Physical Chemistry - Solutions
Q. If 0.5 moles of a non-volatile solute is dissolved in 1 kg of water, what is the expected vapor pressure lowering? (2020)
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A.
0.5 P0
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B.
0.25 P0
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C.
0.75 P0
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D.
0.1 P0
Solution
Vapor pressure lowering = (moles of solute / moles of solvent) * P0 = (0.5 / 55.5) * P0 ≈ 0.25 P0.
Correct Answer: B — 0.25 P0
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Q. What is the effect of adding a non-volatile solute to a solvent on its boiling point? (2019)
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A.
Increases boiling point
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B.
Decreases boiling point
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C.
No effect
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D.
Depends on the solute
Solution
Adding a non-volatile solute increases the boiling point due to boiling point elevation.
Correct Answer: A — Increases boiling point
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Q. What is the freezing point depression of a solution containing 1 mole of NaCl in 1 kg of water? (2022)
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A.
1.86 °C
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B.
3.72 °C
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C.
2.52 °C
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D.
0.93 °C
Solution
Freezing point depression = i * Kf * m = 2 * 1.86 * 1 = 3.72 °C (i = 2 for NaCl).
Correct Answer: A — 1.86 °C
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Q. What is the osmotic pressure of a solution containing 2 moles of glucose in 1 liter of solution at 25 °C? (2021)
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A.
0.0821 atm
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B.
1.0 atm
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C.
2.0 atm
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D.
4.0 atm
Solution
Osmotic pressure (π) = iCRT = 1 * 2 * 0.0821 * 298 = 4.0 atm (i = 1 for glucose).
Correct Answer: C — 2.0 atm
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Q. What is the van 't Hoff factor (i) for a strong electrolyte like Na2SO4 in solution? (2023)
Solution
Na2SO4 dissociates into 3 ions (2 Na⁺ and 1 SO4²⁻), so i = 3.
Correct Answer: C — 3
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Q. What is the vapor pressure of a solution containing 1 mole of solute in 9 moles of solvent, assuming ideal behavior? (2019)
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A.
0.1 P0
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B.
0.9 P0
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C.
0.5 P0
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D.
0.2 P0
Solution
Using Raoult's law, the vapor pressure of the solution = (moles of solvent / total moles) * P0 = (9 / 10) * P0 = 0.9 P0.
Correct Answer: B — 0.9 P0
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