 27

What components make up a buffer?

Answer 27

A weak acid and its conjugate base or a weak base and its conjugate acid

Question 28

On a titration curve, the pH equals the pKa at ________ of the equivalence volume.

Answer 28

One half

Question 29

Is there a point in a titration where a buffer exists? If yes, how is it determined?

Answer 29

Yes, the buffering region is the pH range +/- 1 pKa

(e.g., if pKa is 3, the buffering region is pH levels between 2 and 4)

Question 30

Be very familiar with reading a titration curve.