Answer:
To calculate the molar mass of an unknown gas, we can use the formula:
Molar mass = Given Mass/Number of moles
First let's calculate the number of moles which can be calculated using the ideal gas law:
PV = nRT
where,
- P is pressure ( in atm)
- V is volume (in l)
- n is Number of moles
- R is universal gas constant 0.08206 L atm/Kmol
- T is temperature (in Kelvins)
Given that if a sample weighing 0.389 g is collected in a flask with a volume of 102 cm³ at 97°C and at a pressure of 728 mmHg
Converting the values,
Volume = 102 cm³ = 0.1 L
Temperature = 97°C = 97°C + 273.15 = 370.15 K
Pressure = 728 mm Hg = 728 mmHg / 760 mmHg/at = 0.958 atm
Calculate (n) number of moles:
0.958 0.1 = n 0.0821*370.15
0.0958 = n (30.39)
Divide both sides by 30.39
n = 0.031
Now, calculate the molar mass:
Molar mass = 0.389/0.031
Molar mass = 12.54 g/mol
So, the molar mass of the unknown gas is approximately 12.54 g/mol.
