conc. calculation

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biology_06er
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conc. calculation

Post by biology_06er » Tue Mar 06, 2007 4:04 am

Greetings

not a homework question (part of lab experiment)-just not sure where to but it and I don't know how to work it out...

we have 2ml of distilled water + 8ml 0.154M NaCl...

how do I work out the new conc?....

also how do i make up 0.075M NaCl if I have distilled water available and 0.154M NaCl available--apparently our group came up with 5ml of each-but I don't know how to work that out either...

cheers
biology_06er

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AstusAleator
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Post by AstusAleator » Tue Mar 06, 2007 5:11 am

.154M means it has .154 moles / liter.
1 liter = 1000 mls
so (8ml/1000ml)(.154) = how many moles you have total.
divide that by (8+2)/1000 (your end liters) to get your final concentration.

There's a simpler way to do it, but I can't think of it at the moment. Plus, it's always best to think these things through when you're learning them.

ok so for the second part, you want to get .075M from .154M and dH2O.

One way to do it would be to figure out how much of the .154M NaCl you need to have .075 moles, and then add dH2O to equal a liter.
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