Question

Be sure to answer all parts. the average atomic mass of nitrogen is 14.0067. the atomic masses of the two stable isotopes of nitrogen, 14n and 15n, are 14.003074002 and 15.00010897 amu, respectively. use this information to determine the percent abundance of 14n.

Answer 1

To answe this question, we will assume that the percentage abundance of 14n is y. Since the percentage abundance of 14n + percentage abundance of 15n = 100% = 1
Therefore, percentage abundance of 15n = 1 - y.

Now we know that the average atomic mass of nitrogen is 14.0067
Therefore:
average atomic mass of nitrogen = atomic mass of 14n x its percentage abundance + atomic mass of 14n x its percentage abundance
14.0067 = 14.003074002 y + 15.00010897 (1 - y)
14.0067 = 14.003074002 y + 15.00010897 - 15.00010897 y
14.0067 - 15.00010897 = 14.003074002 y  - 15.00010897 y 
0.99703497 y =  0.99340897

Therefore y =  0.99636

Based on this, the percentage abundance of 14n is  0.99636x100= 99.636%
while percentage abundance of 15n = 100% - 99.636% = 0.364%