Question

2.00 g of an unknown gas at STP fills a 500. mL flask. What is the molar mass of the gas?

Answer 1

Answer:

100g/mol

Explanation:

Given parameters:

Mass of unknown gas  = 2g

Volume of gas in flask  = 500mL  = 0.5dm³

Unknown:

Molar mass of gas = ?

Solution:

Since we know the gas is at STP;  

        1 mole of substance occupies 22.4dm³ of space at STP

    Therefore,

            0.5dm³ will have  0.02mole at STP

                     

Now;

   Number of moles  = $\frac{mass}{molar mass}$  

      Molar mass  = $\frac{mass}{number of moles}$   = $\frac{2}{0.02}$   = 100g/mol