Homework Help

Naturally occurring thallium consists of two stable isotopes, Tl-203 and Tl-205 (atomic...

user profile pic

lak-86 | Student, Undergraduate | Salutatorian

Posted August 21, 2013 at 4:39 AM via web

dislike 1 like

Naturally occurring thallium consists of two stable isotopes, Tl-203 and Tl-205 (atomic masses = 203.0 and 205.0, respectively) and has an average atomic mass of 204.4. What is the percentage of Tl-205?

1 Answer | Add Yours

user profile pic

jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted August 21, 2013 at 4:50 AM (Answer #1)

dislike 1 like

Let us say we have `X%` of Ti-205. Then the rest `(100-X)%` is the Ti-203 percentage.

It is given that average atomic mass of Ti is 204.4.
Mass of Ti-205 in isotope` = X/100xx205`

Mass of Ti-203 in isotope `= (100-X)/100xx203`

`X/100xx205+(100-X)/100xx203 = 204.4`

`205X+20300-203X = 20440`

`X = 70`

So the percentage of Ti-205 in the isotope is 70%.

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes