Nickel Has a Lower Atomic Mass Than Cobalt, Even Though

question 13

Multiple Choice

Nickel has a lower atomic mass than cobalt, even though it has a higher atomic number. One possible explanation is that one of the average atomic masses was miscalculated. In the case of cobalt, there is only one isotope: 100% ⁵⁹Co at a mass of 58.9332 amu. For nickel, however, there are five isotopes as given in the table. $\begin{array}{|l|l|l|}\hline \text { Isotope } & \text { mass }(\mathrm{amu}) & \text { abundance } \\\hline{ }^{58} \mathrm{Ni} & 57.9354 & 67.76 \% \\\hline{ }^{60} \mathrm{Ni} & 59.9308 & 26.16 \% \\\hline{ }^{61} \mathrm{Ni} & 60.9311 & 1.25 \% \\\hline{ }^{62} \mathrm{Ni} & 61.9283 & 3.66 \% \\\hline{ }^{64} \mathrm{Ni} & 63.9280 & 1.16 \% \\\hline\end{array}$ Using the data in the table, what is the average atomic mass for nickel

• A) 60.45 amu
• B) 58.70 amu
• C) 59.75 amu
• D) 58.10 amu
• E) 59.25 amu

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