Question

Element X has two naturally occurring isotopes, 65X (isotopic mass 65.0234 amu, abundance 47.78%) and 67X (isotopic mass 67.1396 amu, abundance 52.22%). Calculate the atomic mass of element X.

_____amu

Answer 1

To calculate the atomic mass of element X with two isotopes, multiply each isotopic mass by its respective fractional abundance and sum the results to get 66.1708 amu.

Step-by-step explanation:

The atomic mass of element X can be calculated by using the isotopic masses and abundances of its naturally occurring isotopes. To find the atomic mass of element X, we multiply the mass of each isotope by its fractional abundance (percentage abundance divided by 100) and then sum the products:

• (65.0234 amu × 0.4778) = 31.0785 amu for isotope 65X
• (67.1396 amu × 0.5222) = 35.0923 amu for isotope 67X

Adding these products together gives us the average atomic mass for element X:

(31.0785 amu + 35.0923 amu) = 66.1708 amu

Therefore, the atomic mass of element X is 66.1708 amu.

Answer 2

• 66.1285 amu

Step-by-step explanation:

The atomic mass of an element is equal to the weigthed average of the atomic masses of its isotopes:

• atomic mass = ∑ (relative abundance × isotopic mass)

• atomic mass = relative abundance of isotope ⁶⁵X × isotopic mass of isotope ⁶⁵X + relative abundance of isotope ⁶⁷X × isotopic mass of isotope ⁶⁷X

• atomic mass = 47.78% × 65.0234 amu + 52.22% × 67.1396 amu

• atomic mass = 66.1285 amu ← answer