Question 1

Carbon tetrachloride, once widely used in fire extinguishers and as a dry cleaning fluid, has been found to cause liver damage to those exposed to its vapors over long periods of time. What is the boiling point of a solution prepared by dissolving 375 g of sulfur (S₈, ℳ= 256.5 g/mol) in 1250 g of CCl₄? K_b = 5.05°C/m, boiling point of pure CCl₄= 76.7°C?

Accepted Answer

The answer of Carbon tetrachloride, once widely used in fire...

Question 2

Dimethylglyoxime, DMG, is an organic compound used to test for aqueous nickel(II) ions. A solution prepared by dissolving 65.0 g of DMG in 375 g of ethanol boils at 80.3°C. What is the molar mass of DMG? K_b = 1.22°C/m, boiling point of pure ethanol = 78.5°C

Accepted Answer

First, we need to calculate the boiling point elevation of the solution compared to pure ethanol:

ΔT = i*K*m
where ΔT is the boiling point elevation, i is the van't Hoff factor (the number of particles into which DMG dissociates in solution, which we will assume to be 1), K is the molal boiling point constant of the solvent (ethanol), and m is the molality of the solution.

We can calculate m as follows:

m = moles of DMG / mass of solvent (in kg)

To calculate the moles of DMG, we need to use the given amount of DMG and its formula:

65.0 g DMG / (2*14.01 g/mol + 4*12.01 g/mol + 4*1.01 g/mol + 2*16.00 g/mol) = 0.319 mol DMG

Now we can calculate the molality:

m = 0.319 mol / 0.375 kg = 0.850 m

Finally, we can calculate the boiling point elevation:

ΔT = 1 * 1.22°C/m * 0.850 m = 1.04°C

The boiling point of the solution is therefore:

boiling point = 80.3°C + 1.04°C = 81.3°C

To calculate the molar mass of DMG, we can use the formula for the boiling point elevation of a nonvolatile solute:

ΔT = K*m*(1 - (1/moles of solute)*mass of solvent/(molar mass of solute))

Solving for the molar mass of DMG:

molar mass of DMG = mass of solute / moles of solute

mass of solute = 65.0 g
moles of solute = 0.319 mol
mass of solvent = 375 g
K = 1.22°C/m
ΔT = 1.04°C
boiling point of pure solvent = 78.5°C

Substituting into the formula and solving:

1.04 = 1.22*(0.850)*(1 - (1/0.319)*0.375/molar mass of DMG)
molar mass of DMG = 117 g/mol

Question 3

Consider the molecular substances I₂, H₂O, and C₈H₁₈. Which of them is/are soluble in CCl₄?

Accepted Answer

The solubility of molecular substances in polar solvents like CCl₄ is primarily determined by their polarity. The more polar the substance, the more soluble it is in polar solvents. Looking at the three molecular substances provided, C₈H₁₈ is the most polar due to the presence of both the polar C-S and C-H bonds. This substance is therefore soluble in CCl₄. I₂ also contains polar C-S bonds, making it somewhat polar and soluble in CCl₄. H₂O, on the other hand, has polar O-H bonds but is otherwise nonpolar, making it insoluble in CCl₄. Therefore, the correct choice is D, I ₂ and C ₈H ₁₈.

Question 4

Lysine is an amino acid that is an essential part of nutrition but which is not synthesized by the human body. What is the molar mass of lysine if 750.0 mL of a solution containing 8.60 g of lysine has an osmotic pressure of 1.918 atm? Temperature = 25.0°C

Accepted Answer

The molar mass of lysine can be calculated using the formula for osmotic pressure: $\pi = \frac{n}{V}RT$, where $\pi$ is the osmotic pressure, $n$ is the number of moles of solute, $V$ is the volume of the solution in liters, $R$ is the ideal gas constant (0.0821 L·atm/K·mol), and $T$ is the temperature in Kelvin. First, convert the temperature to Kelvin: $25.0°C + 273.15 = 298.15 K$. Then, rearrange the formula to solve for $n$: $n = \pi V / RT$. Substituting the given values: $n = (1.918 \, \text{atm} \times 0.750 \, \text{L}) / (0.0821 \, \text{L·atm/K·mol} \times 298.15 \, \text{K})$. This calculation gives the number of moles of lysine, which can then be used to find the molar mass: $M = \text{mass} / n$. Given the mass of lysine is 8.60 g, you can calculate the molar mass. The correct calculation leads to a molar mass close to 146 g/mol, making option B the correct answer.

Question 5

The dimensions of typical colloidal particles are of the order of

Accepted Answer

The answer of The dimensions of typical colloidal particles are...

Question 6

Which one of the following pairs of dispersed phases and dispersing media can never form a colloid?

Accepted Answer

Colloids are mixtures where one substance is dispersed evenly throughout another. The combination of gas in gas does not form a colloid because when gases mix, they form a homogeneous mixture or solution, not a colloid. All other pairs listed can form colloidal systems.

Question 7

A 0.100 m MgSO₄ solution has a freezing point of −0.23°C. What is the van't Hoff factor for this solution? K_f = 1.86°C/m

Accepted Answer

The van't Hoff factor (i) can be calculated using the formula:
i = (ΔTf)experimental / (ΔTf)ideal

where (ΔTf)experimental is the experimental freezing point depression and (ΔTf)ideal is the freezing point depression calculated using the formula:
(ΔTf)ideal = Kf * molality

Given that the solution has a freezing point of −0.23°C and Kf = 1.86°C/m, we can calculate the molality of the solution as follows:

(ΔTf)ideal = Kf * molality
-0.23°C = 1.86°C/m * molality
molality = -0.23°C / 1.86°C/m = 0.124 mol/kg

Now we can use the molality to calculate the van't Hoff factor:

i = (ΔTf)experimental / (ΔTf)ideal
i = (-0.23°C) / (-1.86°C/m * 0.124 mol/kg)
i = 1.2

Therefore, the van't Hoff factor for this solution is 1.2, which is closest to choice C (1.2).

Question 8

An emulsion is a dispersion consisting of a

Accepted Answer

An emulsion is a mixture of two immiscible liquids (usually oil and water), where one liquid is dispersed in the other in the form of small droplets. This makes choice B, "liquid in a liquid," the correct answer.

Question 9

Benzaldehyde ( ℳ = 106.1 g/mol), also known as oil of almonds, is used in the manufacture of dyes and perfumes and in flavorings. What would be the freezing point of a solution prepared by dissolving 75.00 g of benzaldehyde in 850.0 g of ethanol?K_f = 1.99°C/m, freezing point of pure ethanol = -117.3°C.

Accepted Answer

The answer of Benzaldehyde ( ℳ = 106.1 g/mol), also...

Question 10

Calculate the freezing point of a solution made by dissolving 3.50 g of potassium chloride (ℳ = 74.55 g/mol) in 100.0 g of water. Assume ideal behavior for the solution; K_f = 1.86°C/m.

Accepted Answer

The freezing point depression of the solution can be calculated using the formula ΔTf = i * Kf * m, where ΔTf is the freezing point depression, i is the van't Hoff factor (which is 2 for KCl, since it dissociates into K+ and Cl-), Kf is the molal freezing point depression constant for water (1.86°C/m), and m is the molality of the solution. First, calculate the moles of KCl: moles = 3.50 g / 74.55 g/mol = 0.0469 mol. Then, calculate the molality: molality = moles of solute / kg of solvent = 0.0469 mol / 0.100 kg = 0.469 m. Finally, calculate ΔTf: ΔTf = 2 * 1.86°C/m * 0.469 m = 1.746°C, which rounds to −1.7°C, indicating the freezing point of the solution is −1.7°C.

Question 11

Hexachlorophene is used as a disinfectant in germicidal soaps. What mass of hexachlorophene (ℳ = 406.9 g/mol) must be added to 125 g of chloroform to give a solution with a boiling point of 62.60°C? K_b = 3.63°C/m, boiling point of pure chloroform = 61.70°C

Accepted Answer

The correct answer is A because the boiling point elevation is given by the equation ΔTb = Kb * molality, where ΔTb is the change in boiling point, Kb is the boiling point elevation constant, and molality is the concentration of the solution in molality. We can rearrange this equation to solve for molality: molality = ΔTb / Kb. We know that the change in boiling point is 62.60°C - 61.70°C = 0.90°C, and the boiling point elevation constant for chloroform is 3.63°C/m. Therefore, the molality of the solution is 0.90°C / 3.63°C/m = 0.248 m. We can then use the molality to calculate the mass of hexachlorophene that must be added to the solution: mass = molality * molar mass * volume of solution. We know that the volume of the solution is 125 g, and the molar mass of hexachlorophene is 406.9 g/mol. Therefore, the mass of hexachlorophene that must be added to the solution is 0.248 m * 406.9 g/mol * 125 g = 12.6 g.

Question 12

The Tyndall effect

Accepted Answer

The Tyndall effect is the scattering of light by colloidal particles in a transparent medium. Thus, it is observed in colloidal dispersions, which are mixtures that contain particles that are larger than molecules but smaller than can be seen with the naked eye.

Question 13

Barbiturates are synthetic drugs used as sedatives and hypnotics. Barbital (ℳ = 184.2 g/mol) is one of the simplest of these drugs. What is the boiling point of a solution prepared by dissolving 42.5 g of barbital in 825 g of acetic acid? K_b = 3.07°C/m; boiling point of pure acetic acid = 117.9°C

Accepted Answer

The answer of Barbiturates are synthetic drugs used as sedatives...

Question 14

Cinnamaldehyde (ℳ = 132.15 g/mol) is used as a flavoring agent. What mass of cinnamaldehyde must be added to 175 g of ethanol to give a solution whose boiling point is 82.7°C? K_b = 1.22°C/m, boiling point of pure ethanol = 78.5°C

Accepted Answer

The answer of Cinnamaldehyde (ℳ = 132.15 g/mol) is used...

Question 15

Human blood has a molar concentration of solutes of 0.30 M. What is the osmotic pressure of blood at 25°C?

Accepted Answer

The osmotic pressure can be calculated using the formula π = iMRT. Assuming i (van't Hoff factor) is 1 for simplicity, M = 0.30 M, R = 0.0821 L·atm/mol·K, and T = 298 K (25°C). π = (1)(0.30)(0.0821)(298) ≈ 7.3 atm.

Question 16

A 0.100 m K₂SO₄ solution has a freezing point of −0.43°C. What is the van't Hoff factor for this solution? K_f = 1.86°C/m

Accepted Answer

The van't Hoff factor (i) can be calculated using the formula:
ΔTf = iKf*m
where ΔTf is the freezing-point depression, Kf is the freezing-point depression constant for the solvent, and m is the molality of the solution.
By rearranging the formula we get:
i = ΔTf / (Kf * m)

Substituting the given values:
ΔTf = (freezing point of pure solvent - freezing point of solution) = (0°C - (-0.43°C)) = 0.43°C
Kf for water = 1.86°C/m
m = 0.100 mol/kg

i = 0.43°C / (1.86°C/m * 0.100 mol/kg) = 2.31
So the van't Hoff factor is 2.3, which is closest to option C.

Quiz 13: The Properties of Mixtures: Solutions and Colloids

Dimethylglyoxime, DMG, is an organic compound used to test for aqueous nickel(II) ions. A solution prepared by dissolving 65.0 g of DMG in 375 g of ethanol boils at 80.3°C. What is the molar mass of DMG? Kb = 1.22°C/m, boiling point of pure ethanol = 78.5°C

Consider the molecular substances I2, H2O, and C8H18. Which of them is/are soluble in CCl4?