Question

nitrogen has two isotopes. one has an atomic mass of 14.003 amu and a relative abundance of 99.63% while the other isotope has an atomic mass of 15.000 amu and a relative abundance of 0.37%. what is the average atomic mass for nitrogen?
a 14.007 amu
b 14.778 amu
c 14.456 amu
d 14.993 amu

Explanation:

Step1: Convert percentages to decimals

$99.63\% = 0.9963$, $0.37\%=0.0037$

Step2: Calculate weighted - sum

The formula for average atomic mass is $\sum_{i} (m_i\times a_i)$, where $m_i$ is the atomic mass of the isotope and $a_i$ is its relative abundance.
So, $(14.003\times0.9963)+(15.000\times0.0037)$
$=14.003\times0.9963 + 15\times0.0037$
$=13.9411989+0.0555$
$=14.007$ amu

Answer:

A. 14.007 amu