Deck 11: Properties of Solutions

Question 1

Calculate the molality of C₂H₅OH in a water solution that is prepared by mixing 50.0 mL of C₂H₅OH with 112.7 mL of H₂O at 20°C.The density of the C₂H₅OH is 0.789 g/mL at 20°C.(Assume the density of water at this temperature is 1.00 g/mL. )

A)0.00963 m
B)0.155 m
C)0.132 m
D)7.60 m
E)9.63 m

Answer 1

7.60 m

Question 2

The term "proof" is defined as twice the percent by volume of pure ethanol in solution.Thus,a solution that is 95% (by volume)ethanol is 190 proof.What is the molarity of ethanol in a 92 proof ethanol/water solution? density of ethanol
= 0.80 g/cm³
Density of water
= 1.0 g/cm³
Mol.wt.of ethanol
= 46 g/mol

A)0.46 M
B)0.80 M
C)0.92 M
D)8.0 M
E)17 M

Answer 2

8.0 M

Question 3

What is the mole percent of ethanol (C₂H₅OH),which consists of 71.0 g of ethanol for every 16.7 g of water present?

A)62.4%
B)1.66%
C)9.23%
D)81.0%
E)37.6%

Answer 3

62.4%

Question 4

What is the molality of a solution of 30.1 g of propanol (CH₃CH₂CH₂OH)in 152 mL water,if the density of water is 1.00 g/mL?

A)3.29 m
B)0.00330 m
C)0.303 m
D)0.501 m
E)5.01 m

Question 5

Calculate the mole fraction of NaCl in a solution prepared by dissolving 117 g NaCl in 1.15 kg H₂O.

A)9.90 $\times$ 10^-1
B)1.11 $\times$ 10^-2
C)6.08 $\times$ 10^-2
D)1.52 $\times$ 10^-2
E)3.04 $\times$ 10^-2

Question 6

Find the mass percent of CaCl₂ in a solution whose molarity is 2.20 M and whose density is 1.18 g/mL.

A)20.7%
B)26.1%
C)79.3%
D)24.4%
E)none of these

Question 7

A 20.0-g sample of methyl alcohol (CH₃OH,molar mass = 32.04 g/mol)was dissolved in 43.3 g of water.The mole fraction of CH₃OH is:

A)0.260
B)0.624
C)0.316
D)4.85
E)0.206

Question 8

A solution containing 306.5 g of Mg(NO₃)₂ per liter has a density of 1.114 g/mL.The molarity of the solution is:

A)2.066 M
B)1.855 M
C)6.199 M
D)2.302 M
E)none of these

Question 9

A 3.140 molal solution of NaCl is prepared.How many grams of NaCl are present in a sample containing 2.314 kg of water?

A)726.6 g
B)124.3 g
C)257.6 g
D)424.6 g
E)none of these

Question 10

If 2.00 g of helium gas and 3.82 g of oxygen gas are mixed together,what is the mole fraction of helium in the solution?

A)0.344
B)0.193
C)0.807
D)0.119
E)1.24

Question 11

How many molecules of sucrose (table sugar),C₁₂H₂₂O₁₁,dissolved in 450.0 g of water are needed to make a 1.81 m solution?

A)4.90 $\times$ 10²³ molecules
B)8.15 $\times$ 10²³ molecules
C)2.42 $\times$ 10²⁴ molecules
D)2.72 $\times$ 10²⁵ molecules
E)1.50 $\times$ 10²³ molecules

Question 12

How many milliliters of 15.7 M H₂SO₄ are needed to prepare 600.0 mL of 0.10 M H₂SO₄?

A)0.26 mL
B)94 mL
C)3.8 mL
D)1.9 mL
E)4.8 mL

Question 13

Which of the following concentration measures will change in value as the temperature of a solution changes?

A)mass percent
B)mole fraction
C)molality
D)molarity
E)all of these

Question 14

A solution of hydrogen peroxide is 23.6% H₂O₂ by mass and has a density of 1.11 g/cm³.The molarity of the solution is:

A)7.23 M
B)0.262 M
C)7.70 M
D)8.03 M
E)none of these

Question 15

A solution containing 292 g of Mg(NO₃)₂ per liter has a density of 1.108 g/mL.The molality of the solution is:

A)2.00 m
B)2.41 m
C)1.77 m
D)6.39 m
E)none of these

Question 16

Determine the molarity of a solution containing 6.76 g BaCl₂ in 750.0 mL of solution.

A)3.25 $\times$ 10^-2 M
B)2.44 $\times$ 10^-2 M
C)9.01 $\times$ 10^-3 M
D)4.33 $\times$ 10^-2 M
E)9.01 M

Question 17

In a 0.1 molar solution of NaCl in water,which one of the following will be closest to 0.1?

A)The mole fraction of NaCl.
B)The mass fraction of NaCl.
C)The mass percent of NaCl.
D)The molality of NaCl.
E)All of these are about 0.1.

Question 18

For an acid-base reaction,1 M Al(OH)₃ has a normality of 3 N.This is best explained because:

A)The equivalent mass is three times the molar mass.
B)Each mole contains 3 moles of hydroxide ions that can react with 3 moles of hydrated protons.
C)The mole fraction is equal to 3 when aluminum hydroxide is mixed with water.
D)The normality is always three times stronger than the concentration of a solution.
E)At least two of the above statements are correct.

Question 19

Find the mass percent of CuSO₄ in a solution whose density is 1.30 g/mL and whose molarity is 1.36 M.

A)83.3%
B)1.77%
C)16.7%
D)2.66%
E)none of these

Question 20

What volume of a 0.771 M solution of CaCl₂ contains 1.28 g of solute?

A)66.8 mL
B)15.0 mL
C)1.66 mL
D)8.89 mL
E)85.0 mL

Question 21

Which statement about hydrogen bonding is true?

A)Hydrogen bonding is the intermolecular attractive forces between two hydrogen atoms in solution.
B)The hydrogen bonding capabilities of water molecules cause CH₃CH₂CH₂CH₃ to be more soluble in water than CH₃OH.
C)Hydrogen bonding of solvent molecules with a solute will not affect the solubility of the solute.
D)Hydrogen bonding interactions between molecules are stronger than the covalent bonds within the molecule.
E)Hydrogen bonding arises from the dipole moment created by the unequal sharing of electrons within certain covalent bonds within a molecule.

Question 22

We can predict the solubility of a compound by looking at the sign of the enthalpy of solution.

Question 23

The solubility of O₂ in water is 0.590 g/L at an oxygen pressure of around 14.5 atm.What is the Henry's law constant for O₂ (in units of mol/L·atm)?

A)4.07 $\times$ 10^-2
B)1.27 $\times$ 10^-3
C)7.86 $\times$ 10²
D)2.67 $\times$ 10^-1
E)None of the above are within 5% of the correct answer.

Question 24

What partial pressure of nitrogen gas is required in order for 0.00134 g of the gas to dissolve in 13.1 mL of pure water? The Henry's law constant for nitrogen gas is 6.1 $\times$ 10^-4 M atm^-1.

A)6.2 $\times$ 10^-8 atm
B)1.7 $\times$ 10^-1 atm
C)6.0 $\times$ 10⁰ atm
D)2.9 $\times$ 10^-8 atm
E)1.7 $\times$ 10^-2 atm

Question 25

The vapor pressure of water at 25.0°C is 23.8 torr.Determine the mass of glucose (molar mass = 180 g/mol)needed to add to 500.0 g of water to change the vapor pressure to 22.8 torr.

A)21.9 g
B)219 g
C)180 g
D)6.21 kg
E)188 g

Question 26

What is the molarity of a HNO₃ solution prepared by adding 255.4 mL of water to 350.0 mL of 12.3 M HNO₃?

A)16.9 M
B)7.45 M
C)7.11 M
D)2.61 M
E)3.14 M

Question 27

Solid KF has a lattice energy of 804 kJ/mol and a heat of solution (in water)of -15 kJ/mol.RbF has a lattice energy of 768 kJ/mol and a heat of solution (in water)of -24 kJ/mol.Which salt forms stronger attractions with water?

A)KF,since it has a larger lattice energy.
B)RbF,since it has a smaller lattice energy.
C)KF,since it has a more negative heat of hydration.
D)RbF,since it has a more negative heat of hydration
E)They form equally strong attractions with water,since they both have negative heats of mixing.

Question 28

The lattice energy of KF is 808 kJ/mol and its heat of solution is -17.7 kJ/mol.Calculate the hydration of energy of KF(s).

A)-35.4 kJ/mol
B)-790.3 kJ/mol
C)-825.7 kJ/mol
D)790.3 kJ/mol
E)825.7 kJ/mol

Question 29

Which of the following correctly states the relationship between temperature and the solubility of a substance in water?

A)The solubility of a substance in water increases as the temperature rises,especially for gases.
B)The solubility of a substance in water decreases as the temperature rises,especially for ionic solids.
C)The solubility of a substance in water with temperature cannot be accurately predicted,especially for ionic solids.
D)The solubility of a substance in water decreases as the temperature lowers,especially for gases.
E)Both A and D are correct.

Question 30

Rank the following compounds according to increasing solubility in water. I.
CH₃-CH₂-CH₂-CH₃
II.
CH₃-CH₂-O-CH₂-CH₃
III.
CH₃-CH₂-OH
IV.
CH₃-OH

A)I < III < IV < II
B)I < II < IV < III
C)III < IV < II < I
D)I < II < III < IV
E)None of these (A-D)is correct.

Question 31

When solid Ca(CH₃COO)₂ is dissolved in a nearly saturated solution of Ca(CH₃COO)₂,the solution becomes warmer.This information indicates that if the temperature of a solution is decreased:

A)" $\Delta$ H will become negative."
B)" $\Delta$ H will become zero."
C)"The solubility of Ca(CH₃COO)₂ will decrease."
D)"The solubility of Ca(CH₃COO)₂ will increase.'
E)"The solubility of Ca(CH₃COO)₂ will not change."

Question 32

Calculate the molarity of a solution of magnesium chloride with a concentration of 26.8 mg/mL.

A)0.563 M
B)0.281 M
C)0.141 M
D)3.55 M
E)0.448 M

Question 33

When 0.811 g of NH₄NO₃ was added to 150.0 g of water in a Styrofoam cup,the temperature dropped by 0.413°C.The heat capacity of H₂O is 4.18 J/g°C.Assume the specific heat of the solution equals that of pure H₂O and that the calorimeter neither absorbs nor leaks heat.The molar heat of solution of solid NH₄NO₃ is:

A)+257 J/mol
B)+25.7 kJ/mol
C)+2.57 kJ/mol
D)-2.57 kJ/mol
E)-257 J/mol

Question 34

When a substance dissolves in water,heat energy is released if:

A)The lattice energy is positive.
B)The hydration energy is positive.
C)The hydration energy is more negative than the lattice energy is positive.
D)The hydration energy is negative.
E)None of these (A-D).

Question 35

Which of the following favors the solubility of an ionic solid in a liquid solvent?

A)a large magnitude of the solvation energy of the ions
B)a small magnitude of the lattice energy of the solute
C)a large polarity of the solvent
D)all of the above
E)none of the above

Question 36

The solubility of a gas usually increases with increasing temperature.

Question 37

Which of the following chemical or physical changes is an endothermic process?

A)the evaporation of water
B)the combustion of gasoline
C)the mixing of sulfuric acid and water
D)the freezing of water
E)none of these

Question 38

A correct statement of Henry's law is:

A)The concentration of a gas in solution is inversely proportional to temperature.
B)The concentration of a gas in solution is directly proportional to the mole fraction of solvent.
C)The concentration of a gas in solution is independent of pressure.
D)The concentration of a gas in a solution is inversely proportional to pressure.
E)None of these.

Question 39

Use the following drawing of a gaseous solute in equilibrium with a solution to help answer the question below. Which of the following statements are true when the piston is pushed in (downward)?

A)This will cause the pressure of the gas to increase and the concentration of the dissolved gas to go down.
B)This will cause the pressure of the gas to decrease and the concentration of the dissolved gas to go down.
C)This will cause the pressure of the gas to increase and the concentration of the dissolved gas to go up.
D)This will cause the volume of the gas to decrease and the concentration of the dissolved gas to go down.
E)This will cause the volume of the gas to increase and the concentration of the dissolved gas to go up.

Question 40

How many of the following help determine whether or not a solution forms?
I.the polarities of the solute and solvent
II.the densities of the solute and solvent
III.the probability of the mixed state (of the solution)
IV.the energies needed for the solution formation to occur
V.the state of matter of the solute (solid,liquid,gas)

A)1
B)2
C)3
D)4
E)5

Question 41

For each of the following solutions,describe the deviation with respect to Raoult's Law.
hexane (C₆H₁₄)and octane (C₈H₁₈)

A)relatively ideal
B)positive deviation
C)negative deviation
D)more information needed
E)none of these

Question 42

Solutions of benzene and toluene obey Raoult's law.The vapor pressures at 20°C are: benzene,76 torr;toluene,21 torr.
What is the mole fraction of benzene in a benzene-toluene solution whose vapor pressure is 51 torr at 20°C?

A)0.26
B)0.45
C)0.55
D)0.67
E)0.74

Question 43

Liquid A and liquid B form a solution that behaves ideally according to Raoult's law.The vapor pressures of the pure substances A and B are 233 torr and 135 torr,respectively.Determine the vapor pressure over the solution if 1.21 moles of liquid A is added to 5.30 moles of liquid B.

A)153 torr
B)188 torr
C)215 torr
D)760 torr
E)43.3 torr

Question 44

Solutions of benzene and toluene obey Raoult's law.The vapor pressures at 20°C are: benzene,76 torr;toluene,21 torr.
If the mole fraction of benzene in a particular benzene-toluene solution is 0.64,what is the mole fraction of benzene in the vapor phase in equilibrium with that solution?

A)0.24
B)0.50
C)0.64
D)0.78
E)0.87

Question 45

Benzene and toluene form an ideal solution.At 298 K,what is the mole fraction of benzene in the liquid that is in equilibrium with a vapor that has equal partial pressures of benzene and toluene? At 298 K,the vapor pressures of pure benzene and pure toluene are 95 and 28 torr,respectively.

A)0.50
B)0.77
C)0.23
D)0.30
E)none of these

Question 46

A solution contains 1 mole of liquid A and 3 moles of liquid B.This solution has a vapor pressure of 314 torr at 25°C.At 25°C,liquid A has a vapor pressure of 265 torr and liquid B has a vapor pressure of 355 torr.Which of the following is true?

A)This solution exhibits a positive deviation from Raoult's Law.
B)This solution exhibits a negative deviation from Raoult's Law.
C)This solution is ideal.
D)More information is needed to answer this question.
E)None of these (A-D).

Question 47

Solutions of benzene and toluene obey Raoult's law.The vapor pressures at 20°C are: benzene,76 torr;toluene,21 torr.
A benzene-toluene solution is allowed to come to equilibrium with its vapor.The vapor is then condensed and found to contain 50.0 mole percent of each component.Calculate the composition (mole percent)of the original solution.The vapor pressures of pure benzene and toluene at this temperature are: 750.torr and 300.torr,respectively.

A)50.2% benzene
B)28.6% benzene
C)71.0% benzene
D)40.0% benzene
E)none of these

Question 48

A solution of two liquids,A and B,shows negative deviation from Raoult's law.This means that:

A)The molecules of A interact strongly with other A-type molecules.
B)The two liquids have a positive heat of solution.
C)Molecules of A interact weakly,if at all,with B molecules.
D)The molecules of A hinder the strong interaction between B molecules.
E)Molecules of A interact more strongly with B than A with A,or B with B.

Question 49

A solution is prepared from 53.8 g of a nonvolatile,nondissociating solute and 85.0 g of water.The vapor pressure of the solution at 60°C is 132 torr.The vapor pressure of water at 60°C is 150.torr.What is the molar mass of the solute?

A)61.1 g/mol
B)11.4 g/mol
C)34.6 g/mol
D)186 g/mol
E)83.6 g/mol

Question 50

For each of the following solutions,describe the deviation with respect to Raoult's Law.
acetone (C₃H₆O)and water

A)relatively ideal
B)positive deviation
C)negative deviation
D)more information needed
E)none of these

Question 51

At a given temperature,you have a mixture of benzene (vapor pressure of pure benzene = 745 torr)and toluene (vapor pressure of pure toluene = 290.torr).The mole fraction of benzene in the solution is 0.590.Assuming ideal behavior,calculate the mole fraction of toluene in the vapor above the solution.

A)0.213
B)0.778
C)0.641
D)0.359
E)0.590

Question 52

For each of the following solutions,describe the deviation with respect to Raoult's Law.
hexane (C₆H₁₄)and chloroform (CHCl₃)

A)relatively ideal
B)positive deviation
C)negative deviation
D)more information needed
E)none of these

Question 53

At 40°C,heptane has a vapor pressure of about 92.2 torr and octane has a vapor pressure of about 31.2 torr.Assuming ideal behavior,what is the vapor pressure of a solution that contains twice as many moles of heptane as octane?

A)61.5 torr
B)51.5 torr
C)71.9 torr
D)82.3 torr
E)none of these

Question 54

A liquid-liquid solution is called an ideal solution if:
I.It obeys PV = nRT.
II.It obeys Raoult's law.
III.Solute-solute,solvent-solvent,and solute-solvent interactions are very similar.
IV.Solute-solute,solvent-solvent,and solute-solvent interactions are quite different.

A)I,II,III
B)I,II,IV
C)II,III
D)II,IV
E)I,III,IV

Question 55

A salt solution sits in an open beaker.Assuming constant temperature and pressure,the vapor pressure of the solution

A)increases over time
B)decreases over time
C)stays the same over time
D)need to know which salt is in the solution to answer this
E)need to know the temperature and pressure to answer this

Question 56

A solution of CH₃OH in H₂O would most likely

A)be ideal
B)show positive deviations from Raoult's law
C)show negative deviations from Raoult's law
D)not be ideal,but the deviations cannot be predicted
E)obey Raoult's law

Question 57

At a given temperature,you have a mixture of benzene (vapor pressure of pure benzene = 745 torr)and toluene (vapor pressure of pure toluene = 290 torr).The mole fraction of benzene in the vapor above the solution is 0.590.Assuming ideal behavior,calculate the mole fraction of toluene in the solution.

A)0.213
B)0.778
C)0.641
D)0.359
E)0.590

Question 58

A solution is made by adding 0.100 mole of ethyl ether to 0.491 mole of ethyl alcohol.If the vapor pressure of ethyl ether and ethyl alcohol at 20°C are 375 torr and 20.0 torr,respectively,the vapor pressure of the solution at 20°C (assuming ideal behavior)is:

A)80.1 torr
B)315 torr
C)46.8 torr
D)395 torr
E)none of these

Question 59

Two liquids form a solution and release a quantity of heat.How does the pressure above the solution compare to that predicted by Raoult's law?

A)It will be greater.
B)It will be less.
C)It will be the same.
D)It will show positive deviation.
E)None of these.

Question 60

An ideal solution is formed from a mixture of the nonvolatile solute urea,CO(NH₂)₂,and methanol,CH₃OH.The vapor pressure of pure methanol at 20°C is 89 mmHg.If 4.4 g of urea is mixed with 39.9 g of methanol,calculate the vapor pressure of the methanol solution.

A)4.9 mmHg
B)80 mmHg
C)74 mmHg
D)15 mmHg
E)84 mmHg

Question 61

When a 49.1-g sample of an unknown compound is dissolved in 500.g of benzene,the freezing point of the resulting solution is 3.77°C.The freezing point of pure benzene is 5.48°C and K_f for benzene is 5.12°C/m.Calculate the molar mass of the unknown compound.

A)147 g/mol
B)28.7 g/mol
C)251 g/mol
D)588 g/mol
E)294 g/mol

Question 62

A solution of water and a nonvolatile,nonionizing compound is placed in a tube with a semipermeable membrane on one side.The tube is placed in a beaker of pure water.What initial net effect will occur?

A)Water will flow from the beaker to the tube.
B)Water will flow from the tube to the beaker.
C)The compound will pass through the membrane into the solution.
D)Nothing will move through the membrane either way.
E)Equilibrium is immediately established.

Question 63

Osmotic pressure depends on all but which of the following?

A)atmospheric pressure
B)the molarity of the solution
C)temperature
D)the ratio of moles of solute to solution volume
E)none of these

Question 64

The molar mass of a solid as determined by freezing point depression is 10% higher than the true molar mass.Which of the following experimental errors could not account for this discrepancy?

A)Not all the solid was dissolved.
B)More than the recorded amount of solvent was pipetted into the solution.
C)The solid dissociated slightly into two particles when it dissolved.
D)Some solid was left on the weighing paper.
E)Before the solution was prepared,the container was rinsed with solvent and not dried.

Question 65

Consider a solution containing liquids A and B where the mole fraction of B is 0.60.Assuming ideality,calculate the mole fraction of B in the vapor at equilibrium with this solution at 25°C.(The vapor pressures of pure liquid A and B at 25°C are 129.4 torr and 400.0 torr,respectively. )

A)0.18
B)0.22
C)0.33
D)0.78
E)0.82

Question 66

Polyethylene is a synthetic polymer or plastic with many uses.1.36 g of a polyethylene sample was dissolved in enough benzene to make 100.mL of solution,and the osmotic pressure was found to be 1.86 torr at 25^oC.What is the approximate molar mass of the polyethylene?

A)179 g/mol
B)1.14 $\times$ 10⁴ g/mol
C)7.35 $\times$ 10³ g/mol
D)1.24 $\times$ 10⁵ g/mol
E)1.36 $\times$ 10⁵ g/mol

Question 67

Adding salt to water decreases the freezing point of the water since it lowers the vapor pressure of the ice.

Question 68

Determine the change in boiling point for 397.7 g of carbon disulfide (K_b = 2.34°C kg/mol)if 35.0 g of a nonvolatile,nonionizing compound is dissolved in it.The molar mass of the compound is 70.0 g/mol and the boiling point of the pure carbon disulfide is 46.2°C.

A)0.206 °C
B)1.86 °C
C)5.88 °C
D)24.8 °C
E)2.94 °C

Question 69

Consider a solution containing liquids A and B where the mole fraction of B is 0.60.Assuming ideality,calculate the mole fraction of A in the vapor at equilibrium with this solution at 25°C.(The vapor pressures of pure liquid A and B at 25°C are 117.7 torr and 400.0 torr,respectively. )

A)0.16
B)196
C)0.31
D)3.40 $\times$ 10^-3
E)4.90 $\times$ 10^-3

Question 70

A solution consisting of 0.250 mol of methylbenzene,C₆H₅CH₃,in 244 g of nitrobenzene,C₆H₅NO₂,freezes at -1.2°C.Pure nitrobenzene freezes at 6.0°C.What is the freezing-point depression constant of nitrobenzene?

A)4.8°C/m
B)3.5°C/m
C)29°C/m
D)7.0°C/m
E)14°C/m

Question 71

A 6.06-gram sample of a compound is dissolved in 250.grams of benzene.The freezing point of this solution is 1.02°C below that of pure benzene.What is the molar mass of this compound? (Note: K_f for benzene = 5.12°C/m. )Ignore significant figures for this problem.

A)30.4 g/mol
B)122 g/mol
C)243 g/mol
D)4.83 g/mol
E)60.8 g/mol

Question 72

All of the following are colligative properties except:

A)osmotic pressure
B)boiling point elevation
C)freezing point depression
D)density elevation
E)none of these

Question 73

Which of the following will cause the calculated molar mass of a compound determined by the freezing-point depression method to be greater than the true molar mass?

A)Water gets into the solvent after the freezing point of the pure solvent is determined.
B)Some of the solute molecules break apart.
C)The mass of solvent is smaller than determined from the weighing.
D)While adding the solute,some was spilled on the lab bench.
E)All of the above.

Question 74

A cucumber is placed in a concentrated salt solution.What will most likely happen?

A)Water will flow from the cucumber to the solution.
B)Water will flow from the solution to the cucumber.
C)Salt will flow into the cucumber.
D)Salt will precipitate out.
E)No change will occur.

Question 75

To calculate the freezing point of an ideal dilute solution of a single,nondissociating solute of a solvent,the minimum information one must know is:

A)the molality (of the solute)
B)the molality (of the solute)and the freezing point depression constant of the solvent
C)the same quantities as in B,plus the freezing point of the pure solvent
D)all of the quantities in C,plus the molecular weight of the solute
E)all of the quantities in C,plus the weight of the solvent

Question 76

A 0.2 molar solution of a solute,X,in benzene,displays an osmotic pressure given by the formula $\pi$ = (0.1)RT.Which of the following is most likely to be the case?

A)X exists in benzene as X.
B)X exists in benzene as X₂.
C)X exists in benzene dissociated into two particles.
D)This solution strongly deviates from ideal behavior.
E)None of these is plausible.

Question 77

Thyroxine,an important hormone that controls the rate of metabolism in the body,can be isolated from the thyroid gland.If 0.455 g of thyroxine is dissolved in 10.0 g of benzene,the freezing point of the solution could be measured as 5.144°C.Pure benzene freezes at 5.444°C and has a value for the molal freezing point depression constant of K_f of 5.12°C/m.What is the approximate molar mass of thyroxine?

A)7.77 $\times$ 10⁵ g/mol
B)777 g/mol
C)7.77 g/mol
D)11.3 g/mol
E)42.8 g/mol

Question 78

When a nonvolatile solute is added to a volatile solvent,the solution vapor pressure __________,the boiling point __________,the freezing point __________,and the osmotic pressure across a semipermeable membrane __________.

A)decreases,increases,decreases,decreases
B)increases,increases,decreases,increases
C)increases,decreases,increases,decreases
D)decreases,decreases,increases,decreases
E)decreases,increases,decreases,increases

Question 79

What is the boiling point change for a solution containing 0.736 moles of naphthalene (a nonvolatile,nonionizing compound)in 250.g of liquid benzene? (K_b = 2.53°C/m for benzene)

A)7.45 °C
B)0.859 °C
C)3.44 °C
D)1.86 °C
E)0.466 °C

Question 80

A solute added to a solvent raises the boiling point of the solution because:

A)The temperature to cause boiling must be great enough to boil not only the solvent but also the solute.
B)The solute particles lower the solvent's vapor pressure,thus requiring a higher temperature to cause boiling.
C)The solute particles raise the solvent's vapor pressure,thus requiring a higher temperature to cause boiling.
D)The solute increases the volume of the solution,and an increase in volume requires an increase in the temperature to reach the boiling point (derived from PV = nRT).
E)Two of the above are correct.