what is the difference between OSMOLALITY, OSMOLARITY and MOLARITY?use simple terms please! thanks!?

Answer 1

http://en.wikipedia.org/wiki/Osmolal

it is very clear there

Answer 2

In chemistry, the osmole (Osm) is a non-SI unit of measurement that defines the number of moles of a chemical compound that contribute to a solution's osmotic pressure.
Osmolarity is a measure of the osmoles of solute per litre of solution, while the osmolality is a measure of the osmoles of solute per kilogram of solvent. Molarity and Osmolarity are not commonly used in osmometry because they are temperature dependent, that is water changes its volume with temperature. However, if the concentration is very low osmolarity and osmolality are considered equivalent. In calculations for these two measurements, salts are presumed to dissociate into their component ions. For example, a mole of glucose in solution is one osmole, whereas a mole of sodium chloride in solution is two osmoles (one mole of sodium and one mole of chloride). Both sodium and chloride ions affect the osmotic pressure of the solution.

Molarity (M) denotes the number of moles of a given substance per litre of solution. For instance: 4.0 litres of liquid, containing 2.0 moles of dissolved particles, constitutes a solution of 0.5 M. Such a solution may be described as "0.5 molar." (Working with moles can be highly advantageous, as they enable measurement of the absolute number of particles in a solution, irrespective of their weight and volume)

Answer 3

In addition to the link provided by bellerophon, here is another:
http://www.hartnell.cc.ca.us/faculty/awright/osmolality%20problems.doc
Basically, osmols are particles in solution. Molarity is moles of solute in one liter of a solution. Osmolarity refers to osmols in one liter of solution. Osmolality refers to osmols in one kilogram of solvent.