Question

1) Air is 21% oxygen and .03% carbon dioxide STP

a)Asume a person expands their lungs to breath 1.4 L of air. How many moles of oxygen gas have they inhaled?

b) This same person visits Denver where at standard tempertaure the air pressure is .83 atm, do they have to breath more or less to get the same number of moles of oxygen?

c)This same person visits aruba where the the temperature is 95 degrees fahrenheit at standard pressure. Does this person need to breath more or less to get the same number of moles of oxygen?

Answer 1

a)

V =1.4 L air...

at STP --> 1 mol = 22.4 L

so

1.4 L --> 1.4/22.4 mol = 0.0625 mol of air

1 mol of air --> 0.21 mol of O2

0.0625 mol of air --> 0.06250.21 = 0.013125 mol of O2

b)

P = 0.83 atm, vs 1 atm

ratio:

P1/n1 = P2/n2

1/0.013125 = 0.83/n2

n2 = 0.83*0.013125 = 0.01089375mol, which is LESS

c)

T = 273 K, T new = 95 F = 308.15 K

so

n1T1 = n2T2

n2 = n1*(T1/T2) = 0.013125 * 273/308.15 = 0.0116278 mol

this must be less than original, so it reuqires much more air, i.e .more breaths