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Ch.13 - Properties of Solutions
All textbooksBrown 14th EditionCh.13 - Properties of SolutionsProblem 104b
Chapter 13, Problem 104b

Carbon disulfide (CS2) boils at 46.30 °C and has a density of 1.261 g/mL. (b) When 5.39 g of a nondissociating unknown is dissolved in 50.0 mL of CS2, the solution boils at 47.08 °C. What is the molar mass of the unknown?

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First, identify the boiling point elevation formula: ΔT_b = i * K_b * m, where ΔT_b is the boiling point elevation, i is the van't Hoff factor (which is 1 for a nondissociating solute), K_b is the ebullioscopic constant of the solvent, and m is the molality of the solution.
Calculate the boiling point elevation, ΔT_b, by subtracting the boiling point of pure CS2 from the boiling point of the solution: ΔT_b = 47.08 °C - 46.30 °C.
Determine the molality (m) of the solution using the formula: m = moles of solute / kg of solvent. First, convert the volume of CS2 to mass using its density: mass of CS2 = 50.0 mL * 1.261 g/mL.
Rearrange the boiling point elevation formula to solve for the molality: m = ΔT_b / (i * K_b). You will need the ebullioscopic constant (K_b) for CS2, which can be found in a reference source.
Finally, calculate the molar mass of the unknown solute using the formula: molar mass = mass of solute / moles of solute. Use the molality and the mass of the solvent to find the moles of solute, and then use the given mass of the solute (5.39 g) to find its molar mass.

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Carbon disulfide (CS2) boils at 46.30 °C and has a density of 1.261 g/mL. (a) When 0.250 mol of a nondissociating solute is dissolved in 400.0 mL of CS2, the solution boils at 47.46 °C. What is the molal boiling-point-elevation constant for CS2?

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A lithium salt used in lubricating grease has the formula LiC nH2n + 1O2. The salt is soluble in water to the extent of 0.036 g per 100 g of water at 25 °C. The osmotic pressure of this solution is found to be 57.1 torr. Assuming that molality and molarity in such a dilute solution are the same and that the lithium salt is completely dissociated in the solution, determine an appropriate value of n in the formula for the salt.
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Fluorocarbons (compounds that contain both carbon and fluorine) were, until recently, used as refrigerants. The compounds listed in the following table are all gases at 25 °C, and their solubilities in water at 25 °C and 1 atm fluorocarbon pressure are given as mass percentages. (a) For each fluorocarbon, calculate the molality of a saturated solution.

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Fluorocarbons (compounds that contain both carbon and fluorine) were, until recently, used as refrigerants. The compounds listed in the following table are all gases at 25 °C, and their solubilities in water at 25 °C and 1 atm fluorocarbon pressure are given as mass percentages. (b) Which molecular property best predicts the solubility of these gases in water: molar mass, dipole moment, or ability to hydrogen-bond to water?

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