Chemistry

Problem

Element R has two naturally occurring isotopes:

^{63}\text{R}

(62.93 amu, 69.2 % abundance) and

^{65}\text{R}

(64.93 amu, 30.8 % abundance). A student obtained a 0.551 g sample of R that was determined to contain

5.21\times10^{21}

atoms. What is the percent deviation of the student’s experimental molar mass from the accepted value based on isotopic composition? a)

0.79\,\%\;\text{high}

0.23\,\%\;\text{high}

0.97\,\%\;\text{low}

5.1\,\%\;\text{high}