Question 1

The solubility of oxygen in lakes high in mountains is affected by the altitude. If the solubility of O₂ from the air is 2.67 × 10⁻⁴ M at sea level when the pressure is 1.000 atm and the temperature is 25°C, what is the solubility of O₂ at an elevation of 12,000 ft. where the atmospheric pressure is 0.643 atm? Assume the temperature is 25°C, and that the mole fraction of O₂ in air is 0.211 at both 12,000 ft. and at sea level.

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Question 2

What is the freezing point of an aqueous solution of a nonvolatile solute that has a boiling point of 102.45 °C? K_f = 1.86 °C m⁻¹ and K_b = 0.512 °C m⁻¹.

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Question 3

Pure benzene, C₆H₆, has a molar mass of 78.114 g mol⁻¹, a density of 0.8765 g mL⁻¹, a freezing point of 5.45°C, and a boiling point of 80.2°C. Its freezing point depression and boiling point elevation constants are: K_f = 5.07°C m⁻¹; K_b = 2.53°C m⁻¹. A solution was made by taking 33.88 g of an unknown nonelectrolyte and dissolving it in 175.0 g of benzene. The measured freezing point of the solution was -1.65°C. Calculate the molar mass of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.

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Question 4

A solution is made by mixing acetone and methyl alcohol, whose structures are shown as I and II below. Which statement below best describes the characteristics of this mixture?  Hint: How does the strength of hydrogen bonds compare to other intermolecular forces?

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Question 5

Pure cyclohexane, C₆H₁₂, has a molar mass of 84.161 g mol⁻¹, a density of 0.7785 g mL⁻¹, a freezing point of 6.53°C, and a boiling point of 80.72°C. Its freezing point depression and boiling point elevation constants are: K_f = 20.0 °C m⁻¹; K_b = 2.69 °C m⁻¹. A solution was made by taking 9.50 g of an unknown nonelectrolyte and dissolving it in 125.0 g of cyclohexane. The measured freezing point of the solution was -0.78^°C. Calculate the molar mass of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.

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Question 6

Pure cyclohexane, C₆H₁₂, has a molar mass of 84.161 g mol⁻¹ and a density of0.7785 g mL⁻¹, a freezing point of 6.53°C, and a boiling point of 80.72°C. Its freezing point depression and boiling point elevation constants are: K_f = 20.0 °C m⁻¹; K_b = 2.69°C m⁻¹. A solution was made by taking 15.46 g of an unknown nonelectrolyte and dissolving it in 125.0 g of cyclohexane. The measured freezing point of the solution was -4.28°C. Calculate the molar mass of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.

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Question 7

Pure glacial acetic acid, HC₂H₃O₂, has a molar mass of 60.052 g mol⁻¹ and a density of 1.0492 g mL⁻¹, a freezing point of 16.62°C, and a boiling point of 118.3°C. Its freezing point depression and boiling point elevation constants are: K_f = 3.57 °C m⁻¹; K_b = 3.07 °C m⁻¹. A solution was made by taking 19.51 g of an unknown nonelectrolyte and dissolving it in 181.0 g of glacial acetic acid. The measured freezing point of the solution was 8.64°C. Calculate the molar mass of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.

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Question 8

Pure benzene, C₆H₆, has a molar mass of 78.114 g mol⁻¹, a density of 0.8765 g mL⁻¹, a freezing point of 5.45°C, and a boiling point of 80.2°C. Its freezing point depression and boiling point elevation constants are: K_f = 5.07 °C m⁻¹; K_b = 2.53 °C m⁻¹. A solution was made by taking 16.00 g of an unknown nonelectrolyte and dissolving it in 168.0 g of benzene. The measured freezing point of the solution was -1.05°C. Calculate the molar mass of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.

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Question 9

An aqueous solution of fructose, C₆H₁₂O₆, has an osmotic pressure of 10.50 atm at 25.0°C. What is the boiling point of this solution? K_f = 1.86 °C m⁻¹ and K_b = 0.512 °C m⁻¹. The density of the solution is 1.077 g mL⁻¹.Hint: You will need to convert molarity to molality before finding the boiling point elevation.

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Question 10

A solution is made by dissolving 48.07 g of MgSO₄∙7H₂O in 250.0 grams of water. What is the expected freezing point of this solution if the van't Hoff factor is 1.90? K_f = 1.86 °C m⁻¹.Hint: Don't forget to include the 7H₂O when calculating the molar mass of solute.

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Question 11

How many liters of ethylene glycol antifreeze (C₂H₆O₂), with a density of 1.100 g/mL, would you add to your car radiator containing 15.0 kg of water if you needed to protect your engine to -21.5°C? For water, K_f = 1.86°C m⁻¹.Hint: Find molality, moles, grams of solute, milliliters, then liters, making sure to pay attention to units.

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Question 12

A chemist isolates a new compound with an empirical formula C₃H₃O₂. 3.52 g of the unknown compound was dissolved in 100.0 g of water. The resulting solution had a freezing point of -0.307°C. What is the molecular formula for the unknown compound?For water, K_f = 1.86°C m⁻¹.Hint: Use the freezing point depression to find the molar mass of the compound, then find the molecular formula as in Chapter 3.

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Question 13

A phase diagram, like the one below, for an aqueous solution shows a shift in the solid/liquid and liquid/gas phase transitions but there is not a shift in the sublimation line between solids and gases. Explain what causes the shift in the other transitions and why this does not change a shift in the solid/gas transition.Hint: Think about the difference in vapor pressure between a solution and a pure substance.

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Quiz 13: Mixtures at the Molecular Level: Properties of Solutions

What is the freezing point of an aqueous solution of a nonvolatile solute that has a boiling point of 102.45 °C? Kf = 1.86 °C m−1 and Kb = 0.512 °C m−1.

A solution is made by mixing acetone and methyl alcohol, whose structures are shown as I and II below. Which statement below best describes the characteristics of this mixture? Hint: How does the strength of hydrogen bonds compare to other intermolecular forces?

A solution is made by dissolving 48.07 g of MgSO4∙7H2O in 250.0 grams of water. What is the expected freezing point of this solution if the van't Hoff factor is 1.90? Kf = 1.86 °C m−1.Hint: Don't forget to include the 7H2O when calculating the molar mass of solute.

What is the freezing point of an aqueous solution of a nonvolatile solute that has a boiling point of 102.45 °C? K_f = 1.86 °C m⁻¹ and K_b = 0.512 °C m⁻¹.

A solution is made by dissolving 48.07 g of MgSO₄∙7H₂O in 250.0 grams of water. What is the expected freezing point of this solution if the van't Hoff factor is 1.90? K_f = 1.86 °C m⁻¹.Hint: Don't forget to include the 7H₂O when calculating the molar mass of solute.