A chemist isolated a gas in a glass bulb with a volume of 255 mL at a temperature of `25^(@)C` and a pressure (in the bulb) of `10.0` torr. The gas weighed `12.1 mg`. What is the molecular mass of the gas?

Options

A. `78.9 g mol^(-1)`
B. `35.2 g mol^(-1)`
C. `88.2 g mol^(-1)`
D. `96.3 g mol^(-1)`

Answer

C

Explanation

`n = (PV)/(RT) = ((10.0 "torr") ((1 "atm")/(760 "torr")) (255 mL) ((1 L)/(1000 mL)))/((0.0821 ("L atm")/("mol K")) (298.2 K)) = 1.37 xx 10^(-4) ` mol
Molecular mass = `("Mass")/("Number of moles") = ((12.1 mg) ((1g)/(1000 mg)))/(1.37 xx 10^(-4) "mol") = 88.2 g mol^(-1)`