Question 1

A solution of two liquids, A and B, shows negative deviation from Raoult's law. This means that
A) the molecules of A hinder the strong interaction between B molecules.
B) molecules of A interact strongly with other A-type molecules.
C) molecules of A interact more strongly with B than with A or and more strongly than B with B.
D) the two liquids have a positive heat of solution.
E) molecules of A interact weakly, if at all, with B molecules.

Accepted Answer

Negative deviation from Raoult's law means that the molecules in the solution interact more strongly with each other than would be expected based on the ideal behavior according to Raoult's law. In this case, it means that the molecules of A interact more strongly with B than with A or with other A-type molecules.

Question 2

For each of the following solutions, would you expect it with respect to Raoult's law) to be relatively ideal, to show a positive deviation, or to show a negative deviation? -hexane (C₆H₁₄) and chloroform (CHCl₃) A) relatively ideal B) positive deviation C) negative deviation

Accepted Answer

Hexane and chloroform do not have similar intermolecular forces or molecular sizes, so they would not be expected to have a relatively ideal solution. Also, both hexane and chloroform experience some degree of intermolecular attraction (hexane has London dispersion forces and chloroform experiences dipole-dipole interactions and London dispersion forces), so they would be expected to show a positive deviation from Raoult's law. Therefore, B is the best choice.

Question 3

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

Accepted Answer

The heat of solution reflects the net effect of breaking the lattice energy and forming attractions with water (hydration energy). RbF's more negative heat of solution indicates stronger attractions with water, as it suggests a greater release of energy upon hydration.

Question 4

Which of the following statements is(are) true?
A) The rate of dissolution of a solid in a liquid always increases with increasing temperature.
B) The solubility of a solid in a liquid always increases with increasing temperature.
C) According to Henry's law, the amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the liquid.
D) Two of these statements are true.
E) All of these statements are true.

Accepted Answer

Statement A is not always true, as some solids exhibit an increase in solubility with decreasing temperature. Statement B is also not always true, as there are cases where increasing temperature leads to a decrease in solubility. Statement C is true and is known as Henry's Law. Therefore, the correct choice is D, as statements A and B are not always true, while statement C is always true.

Question 5

When 1 mol of a nonvolatile solvent-nondissociating substance is dissolved in 3 mol of solvent, the ratio of vapor pressure of the solution to that of the pure solvent (at the same temperature) is approximately
A) 2/3.
B) 3/4.
C) 1/4.
D) 1/3.
E) none of these

Accepted Answer

The ratio of the vapor pressure of the solution to that of the pure solvent is given by Raoult's law, which states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent. In this case, the mole fraction of the solvent is 3/(1+3) = 3/4.

Question 6

The boiling point of pure benzene at 760. torr is 80.1°C. What is the vapor pressure of benzene over a solution containing 4.40 mol of nonvolatile hydrocarbon and 11.80 mol of benzene at 80.1°C? A) 6.04 × 10² torr B) 5.54 × 10² torr C) 2.06 × 10² torr D) 7.60 × 10² torr E) 1.42 × 10² torr

Accepted Answer

According to Raoult's Law:

P_benzene = X_benzene * P°_benzene

where P_benzene is the vapor pressure of benzene over the solution, X_benzene is the mole fraction of benzene in the solution, and P°_benzene is the vapor pressure of pure benzene.

To find X_benzene, we need to first calculate the total moles of solute and solvent:

n_total = n_benzene + n_hydrocarbon
n_total = 11.80 mol + 4.40 mol
n_total = 16.20 mol

Then, we can calculate X_benzene:

X_benzene = n_benzene / n_total
X_benzene = 11.80 mol / 16.20 mol
X_benzene = 0.728

Now we can use Raoult's Law to find P_benzene:

P_benzene = X_benzene * P°_benzene
P_benzene = 0.728 * 760. torr
P_benzene = 553. torr

Therefore, the vapor pressure of benzene over the solution is 553. torr, which corresponds to choice B.

Question 7

The lattice energy of NaI is -686 kJ/mol, and its heat of solution is -7.6 kJ/mol. Calculate the hydration of energy of NaI(s) in kJ/mol.
A) -678
B) +694
C) -694
D) +678
E) +15.2

Accepted Answer

The hydration energy can be calculated using the formula: Hydration energy = Lattice energy + Heat of solution. Substituting the given values: Hydration energy = -686 kJ/mol + (-7.6 kJ/mol) = -694 kJ/mol.

Question 8

Predict the deviation from Raoult's law when two liquids are mixed and the heat of the solution is small.
A) negative deviation
B) relatively ideal (small or zero deviation)
C) positive deviation

Accepted Answer

When the heat of the solution is small, the intermolecular forces between the two liquids are similar in strength. Thus, the interactions between the molecules of the two liquids are similar to those occurring in the pure liquids, leading to a relatively ideal behavior and a small or zero deviation from Raoult's law.

Question 9

If a solution exhibits a negative deviation from Raoult's law, the vapor pressure of the solution is __________ what would be expected ideally.
A) equal to
B) greater than
C) less than

Accepted Answer

Negative deviations from Raoult's law occur when the intermolecular forces between unlike molecules in the solution are stronger than those between the same molecules in the pure liquids. This leads to a lower vapor pressure than expected by Raoult's law, thus the vapor pressure of the solution is less than what would be expected ideally.

Question 10

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

Accepted Answer

An ideal solution is defined as a liquid-liquid solution in which the solute-solute, solvent-solvent, and solute-solvent interactions are very similar. This means that the solution follows Raoult's law, which states that the vapor pressure of each component of an ideal solution is proportional to its mole fraction in the solution. Therefore, II and III are the correct options. Choice I is incorrect because PV = nRT is the equation of state for any gas, not for an ideal solution. Choice IV is also incorrect because an ideal solution has similar interactions between all components, not quite different as stated in option IV.

Question 11

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

Accepted Answer

Hydrogen bonding arises due to the dipole moment created by the unequal sharing of electrons in polar covalent bonds, particularly when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine, leading to a significant difference in electronegativity.

Question 12

Which of the following chemical or physical changes is an endothermic process?
A) the mixing of sulfuric acid and water
B) the freezing of water
C) the evaporation of water
D) the combustion of gasoline
E) none of these

Accepted Answer

The evaporation of water is an endothermic process because it requires energy input (in the form of heat) to break the hydrogen bonds between water molecules and convert liquid water into water vapor. The mixing of sulfuric acid and water (A) is exothermic because heat is released. The freezing of water (B) and combustion of gasoline (D) are also exothermic because they release heat.

Question 13

For each of the following solutions, would you expect it with respect to Raoult's law) to be relatively ideal, to show a positive deviation, or to show a negative deviation? -acetone (C₃H₆O) and water A) relatively ideal B) positive deviation C) negative deviation

Accepted Answer

Acetone and water form an azeotrope, which means they have a maximum boiling point depression and minimum freezing point elevation. This indicates that they do not follow Raoult's law and show a negative deviation.

Question 14

A salt solution sits in an open beaker. Assuming constant temperature and pressure, the vapor pressure of the solution
A) stays the same over time.
B) We need to know which salt is in the solution to answer this.
C) increases over time.
D) We need to know the temperature and pressure to answer this.
E) decreases over time.

Accepted Answer

The vapor pressure of a salt solution in an open beaker decreases over time because as the water evaporates, the solution becomes more concentrated with salt, which lowers its vapor pressure due to the colligative property of lowering vapor pressure by non-volatile solutes.

Question 15

At a given temperature, the vapor pressure of heptane is 92.0 torr and the vapor pressure of octane is 31.2 torr. Assuming ideal behavior, what is the vapor pressure of a solution that contains three times as many moles of octane as heptane?
A) 87.3 torr
B) 52.4 torr
C) 76.8 torr
D) 46.4 torr
E) none of these

Accepted Answer

The vapor pressure of the solution is calculated using Raoult's Law: P_solution = X_heptane * P_heptane + X_octane * P_octane. With three times as many moles of octane, X_heptane = 1/4 and X_octane = 3/4. Thus, P_solution = (1/4 * 92.0) + (3/4 * 31.2) = 46.4 torr.

Question 16

Predict the deviation from Raoult's law when two liquids are mixed and the heat of the solution is large and the reaction exothermic.
A) positive deviation
B) relatively ideal (small or zero deviation)
C) negative deviation

Accepted Answer

When the heat of the solution is large and the reaction is exothermic, the potential energy of the mixture is lower than that of the individual components. This means that the molecules prefer to be close together and interact with each other, leading to a negative deviation from Raoult’s law.

Question 17

A 48.4-g sample of glucose (a nondissociated, nonvolatile solute with the formula C₆H₁₂O₆) is dissolved in 151.2 g of water. What is the vapor pressure of this solution at 100°C? A) 736 torr B) 576 torr C) 23.6 torr D) 760 torr E) 184 torr

Accepted Answer

The vapor pressure of the solution can be calculated using Raoult's law, which states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent. Since glucose does not dissociate or volatilize, it will not contribute to the vapor pressure directly. The vapor pressure of pure water at 100°C is 760 torr. The mole fraction of water in the solution can be calculated and used to find the vapor pressure of the solution, which will be slightly less than 760 torr due to the presence of glucose. Choice A, 736 torr, is the only option slightly less than 760 torr, indicating it accounts for the presence of glucose reducing the vapor pressure of water.

Question 18

The solubility of O₂ in water is 0.590 g/L at an oxygen pressure of 15 atm. What is the Henry's law constant for O₂ (in units of L atm/mol)? A) 3.93 × 10^-3 B) 1.23 × 10^-3 C) 8.14 × 10² D) 1.26 E) None of the above is within 5% of the correct answer.

Accepted Answer

The answer of The solubility of O₂ in water is...

Question 19

When 0.800 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. What is the molar heat of solution of solid NH₄NO₃? A) +260. J/mol B) -2.60 kJ/mol C) +2.60 kJ/mol D) +26.0 kJ/mol E) none of these

Accepted Answer

The answer of When 0.800 g of NH₄NO₃ was added...

Question 20

Predict the deviation from Raoult's law when two liquids are mixed and the heat of the solution is large and the reaction endothermic.
A) positive deviation
B) relatively ideal (small or zero deviation)
C) negative deviation

Accepted Answer

A large heat of solution in an endothermic reaction indicates that energy is absorbed to overcome intermolecular forces between the two liquids. This results in weaker overall intermolecular attractive forces, leading to an increased likelihood of the liquid molecules escaping into the gas phase. As a result, the actual vapor pressure of the mixture will be greater than predicted by Raoult's law, resulting in a positive deviation.

Quiz 17: Properties of Solutions

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

For each of the following solutions, would you expect it with respect to Raoult's law) to be relatively ideal, to show a positive deviation, or to show a negative deviation? -hexane (C₆H₁₄) and chloroform (CHCl₃)

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?

Which of the following statements is(are) true?

When 1 mol of a nonvolatile solvent-nondissociating substance is dissolved in 3 mol of solvent, the ratio of vapor pressure of the solution to that of the pure solvent (at the same temperature) is approximately

The boiling point of pure benzene at 760. torr is 80.1°C. What is the vapor pressure of benzene over a solution containing 4.40 mol of nonvolatile hydrocarbon and 11.80 mol of benzene at 80.1°C?

The lattice energy of NaI is -686 kJ/mol, and its heat of solution is -7.6 kJ/mol. Calculate the hydration of energy of NaI(s) in kJ/mol.

Predict the deviation from Raoult's law when two liquids are mixed and the heat of the solution is small.

If a solution exhibits a negative deviation from Raoult's law, the vapor pressure of the solution is __________ what would be expected ideally.

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.

Which statement about hydrogen bonding is true?

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

For each of the following solutions, would you expect it with respect to Raoult's law) to be relatively ideal, to show a positive deviation, or to show a negative deviation? -acetone (C₃H₆O) and water

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

At a given temperature, the vapor pressure of heptane is 92.0 torr and the vapor pressure of octane is 31.2 torr. Assuming ideal behavior, what is the vapor pressure of a solution that contains three times as many moles of octane as heptane?

Predict the deviation from Raoult's law when two liquids are mixed and the heat of the solution is large and the reaction exothermic.

A 48.4-g sample of glucose (a nondissociated, nonvolatile solute with the formula C₆H₁₂O₆) is dissolved in 151.2 g of water. What is the vapor pressure of this solution at 100°C?

The solubility of O₂ in water is 0.590 g/L at an oxygen pressure of 15 atm. What is the Henry's law constant for O₂ (in units of L atm/mol) ?

Predict the deviation from Raoult's law when two liquids are mixed and the heat of the solution is large and the reaction endothermic.