AP CHEMISTRY EXAM REVIEW QUIZ #1 / 10 Name: Empirical and Molecular Formulas SHOW ALL WORK. Include proper units and significant figures in all answers. 1. One compound of mercury with a formula mass of 519 g/mol contains 77.26% Hg, 9.25% C, and 1.17% H (with the rest being oxygen) by mass. Calculate the empirical and molecular formulas. (6 points) 2. When 6.853 mg of a hormone (containing only C, H, and O) was burned in a combustion analysis, 19.73 mg of CO2 and 6.391 mg of H2O were obtained. The formula mass was found to be 290 g/mol. What is the molecular formula? (4 points) AP CHEMISTRY EXAM REVIEW QUIZ #2 / 10 Name: Acid-­‐Base Stoichiometry SHOW ALL WORK. Include proper units and significant figures in all answers. 1. 25.0 mL of an acetic acid solution of unknown concentration is titrated with 42.2 mL of a 0.0750 M solution of NaOH. a. Write the BALANCED NET IONIC EQUATION for this reaction. (1 point) b. Determine the concentration of the unknown acid. (4 points) c. Why doesn’t one solve this problem using Ka and knowledge that acetic acid is a weak acid? (1 point) 2. Determine the molecular mass of a diprotic acid if 0.2267 grams of this acid are required to neutralize 34.56 mL of a 0.03200 M solution of potassium hydroxide. (4 points) AP CHEMISTRY EXAM REVIEW QUIZ #3 / 10 Name: Precipitation Stoichiometry SHOW ALL WORK. Include proper units and significant figures in all answers. 1. 205 mL of a 0.0500 M solution of silver nitrate is mixed with 255 mL of a 0.0350 M sodium phosphate solution. Determine the following: a. Write the formulas for silver nitrate and sodium phosphate (1 point) b. Write the BALANCED NET IONIC EQUATION of the precipitation reaction that occurs. (2 points) c. Determine the number of grams of this precipitate that forms. (4 points) d. Which ion in the net ionic equation is in excess? What is the final concentration of this ion? (3 points) AP CHEMISTRY EXAM REVIEW QUIZ #4 / 10 Name: Redox Stoichiometry SHOW ALL WORK. Include proper units and significant figures in all answers. 1. A solution of sodium hypochlorite is mixed with a solution of potassium iodide in acidic solution. The skeletal equation is:
-­‐
-­‐ -­‐
-­‐
I + ClO à I3 + Cl a. Balance the oxidation-­‐reduction equation. Show both half reactions. (6 points) b. 60.0 mL of a 0.0500 M solution of potassium iodide will react with how many mL of a 0.0750 M sodium hypochlorite solution? (4 points) AP CHEMISTRY EXAM REVIEW QUIZ #5 / 10 Name: Thermochemistry SHOW ALL WORK. Include proper units and significant figures in all answers. Average Bond Energies: C-­‐H 413 kJ/mol O=O 495 kJ/mol C=O 799 kJ/mol H-­‐O 467 kJ/mol C-­‐C 347 kJ/mol 1. Write the balanced equation for the combustion of ethane, C2H6. (1 point) 2. Draw Lewis structures for both reactants and both products of the equation above. (3 points) 3. Use the bond energies above to calculate ∆H for the combustion of ethane, C2H6. (3 points) 4. How much energy would be produced from the combustion of 17.563 grams of C2H6? (3 points) AP CHEMISTRY EXAM REVIEW QUIZ #6 / 10 Name: Kinetics SHOW ALL WORK. Include proper units and significant figures in all answers. A(g) + B(g) → C(g) + D(g) 1. For the gas-­‐phase reaction represented above, the following experimental data were obtained. Experiment Initial [A] -­‐1
Initial [B] Initial Reaction Rate (mol L ) (mol L ) -­‐1
(mol L s ) -­‐1 -­‐1
1 0.033 0.034 6.67 x 10 2 0.034 0.137 1.08 x 10 3 0.136 0.136 1.07 x 10 4 0.202 0.233 ? -­‐4
-­‐2
-­‐2
(a) Write the rate law for the overall reaction. (2 points) (b) Determine the value of the rate constant, k, for the reaction. Include units with your answer. (3 points) (c) Calculate the initial reaction rate for experiment 4. (3 points) (d) Propose a mechanism for the reaction that is consistent with the rate law. (2 points) AP CHEMISTRY EXAM REVIEW QUIZ #7 / 10 Name: VSEPR, Hybrids, Lewis Structures SHOW ALL WORK. Include proper units and significant figures in all answers. 1. (a) Draw the Lewis structure for the IF3 molecule. (3 points) (b) Predict the molecular geometry of the IF3 molecule. (2 points) 2. (a) In the SO2 molecule, both of the bonds between sulfur and oxygen have the same length. Explain this observation, supporting your explanation by drawing below a Lewis electron-­‐dot diagram (or diagrams) for the SO2 molecule. (3 points) (b) On the basis of your Lewis electron-­‐dot diagram(s), identify the hybridization of the sulfur atom in the SO2 molecule. (2 points) AP CHEMISTRY EXAM REVIEW QUIZ #8 / 10 Gas Laws Name: SHOW ALL WORK. Include proper units and significant figures in all answers. 1. A rigid 5.00 L cylinder contains 24.5 g of N2(g) and 28.0 g of O2(g). (a) Calculate the total pressure, in atm, of the gas mixture in the cylinder at 298 K. (2 points) (b) The temperature of the gas mixture in the cylinder is decreased to 280 K. Calculate each of the following: (i) The mole fraction of N2(g) in the cylinder. (2 points) (ii) The partial pressure, in atm, of N2(g) in the cylinder. (2 points) (c) If the cylinder develops a pinhole-­‐sized leak and some of the gaseous mixture escapes, would the ratio N2(g) / O2(g) in the cylinder increase, decrease, or remain the same? Justify your answer. (2 points) 2. A different rigid 5.00 L cylinder contains 0.176 mol of NO(g) at 298 K. A 0.176 mol sample of O2(g) is added to the cylinder, where a reaction occurs to produce NO2(g). 2 NO(g) + O2(g) à 2 NO2(g) Calculate the total pressure, in atm, in the cylinder at 298 K after the reaction is complete. (2 points) AP CHEMISTRY EXAM REVIEW QUIZ #9 / 10 Name: Colligative Properties SHOW ALL WORK. Include proper units and significant figures in all answers. 1. A solution that is prepared by dissolving 3.150 grams of an unknown substance in 25.00 grams of benzene, C6H6, has a freezing point of 1.12°C. (The normal freezing point of benzene is 5.50°C and the freezing-­‐point depression constant, Kf, for benzene is 5.12°C/molal.) (a) Using the data gathered from the freezing-­‐point depression method, calculate the molar mass of the unknown substance. (6 points) (b) Calculate the mole fraction of benzene in the solution described above. (1 point) (c) The vapor pressure of pure benzene at 35°C is 150. millimeters of Hg. Calculate the vapor pressure of benzene over the solution described above at 35°C. (3 points) AP CHEMISTRY EXAM REVIEW QUIZ #10 / 10 Name: Electron Configurations SHOW ALL WORK. Include proper units and significant figures in all answers. 14 -­‐1
1. A major line in the emission spectrum of neon corresponds to a frequency of 4.34×10 s . Calculate the wavelength, in nanometers, of light that corresponds to this line. (2 points) 2. In the upper atmosphere, ozone molecules decompose as they absorb ultraviolet (UV) radiation, as shown by the equation below. Ozone serves to block harmful ultraviolet radiation that comes from the Sun. O3(g) O2(g) + O(g) 15 -­‐1
A molecule of O3(g) absorbs a photon with a frequency of 1.00×10 s . (a.) How much energy, in joules, does the O3(g) molecule absorb per photon? (2 points) -­‐1
(b.) The minimum energy needed to break an oxygen-­‐oxygen bond in ozone is 387 kJ mol . Does a photon with a frequency of 15 -­‐1
1.00×10 s have enough energy to break this bond? Support your answer with a calculation. (2 points) 3. Explain the following observations using principles of atomic structure and/or bonding. (a) Potassium has a lower first-­‐ionization energy than lithium. (2 points) (b) Aluminum has a lower first-­‐ionization energy than magnesium. (2 points) AP CHEMISTRY EXAM REVIEW QUIZ #11 / 10 Name: Solubility Product Constant (Ksp) SHOW ALL WORK. Include proper units and significant figures in all answers. 2+
-­‐
MgF2(s) ↔ Mg (aq) + 2 F (aq) 2+
-­‐3
1. In a saturated solution of MgF2 at 18ºC, the concentration of Mg is 1.21´10 molar. The equilibrium is represented by the equation above. (a) Write the expression for the solubility-­‐product constant, Ksp, and calculate its value at 18ºC. (2 points) 2+
(b) Calculate the equilibrium concentration of Mg in 1.000 liter of saturated MgF2 solution at 18ºC to which 0.100 mole of solid KF has been added. The KF dissolves completely. Assume the volume change is negligible. (4 points) -­‐3
(c) Predict whether a precipitate of MgF2 will form when 100.0 milliliters of a 3.00´10 -­‐molar Mg(NO3)2 solution is mixed with -­‐3
200.0 milliliters of a 2.00´l0 -­‐molar NaF solution at 18ºC. Calculations to support your prediction must be shown. (4 points) AP CHEMISTRY EXAM REVIEW QUIZ #12 / 10 Electrochemistry Name: SHOW ALL WORK. Include proper units and significant figures in all answers. 1. Answer the following questions regarding the electrochemical cell shown. (a) Write the balanced net-­‐ionic equation for the spontaneous reaction that occurs as the cell operates, and determine the cell voltage. (b) Which metal strip serves as the cathode? Justify your answer. (c) If 10.0 mL of 3.0-­‐molar AgNO3 solution is added to the half-­‐cell on the right, what will happen to the cell voltage? Calculate the new voltage. (d) If 1.0 gram of solid NaCl is added to each half-­‐cell, what will happen to the cell voltage? Explain. AP CHEMISTRY EXAM REVIEW QUIZ #13 / 10 Name: Weak Acid/Base Titrations; Buffers SHOW ALL WORK. Include proper units and significant figures in all answers. –5
1. What is the pH of a 2.0 molar solution of acetic acid? Ka acetic acid = 1.8×10 . 2. (a) A buffer solution is prepared by adding 0.10 liter of 2.0 molar acetic acid solution to 0.1 liter of a 1.0 molar sodium hydroxide solution. Compute the hydrogen ion concentration of the buffer solution. (b) Suppose that 0.10 liter of 0.50 molar hydrochloric acid is added to 0.040 liter of the buffer prepared in (a). Compute the hydrogen ion concentration of the resulting solution. AP CHEMISTRY EXAM REVIEW QUIZ #14 / 10 Name: Thermochemistry (Hess’s Law) SHOW ALL WORK. Include proper units and significant figures in all answers. 1. The compound BrCl(g) is produced by mixing bromine gas and chlorine gas at 298 K. The mixture reaches equilibrium in a very short time. Br2(g) + Cl2(g) ßà 2 BrCl(g) DHf° (kJ/mol) DGf° (kJ/mol) S° (J/mol·∙K) Br2(g) 30.7 3.14 152.2 BrCl(g) 14.7 -­‐0.88 239.7 Cl2(g) 0 0 222.8 a. What is the standard enthalpy of reaction, DH°, in kJ at 298 K for the reaction between Br2(g) and Cl2(g)? b. What is the numerical value of the standard entropy change, DS°, at 298 K for this reaction? c. What is the numerical value for the equilibrium constant, Kp, for this reaction at 298 K. AP CHEMISTRY EXAM REVIEW QUIZ #15 / 10 Equilibrium Name: SHOW ALL WORK. Include proper units and significant figures in all answers. CO2(g) + H2(g) ↔ H2O(g) + CO(g) 1. When H2(g) is mixed with CO2(g) at 2,000 K, equilibrium is achieved according to the equation above. In one experiment, the following equilibrium concentrations were measured: [H2] = 0.20 mol/L [CO2] = 0.30 mol/L [H2O] = [CO] = 0.55 mol/L (a) What is the mole fraction of CO(g) in the equilibrium mixture? (b) Using the equilibrium concentrations given above, calculate the value of Kc, the equilibrium constant for the reaction. 2. When the system is cooled from 2,000 K to a lower temperature, 30.0 percent of the CO(g) is converted back to CO2(g). Calculate the value of Kc at this lower temperature. 3. In a different experiment, 0.50 mole of H2(g) is mixed with 0.50 mole of CO2(g) in a 3.0-­‐liter reaction vessel at 2,000 K. Calculate the equilibrium concentration, in moles per liter, of CO(g) at this temperature.