If we put a gas in this syringe, the mass of the gas is proportional to its molecular weight if we keep T, P and V constant.

It is easy to keep T, P, and V constant. We need a way to get the value of the proportionality constant, c, in the equation:

MW = c*g

There are two ways to determine the value of c in this equation.

1. Measure the mass of several gases of known molecular weight.

2. Calculate c from theory.

Method 1 works best because it avoids errors in measuring V, T, and P.

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