Question

A fictitious element Q has two naturally occurring isotopes. The first isotope has an abundance of 20.00% and a mass of 39.96 amu and the second isotope of element Q has an abundance of 80.00% and a mass of 43.39amu. Calculate the weighted atomic mass of element Q to the nearest tenth. To earn credit, be sure to show the work that leads to your answer.

Answer 1

Average Atomic mass is the sum of the atomic mass of the isotopes multiplied by the abundance

Thats why we get a fractional number as atomic mass.

The formula to find the average atomic mass is

Average atomic mass

`=\frac{(\text {atomic mass of Isotope1 } * \% \text { Abundance) }+(\text {atomic mass of Isotope2 } * \% \text { Abundance})}{100 \%}`

`\begin{array}{c}{=((39.96 a m u * 20.00 \%)+(43.39 a m u * 80.00 \%))/(100 \%)} \\\\ {=(799.2+3471.2)/(100 \%)} \\\\ {=42.704 \text { amu }}\end{array}`

= 42.7 amu is the Answer to the nearest tenth

Answer 2

42.7 amu

Step-by-step explanation:

The natural element will have an atomic mass that includes 20% of the 39.96 amu isotope, plus 80% of the 43.39 amu isotope. This can be written using the decimal forms of percent as:

0.2 * 39.96 + 0.8 * 43.39 = 42.704 amu

This answer, rounded to the nearest tenth is: 42.7 amu