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What does 5% aqueous solution of glucose mean? Note that it's just 5% and not 5%w/w. Do we assume it to be w/w?

The question is

If the osmotic pressure of 5% aqueous soultion of glucose is $\pi_1$ and that of 5% aqueous solution of urea is $\pi_2$ then:

A) $\pi_1=\pi_2$

B) $\pi_1<\pi_2$

C) $\pi_1>\pi_2$

Does 5% mean that the solutions are equi-molar/molal?

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Generally speaking, percentage aqueous solutions like that are either weight for weight or weight for volume. Either way, in this example, you are comparing how many osmoles there for the same weight of urea ($CO(NH_2)_2$) and glucose ($C_6H_{12}O_6$).

Mole fraction as expressed in a percentage does exist though I have not seen that notation much myself and is usually designated n/n%

From the wording your question I'm guessing that it's a physiology or biochemistry question, in which case they're almost certainly referring to the 5% aqueous solution of glucose as the common IV hydration fluid 5% Dextrose Solution, which is w/w.

Otherwise, it's hard to guess as it's ambiguous!

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  • $\begingroup$ It might be a biochemistry question(the lesson focuses only on solutions and colligative properties and not on their applications) but how would glucose be related to urea in intravenous solutions? $\endgroup$ – user80551 Aug 29 '13 at 9:24
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    $\begingroup$ While urea is not found as commercially available IV solutions, one could see it being used as a hypothetical one in a physiology question. The reason being that urea is a constituent of both intra- and extra-cellular fluid. It also happens to be an ineffective osmole because due to its fat solubility it diffuses freely across the phospholipid bilayer of cell membranes, but obviously aside from that it it can exert an osmotic pressure, just one that cancels out. $\endgroup$ – Tomcat Aug 29 '13 at 9:41
  • $\begingroup$ However, if it's not a biochem question feel free to ignore the second paragraph! $\endgroup$ – Tomcat Aug 29 '13 at 9:42
  • $\begingroup$ Actually the second paragraph was more useful as the given answer was that the osmotic pressure would be equal as 5% would refer to equal concentration. I have never heard of 5% moles(mole fraction as a percentage maybe?) $\endgroup$ – user80551 Aug 29 '13 at 9:45
  • $\begingroup$ Yeah, I don't think that mole percentage is a very commonly used measure even though obviously it exists and can be used. Maybe the other guys might have some idea? I should probably amend my answer though! $\endgroup$ – Tomcat Aug 29 '13 at 9:47

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