Question

1. Ideal gas law and molar mixing ratios

a. CO2 molar mixing ratios are 400 ppmv. What is this as a percent abundance?

b. CFC-11 molar mixing ratios are 250 pptv. What is this as a percent abundance?

c. Calculate the ozone concentration in µg/m3 for a polluted day in Mexico City (200 ppbv ozone, temperature = 30 °C, pressure = 0.77 atmospheres pressure).

d. Helium gas contains trace amounts of methane (helium is obtained from some oil and gas wells and is a non-renewable resource). Consider a helium balloon pressurized to 5 psi. If the methane molar mixing ratio is 800 ppmv, what is the pressure of methane in the balloon?

Answer 1

Ans 3

Pressure P =0.77 atm

Temperature T= 30 + 273 = 303 K

Gas constant R = 0.0821 L-atm/mol-K

From the ideal gas equation

Volume of 1 L gas in a mol

V = RT/P

= 0.0821 x 303/0.77

= 32.31 L/mol

Molecular weight of ozone = 48 g/mol

Concentration in ppm = 200 ppbv x 0.001 ppmv/ppbv

= 0.2 ppmv x (1 ppm)/(29/48)ppmv

= 0.331 ppm

Concentration in µg/m3

= concentration in ppm x molecular weight / V

= (0.331 x 48 ) /(32.31)

= 0.4917 mg/m3 x (1000µg/mg)

= 491.7 µg/m3