Liquid-phase concentrations are often expressed as mass ratios, i.e. , 1 ppm = o

Question

Liquid-phase concentrations are often expressed as mass ratios, i.e., 1 ppm = one gram per million grams of solution (In water solutions, one liter of water weighs approximately one kilogram, and thus 1 ppm = 1 mg/L.) Gas-phase concentrations are usually expressed as volume (or mole) ratios, i.e, 1 ppm = one mole per million moles of total gas. National Ambient Air Quality Standards (NAAQS) include: carbon monoxide - 35 ppm (1 hr exposure); nitrogen dioxide - 0.053 ppm (annual average); ozone - 0.12 ppm (1 hr exposure); and sulfur dioxide - 0.03 ppm (annual average). Express each of these volume (or mole) ratios as concentrations, in units of milligrams per cubic meter of air at STP (1 atmosphere pressure and 273EK).

Explanation / Answer

molar mass of air 28.97 g

molar mass of CO = 28

molar mass of NO2 = 46

molar mass of O3 = 48

molar mass of SO2 = 64

ppm in mass ratios of

CO2 = 35*28/28.97 = 33.8282 ppm

NO2 = 0.053*46/28.97 = 0.08415 ppm

O3 = 0.12*48/28.97 = 0.1988

SO3 = 0.03*64/28.97= 0.0662

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