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Topic: preparing a solution  (Read 2471 times)

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Offline orgo814

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preparing a solution
« on: June 15, 2014, 08:51:07 PM »
This is a VERY basic question. I have not done lab work in chemistry for awhile and am just starting on research.

If I was to prepare a 0.7% NaCl solution, would I just add 0.7 grams of NaCl and then dilute it with 100 mL? This stuff has always confused me.

Offline Arkcon

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Re: preparing a solution
« Reply #1 on: June 15, 2014, 09:33:05 PM »
Everybody find this sort of thing tricky, when they haven't done it in a while.  A useful trick is to keep careful records in your lab book.  As in, what did you want to make -- a 0.7 % solution.  And how did you make it?  The you can make a 0.5%, or 0.3 % next time.

At any rate, when you want to solve such a problem, try a couple of other, close by concentrations, such as 1%, and others.  A 1% solution would require 1 gram in .what, 100 grams total solution weight.  And 0.5% would be exactly half. And 0.7 would have to be between the two.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Borek

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Re: preparing a solution
« Reply #2 on: June 16, 2014, 03:03:00 AM »
If I was to prepare a 0.7% NaCl solution, would I just add 0.7 grams of NaCl and then dilute it with 100 mL? This stuff has always confused me.

Imagine preparing 50% solution with this approach. You take 50 g of NaCl, dilute with 100 mL of water (which weights almost exactly 100 g), so you end with 150 g of the solution.

[tex]\frac{50g}{150g}\times 100\% = 33.3\%[/tex]

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