Question

an air sample consists of 99.6% of nitrogen-14 and 0.4% of nitrogen-15. what is the average mass of nitrogen in this sample?

Answer 1

 The  average mass  of nitrogen   is  14

 

         calculation

 step 1 :  multiply each percentage  by mass  number

 14 x 99.6  =1394

15 x 0.4 =   6

Step 2: add them up

 1394 + 6  = 1400

step 3: Then  divide by 100

= 1400/100 = 14

Answer 2

Answer:The average atomic mass of nitrogen is 14.004

Explanation:

Abundance of nitrogen-14 = 99.6 %

Fractional abundance$=\frac{99.6}{100}=0.996$

Abundance of nitrogen-15 = 0.4 %

Fractional abundance$=\frac{0.4}{100}=0.004$

Average atomic mass of an element =

$\sum(\text{atomic mass of an isotopes}\times (\text{fractional abundance}))$

Average atomic mass of nitrogen =

$14\times 0.996+15\times 0.004amu=14.004$

The approximate atomic mass of nitrogen is 14.004