To identify a diatomic gas (X2), a researcher carried out the following experiment: She weighed an empty 5.8-L bulb, then filled it with the gas at 1.00 atm and 21.0 ∘C and weighed it again. The difference in mass was 6.7 g. Identify the gas. Express your answer as a chemical formula.

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Explanation:

The given data is as follows.

      Volume = 5.8 L,    Pressure = 1.00 atm

      T = [tex]21^{o}C[/tex] = (21 + 273) K = 294 K,   mass = 6.7 g

     R = 0.0821 Latm/mol K

According to the ideal gas equation, we will calculate the number of moles as follows.

             PV = nRT

or,          n = [tex]\frac{PV}{RT}[/tex]

Hence, putting the given values into the above formula as follows.

               n = [tex]\frac{PV}{RT}[/tex]

                  = [tex]\frac{1.00 atm \times 5.8 L}{0.0821 Latm/mol K \times 294 K}[/tex]

                  = 0.24 mol

Now, calculate molar mass of the gas as follows.

            Molar mass = [tex]\frac{mass}{\text{no. of moles}}[/tex]

                                = [tex]\frac{6.7 g}{0.24 mol}[/tex]

                                = 27.91 g/mol

or,                             = 28 g/mol (approx)

As the gas is diatomic so, mass of two atoms of gas X is 28 g/mol. And, mass of one atom of gas is as follows.

                     [tex]\frac{28 g/mol}{2}[/tex]

                          = 14 g/mol

Hence, nitrogen atom has a mass of 14 g/mol. Therefore, we can conclude that the given diatomic gas is [tex]N_{2}[/tex].

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