Question

The equilibrium vapor pressure of mercury at room temperature is about 1.6x10-6 atm. Imagine an old chemistry lab that over the years has experienced enough liquid mercury spills and thereby accumulated enough mercury in cracks in the floor, etc. that mercury liquid-vapor equilibrium has been established. What is the concentration, in the units of milligrams per cubic meter, of Hg0 in the air of the room? Does this value exceed the limit of 0.05 mg m-3 established by the American Conference of Governmental Industrial Hygienists (ACGIH) for safe exposure based upon a 40-hour work week?

Answer 1

first calculate mole fraction of mercury in air

total pressure = 1 atm

pressure of mercury = 1.6 10^-6 atm

we know the formla

X_i = P_i / P where, X_i =mole fraction of indivisual gas, P_i = partial pressure of indivisual gas, P = mole fraction

mole fraction of mercury = 1.6 10^-6 /1 = 0.0000016

1 m³ = 1000 L

at STP 1 mole of gas occupy volume 22.414 L then 1000L = 1000/22.414 = 44.61497 mole

total mole of gas = 44.61497 mole

mole fraction of mercury is 0.0000016 that mean1 mole of gas contain 0.0000016 mole of mercury then 44.61497 mole of gas contain = 44.61497 0.0000016 = 0.00007138395 mole of mercury

molar mass of mercury = 200.59 gm/mole that mean 1 mole of mercury = 200.59 gm then 0.00007138395 mole of mercury = 200.59 0.00007138395 = 0.0143189 gm of mercury

0.0143489 gm = 14.3489 mg

thus concentration of mercury = 14.3489 mg/m³ it is exceed the limit of 0.05 mg/m³