Question

calculating average atomic mass. natural copper (cu) consists of 2 isotopes: copper - 63 (mass = 62.930 g/mol) with 69% abundance and copper - 65 (mass = 64.930 g/mol) with 31% abundance. calculate with average mass of cu.

Explanation:

Step1: Recall the formula for average atomic mass

The formula for the average atomic mass of an element with two isotopes is $A = x_1M_1 + x_2M_2$, where $x_1$ and $x_2$ are the fractional abundances of the isotopes and $M_1$ and $M_2$ are their respective masses. Given that the abundance of Copper - 63 is 69% or 0.69 (so $x_1=0.69$ and $M_1 = 62.930$ g/mol) and the abundance of Copper - 65 is 31% or 0.31 (so $x_2 = 0.31$ and $M_2=64.930$ g/mol).

Step2: Substitute the values into the formula

$A=(0.69\times62.930)+(0.31\times64.930)$. First, calculate $0.69\times62.930 = 43.4217$. Then calculate $0.31\times64.930=20.1283$.

Step3: Sum the results

$A = 43.4217+20.1283=63.55$ g/mol.

Answer:

63.55 g/mol