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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: scorwine on April 25, 2006, 09:58:23 PM

Title: Calculating osmolarity of a 5% glycerol solution
Post by: scorwine on April 25, 2006, 09:58:23 PM

Can anyone tell me how to calculate the osmolarity of a 5% glycerol solution?

Thanks

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Albert on April 26, 2006, 03:18:25 AM

Glycerol is a non-electrolyte, so, its osmolarity and molarity are the same.

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: scorwine on April 26, 2006, 11:31:04 AM

Thanks. I haven't done chemistry for a long time. Could you help me figure out the molarity of the 5% glycerol solution then?

Thanks :-[

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Alberto_Kravina on April 26, 2006, 12:46:05 PM

Quote from: scorwine on April 26, 2006, 11:31:04 AM

Thanks. I haven't done chemistry for a long time. Could you help me figure out the molarity of the 5% glycerol solution then?

You need the density!

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Borek on April 26, 2006, 01:05:14 PM

http://www.chembuddy.com/?left=concentration&right=toc

d (5%) = 1.0101 g/mL

CASC rulez ;)

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Equi on April 26, 2006, 02:08:41 PM

I guess the solution is defined as %(w/v) anyway?

Hence:
5g/100ml
M(glycerol) = 92.09 g/mol
n = m/M = 5/92.09 ~ 0.05 mol of glycerol in 100ml = 0.5 mol/l = 0.5 M (molar) = 0.5 osM (as Albert said there's no difference between molarity and osmolarity in this case)

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Alberto_Kravina on April 26, 2006, 02:13:55 PM

I think that it's 5% (w/w)

5g ? 100g

0,05 mol ? 100g (assuming that your molar mass is right, I didn't check it ;) )

Rho=m/V ? V=m/Rho ? V= 99.000099 mL = 0.099000099L

?c=n/V = 0.50505 mol/L

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Borek on April 26, 2006, 02:21:23 PM

For 5% w/w CASC gives 0.5484M - and that's result I trust :)

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Albert on April 26, 2006, 02:25:28 PM

M = 1.0101 g/mL * (5 g/100 g) * (1 mmol/0.09209 g) = 0.5484

 ??? ???

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Equi on April 26, 2006, 02:28:36 PM

hmm?

(w/w)% would imho be inappropriate. Either you weigh in the glycerol (w/v), or you measure it's volume (v/v). Who would measures the weight of the solution?

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Borek on April 26, 2006, 02:33:17 PM

Quote from: Albert on April 26, 2006, 02:25:28 PM

M = 1.0101 g/mL * (5 g/100 g) * (1 mmol/0.09209 g) = 0.5484

 ??? ???

I assume you have seen my post before I edited it - with 0.5715? It was molality. My programs should be trusted more then I :( I have copied wrong field to the post. I have corrected it in a blink, but for few minutes chemicalforums have been lagging, so the blink was longer then it should.

Still, I was fast enough to edit my post and don't have Edit comment added :)

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Borek on April 26, 2006, 02:34:50 PM

Quote from: Equi on April 26, 2006, 02:28:36 PM

(w/w)% would imho be inappropriate. Either you weigh in the glycerol (w/v), or you measure it's volume (v/v). Who would measures the weight of the solution?

I don't trust 5% solutions unless I have made them by myself.

http://www.chembuddy.com/?left=concentration&right=wrong-percentages

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Albert on April 26, 2006, 02:39:58 PM

Mind you, Borek, are sure 1.0101 to be the right density? What's wrong with the 1.261 I found?

Title: Re: Calculating osmolarity of a 5% glycerol solution
Post by: Borek on April 26, 2006, 03:01:43 PM

Quote from: Albert on April 26, 2006, 02:39:58 PM

Mind you, Borek, are sure 1.0101 to be the right density? What's wrong with the 1.261 I found?

1.261 is density of a pure glycerine, not of 5% solution.