If the given percentage is mole percent or volume percent, that is correct. The mole fraction of CO2 will be 0.04 mol / 1 mol, ÷ 100 = 0.0004 and the partial pressure of CO2 will be (0.0004)(760 mm Hg) = 0.304 mm Hg. If the percentage is percent by mass, then we would need more information to calculate the mole fraction of CO2. The moles of CO2 is mass/molar mass of CO2, but the problem does not give us enough information to calculate the total moles of gases. However, the percentages of the different gases in air are usually given as volume percents. These will be numerically equal to the mole percent. The mole percent is the mole fraction X 100, so the mole fraction is the mole percent divided by 100, as you did.  Steve |
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