Table of contents

1. Intro to General Chemistry3h 48m
2. Atoms & Elements4h 16m
3. Chemical Reactions4h 10m
4. BONUS: Lab Techniques and Procedures1h 38m
5. BONUS: Mathematical Operations and Functions48m
6. Chemical Quantities & Aqueous Reactions3h 53m
7. Gases3h 49m
8. Thermochemistry2h 37m
9. Quantum Mechanics2h 58m
10. Periodic Properties of the Elements3h 9m
11. Bonding & Molecular Structure3h 29m
12. Molecular Shapes & Valence Bond Theory1h 57m
13. Liquids, Solids & Intermolecular Forces2h 23m
14. Solutions3h 1m
15. Chemical Kinetics2h 53m
16. Chemical Equilibrium2h 29m
17. Acid and Base Equilibrium5h 1m
18. Aqueous Equilibrium4h 47m
19. Chemical Thermodynamics1h 50m
20. Electrochemistry2h 42m
21. Nuclear Chemistry2h 36m
22. Organic Chemistry5h 7m
23. Chemistry of the Nonmetals2h 39m
24. Transition Metals and Coordination Compounds3h 16m

14. Solutions

Freezing Point Depression

General Chemistry

14. Solutions

Freezing Point Depression

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Multiple Choice

A solution was prepared by dissolving 2.500 g of a non-dissociating solute in 125 g of pure water. The resulting solution has a freezing point of -0.190°C. The Kf of water is 1.86°C/m. What is the molar mass of the unknown solute?

125 g/mol

245 g/mol

58.5 g/mol

186 g/mol

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Verified step by step guidance

Step 1: Understand the concept of freezing point depression. The freezing point of a solution is lower than that of the pure solvent due to the presence of a solute. The change in freezing point (ΔTf) can be calculated using the formula: ΔTf = i * Kf * m, where i is the van't Hoff factor (which is 1 for non-dissociating solutes), Kf is the freezing point depression constant, and m is the molality of the solution.

Step 2: Calculate the change in freezing point (ΔTf). Since the freezing point of the solution is -0.190°C and the freezing point of pure water is 0°C, the change in freezing point is ΔTf = 0°C - (-0.190°C) = 0.190°C.

Step 3: Use the formula for freezing point depression to find the molality (m) of the solution. Rearrange the formula to solve for m: m = ΔTf / (i * Kf). Substitute the values: m = 0.190°C / (1 * 1.86°C/m).

Step 4: Calculate the number of moles of solute using the molality. Molality (m) is defined as moles of solute per kilogram of solvent. Rearrange the definition to solve for moles of solute: moles of solute = m * mass of solvent (in kg). Convert the mass of water from grams to kilograms: 125 g = 0.125 kg. Substitute the values to find the moles of solute.

Step 5: Determine the molar mass of the solute. Molar mass is defined as the mass of solute divided by the number of moles of solute. Use the mass of the solute (2.500 g) and the moles of solute calculated in the previous step to find the molar mass: molar mass = mass of solute / moles of solute.