Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

9. Solutions

Freezing Point Depression

GOB Chemistry

9. Solutions

Freezing Point Depression

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Multiple Choice

When 825 g of an unknown is dissolved in 3.45 L of water, the freezing point of the solution is decreased by 2.89ºC. Assuming that the unknown compound is a non-electrolyte, calculate its molar mass.

154 g/mol

42.4 g/mol

44.5 g/mol

159 g/mol

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Verified step by step guidance

Identify the formula for freezing point depression: \( \Delta T_f = i \cdot K_f \cdot m \), where \( \Delta T_f \) is the change in freezing point, \( i \) is the van't Hoff factor (which is 1 for non-electrolytes), \( K_f \) is the cryoscopic constant of the solvent (water in this case), and \( m \) is the molality of the solution.

Rearrange the formula to solve for molality \( m \): \( m = \frac{\Delta T_f}{i \cdot K_f} \). Since the unknown compound is a non-electrolyte, \( i = 1 \).

Substitute the given values into the equation: \( \Delta T_f = 2.89 \text{ºC} \) and use the known \( K_f \) for water, which is 1.86 \( \text{ºC} \cdot \text{kg/mol} \). Calculate the molality \( m \).

Use the definition of molality: \( m = \frac{\text{moles of solute}}{\text{kg of solvent}} \). Here, the mass of the solvent (water) is 3.45 kg. Rearrange to find the moles of solute: \( \text{moles of solute} = m \cdot 3.45 \text{ kg} \).

Calculate the molar mass of the unknown compound using the formula: \( \text{molar mass} = \frac{\text{mass of solute}}{\text{moles of solute}} \). Substitute the mass of the solute (825 g) and the moles of solute calculated in the previous step to find the molar mass.