Chemistry vapour pressure, help!?

[匿名]

2020-10-13 1:28 am

Here is the question:
How many grams of sucrose (C12H22O11) must be added to 691 g of water to give a solution with a vapor pressure 0.225 mmHg less than that of pure water at 20°C? (The vapor pressure of water at 20°C is 17.5 mmHg.)

Thank you!

回答 (1)

賣女孩的火柴

2020-10-13 2:02 am

✔ 最佳答案

Molar mass of C₁₂H₂₂O₁₁ = (12.0×12 + 1.0×22 + 16.0×11) g/mol = 342.0 g/mol
Molar mass of H₂O = (1.0×2 + 16.0) g/mol = 18.0 g/mol

v.p. of the solution = X(H₂O) * (v.p. of pure water)
17.5 - 0.225 = X(H₂O) * 17.5
X(H₂O) = 0.98714
X(C₁₂H₂₂O₁₁) = 1 - 0.98714 = 0.01286

Moles of water in the solution = (691 g) / (18.0 g/mol) = 38.39 mol
Moles of C₁₂H₂₂O₁₁ in the solution = (38.39 mol) × (0.01286/0.98714) = 0.5001 mol
Mass of C₁₂H₂₂O₁₁ in the solution = (0.5001 mol) × (342.0 g/mol) = 171 g

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