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# not sure how to get started- as in which equation to use?

Calculate the mass of water vapor presemt in a room of volume 400m^3 that contains air aat 27 degrees Celsius on a day when the relative humidity is 60 percent. I started writing out what was given, but there are a few formulas i can use...so which one would be the best and that would give me an accurate answer?

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- zircaliumLv 61 decade agoFavorite Answer
1. Find the vapor pressure of water at 27C. The partial pressure of water is 60% of this, as the relative humidity is at 60%.

2. Use the ideal gas law, PV=nRT, with the partial pressure of water (not atmospheric pressure) and the volume and temperature of the room to find the moles of water present.

3. Multiply the moles of water by the molar mass of water to get the mass of water vapor present.

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