a lower tank contains water while an upper tank contains air with a negligable concentration of water vapor. tube with a circular cross section and radius 0.050 m is inserted between the two tanks. the length of the tube is 0.25 m. the diffusion coefficent of water vapor is 2.4 * 10^-5 m^2/s. the concentration of water vapor just above the surface of the water is 1.7 * 10^-2 kg/m^3. if the water vapor is removed from the upper tank so that the concentration there remains nearly zero, what mass of water vapor diffuses through the tube each hour?