Calculate the mass of 120 cc of nitrogen at STP. How many numbers of molecules are present in it?

6.02 x 10²⁰ molecules

Explanation:

Given parameters:

Volume of nitrogen  = 120cm³

Unknown:

Mass of Nitrogen = ?

Number of molecules present in it = ?

Solution:

At STP;

       1 mole of a substance contains 22.4dm³ particles

      100cm³ = 1dm³

     24cm³ will give 0.024dm³

        22.4dm³ of particles are in 1 mole of substances at STP

         0.024dm³ of particles will contain     = 0.001mole

Mass of Nitrogen  = Number of moles x molar mass

  molar mass of nitrogen  = 14g/mol

   Mass of nitrogen  = 0.001 x 14  = 0.014g

Number of molecules present;

      1 mole of a substance contains 6.02 x 10²³ molecules

     0.001 mole of Nitrogen will contain 0.001  x  6.02 x 10²³ = 6.02 x 10²⁰

         6.02 x 10²⁰ molecules

2.67 × 10^19

Explaination:

The volume of the gas is 1c.c = 10^ - 3L

∴ Number of moles of the gas is=22.4 × 10^-3

Now,

Number of molecules = n × 6.022 × 10^23

∴ Number of Nitrogen Molecules

= 10^-3/22.4 × 6.023 × 10^23

  = 2.67 × 10^19

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