Question

There are 2 isotopes of copper that occur naturally; 63Cu and 65Cu. The 63Cu atoms have a mass of 62.929601 amu and the 63Cu atoms have a mass of 64.927794 amu. What is the percent natural abundance for each isotope?

Answer 1

⁶³Cu=69.2%

⁶⁵Cu=30.8%

Step-by-step explanation:

for ⁶³cu

f1=x m1=62.9296

for ⁶⁵cu;

f2=y m2=64.9278

f means fraction of abundance

m means mass

Average atomic mass=63.546

Average atomic mass=f1m1 +f2m2

63.546=x * 62.9296 + y* 64.9278

63.546=62.9296x + 64.9278y.........eqn i

remember x+y =1

x=1-y

insert x into eqn i

63.546=62.9296(1-y) + 64.9278y

63.546= 62.9296-62.9296y+ 64.9278y

63.546-62.9296=64.9278y-62.9296y

0.6164÷1.9982= 1.9982y÷1.9982

y=0.308

recall x=1-y

x=1-0.308

=0.692

Therefore,x=69.2%

y=30.8%