PRACTICE PROBLEMS CHEM 162-2007 EXAM I CHAPTER 12 - PROPERTIES OF SOLUTIONS • SOLUTION CONCENTRATIONS CONCEPTS (Molarity, mole fraction, etc.) • SOLUTION CONCENTRATIONS CALCULATIONS (Molarity, mole fraction, etc.) • ENERGETICS OF SOLUTIONS AND SOLUBILITY CONCEPTS • ENERGETICS OF SOLUTIONS AND SOLUBILITY CALCULATIONS • VAPOR PRESSURE OF SOLUTIONS CONCEPTS (Henry’s Law, Raoult’s Law) • VAPOR PRESSURE OF SOLUTIONS CALCULATIONS • COLLIGATIVE PROPERTIES (BOILING POINT, FREEZING POINT, OSMOTIC PRESSURE CHANGES) CONCEPTS • COLLIGATIVE PROPERTIES (BOILING POINT, FREEZING POINT, OSMOTIC PRESSURE CHANGES) CALCULATIONS • MISCELLANEOUS E. Tavss, PhD 1
FORMULAS Mass percent = grams of solute/100 g solution Molarity = moles of solute/L of solution Molality = moles of solute/kilogram of solvent PPM = grams of solute/1,000,000 grams solution Volume percent = volume of solute/100 mL of solution Proof = 2 x Vol. %; e.g., 2 x 40 mL/100 mL solution = 80 proof Mole fraction: X A = n A /(n A + n B ) X A + X B = 1 Particle fraction: i X A = in A /(in A + in B ) i X A + i X B = 1 Raoult’s law: P soln = i X solvent P o solvent i X solvent = in solvent /(in solvent + in solute ) i X A + i X B = 1 P Total = P A + P B = i X A P o A + i X B P o B van’t Hoff factor, “i”; i = moles of particles in solution/moles of solute dissolved Boiling-point elevation: ΔT = T f- T i = K b im solute Freezing-point depression: ΔT = T f- T i = -K f im solute (+K f gives absolute change in temp; -K f gives actual T f or T i ) Osmotic pressure: πV = inRT π = (n/V)iRT = iM solute RT ΔH soln = ΔH solute-solutebondbreaking + ΔH solvent-solventbondbreaking + ΔH solute-solventbondforming ΔH hydr = ΔH solvent-solventbondbreaking + ΔH solute-solventbondforming ΔH soln = ΔH solute-solutebondbreaking + ΔH hydr Henry’s Law: X A =kP A ; X A = mole fraction of dissolved gas in solution 2
SOLUTION CONCENTRATIONS CONCEPTS CHEM 162SG-2001 HOURLY EXAM I CHAPTER 11 - PROPERTIES OF SOLUTIONS SOLUTION CONCENTRATIONS CONCEPTS 14. To 1000 g of water containing 0.010 mole of NaCl, 10.0 g of ethyl alcohol, C 2 H 5 OH(l) are added. Which quantity remains the same? A. the molarity of NaCl B. the mass percentage of NaCl C. the mole fraction of NaCl D . the molality of NaCl E. the vapor pressure of water CHEM 162-2003 HOURLY EXAM 1 + ANSWERS CHAPTER 11 - PROPERTIES OF SOLUTIONS SOLUTION CONCENTRATION CONCEPTS 1. For which of the following conversions must you know the density of the solution? A. mass percent to molality (g solute/100 g solution) x (mol/g) x 1000 g/kg = molality B . mass percent to molarity (g solute/100 g solution) x (mol/g) x (g/mL) x (1000 mL/L) = molarity C. mole fraction to mass percent ((mol A x (g/mol))/(mol A x (g/mol) + mol B x (g/mol))) x 100 = mass percent D. mole fraction to molality (mol A )/(mol A x (g/mol) + mol B x (g/mol)) x 1000 g/kg = molality E. volume percent to proof mL solute /100 mL solution x 2 = proof 1. 1
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