Question

1. copper has an isotope with an atomic mass of 62.93 and an abundance of 69.17%. a second isotope has an atomic mass of 64.93 and an abundance of 30.83%. what is the average atomic mass for copper?

Explanation:

Step1: Recall average - atomic - mass formula

The formula for the average atomic mass ($A_{avg}$) of an element with two isotopes is $A_{avg}=m_1x_1 + m_2x_2$, where $m_1$ and $m_2$ are the atomic masses of the isotopes and $x_1$ and $x_2$ are their respective fractional abundances.

Step2: Convert percentages to fractions

The abundance of the first isotope is $x_1 = 69.17\%=0.6917$ and its atomic mass $m_1 = 62.93$. The abundance of the second isotope is $x_2=30.83\% = 0.3083$ and its atomic mass $m_2 = 64.93$.

Step3: Calculate the average atomic mass

$A_{avg}=m_1x_1 + m_2x_2=(62.93\times0.6917)+(64.93\times0.3083)$
$A_{avg}=62.93\times0.6917 = 43.529581$
$A_{avg}=64.93\times0.3083= 20.017919$
$A_{avg}=43.529581 + 20.017919=63.5475\approx63.55$

Answer:

63.55