Question

Boron has two isotopes ${\mathrm{B}}^{10}$ and ${\mathrm{B}}^{11}$ whose relative abundances are $20\%$ & $80\%$respectively. The average atomic weight of Boron is

Answer 1

Step1. Formula for average atomic weight

$\text{Average atomic weight}=f_1{M}_1+f_2{M}_2+\dots +f_n{M}_n$

Here $f$ is the fraction representing the natural abundance of the isotope and $M$ is the atomic mass of the isotope.

Step2. Calculation of average atomic weight

$$\begin{gathered} \text{Average atomic weight}=0.20\times 10\text{g}+0.8\times 11\text{g} \\ =\left(2+8.8\right)\text{g} \\ =10.8\text{g} \end{gathered}$$

Hence, the average atomic weight of Boron is $10.8\text{g}$.