Homework Help: college Chemistry

Posted by CM on Sunday, October 19, 2008 at 8:37pm.

An adult takes about 15 breaths per minute, with each breath having a volume of 500mL. if the air that is inhaled is "dry", but he exhaled air is 1 atm pressure is saturated with water vapor at 37 degree C(body temp), what mass of water is lost from the body in 1hr? The vapor pressure of water at 37degree C is 47.1 mmHg.

I tried doing this with partial pressures but its not coming out right.Please Help!!

college Chemistry - GK, Sunday, October 19, 2008 at 9:00pm
The volume of air inhaled in 1 hour is
(60 min/hr)(15 br./min) = 900 breaths
(900 br.)(0.500L/breath) = 450 L
To find moles of H2O, use the Ideal Gas Law:
PV = nRT
1 atm = 760 mm Hg
47.1mmHg/760 mmHg/atm = 0.061974 atm
P = 0.061974 atm for water vapor
R = 0.08206 L.atm/K.mol
T = 273 + 37 = 310K
Find moles of H2O:
n = PV / RT
Mass of H2O in grams is:
(moles H2O)(18.015 g/mol.H2O)
- college Chemistry - CM, Sunday, October 19, 2008 at 9:09pm
  but the air that came out has a pressure of 1atm. doesnt that mean it has the partial pressure of air and water in it??
- college Chemistry - CM, Sunday, October 19, 2008 at 9:22pm
  the question was
  ....but the exhaled air at 1atm pressure is saturated with water vapor.....

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