You will far more likely know a quantity of carbon dioxide's volume than its mass. The density of this volume, and its consequent mass, depends on two factors. An increased pressure corresponds with a higher density. An increased temperature corresponds with a lower density. A constant figure, the gas constant, relates these different factors so you can calculate the quantity of carbon dioxide from them.
Multiply the carbon dioxide's volume by its pressure. For this example, imagine 0.001 cubic of meters of carbon dioxide at a pressure of 300,000 Pascals: 0.001 x 300,000 = 300.
Divide this answer by the gas's temperature, measured in Kelvin. If its temperature is, for instance, 400K: 300 / 400 = 0.75.
Divide this answer by the gas constant, which is 8.3145 J/mol K: 0.75 / 8.3145 = 0.0902. This is the number of moles of carbon dioxide in the sample.
Multiply the number of moles by 44, which represents the mass of one mole of carbon dioxide: 0.0902 x 44 = approximately 3.97 grams. The sample contains just under 4 grams of carbon dioxide.
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