Chemistry: Molecular Approach (4th Edition)

Published by Pearson
ISBN 10: 0134112830
ISBN 13: 978-0-13411-283-1

Chapter 2 - Exercises - Page 80: 77


\[\underline{\text{78}\text{.92 amu}}\] and \[\underline{\text{50}\text{.69}\,\text{percent}}\]

Work Step by Step

Calculate the Br-81 fraction as follows: \[\begin{align} & \text{Fraction of isotope Br-}8\text{1}=\frac{49.31}{100} \\ & =0.4931 \end{align}\] Calculate the Br-79 natural abundance as follows: \[\begin{align} & \text{Natural abundance}=\text{100}\,\text{percent}-\text{Natural abundance of Br-81} \\ & =\text{100}\,\text{percent}-\text{49}\text{.31}\,\text{percent} \\ & =\text{50}\text{.69}\,\text{percent} \end{align}\] Calculate the Br-79 fraction as follows: \[\begin{align} & \text{Fraction of isotope Br-79}=\frac{50.69}{100} \\ & =0.5069 \end{align}\] Calculate the atomic mass of element as follows: \[\begin{align} & \text{Atomic mass}=\left( \text{Fraction of Br-81}\times \text{Mass of Br-81} \right)+ \\ & \left( \text{Fraction of Br-79}\times \text{Mass of Br-79} \right) \\ & \text{79}\text{.904 amu}=\left( \text{0}\text{.4931}\times \text{80}\text{.9163 amu} \right)+\left( \text{0}\text{.5069}\times \text{Mass of Br-79} \right) \\ & \text{79}\text{.904 amu}=\text{39}\text{.8998 amu}+\left( \text{0}\text{.5069}\times \text{Mass of Br-79} \right) \\ & \text{Mass of Br-79}=78.9193\text{ amu}\approx \,78.\text{92 amu} \end{align}\] The mass of Br-79 is \[\underline{\text{78}\text{.92 amu}}\] and the natural abundance is \[\underline{\text{50}\text{.69}\,\text{percent}}\].
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