Question

A laboratory requires at least 0.92 mg of a chemical X in order to achieve acceptable laboratory accuracy. Assuming that chemical X has a MW of 178 and the anticipated ppm value is between 50 and 150 ppm. What is the minimum volume of air which must be collected with a pump set at 1 L/min

Answer 1

The required mass of chemical X is = 0.92mg = 0.00092 gm

molar mass of chemical X is = 178gm

number of required moles is given by

a) If air concentration is 50 ppm that is

50ppm = 50mg/L = 0.05gm

number of moles of chemical X in one litre of air is given by

now

minimum volume of air needed to be collected is given by

If 1litre of air consists of 2.8X10^-4mol of chemical X

then

volume of air consisting 0.51 X 10^-5 mol is =

b) if air concentration is 150 ppm then

150ppm = 150 mg/l = 0.15gm

number moles of chemical X in 1Litre is given by

hence if one litre of air possess 8.42X10^-4 mol then

volume of air required to be taken for 0.51X10^-5 mol is given by