Question

Use the information for the isotopes of element X to calculate the average atomic mass of X, and identify the element. Isotope Abundance Mass (amu) 35X 75.77% 34.969 37X 24.23% 36.965

Answer 1

Answer: average atomic mass of the element is 35.4536 amu and the element is chlorine.

Explanation:

Mass of isotope 1 = 34.969

% abundance of isotope 1 = 75.77% = $\frac{75.77}{100}=0.7577$

Mass of isotope 2 = 36.965

% abundance of isotope 2 = (24.23)% = $\frac{24.23}{100}=0.2423$

Formula used for average atomic mass of an element :

$\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {\text{ fractional abundance}})$

$\text{ Average atomic mass of an element}=\sum[34.969\times 0.7577)+36.969\times 0.2423]$

$\text{ Average atomic mass of an element}=35.4536amu$

Therefore, the average atomic mass of the element is 35.4536 amu and the unknown element will be Chlorine.

Answer 2

Answer

36.45 u; X = Cl

Explanation:

The atomic mass of X is the weighted average of the atomic masses of its isotopes.

We multiply the atomic mass of each isotope by a number representing its relative importance (i.e., its percent of the total).

Set up a table for easy calculation .

0.7577  × 34.969 u = 26.496   u

0.2423 × 36.965 u =   8.9566 u

                   TOTAL = 36.45     u

X = Cl