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Topic: what is the number of moles of 4.0mL of 50% NaOH?  (Read 10877 times)

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engineer

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what is the number of moles of 4.0mL of 50% NaOH?
« on: February 24, 2006, 11:40:38 PM »
what is the number of moles of 4.0mL of 50% NaOH (and the 50% is by weight)?

i tried working through it using mol=vol x conc but when calculating the conc i get very large values  ??? so im probably applying the 50% thing in a wrong way.
any ideas?

thank you :)
« Last Edit: February 26, 2006, 03:02:35 PM by Mitch »
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Offline Borek

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Re:moles of NaOH
« Reply #1 on: February 25, 2006, 05:19:10 AM »
Convert percentage to molarity, then n=CV. 50% solution is highly concentrated so your numbers may be correct.

However, to solve this question you need to know density of the solution. My density tables for NaOH end before 50% which may mean solubility of the NaOH is lower and 50% solution siply doesn't exist.
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windtalker

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Re:moles of NaOH
« Reply #2 on: February 25, 2006, 10:30:30 PM »
I've searched the net and I've found this document
http://permanent.access.gpo.gov/websites/epagov/www.epa.gov/ORD/NRMRL/pubs/600R03019/600R03019.pdf
where is stated (page 71) "d2 = density 50% NaOH = 12.9 lb/gal"
Due to the sort of the paper I suppose this value is reliable.
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Offline Borek

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Re:moles of NaOH
« Reply #3 on: February 26, 2006, 05:21:58 AM »
Quote from: windtalker on February 25, 2006, 10:30:30 PM
where is stated (page 71) "d2 = density 50% NaOH = 12.9 lb/gal"
Due to the sort of the paper I suppose this value is reliable.

In a way.

Check page 24 - "50% NaOH freezes at 55°F;"

AFAIR highly concentrated NaOH solutions get easily oversaturated, thus it is difficult to say whether you have "real" solution or not. That's probably why some sources don't give density of 50% NaOH solution for 15 deg C, as it is a "border" case for which data is not precise. Document you quote refers to commercially available solution "known as" 50% NaOH. That's so called "industrial grade" 50% and "industrial grade" 12.9 lb/gal. Anything ± 5% fits ;)

Have you ever heard about "industrial grade prime numbers"?

I have added 50% NaOH density to my table (taken from other source - International Critical Tables) but I have my doubts about this value.
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windtalker

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Re:moles of NaOH
« Reply #4 on: February 26, 2006, 12:41:34 PM »
Quote from: Borek on February 26, 2006, 05:21:58 AM

Have you ever heard about "industrial grade prime numbers"?


No, never heard this expression before. But now I know what it means ;)
By the way, your site is great. One of these days I will post it to my blogs.
Cheers.
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engineer

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Re:moles of NaOH
« Reply #5 on: February 26, 2006, 01:06:33 PM »
Borek, windtalker: thanks alot for your replies. yeah the website is excellent.

cheers  :)
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