Answer to Question #150366 in Chemistry for anthony

Question

Fictitious element X has an a average atomic mass of 254.9 and only 2 isotopes, One of its isotopes has an abundance of 72.00 and a mass of 250.9 amu. What is the atomic mass of the second isotope?

Answer 1

Solution:

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

Average atomic mass = f₁M₁ + f₂M₂ +… + f_nM_n where f is the fraction representing the natural abundance of the isotope and M is the mass number (weight) of the isotope.

In our case: Average atomic mass = f₁M₁ + f₂M₂

Average atomic mass = 254.9 amu

f₁ = 72.00% or 0.72

M₁ = 250.9 amu

f₂ = (1 - f₁) = (1 - 0.72) = 0.28

M₂ = unknowm

Hence,

Average atomic mass of X = f₁M₁ + f₂M₂

254.9 amu = (0.72 × 250.9 amu) + (0.28 × M₂)

254.9 amu = 180.648 amu + 0.28 × M₂

M₂ = (254.9 amu - 180.648 amu) / 0.28 = 265.186 amu = 265.2 amu

M₂ = 265.2 amu

Answer: The atomic mass of the second isotope is 265.2 amu.