Question

a particular element exists in two stable isotopic forms. one isotope has a mass of 62.9296 amu (69.17% abundance). the other isotope has a mass of 64.9278 amu. calculate the average mass of the element and determine its identity. atomic mass: symbol of element:

Explanation:

Step1: Calculate the contribution of the first isotope

The contribution of the first isotope to the average atomic mass is its mass times its abundance. The abundance of the first isotope is $69.17\%=0.6917$, and its mass is $62.9296$ amu. So the contribution is $62.9296\times0.6917 = 62.9296\times\frac{69.17}{100}=43.5284$.

Step2: Calculate the contribution of the second isotope

The abundance of the second isotope is $1 - 0.6917=0.3083$. Its mass is $64.9278$ amu. So the contribution is $64.9278\times0.3083 = 64.9278\times\frac{30.83}{100}=19.8172$.

Step3: Calculate the average atomic mass

The average atomic mass is the sum of the contributions of the two isotopes. So $43.5284 + 19.8172=63.3456$ amu.

Step4: Identify the element

Looking at the periodic - table, the element with an average atomic mass close to $63.3456$ amu is copper (Cu).

Answer:

Atomic mass: $63.35$ amu (rounded to two decimal - places)
Symbol of element: Cu