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Suatu larutan urea mempunyai tekanan uap 98 mmhg. Pada suhu yang sama air murni mempunyai tekanan uap jenuh 100 mmhg. Kadar larutan urea tersebut adalah ... %(mr urea = 60; air = 18)
Accepted Answer
The solution contains 3.33% urea by mass. Here's how to calculate it:
1. Understanding the Concept: The vapor pressure of a solution is lower than the vapor pressure of the pure solvent. This is known as Raoult's Law. The reduction in vapor pressure is directly proportional to the mole fraction of the solute in the solution.
2. Applying Raoult's Law:
- Let the mole fraction of urea in the solution be 'x'.
- Vapor pressure of solution (P) = 98 mmHg.
- Vapor pressure of pure water (P°) = 100 mmHg.
- According to Raoult's Law: P = x
P°
- 98 = x
100
- x = 0.98
3. Calculating Mass Fraction:
- Let the mass of urea be 'm' grams.
- Mass of water = 100 - m grams.
- Moles of urea (nurea) = m / 60
- Moles of water (nwater) = (100-m) / 18
- Mole fraction of urea (x) = nurea / (nurea + nwater)
- 0.98 = (m/60) / [(m/60) + ((100-m)/18)]
- Solving for 'm', we get m ≈ 3.33 grams.
4. Mass Percentage:
- Mass percentage of urea = (mass of urea / total mass of solution)
100
- Mass percentage of urea = (3.33 / 100)
100 = 3.33%
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