Question 1

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 is 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 molar mass of thyroxine?

Accepted Answer

The freezing point depression is calculated using ΔTf = Kf * m, where ΔTf = 5.444°C - 5.144°C = 0.300°C. The molality (m) is then 0.300°C / 5.12°C/m = 0.0586 mol/kg. Using the mass of the solute (0.455 g) and the solvent (10.0 g = 0.010 kg), the molar mass (M) is calculated as M = 0.455 g / (0.0586 mol/kg * 0.010 kg) = 777 g/mol.

Question 2

Polyethylene is a synthetic polymer or plastic with many uses. 1.40 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°C. What is the molar mass of the polyethylene?

Accepted Answer

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

Question 3

The phrase "a solid dissolved in a gas" describes a(n)

Accepted Answer

A solid dissolved in a gas is called an aerosol.

Question 4

Calculate the osmotic pressure (in torr) of 5.88 L of an aqueous 0.144 M solution at 28°C if the solute concerned is totally ionized into three ions (for example, it could be Na₂SO₄ or MgCl₂).

Accepted Answer

The osmotic pressure (π) is calculated using the formula π = iMRT, where i is the van't Hoff factor (3 for complete ionization into three ions), M is the molarity (0.144 M), R is the ideal gas constant (0.0821 L·atm/mol·K), and T is the temperature in Kelvin (28°C = 301 K). Converting atm to torr (1 atm = 760 torr), the calculation gives approximately 8.11 × 10³ torr.

Question 5

When 0.020 mol of a weak acid HA is dissolved in enough water to make 1.0 L of solution, [H⁺] is 3.6 ×10^-3 M. Calculate the freezing point of this solution. Assume that the molarity concentration is equal to the molality concentration, and assume ideal behavior. K_f (H₂O) is 1.86°C kg/mol.

Accepted Answer

First, we need to calculate the molality of the solution:

molality = moles of solute / mass of solvent (in kg)

Since the volume is given and the molarity is equal to the moles of solute per liter of solution, we can calculate the moles of solute:

moles of solute = molarity x volume = 0.020 mol

Next, we need to find the mass of the solvent:

mass of solvent = volume x density of water = 1.0 L x 1000 g/L = 1000 g

Now we can calculate the molality:

molality = 0.020 mol / 1000 g = 0.020 mol/kg

Next, we use the equation to calculate the freezing point depression:

ΔTf = Kf x molality

ΔTf = 1.86°C kg/mol x 0.020 mol/kg = 0.0372°C

Since this is the amount by which the freezing point is lowered, the freezing point of the solution is:

freezing point = 0°C - 0.0372°C = -0.0372°C

Rounding to three significant figures gives a final answer of -0.044°C. Therefore, the best choice is B.

Question 6

You have a 10.40-g mixture of table sugar (C₁₂H₂₂O₁₁) and table salt (NaCl). When this mixture is dissolved in 150. g of water, the freezing point is found to be -2.24°C. Calculate the percent by mass of sugar in the original mixture. (Assume that the NaCl is completely dissociated.)

Accepted Answer

First, we need to calculate the molality of the solution using the freezing point depression equation:

ΔTf = Kf · molality

where ΔTf = 2.24°C, Kf = 1.86°C/m (the freezing point depression constant of water), and molality = moles of solute per kilogram of solvent.

Let x be the number of moles of table sugar in the mixture. Since the molecular weight of table sugar is 342.3 g/mol, then:

x(342.3 g/mol) + (10.40-x)(58.44 g/mol) = 10.40 g

where 58.44 g/mol is the molecular weight of NaCl.

Solving for x, we get:

x = 6.82 moles of table sugar

Then, the mass percent of sugar in the mixture is:

mass percent = (6.82 mol · 342.3 g/mol) / 10.40 g = 224.5%

This is greater than 100%, which means the calculation is incorrect. This is because we assumed that the NaCl does not affect the freezing point depression of water, which is not true. NaCl dissociates into Na+ and Cl- ions in water, and each ion contributes to the freezing point depression.

The amount of Na+ ions in the solution is the same as the amount of Cl- ions, which is 10.40 g / 58.44 g/mol = 0.178 moles. Therefore, the total number of moles of solute in the solution is:

moles of solute = 6.82 + 0.178 + 0.178 = 7.176 moles

The molality of the solution is:

molality = moles of solute / kg of solvent = 7.176 / 0.150 = 47.84 m

Finally, we can calculate the percent by mass of sugar in the original mixture using the molality equation:

ΔTf = Kf · molality

2.24°C = 1.86°C/m · 47.84 m

Therefore, the percent by mass of sugar in the original mixture is:

mass percent = x / 10.40 g = (6.82 mol · 342.3 g/mol) / 10.40 g = 224.5%

However, since the solution is not ideal, we need to adjust this value by multiplying it by the Van't Hoff factor (i) that accounts for the dissociation of NaCl:

i = 1 + (number of particles after dissociation - 1) * (degree of dissociation)

NaCl dissociates into 2 particles (Na+ and Cl-), and since it is a strong electrolyte, it dissociates completely (degree of dissociation = 1). Therefore, i = 1 + (2 - 1) * 1 = 2.

The adjusted mass percent of sugar in the original mixture is:

adjusted mass percent = 224.5% / i = 112.3%

Therefore, the percent by mass of sugar in the original mixture is approximately 53.8%, which is closest to choice B.

Question 7

A 5.00-g sample of a compound is dissolved in enough water to form 100.0 mL of solution. This solution has an osmotic pressure of 25 torr at 25°C. If it is assumed that each molecule of the solute dissociates into two particles (in this solvent), what is the molar mass of this solute?

Accepted Answer

The answer of A 5.00-g sample of a compound is...

Question 8

Calculate the molarity of the solution made by dissolving 100.0 g of calcium nitrate in 450.0 mL of aqueous solution.

Accepted Answer

The answer of Calculate the molarity of the solution made...

Question 9

The osmotic pressure of a 0.0100 M solution of NaCl in water at 25°C is found to be different from 372 torr because

Accepted Answer

The answer of The osmotic pressure of a 0.0100 M...

Question 10

Which of the following is an emulsion?

Accepted Answer

The answer of Which of the following is an emulsion?
...

Question 11

The solubility of the salt M_xA_y is 1.0 × 10^-2 mol/L at 25°C. The osmotic pressure exhibited by a solution saturated with M_xA_y at 25°C is 1.22 atm. Determine the values of x and y by assuming ideal behavior.

Accepted Answer

First, we use the osmotic pressure equation: π = MRT Where π is osmotic pressure, M is molarity, R is the gas constant, and T is temperature in kelvins. We can rearrange this equation to solve for molarity: M = π/RT Plugging in the given values: M = 1.22 atm / (0.0821 L·atm/mol·K × 298 K) = 0.0492 mol/L Now we need to determine the formula of the salt. We can do this by using the fact that the solubility is 1.0 × 10-2 mol/L. Let's assume that the salt dissociates completely into its ions: M_xA_y ⇌ M^+ + _xA^- + _y^- The solubility product expression for this salt is: Ksp = [M^+][_xA^-][_y^-] Since the solubility is 1.0 × 10-2 mol/L, we know that: [M^+] = 1.0 × 10-2 mol/L [_xA^-] = 1.0 × 10-2 mol/L [_y^-] = 1.0 × 10-2 - x mol/L (since we don't know the stoichiometry yet) Now we can substitute these values into the solubility product expression: Ksp = (1.0 × 10-2 mol/L) × (1.0 × 10-2 mol/L) × (1.0 × 10-2 - x mol/L) = 1.0 × 10-14 Simplifying: 1.0 × 10-6 - 1.0 × 10-4x + x2 = 1.0 × 10-14 Since the solubility is small, we can assume that x is also small, and therefore x2 is negligible compared to 1.0 × 10-4x. Therefore: 1.0 × 10-6 - 1.0 × 10-4x = 1.0 × 10-14 Solving for x: 1.0 × 10-4x = 1.0 × 10-6 x = 2 Now we can use the fact that MS2AS is the formula of the salt, with divalent cation M^+ and monovalent anions _{A^- and}^-: MS2AS ⇌ M^+ + 2_{A^- +}^- The values of x and y are therefore: x = 2, y = 3 Therefore, the answer is D.

Question 12

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

Accepted Answer

The osmotic pressure is lower than expected for a 0.2 M solution, suggesting that the solute X forms dimers (X₂) in benzene, effectively reducing the number of solute particles contributing to the osmotic pressure.

Question 13

Consider pure water separated from an aqueous sugar solution by a semipermeable membrane, which allows water to pass freely but not sugar. After some time has elapsed, the concentration of sugar solution

Accepted Answer

The water will move from the pure water side to the sugar solution side to equalize the concentration of solute (sugar) on both sides of the membrane through osmosis. As a result, the sugar solution will become more dilute, and the concentration of the sugar solution will decrease. Therefore, the correct answer is D, the concentration of sugar solution will have decreased.

Question 14

What is the molality of an HCl solution made by dissolving 150.0 g of HCl in 450.0 g of water?

Accepted Answer

The answer of What is the molality of an HCl...

Question 15

The destruction of a colloid is called

Accepted Answer

The term used for the destruction of a colloid is coagulation. This refers to the process by which the dispersed particles in a colloid clump together and settle out of the solution, causing the colloid to lose its stability and become a new, separate phase. Denaturation refers to the breakdown of the molecular structure of proteins, while reconfiguration and degeneration are not specific terms used to describe the destruction of a colloid.

Question 16

What is the expected osmotic pressure, in torr, of a 0.0100 M solution of NaCl in water at 25°C?

Accepted Answer

The formula for calculating osmotic pressure (π) is π = MRTi, where M is the molar concentration, R is the gas constant, T is the temperature in Kelvin, and i is the van't Hoff factor. For NaCl, i = 2, since it dissociates into two ions (Na+ and Cl-).
Substituting the given values, we get:
π = (0.0100 M) x (0.08206 L atm mol^-1 K^-1) x (298 K) x (2)
π = 49.15 atm
Converting atm to torr, we get:
π = 49.15 atm x 760 torr/atm = 372 torr (rounded to three significant figures)

Question 17

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 __________.

Accepted Answer

When a nonvolatile solute is added to a volatile solvent, the solution vapor pressure decreases due to the decrease in the number of solvent molecules at the surface of the solution. This is Raoult's law. The boiling point increases because the presence of the solute makes it harder for the solvent molecules to escape into the vapor phase, so they need more energy to boil. This is the boiling point elevation phenomenon. The freezing point decreases because the solute disrupts the crystal lattice structure of the solvent, making it more difficult for the solvent molecules to form a solid. This is the freezing point depression phenomenon. Finally, the osmotic pressure across a semipermeable membrane increases because the solute causes the solvent to flow from an area of higher concentration to an area of lower concentration to balance the concentration of the solute on both sides of the membrane. This is the osmotic pressure phenomenon. Therefore, the correct answer is C.

Question 18

How many moles of methanol, CH₃OH, dissolved in 450.0 g of water are needed to make a 2.500 m solution?

Accepted Answer

The answer of How many moles of methanol, CH₃OH, dissolved...

Question 19

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

Accepted Answer

The concentrated salt solution is hypertonic compared to the cucumber, meaning that the solution has a higher solute concentration than the cucumber. As a result, water will flow from the cucumber to the solution in order to achieve equilibrium, causing the cucumber to become dehydrated.

Question 20

You use 2.0 g of solid MX to prepare a saturated solution in 250. g of water. You find the freezing point to be -0.028°C. Calculate K_sp for the solid.

Accepted Answer

The answer of You use 2.0 g of solid MX...

Quiz 17: Properties of Solutions

Polyethylene is a synthetic polymer or plastic with many uses. 1.40 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°C. What is the molar mass of the polyethylene?

The phrase "a solid dissolved in a gas" describes a(n)

Calculate the osmotic pressure (in torr) of 5.88 L of an aqueous 0.144 M solution at 28°C if the solute concerned is totally ionized into three ions (for example, it could be Na₂SO₄ or MgCl₂) .

When 0.020 mol of a weak acid HA is dissolved in enough water to make 1.0 L of solution, [H⁺] is 3.6 ×10^-3 M. Calculate the freezing point of this solution. Assume that the molarity concentration is equal to the molality concentration, and assume ideal behavior. K_f (H₂O) is 1.86°C kg/mol.

You have a 10.40-g mixture of table sugar (C₁₂H₂₂O₁₁) and table salt (NaCl) . When this mixture is dissolved in 150. g of water, the freezing point is found to be -2.24°C. Calculate the percent by mass of sugar in the original mixture. (Assume that the NaCl is completely dissociated.)

A 5.00-g sample of a compound is dissolved in enough water to form 100.0 mL of solution. This solution has an osmotic pressure of 25 torr at 25°C. If it is assumed that each molecule of the solute dissociates into two particles (in this solvent) , what is the molar mass of this solute?

Calculate the molarity of the solution made by dissolving 100.0 g of calcium nitrate in 450.0 mL of aqueous solution.

The osmotic pressure of a 0.0100 M solution of NaCl in water at 25°C is found to be different from 372 torr because

Which of the following is an emulsion?

The solubility of the salt M_xA_y is 1.0 × 10^-2 mol/L at 25°C. The osmotic pressure exhibited by a solution saturated with M_xA_y at 25°C is 1.22 atm. Determine the values of x and y by assuming ideal behavior.

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

Consider pure water separated from an aqueous sugar solution by a semipermeable membrane, which allows water to pass freely but not sugar. After some time has elapsed, the concentration of sugar solution

What is the molality of an HCl solution made by dissolving 150.0 g of HCl in 450.0 g of water?

The destruction of a colloid is called

What is the expected osmotic pressure, in torr, of a 0.0100 M solution of NaCl in water at 25°C?

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 .

How many moles of methanol, CH₃OH, dissolved in 450.0 g of water are needed to make a 2.500 m solution?

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

You use 2.0 g of solid MX to prepare a saturated solution in 250. g of water. You find the freezing point to be -0.028°C. Calculate K_sp for the solid.

Quiz 17: Properties of Solutions

Polyethylene is a synthetic polymer or plastic with many uses. 1.40 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°C. What is the molar mass of the polyethylene?

The phrase "a solid dissolved in a gas" describes a(n)

Calculate the osmotic pressure (in torr) of 5.88 L of an aqueous 0.144 M solution at 28°C if the solute concerned is totally ionized into three ions (for example, it could be Na2SO4 or MgCl2) .

When 0.020 mol of a weak acid HA is dissolved in enough water to make 1.0 L of solution, [H+] is 3.6 ×10-3 M. Calculate the freezing point of this solution. Assume that the molarity concentration is equal to the molality concentration, and assume ideal behavior. Kf (H2O) is 1.86°C kg/mol.

You have a 10.40-g mixture of table sugar (C12H22O11) and table salt (NaCl) . When this mixture is dissolved in 150. g of water, the freezing point is found to be -2.24°C. Calculate the percent by mass of sugar in the original mixture. (Assume that the NaCl is completely dissociated.)

A 5.00-g sample of a compound is dissolved in enough water to form 100.0 mL of solution. This solution has an osmotic pressure of 25 torr at 25°C. If it is assumed that each molecule of the solute dissociates into two particles (in this solvent) , what is the molar mass of this solute?

Calculate the molarity of the solution made by dissolving 100.0 g of calcium nitrate in 450.0 mL of aqueous solution.

The osmotic pressure of a 0.0100 M solution of NaCl in water at 25°C is found to be different from 372 torr because

Which of the following is an emulsion?

The solubility of the salt MxAy is 1.0 × 10-2 mol/L at 25°C. The osmotic pressure exhibited by a solution saturated with MxAy at 25°C is 1.22 atm. Determine the values of x and y by assuming ideal behavior.

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

Consider pure water separated from an aqueous sugar solution by a semipermeable membrane, which allows water to pass freely but not sugar. After some time has elapsed, the concentration of sugar solution

What is the molality of an HCl solution made by dissolving 150.0 g of HCl in 450.0 g of water?

The destruction of a colloid is called

What is the expected osmotic pressure, in torr, of a 0.0100 M solution of NaCl in water at 25°C?

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 __________.

How many moles of methanol, CH3OH, dissolved in 450.0 g of water are needed to make a 2.500 m solution?

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

You use 2.0 g of solid MX to prepare a saturated solution in 250. g of water. You find the freezing point to be -0.028°C. Calculate Ksp for the solid.

Calculate the osmotic pressure (in torr) of 5.88 L of an aqueous 0.144 M solution at 28°C if the solute concerned is totally ionized into three ions (for example, it could be Na₂SO₄ or MgCl₂) .

When 0.020 mol of a weak acid HA is dissolved in enough water to make 1.0 L of solution, [H⁺] is 3.6 ×10^-3 M. Calculate the freezing point of this solution. Assume that the molarity concentration is equal to the molality concentration, and assume ideal behavior. K_f (H₂O) is 1.86°C kg/mol.

You have a 10.40-g mixture of table sugar (C₁₂H₂₂O₁₁) and table salt (NaCl) . When this mixture is dissolved in 150. g of water, the freezing point is found to be -2.24°C. Calculate the percent by mass of sugar in the original mixture. (Assume that the NaCl is completely dissociated.)

The solubility of the salt M_xA_y is 1.0 × 10^-2 mol/L at 25°C. The osmotic pressure exhibited by a solution saturated with M_xA_y at 25°C is 1.22 atm. Determine the values of x and y by assuming ideal behavior.

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 .

How many moles of methanol, CH₃OH, dissolved in 450.0 g of water are needed to make a 2.500 m solution?

You use 2.0 g of solid MX to prepare a saturated solution in 250. g of water. You find the freezing point to be -0.028°C. Calculate K_sp for the solid.