Question

Element X has two naturally occurring isotopes, 65X (isotopic mass 65.0457 amu, abundance 20.53%) and 67X (isotopic mass 66.9704 amu, abundance 79.47%). Calculate the atomic mass of element X.

Answer 1

Answer:

66.5753 amu

Explanation:

From the question given above, the following data were obtained:

Isotope A (⁶⁵X):

Mass of A = 65.0457 amu

Abundance of A = 20.53%

Isotope B (⁶⁷X):

Mass of B = 66.9704 amu

Abundance of B = 79.47%

Atomic mass of X =?

The atomic mass of X can be obtained as follow:

Atomic mass = [(mass of A × A%)/100] + [(mass of B × B%)/100]

= [(65.0457 × 20.53)/100] + [(66.9704 × 79.47)/100]

= 13.3539 + 53.2214

= 66.5753 amu

Therefore, the atomic mass of X is 66.5753 amu.

Answer 2

Element X, with an atomic mass of 66.58 amu, has 2 naturally occurring isotopes, ⁶⁵X (65.0457 amu, 20.53%) and ⁶⁷X (66.9704 amu,  79.47%).

What is the average atomic mass?

The average atomic mass (atomic mass) of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance.

Element X has 2 isotopes:

• ⁶⁵X with an isotopic mass of 65.0457 amu and an abundance of 20.53% (0.2053).
• ⁶⁷X with an isotopic mass of 66.9704 amu and an abundance of 79.47% (0.7947).

We can calculate the average atomic mass of X using the following expression.

mX = m⁶⁵X × ab⁶⁵X + m⁶⁷X × ab⁶⁷X

mX = 65.0457 amu × 0.2053 + 66.9704 amu × 0.7947

mX = 66.58 amu

Element X, with an atomic mass of 66.58 amu, has 2 naturally occurring isotopes, ⁶⁵X (65.0457 amu, 20.53%) and ⁶⁷X (66.9704 amu,  79.47%).

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