There are several ways to measure the density of gas. One way is to
take a certain amount of gas and weigh it. (Yes, you really can
weigh a gas.
One way to do this is by filling a container with the gas and weighing
it, then using a vacuum pump to empty the container out completely and
weighing it again.) If you know how much the gas weighs and how much
space it takes up, you can figure out the density. (Density = mass /
volume)
Another way to do this is by taking advantage of something called
the 'Ideal Gas Law' or PV=nRT. In this equation, (which is close to
true for ordinary gases) P is pressure, V is volume, n is the number of
moles (a mole is 6.022*10^23 molecules) of gas, R is a constant that
other people have measured and T is the absolute temperature. To use
this equation, all you have to do is measure the pressure of the gas
and measure the temperature. From this, you can use the equation to
find n/V, (n/V=P/RT). Measuring the pressure of a gas is fairly easy,
and there are lots of instruments made to do just that.If you know what
type of gas you're measuring, you can look up its molecular weight,
which tells you how to convert from moles per volume to grams per
volume. Of course, the table of molecular weights was made by actually
weighing the gases.
-Tamara & Mike
(published on 10/22/2007)
