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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: chimias223 on October 28, 2020, 02:04:41 PM

Hi,
I need a little help with a little question.
The empirical formula of the mineral spodumene is: LiAlSi2O6
Given that the relative prevalence of the 6li isotope in nature is 7.4%
How much moles of Li6 atoms are found in 14 kg of spodumene?
Note: To get accurate results the molar masses should be taken with 3 digits after the decimal point.

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You have to show your attempts or thoughts at solving the question to receive help.
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Sorry. This is waht I tried.
https://pasteboard.co/JxLUA6y.jpg

Only 75.23 moles are OK

Only 75.23 moles are OK
what's about the information ''Given that the relative prevalence of the 6li isotope in nature is 7.4%''.? should not use it?
I think I need to multiply 75.23 with 7.4/100. but I'm not sure.

I think I need to multiply 75.23 with 7.4/100. but I'm not sure.
Idea is sound, but that's not what you did.

I think I need to multiply 75.23 with 7.4/100. but I'm not sure.
Idea is sound, but that's not what you did.
Yea I know. I think It's supposed to be the final soloution but I dont sure (5.567). can you help me with this,please?

Have you ever heard of significant figures?

Question is poorly formulated in this aspect, it asks for using atomic masses to 3 decimal points, yet gives ^{6}Li abundance to only two sigfigs.
That being said, the number is OK, it is just a matter of a correct representation of its uncertainty.

Have you ever heard of significant figures?
No
Question is poorly formulated in this aspect, it asks for using atomic masses to 3 decimal points, yet gives ^{6}Li abundance to only two sigfigs.
That being said, the number is OK, it is just a matter of a correct representation of its uncertainty.
The answer will be 5.567?

The answer will be 5.567?
Yes and no.
Yes  that the answer displayed by the calculator when you correctly key in all numbers given and do the correct calculations.
No  you are told abundance of ^{6}Li is 7.4%. That basically means it is somewhere between 7.35% and 7.449999% as all these numbers will be rounded down to 7.4. So, your final answer should take it into account. https://en.wikipedia.org/wiki/Significant_figures are an approximate (but better than nothing) way of doing so. 5.567 contains too many digits and should be rounded down to a correct number of sigfigs.