Four common concentration units 1. Molarity 2. Weight Percent (Wt %), ppm, ppb 3. Molality 4. Mole Fraction Molarity, M tells you how many s of solute are present in every liter of solution (solute-to-solution) s of solute Molarity, M = liters of solution Weight Percent (Wt %), parts per million (ppm) and parts per billion (ppb) The weight-weight percent, tells you how many grams of solute are present per hundred grams of the solution % mass solution ( w/w) = 100% The weight-volume percent tells you how many grams of solute are present per 100 m of solution. % volume solution ( w/v) = 100% Related concentration Units: parts per million, ppm parts per billion, ppb = = mass solution mass solution (1 10 (1 10 9 6 ppm) ppb) Spring 2016 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. earn quickly. Page 1 of 6
Molality tells you how many s of solute are present in every kilogram of solvent molality, m = s solute solvent Mole Fraction Concentration Units/ Summary units Advantages Disadvantages Molarity, M s Useful in stoichiometry; Temperature dependent s solute M = M V= if V is in liters Must know density to find soln solvent mass Mole fraction, X i s of i X i = total s None, unitless Temperature independent; useful in special applications Must know density to convert to molarity Mass percent, % (m/m) massi % = 100% mass soln % Temperature independent; useful for small amounts Must know density to convert to molarity Molality, m s s solute m = solvent Temperature independent; used in special applications Must know density to convert to molarity Spring 2016 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. earn quickly. Page 2 of 6
Concept Check Which contains more solute particles: a 0.10 M aqueous solution of methanol (CH 3 OH) 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. 116_PSV_02_conc_01 Determine the concentration of H 2 SO 4 in a solution prepared by dissolving 25.0 g of H 2 SO 4 in 1.30 of water in the following units? wt % (w/w) of H 2 SO 4 fraction of H 2 SO 4 Wt %(H 2 SO 4 ) = 1.89 % Molality of H 2 SO 4 X H2SO4 = 0.00352 m = 0.195 116_PSV_02_conc_02 A solution is 7.5 m MgCl 2. What is the fraction of MgCl 2 in the solution? X MgCl2 = 0.12 Spring 2016 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. earn quickly. Page 3 of 6
116_PSV_02_conc_03 A 0.944 M solution of glucose, C 6 H 12 O 6 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 Mass percent (w/w) of glucose X= 0.0187 Molality of glucose 16.0 % 1.06 116_PSV_02_conc_04 The density of a 16.0 % (w/w) solution of sulfuric acid (H 2 SO 4 ) 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 H 2 SO 4 1.81 Spring 2016 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. earn quickly. Page 4 of 6
Molality of H 2 SO 4 1.94 fraction of H 2 SO 4 0.0338 Concept Check Which of the following does not exist in aqueous solution? a. Ca 2+ (aq) b. CH 3 COOH(aq) c. CH 3 COO (aq) d. NaCl(aq) 116_PSV_02_conc_05 The EPA maximum standard for lead (Pb 2+ ) is in drinking water is 15 ppb. If a 5.0 sample of your tap water contains 0.30 mg Pb 2+ (aq), will the EPA deem your water safe to drink? Will the EPA deem your water safe to drink? What is the concentration of Pb 2+ in your tap expressed in molarity No. [Pb 2+ ]= 60. ppb [Pb 2+ ]= 2.9 10 7 Spring 2016 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. earn quickly. Page 5 of 6
Extra Practice Problems 116_PSV_02_conc_06 What is the Weight% (w/w) concentration of each of the following solutions? Dissolve 0.655 s of citric acid, C 6 H 8 O 7, in 1.00 water. 11.2 % 116_PSV_02_conc_07 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/m 2.272 116_PSV_02_conc_08 An aqueous solution of glycerol, C 3 H 8 O 3 (MM = 92.09), is 48.0% glycerol by mass and has a density of 1.120 g m -1. Calculate the molarity of the glycerol solution 5.84 116_PSV_02_conc_09 Sodium hydroxide is a common ingredient in drain cleaners such as Drano. The fraction of sodium hydroxide in a saturated aqueous solution is 0.310. What is the molality of NaOH in the solution? (MM of H 2 O is= 18.02 /) 24.9 Spring 2016 (Ratcliff) Everything in life comes to you as a teacher. Pay attention. earn quickly. Page 6 of 6