What is Osmolality?

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Definitions:
Following are key terms relevant to the science of osmolality and will help you to develop a better understanding.

Solutions: A homogeneous mixture of solutes in a solvent

Solvent: The major, liquid component of a solution

Solutes: The minor components of a solution – usually solids

Concentration: The relative amount of solute in a solution. Can be expressed in many ways: solute to solvent, solute to solution, mass to mass, mass to volume, etc.

Molarity: Molar concentration: grams of solute per liter of solution

Molality: Molal concentration: grams of solute per kilogram of solvent

Molecular weight: The sum of the atomic weights of all the atoms in a molecule

Mole: Gram molecular weight, molecular weight expressed in grams. One mole of sodium chloride weighs 58.44 grams.

Ionic solution: Certain molecules, when dissolved, dissociate into charged particles called ions

Non-ionic solution: Certain molecules, when dissolved, do not dissociate or ionize into charged particles.

Avogadro’s Number: The number of molecules in one mole (gram molecular weight) of a substance. One mole of non-ionic solute (such as sucrose) dissolved in one kilogram of water will yield Avogadro’s number of molecules. One mole of ionic solute dissolved in one kilogram of water will yield almost twice Avogadro’s number of particles.

Concentrative properties: When a solute is dissolved in a solvent, certain properties of the solvent (freezing point, boiling point, vapor pressure and osmotic pressure) are changed nearly in proportion to the concentration of the solute, expressed in dissolved particles. Avogadro’s number of particles, regardless of their size or shape, when dissolved in a kilogram of water, will change each of the concentrative properties a specific amount.


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