Question

A. Calculate the density of sulfur hexafluoride gas at 706 torr and 20 ?C.

B. Calculate the molar mass of a vapor that has a density of 7.130 g/L at 13 ?C and 744 torr .

Answer 1

Solution :-

Given data

Sulfur hexafluoride = SF6

Pressure = 706 torr

Temperature = 20 ^oC +273 = 293 K

Density of SF6 = ?

Lets convert given pressure from torr to atm

706 torr * 1 atm / 760 torr = 0.929 atm

Formula to calculate the density of the gas is

PM= dRT

Where, p =pressure , M= molar mass , R= gas constant (0.08206 L atm per K. mol), T= temperature in K

Now we need molar mass of SF6

Molar mass is the sum of atomic masses of the atoms of the elements present in the formula

Molar mass of SF6 =

Now lets use this molar mass in the formula and calculate the density of the SF6 gas at given conditions of the temperature and pressure.

PM= dRT

Therefore ,d= PM/RT

Lets put the values in the formula

d= (0.929 atm * 146.0554 g per mol) / (0.08206 L atm per K.mol* 293 K)

d=5.643 g/ L

So the density of the SF6 gas = 5.643 g/L

b) calculating molar mass of the vapor at 13^oC and 744 torr

density = 7.130 g/L

lets first convert pressure from torr to atm

744 torr * 1 atm / 760 torr= 0.979 atm

T= 13^oC +273 = 286 K

Formula to calculate the density of the gasis

PM = dRT

Lets rearrange this formula to calculate molar mass then we get

M= dRT/P

Lets put the values in the formula

M= (7.130g per L * 0.08206 L atm per K.mol* 286 K) / 0.979 atm

M= 170.9 g/mol

Therefore molar mass of vapor = 170.9 g/mol