The composition of a compound used to make polyvinyl chloride (pvc) is 38.4% c, 4.8% h and 56.8% cl by mass. it took 7.73 min for a given volume of the compound to effuse through a porous plug, but it took only 6.18 min for the same amount of ar to diffuse at the same temperature and pressure. what is the molecular formula of the compound?

C₂H₃Cl

Explanation:

We can calculate the compound's molar mass using the data given by the problem and Graham's law:

Rate₁/Rate₂ =

In this case the subscript 1 refers to the compound and 2 refers to Ar.

Keeping in mind that Rate = volume/time, and that the volume is the same for both compounds, we can rewrite the equation as:

Time₂/Time₁ =

6.18/7.73 =  

M₁ = 62.5 g/mol

Now we determine the molecular formula by using the elemental % analysis:

Assuming we have 1 mol of the compound:

C ⇒ 62.5 g * 38.4/100 = 24 g C = 2 mol C

H ⇒ 62.5 g * 4.8/100 = 3 g H = 3 mol H

C ⇒ 62.5 g * 56.8/100 = 35.5 g Cl = 1 mol Cl

Thus the molecular formula is C₂H₃Cl

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