Copper has two naturally occurring isotopes with atomic masses of 62.9296 u ( )and 64.9278 u ( ).The atomic mass of copper is 63.546 u.What is the percent distribution of the isotopes?

Question

Copper has two naturally occurring isotopes with atomic masses of 62.9296 u (  )and 64.9278 u (  ).The atomic mass of copper is 63.546 u.What is the percent distribution of the isotopes?

Quizplus · Accepted Answer

Let x be the percent abundance of the isotope with mass 62.9296 u, then the percent abundance of the isotope with mass 64.9278 u is (100-x). 
Using the weighted average formula, we have:
63.546 u = (62.9296 u)(x/100) + (64.9278 u)((100-x)/100)
63.546 u = (62.9296x + 64.9278(100-x))/100
6354.6 u = 6292.96x + 6492.78 - 64.9278x
161.38 = 35.0338x
x = 4.6034
Therefore, the percent abundance of the isotope with mass 62.9296 u is 4.6034%, and the percent abundance of the isotope with mass 64.9278 u is (100-4.6034)% = 95.3966%. 
Thus, the best choice is A with percent abundances of approximately 4.6% and 95.4%.

Copper Has Two Naturally Occurring Isotopes with Atomic Masses of 62.9296