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

The molar mass of the unknown gas in the 500 mL flask at stp is 89.7 g/mol

We'll begin by calculating the number of mole of the gas that occupied 500 mL at stp.

Recall at stp:

22400 mL = 1 mole of the gas

Therefore,

500 mL = 500 / 22400 = 0.0223 mole of gas.

Finally, we shall determine the molar mass of the gas. This can be obtained as follow:

Mass of gas = 2 g

Mole of gas = 0.0223 mole

Molar mass = mass / mole

Molar mass of gas = 2 / 0.0223

Therefore, the molar mass of the unknown gas is 89.7 g/mol

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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  =  

      Molar mass  =   =   = 100g/mol

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