Solution Concentration

Concentration: the quantity of a given solute in solution Dilute: having a relatively small quantity of solute per unit volume of solution Concentrated: having a relatively large quantity of solute per unit volume of solution

In general, the concentration, “c” (lower case letter c), of any solution is expressed by the ratio Concentration = quantity of solvent quantity of solute

Amount Concentration A chemists way of expressing solution concentration in terms of the amount (in moles) of solute per litre of solution Traditionally, called molar concentration or molarity, used the symbol “M” According to IUPAC, these terms are no longer correct and have been replaced with “amount concentration”

Amount Concentration The amount concentration, c, of a solution is determined by dividing the amount (in moles) of solute, n, by the volume (in litres) of the solution, V: amount = concentration volume of solution (in L) amount of solute (in mol)

Weight/Volume Percent percent (w/v) or percent (m/v) Used with one solid and one liquid Often used when describing unsaturated solutions weight/volume = percent volume of solution (in mL) mass of solute (in g) X 100% Example: Intravenous fluid is 0.9% (w/v) NaCl = 0.9 g of NaCl dissolved in 100 mL of solution

Weight/Weight Percent weight percent, mass percent, percent (w/w) or percent (m/m) Used with two solids or solutions of a solid dissolved in a liquid Useful when dealing with alloys of precious metals weight/weight = percent mass of solution (in g) mass of solute (in g) X 100%

Weight/Weight Percent Example: The concentration of Mg 2+ in seawater is 0.129% (w/w) = g of Mg 2+ dissolved in 100 g of seawater

Parts Per Million, Billion, and Trillion Environmental solutions are often very low concentration. Convenient to express concentrations in terms of parts per million (ppm) or parts per billion (ppb).

Both parts per million and parts per billion are fractions, with the mass of the solute divided by the mass of the solution ppm = mass of solute x 10 6 mass of solution ppb = mass of solute x 10 9 mass of solution

Calculating Concentration in ppm Health Canada’s guideline for the maximum mercury content in commercial fish is 0.5 ppm. When a 1.6 kg salmon was tested, it was found to contain 0.6 mg of mercury. Would this salmon be safe to eat?

Substitute given data. Express BOTH masses in grams allowing cancellation. ppm = mass of solute x 10 6 mass of solution ppm = 0.6 mg x 10 6 = 6 x g x kg 1.6x 10 3 g = 0.4 ppm Less than minimum guideline, therefore salmon is safe to eat.