Question

A particular element found in nature exists as two stable isotopes. 60.4% of the element has a mass of 68.9257amu, the rest of the element is found with a mass of 70.9249 amu. Calculate the average atomic mass of the element.

Answer 1

Mass           %abundance        # of atoms (pick 1000 sample)
68.9257         60.4%                  604
70.9249         39.6%                  396
*39.6* ( i got this by subtracting 100 as most percentage is out of 100)
*# of atoms* ( i just moved it one decimal place, then i am going to make the sample out of 1000, to get the decimal place)

Formula= total mass/ total #atoms

x= (68.9257u* 604) + (70. 9249*396)/ 1000
x- 69717. 3832/ 1000
x= 69.717amu or 69.72 amu 

if you look on the periodic table the closet element with that mass is gallium ( amu is 69.72)