We filled a 20 litre gas flask up to 7 mbar with pure CO and then topped it up with nitrogen to 15 bar, what would the final CO concentration be in ppm?

Answer 1

Concentration in gas is moles to moles not grams to grams as in liquids. A millibar is one thousandth of a bar. By using the gas law equation PV=nRT moles can be found to be proportional to pressure. (divide both sides by V to have P= n (RT/V). RT/V is the proportional constant since volume and the sum of the pressures is constant. Remember Dalton's Law that the pressure of the whole is equal to the sum of the partials. Now compare the pressures: 7/1,000 CO : 15 N2 ; multiply each side by 1000: 7 CO : 15,000 N2. Set up a proportion : 7/15,000 = x/1,000,000 for parts per million and use cross multiplication for solving for x. 7,000,000 = 15,000 x. Divide both sides by 15,000 and find x = 467 ppm. But the data with the lowest significant figures is 7 so the answer can only have 1 significant figure. Thus the answer is 5 X 10^2 ppm.