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Chemistry problem - anyone remember how to do this stuff?
Posted by: hal
Date: February 28, 2013 03:55PM
I'm working on my backpacking setup for the upcoming season. I've reworked everything... been searching google and youtube for new stuff... new ideas...

and one quest is for better light weight backpacking food... there are a few well known brands that I'm not particularly pleased with so I found a few other smaller sources and I'm wanting to test this stuff out...

These are the boil water, poor into a bag of freeze dried and or dehydrated food, seal, wait, then eat method. But I want to have a realistic test... I hike in higher altitude (7-10k') and thought it would be interesting to do a test with water that is the same temperature as boiling water at high altitude... was going to post THAT question here, but thought to run a google search first and found a grid of numbers that I need.

It says that at 2000m (6561') water boils at 93.3ºC (200ºF) and at only 190º F at 4000m (13100').

I'd love to have a number for 8000ft too, but these numbers are good enough.

MY QUESTION for you chemistry types is: how much salt needs to be added to bring the temperature back up to sea level boiling temps?

Would a bit of salt help? That's one thing that I HATE about the well known backpacking foods - they are WAY overloaded with salt. Others that I've found have no added salt, so adding salt to the boiling water might be beneficial IF it's worth the effort.

anyone?
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: testcase
Date: February 28, 2013 04:06PM
So you lose about 10ºF for each 2000M, right? At 8000M temp of boiling water should be about 170º ~175ºF. Why wouldn't that be hot enough? Then, you add salt / condiments to your preferred taste and, not have to dick around, possibly ruining expensive food.

If its really important to know, bring a thermometer with you and run a simple experiment or two, on just when water boils with given amounts of salt added.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: MGS_forgot_password
Date: February 28, 2013 04:07PM
FWIW, it's not the altitude that affects the boiling point, it's the air pressure.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: Buck
Date: February 28, 2013 04:09PM
Bring a pressure cooker!
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: hal
Date: February 28, 2013 04:15PM
Quote
testcase
So you lose about 10ºF for each 2000M, right? At 8000M temp of boiling water should be about 170º ~175ºF. Why wouldn't that be hot enough? Then, you add salt / condiments to your preferred taste and, not have to dick around, possibly ruining expensive food.

If its really important to know, bring a thermometer with you and run a simple experiment or two, on just when water boils with given amounts of salt added.

Clearly, you've never eaten not quite reconstituted chicken before... it's not pleasant... we hikers know the problems with this technique - it only barely works at higher altitude. You have to compensate by adding a bit more water and letting it stand for longer than the directions say. Raising the temp of the water would help a lot.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: wowzer
Date: February 28, 2013 04:29PM
[en.wikipedia.org]

Read the bottom...effectively, adding salt will not significantly increase the temperature of boiling water.



All I ever really needed to know, I learned from watching Star Trek.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: hal
Date: February 28, 2013 04:38PM
Quote
wowzer
[en.wikipedia.org]

Read the bottom...effectively, adding salt will not significantly increase the temperature of boiling water.

THANKS! That's the answer I was looking for...

"However, at the approximate concentration of salt in water for cooking (10 g of salt per 1 kg of water, or 1 teaspoon per quart), the ebullioscopic increase is approximately 0.17 °C (0.31 °F), which will arguably make no practical difference for cooking."
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: space-time
Date: February 28, 2013 09:54PM
D2O

That would help a bit, not much though.

How would you find D2O on a mountain, that is the question.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: Pat
Date: March 01, 2013 10:38AM
Quote
hal
.....You have to compensate by adding a bit more water and letting it stand for longer than the directions say.

And you still get a pocket of crunchy rice and chicken.



Edited 1 time(s). Last edit at 03/01/2013 10:39AM by Pat.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: pbarra1
Date: March 01, 2013 12:22PM
At 8000 feet BP of water is 91.6 C
You would need to increase the BP by 8.4 degrees to get it back to 100 C

That would require 477 g salt in 1000 mL or one liter of water. Based on the solubility of salt (40 g per 100 mL water at 100 C) you would only be able to dissolve 400 grams of salt in 1 liter of water which would bring the BP to 98.6 C

Pressure cooker sounds like a better idea.

delta Tb = 0.515 x molality x i



Edited 1 time(s). Last edit at 03/01/2013 12:23PM by pbarra1.
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Re: Chemistry problem - anyone remember how to do this stuff?
Posted by: hal
Date: March 01, 2013 01:14PM
AWESOME pbarra... glad someone retains these skills

It's a question that I've always wondered

400g of salt in a liter might be a bit too much :-)
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