Question

two isotopes of copper occur naturally. isotope of copper: copper - 63, copper - 65; percent abundance: 69.17 %, 30.83 %; atomic mass: 62.956, 64.705; calculate the average atomic mass of copper to 3 decimal places. answer

Explanation:

Step1: Convert percentages to decimals

$69.17\% = 0.6917$, $30.83\%=0.3083$

Step2: Use the formula for average atomic mass

The formula for average atomic mass $A = m_1x_1 + m_2x_2$, where $m_1$ and $m_2$ are the atomic masses of the isotopes and $x_1$ and $x_2$ are their respective abundances. Here, $m_1 = 62.956$, $x_1=0.6917$, $m_2 = 64.705$, $x_2 = 0.3083$.
$A=(62.956\times0.6917)+(64.705\times0.3083)$
$A = 62.956\times0.6917=43.5467$ (first - product)
$A = 64.705\times0.3083 = 19.9585$ (second - product)
$A=43.5467 + 19.9585=63.5052\approx63.505$

Answer:

$63.505$