Question

An element consists of two isotopes. The abundance of one isotope is 60.40% and its atomic mass is 68.9257 u. The atomic mass of the second isotope is 70.9249 u. What is the average atomic mass of the element? *

Answer 1

average atomic mass is 69.7173 u

Step-by-step explanation:

atomic mass m1 = 68.9257 u

atomic mass m2 = 70.9249 u

abundance one isotope = 60.40%

to find out

average atomic mass

solution

we know here average atomic mass formula that is

average atomic mass = sum of ( abundance × atomic mass )

from table we know Ga is 69.72 so abundance is 39.6

so

atomic mass = ( abundance 1 × m1 ) + ( abundance 2 × m2 ) /100

atomic mass = ( 60.40 × 68.9257 ) + ( 39.6 × 70.9249 ) /100

atomic mass = 69.7173

so average atomic mass is 69.7173 u

Answer 2

69.7173 u

Step-by-step explanation:

The abundance of the first isotope is =60.40%

So the abundance of the second isotope =100%-60.40%=39.6%

Atomic mass of first isotope = 68.9257

So the average atomic mass of the first isotope =68.9257×0.6040=41.6311 u

Atomic mass of the second isotope =70.9249 u

So average atomic mass of second isotope =70.9249×0.396=28.086

Now the average atomic mass =41.6311+28.086=69.7173 u