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# Magnesium exists as three isotopes, deducing the percentages of them in a sample watch

1. Magnesium exists as three isotopes: Mg24, Mg25, Mg26
Mg25 atoms make up 10% by mass in a sample or magnesium. Magnesium has Ar = 24.3

Use this information to deduce the percentages of the other two magnesium isotopes present in the sample.
I'm stuck how to do this (I have two unknowns in one equation- probably doing it wrong), any help would be appreciated. Thanks
2. Mg26 - Mg24 = 2

2 = too

too = too many tories

exactly
3. no mass spectrum?! *malfunctions*

hmmm...

i found this?
4. (Original post by Tim73)
Magnesium exists as three isotopes: Mg24, Mg25, Mg26
Mg25 atoms make up 10% by mass in a sample or magnesium. Magnesium has Ar = 24.3

Use this information to deduce the percentages of the other two magnesium isotopes present in the sample.
I'm stuck how to do this (I have two unknowns in one equation- probably doing it wrong), any help would be appreciated. Thanks
Fun, fun, fun ...

You can use the 10% of 25-Mg to work out an average mass of the other two isotopes together.

Then you can use that value and the two other masses to find the relative proportions of those two isotopes (remembering that they add up to 90%)

Never seen a question of this type before ... fun fun fun.
5. (Original post by charco)
You can use the 10% of 25-Mg to work out an average mass of the other two isotopes together.
.
I'm confused, how do I do that?
6. (0.1*25+x*24+(0.9-x)*26)/3 = 24.3

Just use a bit of algebra, easy.
7. (Original post by Maker)
(0.1*25+x*24+(0.9-x)*26)/3 = 24.3

Just use a bit of algebra, easy.
How come it's not divided by 100? Since I thought it should be divided by the total abundance and that would be 100%.
Um and I tried it and got a negative answer of -23.5 for x? Either I went wrong somewhere or that doesn't work.
8. (Original post by Tim73)
How come it's not divided by 100? Since I thought it should be divided by the total abundance and that would be 100%.
Um and I tried it and got a negative answer of -23.5 for x? Either I went wrong somewhere or that doesn't work.
Here you go ...

https://youtu.be/J9j28QNUvhI

9. (Original post by charco)
Here you go ...
Thank you! You saved me lol

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