Old Exam 2 PDF

1. What is the reducing agent in the reaction shown below? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) a. CH4(g) b. O2(g) c. CO2(g) d. There is no reducing agent because this is not a redox reaction 2. The reaction between phosphoric acid and calcium hydroxide is shown below:...

1. What is the reducing agent in the reaction shown below? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) a. CH4(g) b. O2(g) c. CO2(g) d. There is no reducing agent because this is not a redox reaction 2. The reaction between phosphoric acid and calcium hydroxide is shown below: 2 H3PO4(aq) + 3 Ca(OH)2(aq) → Ca3(PO4)2(s) + 6 H2O(l) A student titrates a 50.00 mL sample of calcium hydroxide with 0.0100 M phosphoric acid. If 25.00 mL of acid are required to reach the equivalence point then what is the concentration of the calcium hydroxide sample? a. 0.00500 M b. 0.00750 M c. 0.0333 M d. 0.0200 M 3. The molecular equation for a chemical reaction is shown below: H3PO4(aq) + 3 NaOH(aq) → Na3PO4(aq) + 3 H2O(l) What is/are the spectator ion(s) for this reaction? a. Na+ only b. PO43- only c. Na+ and PO43- d. There are no spectator ions 4. Which aqueous solution do you expect to have a conductivity closest to that of 0.20 M CaCl2(aq)? a. 0.10 M MgSO4(aq) b. 0.30 M KNO3(aq) c. 0.20 M NaCl(aq) d. 0.10 M AlCl3(aq) 1 5. A student dissolves 3.708 grams of Mg(NO3)2 (molar mass = 148.32 g/mol) in enough water to make 0.250 L of solution. What is the concentration of nitrate ions in this solution? a. 0.0500 M b. 0.100 M c. 0.200 M d. 0.400 M 6. 25.0 mL of a gas has a pressure of 2.00 atm at 20.0oC. What volume will the gas occupy if the pressure is decreased to 1.00 atm and the temperature increased to 40.0oC? The moles of gas remain constant. a. 6.25 mL b. 25.0 mL c. 53.4 mL d. 100. mL 7. What is the density of 1.50 atm of xenon gas at 35oC? a. 0.522 g/L b. 0.677 g/L c. 7.79 g/L d. 0.0769 g/L 8. How much 18.4 M H2SO4(aq) is needed to prepare 1.50 L of a 2.50 M solution of H2SO4(aq)? Assume that volumes are additive. a. 11.0 mL b. 90.6 mL c. 32.6 mL d. 204 mL 9. A gas tank contains three different gases – argon, helium, and neon. The mole fraction of each gas is the same. A small hole is then made in the tank and the gases escape into the surroundings. Which gas will have the smallest mole fraction inside of the tank after a few minutes? Assume that there is still some of each gas present. a. Argon b. Helium c. Neon d. All three gases will have the same mole fraction 2 10. Consider the following reaction: 5 O2(g) + 4 NH3(g) → 4 NO(g) + 6 H2O(g) A scientist adds 1.50 atm of O2(g) and 1.25 atm of NH3(g) to an empty 2.00 L container at 400oC. If the reaction proceeds to completion then what will the partial pressure of water be inside of the container be after the reaction is complete? The temperature and volume are kept constant. a. 1.88 atm b. 1.80 atm c. 1.83 atm d. 3.00 atm Short Answer 1: Note that you must clearly show all of your work to receive any credit (6 points) Consider the following decomposition reaction of solid ammonium nitrate: 2 NH4NO3(s) → 2 N2(g) + 3 O2(g) + 4 H2(g) A scientist uses a setup similar to the one you used in lab to study this reaction (see a sample setup below). When some solid ammonium nitrate decomposes the total pressure of gas collected over water is 1.048 atm. 841 mL of gas is collected and temperature is 25oC. The vapor pressure of water at this temperature is 0.031 atm. How many moles of ammonium nitrate decomposed? 3 Short Answer 2: Note that you must clearly show all of your work to receive any credit (8 points total) 0.150 L of aqueous scandium(III) nitrate (Sc(NO3)3) is mixed with 0.250 L of aqueous sodium sulfide (Na2S). The reaction that occurs is shown below. 2 Sc(NO3)3(aq) + 3 Na2S(aq) → Sc2S3(s) + 6 NaNO3(aq) 0.0110 moles of precipitate form and [Sc3+] = 0.0845 M in the final mixed solution. Volumes are additive and the precipitation reaction goes to completion. a) Calculate the original concentration of the 0.250 L sodium sulfide solution. b) Calculate the original concentration of the 0.150 L scandium(III) nitrate solution. 4 Short Answer 3 (6 points) Consider the following unbalanced redox reaction that takes place in an acidic solution: MnO4-(aq) + Cu(s) → Mn2+(aq) + Cu2+(aq) ONE of the balanced half reactions is written below with its lowest whole number coefficients: Cu(s) → Cu2+(aq) + 2e- a) Is the half reaction shown above an oxidation or reduction? Circle your choice below. Oxidation Reduction b) Write the balanced half reaction with MnO4- and Mn2+. You should write this with the lowest whole number coefficients. c) Write the overall balanced equation with the lowest whole number coefficients. 5