Question

An ideal gas, of volume $189mL$, is collected over water. The temperature is ${27}^{\circ }C$, and the barometric pressure is $756mmHg$. At ${27}^{\circ }C$, the vapor pressure of water is $27mmHg$.

Which of the following CORRECTLY gives the mole fraction of water vapor in the collection vessel?

• A. $\frac{27}{756}$
• B. $\frac{27}{729}$
• C. $\frac{729}{756}$
• D. $\frac{729}{27}$

Answer 1

The correct option is A $\frac{27}{756}$

Mole fraction of water $=\frac{\text{vapor pressure of water}}{\text{barometric pressure}}=\frac{27}{756}$