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What is the osmotic pressure formed by dissolving 44.2 mg of aspirin (C9H8O4) in 0.358 L of water at 25 °C?
Ch.13 - Properties of Solutions
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970
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Table of contents
- Ch.1 - Introduction: Matter, Energy, and Measurement146
- Ch.2 - Atoms, Molecules, and Ions200
- Ch.3 - Chemical Reactions and Reaction Stoichiometry176
- Ch.4 - Reactions in Aqueous Solution155
- Ch.5 - Thermochemistry126
- Ch.6 - Electronic Structure of Atoms131
- Ch.7 - Periodic Properties of the Elements126
- Ch.8 - Basic Concepts of Chemical Bonding123
- Ch.9 - Molecular Geometry and Bonding Theories143
- Ch.10 - Gases147
- Ch.11 - Liquids and Intermolecular Forces91
- Ch.12 - Solids and Modern Materials122
- Ch.13 - Properties of Solutions126
- Ch.14 - Chemical Kinetics174
- Ch.15 - Chemical Equilibrium101
- Ch.16 - Acid-Base Equilibria139
- Ch.17 - Additional Aspects of Aqueous Equilibria146
- Ch.18 - Chemistry of the Environment72
- Ch.19 - Chemical Thermodynamics129
- Ch.20 - Electrochemistry142
- Ch.21 - Nuclear Chemistry101
- Ch.22 - Chemistry of the Nonmetals68
- Ch.23 - Transition Metals and Coordination Chemistry66
- Ch.24 - The Chemistry of Life: Organic and Biological Chemistry10
Chapter 13, Problem 82
Lauryl alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00 g of lauryl alcohol in 0.100 kg of benzene freezes at 4.1 °C. What is the molar mass of lauryl alcohol from these data? See Table 13.3 for the normal freezing point and 𝐾f of benzene.
Verified step by step guidance1
Determine the normal freezing point and the cryoscopic constant (Kf) of benzene from Table 13.3. The normal freezing point is the temperature at which pure benzene freezes, and Kf is a constant used in calculating the freezing point depression.
Calculate the freezing point depression (ΔTf) by subtracting the freezing point of the solution from the normal freezing point of benzene. ΔTf = (normal freezing point of benzene) - (freezing point of the solution).
Use the freezing point depression equation ΔTf = Kf * m, where m is the molality of the solution (moles of solute per kilogram of solvent), to solve for the molality of the solution. Rearrange the equation to find m: m = ΔTf / Kf.
Convert the mass of lauryl alcohol to moles using its molar mass (M), which is unknown. The relationship is moles = mass / molar mass (moles = 5.00 g / M).
Finally, use the definition of molality (moles of solute per kilogram of solvent) and the molality calculated in step 3 to find the molar mass of lauryl alcohol. Rearrange m = moles / mass of solvent (in kg) to solve for M: M = mass of lauryl alcohol / (molality * mass of solvent).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Freezing Point Depression
Freezing point depression is a colligative property that describes how the freezing point of a solvent decreases when a solute is added. The extent of this depression is directly proportional to the molality of the solution and the freezing point depression constant (Kf) of the solvent. This principle is crucial for determining the molar mass of a solute by measuring the change in freezing point.
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Freezing Point Depression
Molality
Molality is a measure of the concentration of a solute in a solution, defined as the number of moles of solute per kilogram of solvent. It is an important concept in colligative properties because it provides a direct relationship between the amount of solute and the effect on the physical properties of the solvent, such as freezing point and boiling point.
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Molar Mass Calculation
Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To calculate the molar mass of a solute using freezing point depression, one can rearrange the formula that relates freezing point change to molality and Kf, allowing for the determination of the molar mass based on the mass of the solute and the observed freezing point change.
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Related Practice
Textbook Question
Seawater contains 34 g of salts for every liter of solution. Assuming that the solute consists entirely of NaCl (in fact, over 90% of the salt is indeed NaCl), calculate the osmotic pressure of seawater at 20 °C
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Textbook Question
Adrenaline is the hormone that triggers the release of extra glucose molecules in times of stress or emergency. A solution of 0.64 g of adrenaline in 36.0 g of CCl4 elevates the boiling point by 0.49 °C. Calculate the approximate molar mass of adrenaline from this data.
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Textbook Question
Lysozyme is an enzyme that breaks bacterial cell walls. A solution containing 0.150 g of this enzyme in 210 mL of solution has an osmotic pressure of 0.953 torr at 25 °C. What is the molar mass of lysozyme?
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Textbook Question
A dilute aqueous solution of an organic compound soluble in water is formed by dissolving 2.35 g of the compound in water to form 0.250 L of solution. The resulting solution has an osmotic pressure of 0.605 atm at 25 °C. Assuming that the organic compound is a nonelectrolyte, what is its molar mass?
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Textbook Question
The osmotic pressure of a 0.010 M aqueous solution of CaCl2 is found to be 0.674 atm at 25 °C. Calculate the van't Hoff factor, i, for the solution.
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