Isotope Chemistry Example 3

Follow the full solution, then compare it with the other examples linked below.

hard

Copper has two stable isotopes:

{}^{63}\text{Cu}

and

{}^{65}\text{Cu}

. The average atomic mass of copper is

63.55

amu. Calculate the percent abundance of each isotope.

1
Let $x$ = fraction of ${}^{63}\text{Cu}$ . Then $1 - x$ = fraction of ${}^{65}\text{Cu}$ .
2
Set up: $63x + 65(1 - x) = 63.55$ . Simplify: $63x + 65 - 65x = 63.55$ , so $-2x = -1.45$ , $x = 0.725$ .
3
${}^{63}\text{Cu}$ : $72.5\%$ , ${}^{65}\text{Cu}$ : $27.5\%$ .

Answer

{}^{63}\text{Cu: } 72.5\%,\quad {}^{65}\text{Cu: } 27.5\%

When the average atomic mass is known, you can set up a linear equation to solve for the unknown abundances of two isotopes.

About Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons, giving them different mass numbers.

Carbon has three naturally occurring isotopes: [formula], [formula], and [formula]. How many protons

Boron has two stable isotopes: [formula] (19.9%) and [formula] (80.1%). Calculate the average atomic

Chlorine-35 and chlorine-37 are both chlorine. What is different about them, and what stays the same