Question

Find the average atomic mass of an element X if the element is available in its two isotopic forms 23X(80%) and 25X (20%).​

Answer 1

Answer:

Average atomic mass =

100

∑% abundance × A.M

20.18=

100

20×90+x×21+(10−x)22

2018=1800+21x+220−22x

x=2020−2018

x=2%

Answer 2

Given:

An element is available in its two isotopic forms 23X(80%) and 25X (20%).​

To Find:

The average atomic mass of the element

Solution:

When percentage abundances of an element are given, they are first converted to decimal form.

So, divide the given percentages by 100

If f₁ and f₂ are the abundances of both isotopes respectively,

f₁ = 0.8 and f₂ = 0.2

m₁ = 23 and m₂= 25 (Given)

Average atomic mass = f₁m₁ + f₂m₂

                                    = (0.8 x 23) + (0.2 x 25)

                                     = 23.4u

Hence the average atomic mass of the given element is 23.4u