Question

An element has two naturally occurring isotopes, X-85 with a mass of 84.9118 amu and a natural abundance of 72.17%, and X-87 with a mass of 86.9092 amu and a natural abundance of 27.83%. Calculate the atomic mass of this element.

Answer 1

To calculate the average atomic mass of an element with three naturally occurring isotopes, multiply the mass of each isotope by its natural abundance in decimal form, and then sum the results.

Step-by-step explanation:

To calculate the average atomic mass of an element with three naturally occurring isotopes, we need to multiply the mass of each isotope by its natural abundance in decimal form, and then sum the results. Let's use an example to illustrate this calculation. Suppose an element has three isotopes: X-1 with a mass of 1.000 amu and a natural abundance of 40%, X-2 with a mass of 2.000 amu and a natural abundance of 50%, and X-3 with a mass of 3.000 amu and a natural abundance of 10%. We can calculate the average atomic mass as follows:

(1.000 amu * 0.40) + (2.000 amu * 0.50) + (3.000 amu * 0.10) = 0.400 amu + 1.000 amu + 0.300 amu = 1.700 amu

Answer 2

This element is Rubidium (Rb) and has an average atomic mass of 85.468 u

Step-by-step explanation:

The average mass of an element is calculated by taking the average of the atomic masses of its stable isotopes.

The enitre atomic mass = 100 % or 1

⇒ this consists of X-85 with 72.17 % abundance with atomic massof 84.9118 g/mol

72.17 % = 0.7217

⇒ this consists of X-87 with 27.83 % abundance with atomic mass of 86.9092 g/mol

27.83 % = 0.2783

To calculate the mass of this isotope we use the following:

0.7271 * 84.9118 + 0.2783 * 86.9092 =85.468 g/mol

This element is Rubidium(Rb) and has an average atomic mass of 85.468 u