August 09, 2022, 12:19:53 AM
Forum Rules: Read This Before Posting

### Topic: Osmolarity  (Read 11357 times)

0 Members and 1 Guest are viewing this topic.

#### justwonder

• Guest
##### Osmolarity
« on: September 06, 2004, 08:24:08 AM »
hello guys!

i am stucked at this one. i hope you can help me out. i have to make this solution;

41g/l  NaCl
Hepes-buffer 10mM
Osm. 960 mOsm
pH8.2

i know how to prepare all the components, EXCEPT for 960mOsm. i wonder ;
1. how do i know that i have 960mOsm?
2. how to adjust the Osm, if the value is not correct.

and lastly, what is so important with mOsm?

thank you all for your time and sharing!

#### Demotivator

• Guest
##### Re:Osmolarity
« Reply #1 on: September 06, 2004, 05:04:50 PM »
Osmolar measurement is used in biological systems because of the role of osmotic pressure in cell membranes. Osmotic pressure depends on the number of particles in solution as opposed to just moles of compound. For eg, 1 mole NaCl is 2 Osmoles.

The NaCl solution is an Osmolar buffer that doesn't affect the PH much. It's added to hepes to adjust the mOsmolar value to 960.

Assuming Hepes is the monosodium salt, 10 mM is about 20 mOsm.
Need to calculate amount of NaCl to produce 940 additional mOsm. total vol of all ingredients is 1 liter.

41 g/l stock NaCl is 701 mM = 1402 mOsm
(940/1402)(1000 ml)= 670 ml of NaCl solution need to be included in 1 L buffer mixture..

#### justwonder

• Guest
##### Re:Osmolarity
« Reply #2 on: September 06, 2004, 06:23:16 PM »
thanks a bunch!