Question

An element E has three isotopes:
\(28\\14 E\) (abundance 92.21%, atomic mass: 27.977 a.m.u.), 
\(29\\14 E\) (abundance 4.70%, atomic mass: 28.976 a.m.u.), and 
\(30\\14 E\) (abundance 3.09%, atomic mass: 29.974 a.m.u). 
The atomic mass of E is _______ a.m.u. 
(rounded off to three decimal places

Answer 1

Correct Answer: 28.082 - 28.089

The atomic mass of element E can be calculated using the formula for the weighted average of the atomic masses of its isotopes:

Atomic mass of E = \( \sum \left( \text{abundance of isotope} \times \text{atomic mass of isotope} \right) \)

Substituting the given values:

Atomic mass of E = \( (0.9221 \times 27.977) + (0.0470 \times 28.976) + (0.0309 \times 29.974) \)

Atomic mass of E = 25.7766 + 1.3628 + 0.9260 = 28.082 a.m.u.

Thus, the atomic mass of element E is 28.082 a.m.u. (rounded to three decimal places).