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Given that Rubidium has two isotopes, 85Rb and 87Rb. Calculate the average atomic mass of rubidium.


Note that 85Rb has an atomic mass of 84.912 amu and occurs at an abundance of 72.17% while 87Rb has an atomic mass of 86.909 amu and occurs at an abundance of 27.83%.

Verified Answer :

meerkat18


The mass of the element is equal to the summation of the mass of the isotopes multiplied by the percent abundance of the isotope. Isotopes differ in the number of neutrons but the number of protons  remains the same. Hence in this problem, the answer is 85.47 g/mol

Answer:

85.47 amu

Explanation:

the average atomic mass is calculated, with the atomic mass and the abundance of the element isotopes

To calculate the average atomic mass of Rb we do it with the following formula

\(m=\frac{(m_1.\%_1=m_2.\%_2)}{100}\)

\(m_1= 84.912 amu\\\%_1= 72.17\%\\m_2= 86.909 amu\\\%_2= 27.83\%\)

\(m=\frac{((84.912)(72.17))+((86.909)(27.83))}{100}\\m= 85.47 amu\)

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