Chemistry 153 @ Farmingdale

Chemistry 153 @ Farmingdale - CHM 153 Ways of Expressing...

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Ways of Expressing the Concentration of Solutions Solution: A mixture of two or more components which is homogeneous (the same composition throughout) o Components: Solute: usually a solid and is the smaller amount Solvent: usually a liquid and is the larger amount Example: salt dissolved in water. Salt is the solute and water is the solvent You can have a solution made of two liquids, two solids, gas and a solid or of a gas and a liquid such as alcohol dissolved in water; e.g., CO 2 + H 2 O H 2 CO 3 (carbonic acid) When two solids are in solution, the solution is called an alloy. Molarity (M): a measure of moles by volume. Moles of solute per liter of solution. o Moles of solute_ = grams of solute = Molarity of a solution (M) Liters of solution (M.W.)(liters of solution) How many grams of magnesium phosphate would be needed to prepare 125 mL of 0.11M solution? M.W.: Mg = 24, P = 31, O = 16 0.11M = x_______ = x = (0.11)(32.75g) so x = 3.6g Mg 2+ + PO 4 3- Mg 3 (PO 4 ) 2 = 262 g/mole (262 g/mole)(.125L) o Molarity is the main measure of concentration Molality (m): a measure of moles by mass. Moles of solute per Kg of solvent o moles of solute = grams of solute = Molality of a solution (m) Kg of solvent (M.W.) (liters of solvent) moles Colligative Properties: are properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties (e.g. size or mass) of the molecules and are ALWAYS EXPRESSED IN MOLALITY! o Depression of freezing point and elevation of boiling point. Percent: expressed as: o Mass/Volume %: g of solute/100 mL of solvent o Volume/Volume %: mL of solute/100 mL of solvent % concentration is the norm, but it is only an approximation unless it is specified how the solution was made. Parts per million (PPM) or parts per billion (PPB): o 3mg SO 2 is mixed with 20g air 3 parts contaminant/million parts total = PPM 3 parts contaminant/billion parts total = PPB o 3 mg SO 2 ___ x 10 6 = 150 ppm 20,000 mg total o 3 mg SO 2 ___ x 10 9 = 150,000 ppb 20,000 mg total o A 3.5 lb sample of fish fillet was found to contain 1.2mg of mercury (Hg). The allowable limit set by the FDA is 5.0 ppm. Is the shipment acceptable? 3.5 lbs x 10 6 = x 3.5 lbs fish x 454 g x 1000mg = 1,589,000 mg fish = 1.2 mg Hg___ = .76 ppm so the shipment is OK. 1.2mg 1 lb 1 g 1,589,000 mg fish Mole Fraction: part of total Mole Percent: part of 100 total (mole fraction x 100) o A solution contains 3.2 g of benzene, 5.6 g of ethanol and 1.6 g of acetone. What is the mole fraction and the mole % of each component? Benzene: 78 g/mole Ethanol: 46 g/mole Acetone: 58 g/mole Total Moles/Total % 3.2 g__ = 0.04 moles 78 g/mole Mole Fraction = .04 = .21 .19 Mole % = .21 x 100 = 21% 5.6 g_ _ = 0.12 moles 46 g/mole Mole Fraction = .12 = .63 .19 Mole % = .63 x 100 = 63% 1.6 g_ _ = 0.03 moles 58 g/mole Mole Fraction = .03 = .16 .19 Mole % = .16 x 100
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This note was uploaded on 10/10/2010 for the course CHM 153 taught by Professor S during the Summer '09 term at SUNY Farmingdale.

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Chemistry 153 @ Farmingdale - CHM 153 Ways of Expressing...

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