Ch 11 Solutions What is the molality

AP Chemistry Ch 11 Solutions PRACTICE TEST 1. What is the molality of 7.80% by weight glucose (C₆H₁₂O₆), molar mass = 180.16 g/mol, solution? (a) 0.470 m (b) 0.845 m (c) 0.0432 m (d) 0.0454 m (e) 0.0844 m 2. The mol fraction of NH₄Cl in a solution is 0.0311. What is its molality? (The molar mass of water is 18.016 g/mol.) (a) 1.78 m (b) 1.66 m (c) 0.969 m (d) 0.562 m (e) 0.0983 m   3. What is the mol fraction Na₂SO₄ in a solution which is 11.5% by weight Na₂SO₄ (molar mass Na₂SO₄=142.06 g/mol) and H₂O=18.016 g/mol)? (a) 0.0810 (b) 0.0914 (c) 0.0745 (d) 0.0173 (e) 0.0162 4. What is the mol fraction NaCl in a solution which is 2.15 m? (a) 0.0180 (b) 0.0268 (c) 0.0373 (d) 0.0938 (e) 0.0785 5. A 1.34 M NiCl₂ (molar mass = 129.6 g/mol) solution has a density of 1.12 g/cm³. What is the weight percent NiCl₂ of the solution? (a) 1.73% (b) 8.64% (c) 15.5% (d) 25.4% (e) 29.8% 6. A 1.25 M Cu(NO₃)₂ (molar mass = 187.56 g/mol) solution has a density of 1.19 g/cm³. What is the weight percent Cu(NO₃)₂ of the solution? (a) 1.88% (b) 2.36% (c) 10.5% (d) 14.3% (e) 19.9% 7. Hydrobromic acid (molar mass = 80.9 g/mol) is commercially available in a 34.0% by weight solution which has a density of 1.31 g/cm³. What is the molarity of the commercially available hydrobromic acid? (a) 2.75 M (b) 4.45 M (c) 5.50 M (d) 9.02 M (e) 10.2 M 8. The maximum contamination level of arsenic ion in a water system is 0.050 parts per million. If the arsenic is present as AsCl₃, how many grams of arsenic chloride could be present in a system that contains 8.2 x 10⁵ liters?   (a) 0.55 g (b) 7.3 g (c) 41 g (d) 62 g (e) 74 g 9. A student prepared a solution containing 0.30 mol of solute and 1.00 mole of solvent. The mole fraction of solvent is (a) 1.30 (b) 1.00 (c) 0.77 (d) 0.30 (e) 0.23 10. Which measure of concentration is most appropriate for the calculation of the vapor pressure of a solution? (a) mol fraction (b) molarity (c) molality (d) weight % (e) ppm   11. A chemist knows the empirical formula of a new compound but not the molecular formula. What must be determined experimentally so that the molecular formula can be determined?   (a) density (b) viscosity (c) % composition (d) melting point (e) molar mass   12. A volumetric flask is necessary for the preparation of which one of the following concentration measurements? (a) molality (b) % (c) mass% (d) molarity (e) ppm   13. If the pressure of a gas over a liquid increases, the amount of gas dissolved in the liquid will (a) increase (b) decrease (c) remain the same (d) have a higher vapor pressure (e) depends on the polarity of the gas   14. Which of the following solutions would have the lowest vapor pressure? (a) 1 m glucose (C₆H₁₂O₆) (b) 1 m MgCl₂ (c) 1 m NaNO₃ (d) 1 m NaBr (e) pure H₂O   15. What is the primary energetic factor in the lack of miscibility between CCl₄(l) and water? (a) the strength of intermolecular forces between CCl₄ molecules (b) the strength of intermolecular forces between H₂O molecules (c) the charge on the C atom in CCl₄ (d) the difference between the molecular weights of the molecules (e) the electronegativity difference between carbon and chlorine 16. Which of the following would have a boiling point closest to that of 1 m NaCl?   (a) 1 m sucrose (C₁₂H₂₂O₁₁) (b) pure H₂O (c) 1 m NaNO₃ (d) 0.5 m CH₃OH (e) 1 m MgCl₂ 17. Which of the following would have the highest freezing point? (a) 1 m glucose (C₆H₁₂O₆) (b) 1 m MgCl₂ (c) 1 m NaNO₃ (d) 1 m (NH₄)₂SO₄ (e) pure H₂O 18. You need a solution that is 0.15 m in ions. How many grams of MgCl₂ (molar mass = 95.2 g/mol) must you dissolve in 400. g of water? (Assume total dissociation of the ionic salt.) (a) 0.060 g (b) 1.9 g (c) 5.7 g (d) 7.6 g (e) 17 g 19. A solution is prepared by dissolving 0.500 g of non-dissociating solute in 12.0 g of cyclohexane. The freezing point depression of the solution is 8.94°C. The K_f for cyclohexane is -20.0°C/m. Calculate the molar mass of the solute.   (a) 93.2 g/mol (b) 112 g/mol (c) 128 g/mol (d) 182 g/mol (e) 205 g/mol 20. What is the freezing point of a solution containing 4.134 grams naphthalene (molar mass = 128.2) dissolved in 30.0 grams of paradichlorobenzene? The freezing point of pure paradichlorobenzene is 53.0°C and the freezing point depressing constant (K) is -7.10°C/m.   (a) 52.0°C (b) 48.7°C (c) 45.4°C (d) 17.6°C (e) 7.63°C 21. What is the molar mass of a compound if 4.28 grams is dissolved in 25.0 grams of chloroform solvent to form a solution which has a boiling point elevation of 2.30°C. The boiling point constant of chloroform (K) is +3.63°C/m.   (a) 34.5 g/mol (b) 67.5 g/mol (c) 135 g/mol (d) 168 g/mol (e) 270 g/mol 22. Concentrated salt solutions have boiling points lower than those calculated using the equation, T = K ∙ m. Which of the following is a reasonable explanation of this observation?   (a) Positive ions repel each other more at high concentration. (b) Ions of opposite charge will tend to stay paired instead of breaking up. (c) The water molecules will have a greater attraction for each other. (d) Concentrated solutions really have smaller particles of non-dissolved salt, thus lowering the molality. (e) The difference between the crystal lattice energy and the heat of hydration must be taken into consideration.