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?

265.2

20.80

245.9

251.9

none of the above

all of the above

Answer 1

265.2amu

Step-by-step explanation:

Given parameters:

Atomic mass = 254.9amu

Abundance of isotope 1 = 72%

Atomic mass of isotope 1 = 250.9amu

Abundance of isotope 2 = 100 - 72 = 28%

Unknown:

Atomic mass of isotope 2 = ?

Solution:

To find the atomic mass of isotope 2, use the expression below:

Atomic mass = (abundance of isotope 1 x atomic mass of isotope 1) + (abundance of isotope 2 x atomic mass of isotope 2)

Now insert the parameters and find the unknown;

254.9 = (0.72 x 250.9) + (0.28 x Atomic mass of isotope 2)

254.9 = 180.648 + 0.28x atomic mass of isotope 2

254.9 - 180.648 = 0.28x atomic mass of isotope 2

74.25 = 0.28 x atomic mass of isotope 2

Atomic mass of isotope 2 = 265.2amu