96 gram of gas occupies a volume is 84 gram of nitrogen gas are the similar condition of temperature and pressure find the molecular weight of unknown gas
Answers
Answer:
I would determine the mass of a fixed volume of the gas at a known temperature and pressure and then use the Ideal Gas Law to calculate the molar mass.
Explanation:
EXAMPLE
The mass of an evacuated 255 mL flask is 143.187 g. The mass of the flask filled with an unknown gas at 25.0 °C and 265 Torr is 143.289 g.
Solution
The Ideal Gas Law is
∣
∣
∣
∣
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
a
a
P
V
=
n
R
T
a
a
∣
∣
−−−−−−−−−−−−−−−
Since
n
=
mass
molar mass
=
m
M
, we can write the Ideal Gas Law as
∣
∣
∣
∣
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
a
a
P
V
=
m
M
R
T
a
a
∣
∣
−−−−−−−−−−−−−−−−
We can rearrange this to get
M
=
m
R
T
P
V
m
=
143.289 g - 143.187 g
=
0.102 g
R
=
0.082 06 L⋅atm⋅K
-1
mol
-1
T
=
(25.0 + 273.15) K
=
298.75 K
P
=
265
torr
×
1 atm
760
torr
=
0.3487 atm
V
=
0.255 L
∴
M
=
0.102 g
×
0.082 06
L⋅atm⋅K
-1
mol
-1
×
298.15
K
0.3487
atm
×
0.255
L
=
28.1 g/mol
The molar mass is 28.1 g/mol.
∴ The molecular mass is 28.1 u.