Ch 14: Solutions

Question 1

A solution is a __________ mixture of two or more substances or components. The majority component is the _______, (or the one added “in excess”) and the minority component is the ______.

Answer 1

homogeneous
solvent
solute

p. 580

Question 2

How does seawater dehydrate you if you drink it?

Answer 2

As the seawater passes through the body, is causes a flow of “solvent”, or water, out of the body’s cells into the seawater. In this way, the two solutions become more similar in concentration. The accumulation of extra fluid in the intestines then causes diarrhea. The decrease in intracellular fluid volume causes dehydration.

p. 581

Question 3

Is club soda considered a solution?

Answer 3

Yes! An aqueous solution can be water plus any solid, liquid, or gas that distributes homogeneously.

Question 4

Solutions themselves can be gaseous, liquid, or solid. Name 3 examples - one of each of these.

Answer 4

Gaseous: Air is made of mostly nitrogen and oxygen
Liquid: Vodka is ethanol and water
Solid: Brass is an alloy made of copper and zinc

p. 581

Question 5

Why does water alone not remove grease from your hands?

Answer 5

Grease is insoluble in water, but is soluble is something like paint thinner.

Question 6

Two particles with opposite charges move toward each other because their _______ ______ decreases as their separation decreases according to Coulomb’s law. However, the formation of a solution, DOES NOT necessarily lower the potential energy of its constituent particles. For example, mixing neon and argon together, they behave as ideal gases and do not interact with each other in any way. (i.e. There are no significant intermolecular forces between their particles.)

Answer 6

potential energy

p. 582

Question 7

Define entropy.

Answer 7

A measure of energy randomization or energy dispersal in a system.

p. 582

Question 8

The pervasive tendency for energy to spread out, or disperse, whenever it is not restrained from doing so is the reason that two ideal gases mix. We can see this most clearly in the example of _______ energy.

Answer 8

thermal

Question 9

Which statement is true?

a. Ideal gases mix because mixing decreases their potential energy.
b. Ideal gases mix because mixing increases their potential energy.
c. Ideal gases mix because mixing decreases their entropy.
d. Ideal gases mix because mixing increases their entropy.

Answer 9

d. When gases mix, the kinetic energy of each gas is spread out over more space, so entropy increases.

Question 10

A solution always forms if the _______-_______ interactions are comparable to, or stronger than, the solvent-solvent interactions and the solute-solute interactions.

Answer 10

solvent-solute

p. 583

Question 11

What does miscible mean?

Answer 11

Soluble in each other in all proportions.

p. 583

Question 12

Even if the solvent-solute interactions are weak, a solution can still sometimes form. When the disparity is small, the tendency to ___ results in the formation of a solution even though the process is energetically uphill.

Answer 12

mix

Question 13

Separating a solute into its constituent particles is always an ___________ process (ΔH is _), because energy is required to overcome the forces that hold the solute particles together.

Similarly, separating solvent particles is also always __________ for the same reason.

Answer 13

endothermic
ΔH is +

endothermic

p. 586

Question 14

The ΔH of mixing is always __________ (ΔH is _) because energy is released as the solute particles interact (through intermolecular forces) with the solvent particles.

Answer 14

exothermic
ΔH is -

p. 586

Question 15

ΔH_soln = ΔH_solute + ΔH_solvent + ΔH_mix

(+) (+) (-)

Question 16

What is the heat of hydration? (ΔH_hydration)

Answer 16

ΔH_solvent and ΔH_mix

In aqueous solutions where an ionic compound is dissolved in water, the terms above can be combined into a single term called the heat of hydration.

Question 17

Because the ion-dipole interactions that occur between a dissolved ion and the surrounding water molecules are much ________ than the hydrogen bonds in water, ΔH_hydration is always largely negative (exothermic) for ionic compounds.

Answer 17

stronger

Question 18

What is lattice energy?

Answer 18

The energy associated with the formation of a crystalline lattice of alternating cations and anions from the gaseous ions. Because the cations are + and the anions are -, the potential energy decreases–as prescribed by Coulomb’s law–when these ions come together to form a lattice. That energy is emitted as heat when the lattice forms. The most straightforward way calculate lattice energy is with the Born-Haber cycle.

p. 398 (borrowed from Ch 10); move this card to that deck if we cover Ch 10.

Question 19

For ionic compounds, the ΔH_solute is = -ΔH_lattice

Question 20

The definition of molarity (M) is…

Answer 20

….the amount of solute (in mol) divided by

the volume of solution (in L)

p. 595

Question 21

The definition of molality (m) is…

Answer 21

…the amount of solute (in mol) divided by

the MASS of solvent (in kg)

Question 22

The definition of mole fraction (χ) is…

Answer 22

…the amount of solute (in mol) divided by

the TOTAL amount of solute AND solvent (in mol)

Can also be expressed as a percent. Neither mole fraction nor mole percent has any units.

Question 23

The definition of parts by mass is….

Answer 23

….mass solute divided by

mass solution

may be multiplied by a certain factor.

If percent by mass, multiply by 100.

If parts per million (ppm), multiply by 10⁶

If parts per billion (ppb), multiply by 10⁹

Question 24

The definition of parts by volume is….

Answer 24

….the volume of solute divided by

the volume of solution

may be multiplied by a multiplication factor, just like parts by mass

p. 595

Question 25

The solubility “rules” of solids and gases in liquid are different. The solubility of most solids in water ________ with increasing temperature.

In contrast, the solubility of gases in water ________ with increasing temperature.

Answer 25

increases

decrease

p. 591

Question 26

Increasing pressure of a gas ________ its solubility in a liquid.

Answer 26

increases

p. 592

Question 27

What equation quantifies the solubility of gases with increasing pressure?

Answer 27

Henry’s law

S_gas = k_HP_gas

S_gas (units: M); k_H (units: M/atm); P_gas (units: atm)

p. 593

Question 28

Salt ______ the temperature at which a saltwater solution freezes.

Answer 28

lowers

Question 29

What is a colligative property?

Answer 29

A property that depends on the number of particles dissolved in solution, not on the type of particle.

p. 601

Question 30

We can quantify the vapor pressure of a solution with Raoult’s law:

Answer 30

• P_solution = χ_solvent P* °_solvent
• P*_solution is the vapor pressure of the solution.
• χ*_solvent is the mole fraction of the solvent
• P* °_solvent is the vapor pressure of the pure solvent at the same temperature
  p. 603

Question 31

Non-ideal solutions do not follow Raoult’s law. If an experimentally measured pressure is lower than the calculated (ideal) pressure, you can conclude that solute-solvent interactions are ________ than solute-solute interactions and the solvent-solvent interactions.

Answer 31

stronger

Question 32

Name the 4 colligative properties.

Answer 32

(1) vapor pressure lowering
(2) boiling point elevation
(3) freezing point depression
(4) osmotic pressure

Question 33

With nonvolatile solutes, the vapor pressure of the solution depends only on….

Answer 33

…..the solvent. Therefore P_solution = P_solvent

Question 34

If an experimentally measured pressure is higher than the calculated (ideal) pressure, you can conclude that solute-solvent interactions are ________ than solute-solute interactions and the solvent-solvent interactions.

Answer 34

weaker

Question 35

What does w/v% mean?

(Explain example of 5% m/v solution

Answer 35

It is the mass of solute (in grams)

divided by

the volume of solution (in mL)

A 5% m/v solution would have 5 g of solute in 100 mL of solution