Question

A 1.30-gg sample of an unknown gas occupies 798 mLmL at 25.0 ∘C∘C and a pressure of 1.00 atmatm. Find the molar mass of the gas.

Answer 1

First we need to know how to determine the molar mass and what variables we need to know. The molar mass is calculated as follows:

`\text{Molar mass = }\frac{\text{Mass of compound}}{Number\text{ of mol}}`

We already know the mass of our compound is equal to 1.30 g, but we need to know the number of moles present. We will determine them by applying the ideal gas equation:

`PV=n.R.T`

Where:

P = Pressure, atm

V= Volumen, L

n= Number of moles

R= Ideal constant gas

T= Temperature, K

Now, we clear n and we replace known terms:

`n=(PV)/(RT)=\frac{1\text{atm}*0.798L}{0.08206\text{ }\frac{\text{L}.atm}{\text{mol}.K}*\text{ 298.15 K}}=0.03\text{ mol of gas}`

Now, we calculate the molar mass using the first question:

`\text{Molar mass= }\frac{\text{Mass of gas}}{n}=\frac{1.30\text{ g}}{0.03\text{ mol}}=39.9\text{ g/mol}`

The molar mass of the gas will be 39.9 g/mol