Calculate the mass of 120cc of nitrogen at stp .how many numbers of molecules are prrsent

3.2 x 10²¹molecules

Explanation:

Given parameters:

Volume of nitrogen gas = 120cm³

Unknown:

Mass of nitrogen gas = ?

Number of molecules  = ?

Solution:

To solve this problem, note that;

   1 mole of gas occupies a volume of 22.4L at STP

  Now;

   convert 120cm³ to L ;

           1000cm³  = 1L

           120cm³ gives 0.12L

    Since;

            22.4L of gas has 1 mole at STP

            0.12L of gas will have   = 0.0054mole at STP

So;

    Mass of N₂  = number of moles x molar mass

 Molar mass of N₂  = 2(14) = 28g/mol

    Mass of N₂  = 0.0054 x 28  = 0.15g

Now;

        1 mole of a gas will have 6.02  x  10²³ molecules

      0.0054 mole of N₂ will contain   0.0054 x  6.02  x  10²³ =

                          3.2 x 10²¹molecules