Chemistry Answers for Quiz 1

Answers for Quiz 1 14/11/2020 Q.1 Which one of the following substances is expected to have the highest boiling point? • Br2 • Cl2 • F2 • I2 Q.2 Helium atoms do not combine to form He2 molecules, yet He atoms do attract one another weakly through: • Dipole-dipole forces • Hydrogen bonding • Dispersion forces • Ion-dipole forces Q.3 Which one of the following substances should exhibit hydrogen bonding in the liquid state? • • • • • PH3 H2 S CH4 NH3 H2 Q.4 1 Which of the following characteristics indicates the presence of weak intermolecular forces in a liquid? • A high boiling point • A low heat of vaporization • A low vapor pressure • A high critical temperature Q.5 Which of the following would be expected to have the highest vapor pressure at room temperature? • Ethanol, boiling pt. = 78°C • Water, boiling pt. = 100°C • Methanol, boiling pt. = 65°C • Acetone, boiling pt. = 56°C Q.6 Which property of water allows a razor blade to float on it without sinking? • Surface tension • Viscosity • Specific heat • Triple point • Density Q.7 Acetic acid has a heat of fusion of 10.8 kJ/mol and a heat of vaporization of 24.3 kJ/mol. What is the expected value for the heat of sublimation of acetic acid? • 35.1 kJ/mol 2 • –13.5 kJ/mol • +13.5 kJ/mol • –35.1 kJ/mol • Not enough information is given to answer the question. Q.8 Which of the following is not an endothermic process? • Melting of a solid • Condensation of water vapor • Vaporization • Sublimation of dry ice • Raising the temperature of a gas Q.9 The vapor pressure of ethanol is 400 mmHg at 63.5°C. Its molar heat of vaporization is 39.3 kJ/mol. What is vapor pressure of ethanol, in mmHg, at 34.9°C? • 1,510 mmHg • 200 mmHg • 100 mmHg • 0.0099 mmHg • 4.61 mmHg Q.10 Arrange the following in order of increasing boiling point: RbCl, CH3Cl, CH3OH, CH4. • CH3OH < CH3Cl < RbCl < CH4 • CH3OH < CH4 < CH3Cl < RbCl • RbCl < CH3Cl < CH3OH < CH4 3 • CH4 < CH3OH < CH3Cl < RbCl • CH4 < CH3Cl < CH3OH < RbCl Which of the following concerning solutions is/are correct? 1. The solvent in a mixture of gases is generally considered to be the substance in a greater amount. 2. The solid that dissolved in a solution is known as the solute. 3. Alloys are examples of solid solutions. a. 1 only b. 2 only c. 3 only d. 1 and 2 e. 1, 2, and 3 Which of the following molecules is most soluble in heptane, C7H16? a. H2O b. CH3NH2 c. CH3CH2CH2CH3 d. CH3OH e. H2S Which of the following concerning the topic of concentration is/are correct? 1. A 5.0 m (5.0 molal) HCl solution consists of 5.5 moles HCl dissolved in 1.0 kg of solution. 2. The mass percent and mole percent of a particular component in a solution are identical. 3. The mole fraction of a component in a solution may never be greater than 1. a. 1 only b. 2 only c. 3 only d. 1 and 2 e. None of the above What is the mass percent of an aqueous sodium hydroxide solution in which the mole fraction of NaOH is 0.1010? The density of the solution is 1.2219 g/mL. 4 a. 20.0% b. 12.0% c. 68.9% d. 12.3% e. 3.3% What is the molarity of a solution of 12.5% by mass cadmium sulfate, CdSO4 (molar mass = 208.46 g/mol) by mass? The density of the solution is 1.10 g/mL. a) 0.778 M b) 0.436 M c) 0.479 M d) 0.048 M e) 0.660 M Calculate the molality of a solution containing 14.3 g of NaCl (molar mass = 58.44 g/mol) in 42.2 g of water. a) 2.45  10-1 m b) 5.80  10-4 m c) 103 m d) 5.80 m e) 2.45  10-4 m 5 Identify the conjugate base of H2PO4- in the following reaction: H2PO4- (aq) + NH3 (aq)  HPO4-2 (aq) + NH4+ (aq) − NH4+ − HPO4-2 − NH3 − H2PO4− None of the above ----------------------------------------------------------------------------------------------At 2200 oC, Kp for the reaction: N2(g) + O2(g)  2NO(g) Is 0.050, if a mixture of reactants and products composed of 0.10 atm N2, 0.60 atm O2, and 0.20 atm NO, then the reaction: − − − − − Will shift to left (produce reactants) to reach equilibrium. Will shift to right (produce products) to reach equilibrium. Will have a different value of Kp. Is already at equilibrium. We do not have enough information to predict the behavior of the reaction. ----------------------------------------------------------------------------------------------At 400 oC, the for the reaction (Kc=36): H2(g) + I2(g)  2HI(g) If 2.0 mol H2 and 2.0 mol I2 are introduced into n empty 4.0 L flask. Determine the equilibrium concentration of HI at this temperature? − − − − − 6.4 M 3.6 M 0.80 M 4.0 M 0.75 M ------------------------------------------------------------------------------- --------------------Calculate the pH of a 5.8 X 10-4 M Ba(OH)2 solution. − − − − − 2.49 7.00 3.25 11.1 10.7 ------------------------------------------------------------------------------- --------------------Calculate the H+ ion concentration of the rainwater that has a pH value of 5.1. − − − − − 125892.5 8.9 1.3 X 10-9 -0.708 7.9 X 10-6 ------------------------------------------------------------------------------- --------------------Which of the following conjugate bases is the strongest? − − − − − INO3NO2ClO4HSO4- ------------------------------------------------------------------------------- --------------------Consider the following equilibrium process between dinitrogen tetrafluoride (N2F4) and nitrogen difluoride (NF2): N2F4(g)  2NF2(g) ΔH° = 38.5 kJ/mol − Which of the following changes produce more product (more NF2): − Decreasing the temperature. − If some N2F4 gas is removed from the reacting mixture at constant temperature and volume. − If the pressure on the reacting mixture is decreased at constant temperature. − Adding a catalyst to the reacting mixture. − Decreasing the volume of the reacting mixture at constant temperature. A solution is made by dissolving 1.09 g of a protein in water to make 450.0 mL aqueous solution at 25.0 oC. Calculate the molar mass of the protein if the osmotic pressure of the solution is 1.32 mmHg. (1 atm = 760 mmHg) (R=0.0821 L. atm./K. mol) a. 6.14×104 g/mol b. 1.20 ×104 g/mol c. 2.89 ×104 g/mol d. 4.45×104 g/mol e. 3.46×104 g/mol Which aqueous solution will have the highest boiling point temperature? a. 0.150 molal Na2SO4(aq) b. 0.100 molal MgSO4(aq) c. 0.150 molal NH4NO3(aq) d. 0.100 molal NiBr2(aq) e. 0.250 molal CH3OH(aq) Which of the following statement is correct? a) Tb and Tb might have negative values. b) Osmotic pressure is the pressure required to stop osmosis. c) Vapor pressure of pure solvent is always smaller than the vapor pressure of solution. d) Increasing the mass of solute, decreases the boiling point of the solution (decreasing the Tb). e) The mole fraction of the solvent is inversely proportional with the vapor pressure of solution. When a 33.8-g sample of an unknown compound is dissolved in 500. g of benzene, the freezing point of the resulting solution is 3.77°C. The freezing point of pure benzene is 5.48°C, and Kf for benzene is 5.12°C/m. Calculate the molar mass of the unknown compound a. 173 g/mol b. 202. g/mol c. 101.2 g/mol d. 405 g/mol e. 19.8 g/mol A solution consisting of 0.276 mol of methylbenzene, C6H5CH3, in 242 g of nitrobenzene, C6H5NO2, freezes at –2.0 °C. Pure nitrobenzene freezes at 6.0°C. What is the freezing-point depression constant of nitrobenzene? a. 7.3°C/m b. 29°C/m c. 14.0°C/m d. 3.5°C/m e. 7.0°C/m During osmosis, pure solute passes through a porous membrane but solvent does not. [ False ] Answer Key for Quiz 4 If the Ka of NH4+ is 5.6 x 10-10 and the Kb for F- is1.4 x 10-11. When the NH4F salt is dissolved in water, the solution will be: (a) Neutral (b) Acidic (c) Basic (d) Cannot be determined from the data given A 0.20 M solution of a weak monoprotic acid is 0.22 % ionized. What is the acidionization constant, Ka, for this acid? (a) 1.9 × 10–6 (b) 2.2 × 10–6 (c) 1.1 × 10–4 (d) 2.4 × 10–5 (e) 9.7 × 10–7 For which of the following equilibria does Kc correspond to a base-ionization constant, Kb? a. H3O+(aq) + OH–(aq) 2H2O(l) b. HCO3–(aq) + OH–(aq) c. HOCl(aq) + H2O(l) H3O+(aq) + OCl–(aq) d. CO32–(aq) + H2O(l) HCO3–(aq) + OH–(aq) e. HCHO2(aq) + NH3(aq) CO32–(aq) + H2O(l) CHO2–(aq) + NH4+(aq) What is the pH of a 0.35 M solution of methylamine (CH3NH2, Kb = 4.4 × 10–4) at 25oC? (a) (b) (c) (d) (e) 5.55 8.16 12.09 13.54 1.91 The two acid-ionization constants for sulfurous acid, H2SO3, are 1.3 × 10–2 and 6.3 × 10–8 at 25°C. What is Kb for the HSO3– ion? a. 6.3 × 10–8 b. 6.2 × 10–22 c. 7.7 × 10–13 d. 1.3 × 10–2 e. 8.2 × 10–10 What is the pH of a solution that is 0.14 M in acetic acid, HC2H3O2, and 0.50 M in sodium acetate, NaC2H3O2, at 25°C? Ka of acetic acid is 1.8 × 10–5. a. 4.19 b. 1.23 c. 4.74 d. 2.47 e. 5.30 Which of the following solutions has the largest buffer capacity (the best buffer solution)? (a) 0.50 M HCl, 0.50 M NaOH (b) 0.15 M HF, 0.15 M NaF (c) 1.25 M HNO3, 0.75 M NaNO3 (d) 0.75 M HF, 0.75 M KF If you have prepared 1.0 L of a HF buffer solution that having the concentrations: [HF] = 0.24 M , [F-] = 0.16 M. What is the pH of the buffer solution after adding 0.05 M HCl? pKa = 4.75 for HF. (a) 5.17 (b) 4.33 (c) 4.57 (d) 4.41 (e) 4.75 Answer Key for Quiz 4 If the Ka of NH4+ is 5.6 x 10-10 and the Kb for F- is1.4 x 10-11. When the NH4F salt is dissolved in water, the solution will be: (a) Neutral (b) Acidic (c) Basic (d) Cannot be determined from the data given A 0.20 M solution of a weak monoprotic acid is 0.22 % ionized. What is the acidionization constant, Ka, for this acid? (a) 1.9 × 10–6 (b) 2.2 × 10–6 (c) 1.1 × 10–4 (d) 2.4 × 10–5 (e) 9.7 × 10–7 For which of the following equilibria does Kc correspond to a base-ionization constant, Kb? a. H3O+(aq) + OH–(aq) 2H2O(l) b. HCO3–(aq) + OH–(aq) c. HOCl(aq) + H2O(l) H3O+(aq) + OCl–(aq) d. CO32–(aq) + H2O(l) HCO3–(aq) + OH–(aq) e. HCHO2(aq) + NH3(aq) CO32–(aq) + H2O(l) CHO2–(aq) + NH4+(aq) What is the pH of a 0.35 M solution of methylamine (CH3NH2, Kb = 4.4 × 10–4) at 25oC? (a) (b) (c) (d) (e) 5.55 8.16 12.09 13.54 1.91 The two acid-ionization constants for sulfurous acid, H2SO3, are 1.3 × 10–2 and 6.3 × 10–8 at 25°C. What is Kb for the HSO3– ion? a. 6.3 × 10–8 b. 6.2 × 10–22 c. 7.7 × 10–13 d. 1.3 × 10–2 e. 8.2 × 10–10 What is the pH of a solution that is 0.14 M in acetic acid, HC2H3O2, and 0.50 M in sodium acetate, NaC2H3O2, at 25°C? Ka of acetic acid is 1.8 × 10–5. a. 4.19 b. 1.23 c. 4.74 d. 2.47 e. 5.30 Which of the following solutions has the largest buffer capacity (the best buffer solution)? (a) 0.50 M HCl, 0.50 M NaOH (b) 0.15 M HF, 0.15 M NaF (c) 1.25 M HNO3, 0.75 M NaNO3 (d) 0.75 M HF, 0.75 M KF If you have prepared 1.0 L of a HF buffer solution that having the concentrations: [HF] = 0.24 M , [F-] = 0.16 M. What is the pH of the buffer solution after adding 0.05 M HCl? pKa = 4.75 for HF. (a) 5.17 (b) 4.33 (c) 4.57 (d) 4.41 (e) 4.75