## Chemistry: Molecular Approach (4th Edition)

$\underline{\text{152 amu}}$
Calculate the abundance of Eu-153 as follows: \begin{align} & \text{Abundance of Eu-}153=\frac{100\,\text{percent}}{100\,\text{percent}+88\,\text{percent}}\times 100\,\text{percent} \\ & =53.19\,\text{percent} \end{align} Calculate the abundance of Eu-151 as follows: \begin{align} & \text{Abundance of Eu-}151=\frac{88\,\text{percent}}{100\,\text{percent}+88\,\text{percent}}\times 100\,\text{percent} \\ & =46.81\,\text{percent} \end{align} Calculate the Eu-153 fraction as follows: \begin{align} & \text{Fraction isotope Eu-}153=\frac{53.19}{100} \\ & =0.5319 \end{align} Calculate the Eu-151 fraction as follows: \begin{align} & \text{Fraction isotope Eu-}151=\frac{46.81}{100} \\ & =0.4681 \end{align} Calculate the atomic mass of the element as follows: \begin{align} & \text{Atomic mass}=\left( \text{fraction of Eu-}153\times \text{mass of Eu-}153 \right)+ \\ & \left( \text{fraction of Eu-}151\times \text{mass of Eu-}151 \right) \\ & =\left( 0.5319\times 153\text{ amu} \right)+\left( 0.4681\times 151\text{ amu} \right) \\ & =81.38\text{ amu}+70.68\text{ amu} \\ & =152.06\text{ amu}\,\,\approx \,\,152\text{ amu}\, \end{align} The atomic mass of europium is $\underline{\text{152 amu}}$.