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

Water has a molal freezing point constant of 1.86°C kg/mol. Calculate the freezing point of a solution containing 34.335 grams of calcium chloride (CaCl2) dissolved in 163.896 grams of water, assuming complete dissociation.

-7.44°C

-1.86°C

-3.72°C

-5.58°C

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Verified step by step guidance

First, calculate the molar mass of calcium chloride (CaCl2). The molar mass is the sum of the atomic masses of calcium (Ca), chlorine (Cl), and chlorine (Cl) again. Use the periodic table to find these values: Ca = 40.08 g/mol, Cl = 35.45 g/mol. Therefore, the molar mass of CaCl2 is 40.08 + 35.45 + 35.45 g/mol.

Next, determine the number of moles of CaCl2 in the solution. Use the formula: \( \text{moles} = \frac{\text{mass}}{\text{molar mass}} \). Substitute the mass of CaCl2 (34.335 g) and the molar mass calculated in the previous step to find the moles.

Calculate the molality of the solution. Molality (m) is defined as moles of solute per kilogram of solvent. Use the formula: \( m = \frac{\text{moles of solute}}{\text{mass of solvent in kg}} \). Convert the mass of water from grams to kilograms (163.896 g = 0.163896 kg) and use the moles of CaCl2 from the previous step.

Consider the van't Hoff factor (i) for CaCl2, which dissociates into three ions: one Ca²⁺ and two Cl⁻ ions. Therefore, \( i = 3 \). Use the formula for freezing point depression: \( \Delta T_f = i \cdot K_f \cdot m \), where \( K_f \) is the molal freezing point depression constant (1.86°C kg/mol). Substitute the values for \( i \), \( K_f \), and molality to find \( \Delta T_f \).

Finally, calculate the new freezing point of the solution. The freezing point depression \( \Delta T_f \) is subtracted from the normal freezing point of water (0°C) to find the freezing point of the solution. Use the formula: \( \text{Freezing point} = 0°C - \Delta T_f \).