Finding the Specific Activity of Rubidium Chloride

[Phillyfan321]

Homework Statement

The element rubidium consists of two isotopes, the stable 85Rb and radioactive 87Rb (abundance 27.83%). What is the specific activity of natural rubidium chloride? Use Ar85.47 gmol-1 for rubidium element, Ar 86.91 gmol-1 for 87Rb, and Mr 120.92 gmol-1 for RbCl.

Homework Equations

A2 = (λ2A1 /λ2-λ1) (e^-λ2 *t)
M = (N#/ avag const)* Ar

The Attempt at a Solution

I tried to convert 1g (subjective choice) of RbCl to 5 x 10^21 molecules, then apply percent abundance to get 1.4 x 10^21 Rb87. I converted that back to grams and got .2. I really don't know if I am on the right track or not, because I can't seem to figure out where I am going with this and if I need the other Ar value. Thanks.

 

[haruspex]

Homework Statement

The element rubidium consists of two isotopes, the stable 85Rb and radioactive 87Rb (abundance 27.83%). What is the specific activity of natural rubidium chloride? Use Ar85.47 gmol-1 for rubidium element, Ar 86.91 gmol-1 for 87Rb, and Mr 120.92 gmol-1 for RbCl.

Homework Equations

A2 = (λ2A1 /λ2-λ1) (e^-λ2 *t)
M = (N#/ avag const)* Ar

The Attempt at a Solution

I tried to convert 1g (subjective choice) of RbCl to 5 x 10^21 molecules, then apply percent abundance to get 1.4 x 10^21 Rb87. I converted that back to grams and got .2. I really don't know if I am on the right track or not, because I can't seem to figure out where I am going with this and if I need the other Ar value. Thanks.

Since this is not a chemistry forum, you will need to phrase your question in a way that assumes little knowledge of chemistry.

 

[Phillyfan321]

Well... Specific Activity in this case is Bq per unit mass (Disintegration/sg) which is what I need to find. Only part (28%) of the total compound is radioactive but when I thought of doing a sum for the components the stable isotope doesn't have a decay factor so I ran into a wall.

 

[haruspex]

Well... Specific Activity in this case is Bq per unit mass (Disintegration/sg) which is what I need to find. Only part (28%) of the total compound is radioactive but when I thought of doing a sum for the components the stable isotope doesn't have a decay factor so I ran into a wall.

Doesn't help me. E.g. what are Ar and Mr?