Find the average atomic mass for boron if 19.9% of boron atoms have a mass of 10.0129371 amu and 80.1% have a mass of 11.0093055 amu. Round to 3 significant figures.

Average atomic mass  = 10.8  amu

Explanation:

Given data:

Average atomic mass = ?

Percentage of boron having mass 10.0129371 amu = 19.9%

Percentage of boron having mass 11.0093055 amu = 80.1%

Solution:

Average atomic mass  = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass  = (19.9×10.0129371 )+(80.1×11.0093055) /100

Average atomic mass =  199.3 + 881.8 / 100

Average atomic mass = 1081.1  / 100

Average atomic mass  = 10.8  amu.

answer : (a) volume of the gas = 8.67 ×   l

                (b) second virial coefficient b = -1.21226 l/mole

solution :   given,     t = 300k

                                p = 20atm

                                z = 0.86

                                n = 8.2 mmoles = 8.2 × moles

                                r =   0.082 l atm/k/mol

        find,     (a) volume of gas   and (b) second virial coefficient b at 300k.

formula used :            

                          and            

(a)            

                    = \times 0.082\times 300}{20}[/tex]

                    = 8.67 ×   l

(b)      

                    = (0.00867-1) × 8.659

                    = - 8.5839 l/mole