You have a sample of a gaseous compound which has a density of 7.11 kg/m^3 at 58

Question

You have a sample of a gaseous compound which has a density of 7.11 kg/m^3 at 58 degree C and 82.2 kPa. What is the molar mass of this gas? This same gas sample is (by mass) 20.2% C and 79.8% F. Find the empirical formula of the compound. What is the molecular formula of this compound? A sample of neon gas occupies 725 mL at 635 torr. What will the pressure be if the volume is expanded to 8.00 L at the same temperature? A sample of carbon dioxide gas occupies 12.37 liters at 544 kPa and 28.44 degree C. At what temperature (degree C) will the carbon dioxide occupy 31.44 liters if the pressure changes to 3.000 atm?

Explanation / Answer

PM = density RT hence,

Here p = pressure 82.2 kPa = 0.811 atm

M = molar mass, g/ mole

Density = 7.11 kg / m^3 = 7.11 g / L

R = gas constant, 0.08206 L atm K1 mol1

T = 58 C = 273+58= 331 K

Then;

M = density RT / P

= 7.11 g/L * 0.08205 Latm K^-1 mol^-1 * 331K / 0.811atm

= 238 g/mol

b.

given that 20.2% C and 79.8 F

assume that compound is 100 g

then

amount of C = 20.2 g

and F= 79.8 g

number of moles of C= 20.2 g/ 12.02 g/ mole

= 1.7 mole

Mole of F = 79.8 g/ 18.99 g/ mole

= 4.2 mole

Now calculate mole ratio:

C= 1.7/1.7=1

F = 4.2/1.7= 2.5 or 3

Then C= 1 and F= 3

Then molecular formula:

Mass of CF3 = 69.00591 g/ mole

Here molar mass= 238 g/ mole

Number of units of empirical formula in compound = 238/69= 3.5 or=4

Then molecular formula id C4F10. Perfluorobutane

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