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Concentrations and Consumer Products

Percentage Volume/Volume (% v/v) Commonly used when both the solute and the solvent are liquids volume/volume = percent volume of solution (in mL) volume of solute (in mL) X 100% Example: Rubbing alcohol is 70% (v/v) solution = 70 mL of alcohol (30 mL water) in 100 mL solution

Percentage Weight/Volume (% w/v) The term “weight” on product label actually refers to the mass of the solute 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

Percentage Weight/Weight (% w/w) 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%

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

Extremely Low Concentrations Used by scientists in the medical and environmental fields very dilute concentrations are often expressed in parts per million (ppm, 1:10 6 ), parts per billion (ppb, 1:10 9 ), and even parts per trillion (ppt, 1:10 12 )

Both parts per million, parts per billion, and parts per trillion 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 ppt = mass of solute x 10 12 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 10 -4 g x 10 6 1.6 kg 1.6x 10 3 g = 0.4 ppm Less than minimum guideline, therefore salmon is safe to eat.

When the solvent is water, we can use several units of these concentrations. Select the unit that best matches the information given in the problem.

ppm Example: A 1.5 L sample of pool water contains 4.5 mg of chlorine. Determine the concentration in ppm.

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