Question

Calculate the density, in grams per liter, of a gas at STP if 3.16 L of the gas at 28.5 °C and 734.2 mmHg weighs 0.269 g

Answer 1

Given: Temperature = 28.5 ^oC = 28.5+273.15 = 301.65 K

          Pressure = 734.2 mm Hg

          Volume = 3.16 L

          Weight of the gas = 0.269 g

       And The density of the gas is to be found out at STP conditions which is standard temperature and pressure

So Standard conditions are T = 273.15 K and P = 1 atm = 760 mm Hg

Now, we have the temperature and pressure at both the given condition and standard condition

So we need to find the volume :

For this, we need to use the ideal gas law, which is PV= nRT

R and n remain constant because number of moles for a particular gas remains constant

        So, PV/T = constant

   So, (PV/T)_STP = (PV/T)_given

                 V_STP = (PV/T)_given / (P/T)_STP

                                   = (734.2 * 3.16*273.15)/(301.65*760)

                          = 2.764 L

          To find the density:

            Density = Mass/Volume = 0.269/2.764

                          = 0.097 g/L

So density = 0.097 g/L at STP conditions