Question 1

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

Accepted Answer

The freezing point depression is calculated as ΔTf = 5.48°C - 3.77°C = 1.71°C. Using the formula ΔTf = Kf * m, where m is the molality, we find m = 1.71°C / 5.12°C/m = 0.334 mol/kg. The molality is moles of solute per kg of solvent, so moles of solute = 0.334 mol/kg * 0.500 kg = 0.167 mol. The molar mass is mass of solute / moles of solute = 49.1 g / 0.167 mol = 294 g/mol.

Question 2

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.

Accepted Answer

The solution in the tube contains a nonvolatile, nonionizing compound, which means that it will not affect the concentration of water molecules in the solution. However, the solution in the tube will have a lower water concentration compared to the pure water in the beaker. Therefore, water molecules will diffuse from the higher concentration in the beaker to the lower concentration in the tube across the semipermeable membrane until equilibrium is reached. This means that water will net flow from the beaker to the tube.

Question 3

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

Accepted Answer

Osmotic pressure does not depend on atmospheric pressure. It is solely determined by the concentration of solute particles in solution, which is influenced by the molarity of the solution, temperature, and the ratio of moles of solute to solution volume.

Question 4

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.

Accepted Answer

Option C (The solid dissociated slightly into two particles when it dissolved) would actually lead to a lower calculated molar mass, not a higher one, because the presence of more particles in solution would increase the freezing point depression more than expected for a non-dissociating solute.

Question 5

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

Accepted Answer

The mole fraction of B in the vapor phase can be calculated using Raoult's Law and Dalton's Law. The partial pressure of B is 0.60 * 400.0 torr = 240.0 torr, and for A, it is 0.40 * 129.4 torr = 51.76 torr. The total pressure is 240.0 + 51.76 = 291.76 torr. The mole fraction of B in the vapor is 240.0 / 291.76 ≈ 0.82.

Question 6

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

Accepted Answer

The answer of Polyethylene is a synthetic polymer or plastic...

Question 7

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

Accepted Answer

The answer of Adding salt to water decreases the freezing...

Question 8

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

Accepted Answer

The change in boiling point (ΔT_b) can be calculated using the formula ΔT_b = i * K_b * m, where i is the van't Hoff factor (which is 1 for non-ionizing compounds), K_b is the ebullioscopic constant, and m is the molality of the solution. First, calculate the molality: m = moles of solute / kg of solvent = (35.0 g / 70.0 g/mol) / (397.7 g / 1000 g/kg) = 0.125 mol / 0.3977 kg = 0.314 mol/kg. Then, ΔT_b = 1 * 2.34°C kg/mol * 0.314 mol/kg = 0.735°C. However, the closest answer choice is 2.94°C, which suggests a calculation error or misinterpretation in the options provided.

Question 9

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

Accepted Answer

Raoult's law states that the partial pressure of a component in a vapor is equal to the product of its mole fraction in the liquid and the vapor pressure of the pure component. Therefore, the mole fraction of A in the vapor is:XA = PA / Ptotal = (1 - XB) * PA / (PA + PB) = (1 - 0.60) * 117.7 torr / (117.7 torr + 400.0 torr) = 0.16

Question 10

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

Accepted Answer

The answer of A solution consisting of 0.250 mol of...

Question 11

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

Accepted Answer

The freezing point depression ($\Delta T_f$) is given as 1.02°C. The molal freezing point depression constant ($K_f$) for benzene is 5.12°C/m. Using the formula $\Delta T_f = K_f \times m$, where $m$ is the molality of the solution, we can find the molality: $m = \frac{\Delta T_f}{K_f} = \frac{1.02°C}{5.12°C/m} = 0.1992 m$. Molality is defined as moles of solute per kilogram of solvent, so $0.1992 = \frac{\text{moles of solute}}{0.250 \text{ kg}}$. Solving for moles of solute gives $0.0498 \text{ moles}$. The molar mass ($M$) of the compound is then calculated using the mass of the sample divided by the moles of solute: $M = \frac{6.06 \text{ g}}{0.0498 \text{ moles}} = 121.69 \text{ g/mol}$, which rounds to 122 g/mol.

Question 12

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

Accepted Answer

Density elevation is not a colligative property. Colligative properties depend only on the number of solute particles in a solution, not on the identity of the solute particles. Osmotic pressure, boiling point elevation, and freezing point depression are all examples of colligative properties.

Question 13

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.

Accepted Answer

The answer of Which of the following will cause the...

Question 14

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.

Accepted Answer

When a cucumber is placed in a concentrated salt solution, the water potential outside the cucumber decreases due to the presence of salt. This creates a water potential gradient, causing water to move from an area of higher water potential (inside the cucumber) to an area of lower water potential (outside the cucumber). As a result, water will flow from the cucumber to the salt solution, leading to a loss of turgor pressure and wilting of the cucumber.

Question 15

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

Accepted Answer

To calculate the freezing point of a solution, you need the molality of the solute, the freezing point depression constant of the solvent, and the freezing point of the pure solvent.

Question 16

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.

Accepted Answer

The osmotic pressure is half of what would be expected for a 0.2 molar solution, suggesting that the solute exists as dimers (X₂) in benzene, effectively reducing the number of particles contributing to osmotic pressure.

Question 17

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

Accepted Answer

The molar mass of thyroxine can be calculated using the formula ΔTf = i * Kf * m, where ΔTf is the freezing point depression, Kf is the molal freezing point depression constant, and m is the molality of the solution. Given ΔTf = 5.444°C - 5.144°C = 0.3°C, Kf = 5.12°C/m, and the mass of thyroxine is 0.455 g dissolved in 10.0 g of benzene, we can find the molality and then calculate the molar mass. The calculation yields a molar mass of approximately 777 g/mol.

Question 18

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

Accepted Answer

Adding a nonvolatile solute to a volatile solvent decreases the solution vapor pressure due to the solute particles occupying surface area and reducing the number of solvent molecules that can escape into the vapor phase. This leads to an increase in boiling point (colligative property) because a higher temperature is needed to make the vapor pressure equal to the external pressure. The freezing point decreases because the presence of solute particles disrupts the formation of a solid structure, requiring a lower temperature to freeze. The osmotic pressure increases because the solute creates a concentration gradient across a semipermeable membrane, causing solvent molecules to move into the solution to equalize the concentration, generating pressure.

Question 19

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

Accepted Answer

The boiling point change is given by the equation:ΔT_b = K_b * mwhere K_b is the boiling point elevation constant for the solvent, and m is the molality of the solution.In this case, K_b = 2.53°C/m and m = 0.736 moles / 0.250 kg = 2.94 m.Therefore, ΔT_b = 2.53°C/m * 2.94 m = 7.45 °C.

Question 20

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.

Accepted Answer

When a solute is added to a solvent, it lowers the vapor pressure of the solvent. This is because the solute particles occupy space at the surface of the solution, making it harder for the solvent particles to escape and enter the gas phase. As a result, the solution's boiling point is raised, as a higher temperature is needed to make the vapor pressure equal to the surrounding pressure and cause boiling.

Quiz 11: Properties of Solutions

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 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?

Osmotic pressure depends on all but which of the following?

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?

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. )

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?

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

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.

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 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 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.

All of the following are colligative properties except:

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

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 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?

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 .

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

Quiz 11: Properties of Solutions

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 Kf for benzene is 5.12°C/m.Calculate the molar mass of the unknown compound.

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?

Osmotic pressure depends on all but which of the following?

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?

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. )

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 25oC.What is the approximate molar mass of the polyethylene?

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

Determine the change in boiling point for 397.7 g of carbon disulfide (Kb = 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.

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 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 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: Kf for benzene = 5.12°C/m. ) Ignore significant figures for this problem.

All of the following are colligative properties except:

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

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

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 __________.

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? (Kb = 2.53°C/m for benzene)

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

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.

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?

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 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 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 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?

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 .

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)