Calculating Water Molecules and Kg/m³ in Plant's Environment

[meling]

hey guys,

could you'll help me with the following problem...
Inside the leaf of a plant, water vapour passes from the liquid phase to the vapour phase at the walls of the mesophyll cells, as shown in the figure. The water vapour then diffuses through the intercellular air spaces and eventually exits the leaf through the stomatal pores. The diffusion constant for water vapor in air is D = 2.4 x 10-5 m2s-1. A stomatal pore has a cross-sectional area A = 5.5 x 10-11 m2 and a length L = 9.5 x 10-5 m. The plant is being propagated in a controlled environment: T = 31 °C, relative humidity 76 %. The saturated vapour pressure of water at 31 °C is 4.46 kPa.

(a) Assuming that the air around the plant is an ideal gas, what is the concentration of water molecules per cubic meter in the air?
__________ molecules/m³
(b) Given that the molar mass of water is 18.0 g mol-1, what is the concentration of water in the air in kg/m³?
_______kg/m³

Thanks in advance for the help,
Meling

 

[Astronuc]

One is given the partial pressure of the water in the air (4.46 kPa) and ostensibly one can determine the concentration of water molecules per cubic meter in the air. Part b can be determined from part a.

See - http://wine1.sb.fsu.edu/chm1045/notes/Gases/Mixtures/Gases06.htm

http://en.wikipedia.org/wiki/Partial_pressure