Q48P - Chemistry: Molecular Nature Of Matter And Change

Question

Magnesium has three naturally occurring isotopes, ²⁴Mg(isotopic mass 23.9850 amu, abundance 78.99%), ²⁵Mg(isotopic mass 24.9858 amu, abundance 10.00%), and ²⁶Mg (isotopic mass 25.9826 amu, abundance 11.01%). Calculate the atomic mass of magnesium.

Step-by-Step Solution

Answer

Atomic mass of magnesium is total sum of atomic mass from isotope ²⁴Mg, isotope ²⁵Mg, and isotope ²⁶Mg..

Step 1 Calculation of portion of atomic mass from 24 Mg

Portion of atomic mass from ²⁴Mg= isotopic mass x fractional abundance

                                                        = 23.9850 x 78.99/100 

                                                        = 18.95 amu

Step 2 Calculation of portion of atomic mass from

Portion of atomic mass from ²⁵Mg = isotopic mass x fractional abundance

                                                        = 24.9858 x 10.00/100

                                                        = 2.49 amu

Step 3 Calculation of portion of atomic mass from

Portion of atomic mass from ²⁶Mg = isotopic mass x fractional abundance

                                                        = 25.9826 x 11.1/100 

                                                        = 2.88 amu                     

Step 4 Total Atomic mass of magnesium

Atomic mass of magnesium = atomic mass from ²⁴Mg + atomic mass from ²⁵Mg + atomic mass from ²⁶Mg

                                             = 18.95 amu + 2.49 amu + 2.88 amu 

                                             = 24.32 amu