Question

The mass of an evacuated 260 mLmL flask is 143.187 g . The mass of the flask filled with 268 torr of an unknown gas at 30 C is 144.237 g .

Answer 1

The molar mass of unknown compound is 286.76 g/ mol

Explanation:

From ideal gas equation

PV=nRT

n=w/MW

Where

w= weight of compound

w=144.237-143.187=1.05gm

MW= molecular weight =?

So the formula is

PV=wRT/MW

MW=mRT/PV

From the given data

w=144.237-143.187=1.05gm

P=pressure=268/765=0.3503 atm

V= volume =260ml=0.260L

R=ideal gas constant =0.0821atm.L/mole.K

T=absolute temperature =30+273=303K

So on substituting above values in formula

MW= (1.05×0.0821×303)/(0.3503×0.26)

MW=286.76 gm/mole.

So the molar mass of unknown compound is 286.76gm/mol.