# Chemical Forums

• February 21, 2019, 07:32:17 AM
• Welcome, Guest

•

Pages: [1]   Go Down

### AuthorTopic: How do you calculate molality, millimolality, and milliosmolality????  (Read 48077 times) !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="https://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() {var po = document.createElement("script"); po.type = "text/javascript"; po.async = true;po.src = "https://apis.google.com/js/plusone.js";var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(po, s);})();

0 Members and 1 Guest are viewing this topic.

#### shaina2006

• Very New Member
• Mole Snacks: +0/-0
• Offline
• Posts: 2
##### How do you calculate molality, millimolality, and milliosmolality????
« on: September 14, 2007, 10:38:22 AM »

The NaCl solution has a concentration of 1.95 g per 250 ml (molecular weight= 58.5). The glucose solution has a concentration of 9.0 g per 250 ml (molecular weight= 180). Calculate the molality, millimolality, and milliosmolality of both solutions.
Logged

#### Sev

• Full Member
• Mole Snacks: +43/-6
• Offline
• Gender:
• Posts: 231
##### Re: How do you calculate molality, millimolality, and milliosmolality????
« Reply #1 on: September 14, 2007, 12:57:05 PM »

molality = moles of solute/kilogram of solvent.

osmolality = osmoles of solute/kilogram of solvent.
(an osmole is the number of moles that contribute an osmotic pressure.)
http://en.wikipedia.org/wiki/Osmolality

Also, milli is 10^-3

Logged

#### shaina2006

• Very New Member
• Mole Snacks: +0/-0
• Offline
• Posts: 2
##### Re: How do you calculate molality, millimolality, and milliosmolality????
« Reply #2 on: September 17, 2007, 06:37:34 AM »

molality = moles of solute/kilogram of solvent.

osmolality = osmoles of solute/kilogram of solvent.
(an osmole is the number of moles that contribute an osmotic pressure.)
http://en.wikipedia.org/wiki/Osmolality

Also, milli is 10^-3

could u please show me how 2 do it? I have no clue wat 2 do!!
Logged

#### Sev

• Full Member
• Mole Snacks: +43/-6
• Offline
• Gender:
• Posts: 231
##### Re: How do you calculate molality, millimolality, and milliosmolality????
« Reply #3 on: September 20, 2007, 08:12:25 PM »

For the first solution, start by calculating the number of moles of NaCl in 1.95g.  n=m/M= 1.95g / 58.44g/mol = 0.033mol.
0.033mol per 250mL of water, is the same as 0.033 x 4 = 0.133 mol per litre of water.

So the molality is 0.133 M.
'milli' is 10^-3.  For example, a millimeter is 1/1000 (which is 10^-3) of a meter.  So the millimolality of the solution will be 133 mM.  Are you following?

osmolality is slightly more complex.  It takes into account that a molecule may dissociate (split apart) in solution.
For the first solution, the milliosmolality is simply the millimolality (133mM) multiplied by 2 (since NaCl dissociates into 2 ions in solution - Na+ and Cl-).

Glucose however does not dissociate, so in the case of solution 2 the millimolality and milliosmolality will be the same.

Logged
Pages: [1]   Go Up

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 1.234 seconds with 23 queries.