Agaseous compound is 78.14 percent boron and 21.86 percent hydrogen. at 27°c, 74.3 ml of the gas exerted a pressure of 1.12 atm. if the mass of the gas was 0.0934 g, what is its molecular formula?

B₂H₆

Explanation:

Given parameters:

Mass percentage of hydrogen = 21.86%

Mass percentage of boron = 78.14%

Temperature of the compound = 27°C

Pressure exerted by the gas = 1.12atm

Volume of the gas = 74.3mL = 0.0743L or 0.0743dm³

Mass of the gas = 0.0934g

Unknown:

Molecular formula of the gas = ?

We have to convert the temperature to a unit we can work with which is Kelvin:

      27°C to K gives 273 + 27, which is 300K

Solution

      The empirical formula is the simplest formula of a compound.

The procedure is shown below:

                                                      B                                      H

Mass precentage                       78.14                                21.86

Number of moles                   78.14/10.8                           21.86/1

                                                    7.24                                  21.86

Dividing by the

smallest                                    7.24/7.24                          21.86/7.24

                                                        1                                         3

The empirical formula of the compound is BH₃

To derive the molecular formula:

               M.F = (E.F) x n

n is the number of repeating units of the empirical formula present in one mole.

          ideal gas law:  PV = nRT

     The unknown is n, and we make it the subject of the expression:

                            n =

Where P is pressure of the gas

            V is the volume of the gas

            R is the gas constant which is given as 0.082atmdm³mol⁻¹K⁻¹

            T is the temperature

         n =

         n = 0.0034mole

  From the expression:

                 number of moles =

                 molar mass =

                 molar mass =

                 molar mass =  27.5g/mol of the molecular formula

From M.F = (E.F) x n we need to solve for n:

    E.F is BH₃ this gives a mass of [10.8 + 3(1)] = 13.8g/mol

     n =

     n = = 2

Molecular formula of the compound is then (BH₃)₂ which gives B₂H₆

both adhesion and cohesion are attractions.

they are different in that adhesion is the force of attraction between the molecules of two different substances, whereas cohesion is the force of attraction between molecules of the same substance.

possible examples include capillary action, in which the adhesion between water and glass causes the water to rise in a narrow tube against the force of gravity.

because of hydrogen bonding, water is extremely cohesive.

this causes molecules on the surface of water to be drawn inward, which is why drops of water form beads on smooth surfaces.

hope this .