December 02, 2020, 10:12:21 AM
Forum Rules: Read This Before Posting


Topic: Simple question  (Read 350 times)

0 Members and 1 Guest are viewing this topic.

Offline chimias223

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Simple question
« 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 6-li isotope in nature is 7.4%
How much moles of Li-6 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.

Offline billnotgatez

  • Global Moderator
  • Sr. Member
  • ***
  • Posts: 4086
  • Mole Snacks: +215/-58
  • Gender: Male
Re: Simple question
« Reply #1 on: October 28, 2020, 02:10:58 PM »
You have to show your attempts or thoughts at solving the question to receive help.
This is a forum policy.
Click on the link near the top center of the forum page.
Forum Rules: Read This Before Posting.
http://www.chemicalforums.com/index.php?topic=65859.0

Offline chimias223

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: Simple question
« Reply #2 on: October 28, 2020, 02:26:46 PM »
You have to show your attempts or thoughts at solving the question to receive help.
This is a forum policy.
Click on the link near the top center of the forum page.
Forum Rules: Read This Before Posting.
http://www.chemicalforums.com/index.php?topic=65859.0

Sorry. This is waht I tried.
https://pasteboard.co/JxLUA6y.jpg
« Last Edit: October 28, 2020, 05:06:53 PM by Borek »

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7695
  • Mole Snacks: +538/-92
  • Gender: Male
Re: Simple question
« Reply #3 on: October 28, 2020, 04:29:37 PM »
Only 75.23 moles are OK
AWK

Offline chimias223

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: Simple question
« Reply #4 on: October 28, 2020, 04:58:44 PM »
Only 75.23 moles are OK

what's about the information ''Given that the relative prevalence of the 6-li 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.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26153
  • Mole Snacks: +1703/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Simple question
« Reply #5 on: October 28, 2020, 05:04:59 PM »
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.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline chimias223

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: Simple question
« Reply #6 on: October 28, 2020, 05:14:09 PM »
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?

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7695
  • Mole Snacks: +538/-92
  • Gender: Male
Re: Simple question
« Reply #7 on: October 29, 2020, 03:54:44 AM »
Have you ever heard of significant figures?
AWK

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26153
  • Mole Snacks: +1703/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Simple question
« Reply #8 on: October 29, 2020, 04:32:21 AM »
Question is poorly formulated in this aspect, it asks for using atomic masses to 3 decimal points, yet gives 6Li abundance to only two sigfigs.

That being said, the number is OK, it is just a matter of a correct representation of its uncertainty.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline chimias223

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +0/-0
Re: Simple question
« Reply #9 on: October 29, 2020, 06:03:41 AM »
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 6Li 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?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26153
  • Mole Snacks: +1703/-402
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Simple question
« Reply #10 on: October 29, 2020, 07:59:10 AM »
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 6Li 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.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Sponsored Links