Multiple choice

Equal masses of methane and oxygen are mixed in an empty container at ${25}^{o}C$. The fraction of total pressure exerted by oxygen is:

  1. $1/3$
  2. $1/2$
  3. $2/3$
  4. $\cfrac{1}{3}\times \cfrac{273}{308}$
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A Correct answer
Explanation

Equal masses means moles of CH4 = m/16 and moles of O2 = m/32. Total moles = m(1/16 + 1/32) = 3m/32. Mole fraction of O2 = (m/32) / (3m/32) = 1/3. Pressure fraction equals mole fraction.

AI explanation

Let the equal masses of methane and oxygen be w grams, meaning their respective moles are w divided by 16 and w divided by 32. The ratio of their moles simplifies to 2 to 1, making the total parts 3. The mole fraction of oxygen is 1 divided by 3, and by Dalton's law of partial pressures, its fraction of the total pressure is 1/3.

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