The element X has three naturally occurring isotopes.The isotopic masses (amu)and % abundances of the isotopes are given in the table below.The average atomic mass of the element is ________ amu.
A)33.33
B)55.74
C)56.11
D)57.23
E)56.29

Question

The element X has three naturally occurring isotopes.The isotopic masses (amu)and % abundances of the isotopes are given in the table below.The average atomic mass of the element is ________ amu. 
A)33.33 
B)55.74 
C)56.11 
D)57.23 
E)56.29

Quizplus · Accepted Answer

To calculate the average atomic mass of the element, we need to use the following formula:

average atomic mass = (mass of isotope 1 x % abundance of isotope 1/100) + (mass of isotope 2 x % abundance of isotope 2/100) + (mass of isotope 3 x % abundance of isotope 3/100)

Substituting the values from the table, we get:

average atomic mass = (55.92 x 91.75/100) + (56.94 x 0.89/100) + (57.97 x 7.36/100)

Simplifying this expression, we get:

average atomic mass = 51.371 + 0.507 + 4.271

average atomic mass = 56.149

Rounding this to two decimal places, we get an average atomic mass of 56.11 amu. Therefore, the best choice is C).

The Element X Has Three Naturally Occurring Isotopes