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Concentrations and Consumer Products

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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

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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

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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%

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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)

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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 )

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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

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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?

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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.

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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.

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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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