Solutions

SolutionsContributions by:

John L. Falconer & Will MedlinDepartment of Chemical and Biological Engineering

University of ColoradoBoulder, CO 80309-0424

Supported by the National Science Foundation

Phase a and b each contain component A. The two phases are not in equilibrium. The direction of mass transport of component A is ________.

A. from a to b

B. from b to a

C. Cannot tell from this information.

D. No mass transfer occurs.

CA=0.001

CA=0.020

a

b

Phase a and b each contain component A. The two phases are not in equilibrium. What is the direction of mass transport of component A?

A. From a to b

B. From b to a

C. Cannot tell from this information

D. No mass transfer occurs

CA=0.005 mol/L

CA=0.100 mol/L

a

b

Consider two immiscible mixtures. The concentration of A is much greater in the bottom solution. The direction of mass transfer of component A is _________.

A. into mixture 1

B. into mixture 2

C. Could be in either direction.

D. No mass transfer occurs.

CA=0.001

CA=0.200

Mixture 1

Mixture 2

The concentration of A is different in two liquids that do not mix. What determines the direction of mass transfer of component A?

A. Concentration

B. Pressure

C. Solubility

D. Energy

E. Other

A in B

A in C

Phases a and b are comprised of component A. The two phases are not in equilibrium. If the system is at constant temperature, which phase has the higher fugacity?

A. Phase a

B. Phase b

C. Both phases have same fugacity

D. Not enough information

CA=0.01 mol/L

CA=0.50 mol/L

a

b

Two liquid phases are in equilibrium at 2 bar. The bottom liquid is pure A; the top liquid is a mixture of A and B with xA = 0.05. If PA

sat = 0.5 bar, PBsat = 0.8 bar,

the fugacity of liquid A in the mixture is _____ bar.

A. 1.0

B. 0.8

C. 0.5

D. 0.1

E. 0.05

Mixtureof

A & BxA=0.05

Liquid A

Compounds A and B do not mix, and compound B is more dense. This figure shows the situation immediately after the 3 mol% C in A was added on top of the 4 mol% C in B solution. Over time, compound C will _________.

A. move from liquid A to liquid B

B. move from liquid B to liquid A

C. remains as they are since A & B are immiscible

3 mol%C in AgC = 2

4 mol%C in BgC = 1.1

This system is not in equilibrium. Which happens to reach equilibrium?

A. Liquid evaporates

B. Vapor condenses

C. Cannot predict without more information

Vapor

C1= 0.25 kg/m3

Water

C1= 975 kg/m3

75°C

For the system below, which only contains component A, what will happen next?

A. Some vapor will condense

B. All the liquid will vaporize

C. All the vapor will condense

D. Some liquid will vaporize

LiquidfALiq =

0.6 bar

VaporfAGas =

0.4 bar

These tubes, with an aqueous BSA* solution on theleft and pure water on the right are at equilibrium.When you add salt to the pure water on the right, __________________.

A. the water level on the right increases

B. the BSA solution level on the left increases

C. no change in the levels occur

*BSA= bovine serum albumin proteinH2O permeable

membrane

Aqueous BSA

Pure water

An aqueous BSA* solution on the leftleft and pure water on the right are at equilibrium.When you add more BSA to the solution on the left, ___________________.

A. the water level on the right increases

B. the BSA solution level on the left increases

C. no change in levels occur

*BSA= bovine serum albumin proteinH2O permeable

membrane

Aqueous BSA

Pure water

*BSA= bovine serum albumin protein

These tubes each have an aqueous BSA* solution onthe left and pure water on the right. A membrane thatis only permeable to water separates the two sides.Which one is at equilibrium?

A B C D

H2OH2O + BSA

H2OH2O + BSA

H2OH2O + BSA

H2OH2O + BSA

Which component (A or B) has the higher molecule weight? Neither A nor B dissociates.

A. A

B. B

C. They are the same

D. Need more information

H2O permeablemembrane

H2O permeablemembrane

H2O+

10 g A

H2O

H2O+

10 g B

H2O

Which component (A or B) has the higher molecule weight? Neither A nor B dissociates.

A. A

B. B

C. They are the same

D. Need more information

H2O permeablemembrane

H2O permeablemembrane

H2O+

10g A

H2O

H2O+

20g B

H2O

A container with water and NaCl is boiling at 105°C on a stove. The amount of NaCl in the water is half of the maximum amount of salt that can dissolve. Which is the correct plot of the chemical potential of the liquid water versus time as the water boils away to 10% of its initial volume.

μ(l)

Time Time Time Time

A B C D

E. None of the above.

Liquids A and B are immiscible. When each liquid is present, it exerts its own vapor pressure. A vapor contains a mixture of A and B at low pressure. The pressure is increased at constant temperature. At 4 bar, liquid A appears; At 6 bar, liquid B appears.Which is the correct plot of the partial pressures of A and B vs. total pressure?

0 2 4 6

2

4

8

08

Pressure (bar)

6

0 2 4 6

2

4

8

08

Pressure (bar)

6B C

0 2 4 6

2

4

8

08

P i (b

ar)

Pressure (bar)

6A

Components A and B are immiscible. When each liquid is present, it exerts its own vapor pressure. A vapor contains 5 mol A and 5 mol B at low pressure. The pressure is increased at constant temperature. At 4 bar, liquid A appears; At 6 bar, liquid B appears.Which is the correct plot of the partial pressures of A and B vs. total pressure?

0 2 4 6

2

4

8

08

Pressure (bar)

6

0 2 4 6

2

4

8

08

Pressure (bar)

6B C

0 2 4 6

2

4

8

08

P i (b

ar)

Pressure (bar)

6A

When component A is mixed with component B, the activity coefficient of component A is greater than one for all mixtures. When component A is mixed with component C, the activity coefficient of component A is less than one for all mixtures. Which plot is closest for the fugacity of A vs. the mole fraction of A for A-B mixtures (red) and for A-C mixtures (blue)?

f A (b

ar)

A C DB

mole fraction xAmole fraction xA mole fraction xA mole fraction xA

When component A is mixed with component B, the activity coefficient of component A is greater than one for all mixtures. When component A is mixed with component C, the activity coefficient of component A is less than one for all mixtures. Which plot is closest for the fugacity of A vs. the mole fraction of A for A-B mixtures (red) and for A-C mixtures (blue)?

f A (b

ar)

mole fraction xA

A B C D

mole fraction xA mole fraction xA mole fraction xA

A liquid containing 60 mol% salt and 40 mol% wateris in equilibrium with water vapor at 0.5 atm. Which species has the higher fugacity in the liquid?

A. Salt

B. Water

C. Their fugacities are equal

D. Need more information

Sugar was dissolved in hot tea until it was saturated. When the tea was cooled, the solution was supersaturated with sugar and not at equilibrium. The chemical potential of the sugar in the solution is _____________ solid sugar at the same temperature .

A. higher than

B. lower than

C. the same as

D. Insufficient information.

Sugar was added to pure water until the water was saturated and the excess sugar settled to the bottom of the container. If the reference state for sugar is solid sugar at 1 bar, the activity of the dissolved sugar is ______________.

A. Zero

B. The mole fraction of sugar in water

C. < 0.1

D. 1.0

E. None of the above

A liquid mixture that is 25% A and 75% B is in equilibrium with an ideal gas at 1 bar that is 60% A and 40% B. The chemical potential of component A is ___________ component B in the liquid phase.

A. greater than

B. less than

C. the same as

If you add salt to water, what happens to the fugacity of the water?

A. It increases

B. It decreases

C. It remains the same

When 10 mL of liquid water and 10 mL of liquid ethanol are mixed, the resulting solution has a volume of about 19 mL. Heat is also released during the mixing process. Which of the following statements is true?

A. Water and ethanol form an ideal solution

B. Water and ethanol are immiscible (i.e. separate into two layers)

C. Water and ethanol repel each other in liquid mixtures

D. Water and ethanol experience attractive interactions

Water and ethanol form an azeotrope at approximately 90% ethanol. From a 50/50 mixture of water-ethanol, which is currently below its bubble T, your aim is to produce a phase containing 95% ethanol. What can you do?

A. Heat up the mixture to the bubble T

B. Heat up the mixture to the dew T

C. Heat up the mixture to a very high T (above the dew T)

D. None of the above

Mixing two liquid compounds results in a decrease in the total Gibbs free energy of the system. Which of the following MUST be true?

A. The solution is not ideal

B. The two components attract each other

C. The enthalpy of mixing is negative

D. None of the above

For a 50/50 binary mixture, the activity coefficients in a modified Raoult’s law model of each component will be closest to ____________.

A. one as the solution is more ideal

B. one if the two components attract each other strongly

C. zero if the components repel each other

Consider a 95/5 mixture of the acetone(1) ‐ acetic acid(2) system. Which component will have an activity coefficient closer to 1?

A. Acetone

B. Acetic acid

C. Both should be close to 1.

Which of the following statements is true?For an ideal solution, __________.

A. ΔHmix = 0 but HE > 0

B. ΔGmix = 0 but GE > 0

C. ΔSmix > 0 but SE = 0

D. ΔGmix < 0 but GE = 0

E. Answers C and D

When 1 mol ethylamine and 1 mol acetylacetone are mixed adiabatically, starting at 15°C, the mixture would be __________ 15oC. The excess enthalpy plot is shown in the figure.

A. greater than

B. less than

C. equal to

D. Depends on SE

0 0.25 0.5 0.75

0.10

0.15

0.30

0.001

HE

x1

0.20

0.25

0.05

Which curve is for component 1 of a binary mixture?

A. A B. B C. A or B

0 0.25 0.5 0.75

1.8

2.6

1.01

Act

ivity

coe

ffici

ents

x1

2.2

1.4

AB

A B C

D E

Which is the correct plot of Helmholtz free energy vs. the mole fraction for a binary, ideal liquid solution at constant temperature?

yi

A

yi

A

yi

A

yi

A

yi

A

As the mole fraction of a species in an ideal solution approaches one, its partial molar Gibbs free energy ____________.

A. increases

B. decreases

C. remains the same

D. depends on the mole fraction

As the mole fraction of a species in an ideal solution approaches one, its partial molar entropy _______.

A. increases

B. decreases

C. remains the same

Which statement is most likely correct if molecule 1 is represented by blue and molecule by red?

A = 1B = 2

A. a22 = a11

B. a21 > a12

C. a12 > a22 & a12 > a11

D. a12 < (a11a22)½

E. a12 = a11a22