LR 12 03 2014 1 What is the concentration in percent by mass if 24 7 g of ethanol C2H5OH are dissolved in 215 grams of water 24 7g C2H5OH x 100 10 3 24 7g C2H5OH 215 g H2O 2 What is the molality of the solution in questions 2 24 7g C2H5OH x 0 215 kg H2O 3 4 1 mol C2H5OH 46 0g C2H5OH 2 50 m What are the mole fractions of methanol CH3OH and water in a solution that contains 40 0 g of CH3OH and 54 0 g of water 40 0g CH3OH x 1 mol CH3OH 1 25 mol 32 0g CH3OH Xmethanol 1 25 mol 0 294 4 25 mol 54 0g H2O x 1 mol H2O 18 0g H2O Xwater 3 00 mol 4 25 mol 3 00 mol 0 706 4 25 mol How many grams of urea must be added to 300 mL of water to form a 0 50 molal solution The molar mass of urea is 60 0 g mol Assume that the density of water is 1 00g mL m mol moles 0 500 kg 0 300kg g moles kg 0 500mol kg 60 0g mol 5 9 00 g urea Calculate the molarity and the molality of a 15 0 by mass solution of MgCl2 in H2O The density of this solution is 1 127 g mL Assume 100 g of solution 15 0g is MgCl2 and 85 0g is water Molarity mol L 15 0g MgCl2 x 1 mol MgCl2 0 158 mol MgCl2 95 2g MgCl2 100g of solution x 1 00 mL 88 7 mL 0 0887L 1 127 g Molarity 0 158 mol 0 0887 L of solution Molality mol kg of solvent 1 78 M 0 158 mol 1 86 m 0 085 kg water
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