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Chem 116 Lecture Note Outlines Set 02: Concentration Units Spring 2015 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. Learn quickly. Page 1 of 6 Four common concentration units ♦ Molarity ♦ Weight Percent (Wt %), ppm, ppb ♦ Mole Fraction ♦ Molality All provide same basic information—the relative amounts of the different constituent components ♦ Molarity, M ♦ tells you how many moles of solute are present in every liter of solution (solute-to-solution) solution of literssolute of molesM Molarity, = example: 0.46 M NaBr solution implies that there are 0.46 moles in exactly one liter of solution ♦ density is temperature dependent so Molarity is temperature dependent Weight Percent (Wt %), parts per million (ppm) and parts per billion (ppb) 1. The weight-weight percent, or %(w/w), tells you how many grams of solute are present per hundred grams of the solution (solute-to-solution). ( )100%solution masssolute massw/w% ×= example: 7.5 % KCl (w/w) implies that 2. The weight-volume percent, or %(w/v), tells you how many grams of solute are present per 100 mL of solution. (solute-to-solution) ( )100%solution volumesolute massw/v% ×= example: 5.0 % NaCl (w/v) implies that 3. Related concentration Units: ppm)10(1solution masssolute massppm million,per parts6×= ppb)10(1solution masssolute massppb billion,per parts9×= ♦ Mass is not temperature dependent “Weight Percent is NOT temperature dependent”Chem 116 Lecture Note Outlines Set 02: Concentration Units Spring 2015 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. Learn quickly. Page 2 of 6 Mole Fraction totalcomponentnnsolution up making moles totalcomponent of molesX fraction, Mole == Be careful to note what component is specified solution of moles totalsolute of molesX solute,fraction Molesolute= solution of moles totalsolvent of molesX solvent,fraction Molesolvent= An invaluable factoid: 1Xii=∑ [or Xsolute + Xsolvent = 1 for a solution with only one solute] ♦ Note: # moles is not temp dependent so “Mole fraction is NOT temperature dependent” Molality ♦ tells you how many moles of solute are present in every kilogram of solvent solvent kgsolute molesmmolality, = example: : 0.89 m CaCl2 implies that ♦ Mass is not temperature dependent “Molality is NOT temperature dependent” Concentration Units/ Summary units Advantages Disadvantages Molarity, M soln Lsolute molesM = Lmoles Useful in stoichiometry; M×V= mole if V is in liters Temperature dependent Must know density to find solvent mass Mole fraction, Xi moles totali of molesXi= None, unitless Temperature independent; useful in special applications Must know density to convert to molarity Mass percent, % (m/m) %100massmass%solni×= % Temperature independent; useful for small amounts Must know density to convert to molarity Molality, m solvent kgsolute molesm = kgmoles Temperature independent; used in special applications Must know density to convert to molarityChem 116 Lecture Note Outlines Set 02: Concentration Units Spring 2015 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. Learn quickly. Page 3 of 6 Concept Check Which contains more solute particles: a 0.10 M aqueous solution of methanol (CH3OH) or a 0.10 M aqueous solution of salt (NaCl)? a. Neither solution contains solute particles. b. They contain the same number of solute particles c. The salt solution contains twice as many particles as the methanol solution. d. The methanol solution contains three times as many particles as the salt solution. Determine the concentration of H2SO4 in a solution prepared by dissolving 25.0 g of H2SO4 in 1.30 kg of water in the following units? wt % (w/w) of H2SO4 Wt %(H2SO4) = 1.89 % mole fraction of H2SO4 XH2SO4 = 0.00352 Molality of H2SO4 m = 0.196 kgmole A solution is 7.5 m MgCl2. What is the mole fraction of MgCl2 in the solution? XMgCl2 = 0.12Chem 116 Lecture Note Outlines Set 02: Concentration Units Spring 2015 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. Learn quickly. Page 4 of 6 A 0.944 M solution of glucose, C6H12O6 in water has a density of 1.0624 g/ml at 20 ºC. What is the concentration of this solution in the following units? Mole fraction of glucose X= 0.0187 Mass percent (w/w) of glucose 16.1 % Molality of glucose 1.06 kgmole The density of a 16.0 % (w/w) solution of sulfuric acid (H2SO4) in water is 1.1094 g/ml at 25.0 ºC. What is the concentration of this solution in the following concentration units? molarity of H2SO4 1.81 LmoleChem 116 Lecture Note Outlines Set 02: Concentration Units Spring 2015 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. Learn quickly. Page 5 of 6 Molality of H2SO4 1.94 kgmole mole fraction of H2SO4 0.0338 Concept Check Which of the following does not exist in aqueous solution? a. Ca2+(aq) b. CH3COOH(aq) c. CH3COO–(aq) d. NaCl(aq) The EPA maximum standard for lead (Pb2+) is in drinking water is 15 ppb. If a 5.0 L sample of your tap water contains 0.30 mg Pb2+(aq), will the EPA deem your water safe to drink? Will the EPA deem your water safe to drink? No. [Pb2+]= 60. ppb What is the concentration of Pb2+ in your tap expressed in molarity [Pb2+]= 2.9×10−7LmoleChem 116 Lecture Note Outlines Set 02: Concentration Units Spring 2015 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. Learn quickly. Page 6 of 6 Extra Practice Problems What is the Weight% (w/w) concentration of each of the following solutions? Dissolve 0.655 moles of citric acid, C6H8O7, in 1.00 kg water. 11.2 % Procaine hydrochloride (MM = 272.77 g/mol) is used as a local anesthetic. Calculate the molarity of a 4.666 m solution which has a density of 1.1066 g/mL 2.272 Lmole An aqueous solution of glycerol, C3H8O3 (MM = 92.09), is 48.0% glycerol by mass and has a density of 1.120 g mL-1. Calculate the molarity of the glycerol solution 5.84 Lmole Sodium hydroxide is a common ingredient in drain cleaners such as Drano. The mole fraction of sodium

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