Solutions - Saturated, Dilute, and Concentrated   

A saturated solution is one which can exist in equilibrium with undissolved solute.  The concentration reached is called the solubility of that solid in the liquid at the given temperature. 

Solubilities of solids in liquids range from very high to very low.  The terms concentrated and dilute are purely relative and convey little useful information.

   Examples: 

   The solubility of NaCl in H₂O at 20^oC is about 6 moles per liter of solution, 6 M.  Thus, a saturated NaCl solution is relatively concentrated.

   The solubility of AgCl in H₂O at 20^oC is about 1 x 10^-5 moles per liter of solution, 0.00001 M.  Thus a saturated solution of AgCl is a very dilute solution.

Solutions - Expressing Concentrations

Molarity (M) - the number of moles of the solute contained in one liter of the solution.

Example:  A 0.5 molar (0.5 M) solution of HCl contains 18.25 g of HCl per liter of solution, since 18.25 g is half the molecular weight of HCl, 36.5 g/mole.

Normality (N) - the number of gram-equivalent weight of the solute in one liter of the solution.  (Gram-equivalent weight is the amount in grams equal to the formula weight divided by the number of moles of replaceable H⁺ or OH^- in the substance.)

Example:  1 mole of HCl (36.5 g) per liter of solution = 1 N HCl

            1/2 mole H₂SO₄ (49 g) per liter of solution = 1 N H₂SO₄

            1/3 mole Al(OH)₃ (26 g) per liter of solution = 1 N Al(OH)₃

Molality (m) - the number of moles of the solute per kilogram (1000 g) of solvent contained in a solution.

Example:  A 0.5 molal (0.5 m) solution of HCl contains 18.25 g of HCl in 1 kilogram (1000 g) of water.

Solubility Rules

Volumetric Flask

PowerPoint

Properties of Solutions, Colloids, and Suspensions

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