Question

(a) Air contains 5.2 ppmV of Helium at STP (25o C and 1 atm). Determine the concentration of Helium in ug/L at same condition. (Mw of Helium=2)

(b) EPA limits (maximum allowable) benzene (C6H6) concentration in gasoline to 1.3% by weight. If both Benzene and Gasoline has a density of 0.84 g/mL, what is maximum allowable concentration of Benzene in ppmM.

Answer 1

a)

ppmV = part per million in volume

typically --> mg/L is 1 ppmV

therefore

5.2 ppmV --> 5.2 mg / L

but we require micrograms...

5.2 mg = 5.2*10^3 micogram

so

Concentration of Helium --> 5200 micrograms per liter

b)

w/w = 1.3% B in Gasoline

find ppmM

ppmM = part per million in mass = mg / kg

so....

assume 1 kg of solvent (i.e. gasoline)

then

1.3/100*1000 = 13 grams of benzene allowed

then.. change to miligrams --> 13000 milligrams of benzene per kg of solvent (i.e. ppmM)