Finding the Specific Activity of Rubidium Chloride

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The discussion centers on calculating the specific activity of natural rubidium chloride (RbCl), considering its isotopes, stable 85Rb and radioactive 87Rb, with the latter having an abundance of 27.83%. The user attempts to convert 1 gram of RbCl into molecules and applies the isotopic abundance to estimate the amount of 87Rb, but struggles with the calculations and the relevance of atomic mass values. Specific activity is defined as disintegrations per second per unit mass, and the user notes that only the radioactive isotope contributes to this value. Clarification is sought on the terms Ar (atomic mass) and Mr (molar mass), indicating a need for foundational chemistry knowledge to proceed. The conversation highlights the complexities involved in calculating specific activity in mixed-isotope compounds.
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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.
 
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Phillyfan321 said:

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.
 
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.
 
Phillyfan321 said:
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?
 

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