CHM 151 Exam 3 Chapters 3 and 4

Name: ____KEY_________________________ Section: _________________ Exam 3: Chapters 3 and 4 You must show all work to receive credit. Clearly mark your final answer! 1. (11 pts) Balancing equations: a. _2_ FeCl3 (aq) + ___ Be3(PO4)2 (aq)  _3_ BeCl2 (aq) + _2_ FePO4 (aq) b. ___ (NH4)2CO3 (s)  _2_ NH3 (g) + ___ CO2 (g) + ___ H2O (l) c. _2_ N2 (g) + _5_ O2 (g)  _2_ N2O5 (g) 2. (6 pts) You are working in a chemistry stockroom and are asked to prepare a demo of 1 mole of the following substances. Indicate what type of particle each formula represents (atom, molecule, formula unit). Also determine what mass you must measure to show 1 mole of each of the following. particle type mass a. CCl4: __molecule_______________ ___153.811 g_______________ b. Ca: __atom__________________ ___40.08 g_________________ c. Fe(OH)3 __formula unit____________ ___106.874 g_______________ 3. (4 pts) How many molecules of water are in 1.000 teaspoon? (1 teaspoon = 4.914 g at room temperature) 4.914 g H2O * (1 mol / 18.016 g) * (6.022 x 1023 molecules / 1 mol) = 1.643 x 1023 molecules H2O 4. (6 pts) Draw what 1 mole of the following compounds would look like if dissolved in each beaker of water. Na2SO4 CH3OH Ni(OH)2 Ca(NO3)2 5. (9 pts) A student is asked to combine copper (II) nitrate and sodium carbonate in a lab experiment. Complete the molecular equation with products (including phases) and balancing. Then write the complete ionic and net ionic equations for this reaction. Molecular: ___ Cu(NO3)2 (aq) + ___Na2CO3(aq)  ___CuCO3(s) + 2NaNO3(aq)______________________ Ionic: _Cu2+(aq) + 2NO3-(aq) + 2Na+(aq) + CO32-(aq)  CuCO3(s) + 2Na+(aq) + 2NO3-(aq)_______________ Net Ionic: __ Cu2+(aq) + CO32-(aq)  CuCO3(s) _________________________________________ page 1 of 3 Name: ____KEY_________________________ 6. (13 pts) For the following reactants, Section: _________________ a) Determine what type of reaction will occur Combination (C), Decomposition (D), Single-replacement (SR), DoubleReplacement/Precipitation (P), Double-replacement/Acid-Base Neutralization (AB), Combustion (B) or No Reaction (NR) b) Predict the product(s) of the reaction c) Write correct phases of the product(s) d) Balance the equation Reaction Type Reactants Products __NR___ ___Ag(s) + ___Zn(NO3)2(aq)  __NR____________________ __C___ ___K(s) + ___Cl2(g)  ___2 KCl(s)_____________________ __B___ _2_C4H10(l) + _13_O2(g)  __8 CO2(g) + 10 H2O(g)_________ __SR____ ___Ca(s) + _2_HCl(aq)  _CaCl2(aq) + H2(g) ____________ _D_ 7. (5 pts) When H2SO4 reacts with NaOH, which of the following represents the net ionic equation? a. No net ionic equation (no reaction) b. Na+(aq) + SO42-(aq)  Na2SO4(s) c. Na+(aq) + SO42-(aq)  Na2SO4(aq) d. H+(aq) + OH-(aq)  H2O(l) e. H+(aq) + OH-(aq)  H2O(aq) 8. (5 pts) Identify the oxidation number of each element in the following substances: a) CdS b) ClO41- Cd: +2 S: -2 Cl: +7 O: -2 c) O2(g) O2: 0 9. (5 pts) In the following equation, identify the a) species being reduced, b) species being oxidized, c) reducing agent, and d) oxidizing agent. Cu(NO3)2 (aq) + Ni (s)  Ni(NO3)2 (aq) + Cu (s) Oxidized: __Ni____________ Oxidizing agent: _Cu(NO3)2___________ Reduced: __Cu2+ in Cu(NO3)2_ Reducing agent: __Ni_______________ _C_ 10. (5 pts) What will be the concentration (in M) of a solution made by adding 2.3656 g of NaOH to 500.00 mL of deionized water? a. 0.0047312 M b. 0.059143 M c. 0.11829 M d. 1.1828 M 11. (2 pts) What is the concentration of the above solution if you add 500.0 mL of water to it? Double volume = ½ concentration M1V1 = M2V2 0.11829 M / 2 = 0.059143 M (0.11829 M)(500.00 mL) = (x M)(1000.0 mL) page 2 of 3 Name: ____KEY_________________________ Section: _________________ 12. (14 pts) In lab, you are asked to combine solid NaOH and aqueous FeCl3 in a beaker and separate the precipitate. Complete the equation by indicating the phases of the products and balancing it. Then determine the theoretical mass of precipitate. _3_NaOH (s) + ____ FeCl3 (aq)  ___ Fe(OH)3_(s)_ + _3__ NaCl_(aq)_ a) (10 pts) Determine the theoretical mass of precipitate formed if 2.6890 g of NaOH are reacted with 25.54 mL of 0.5012 M FeCl3. 2.6890 g NaOH * (1 mol / 39.998 g) * (1 mol Fe(OH)3 / 3 mol NaOH) * (106.874 g Fe(OH)3 / 1 mol) = 2.39499 g Fe(OH)3 (0.02554 L)(0.5012 mol/L) = 0.0128006 mol FeCl3 * (1 mol Fe(OH)3 / 1 mol FeCl3) * (106.874 g / 1 mol) = 1.36806 g Fe(OH)3 Theoretical mass = 1.368 g Fe(OH)3 b) (2 pts) Calculate the percent yield if 1.2556 g of precipitate are actually formed. 1.2556 g / 1.368 g x 100% = 91.78% 14. (8 pts) Complete the equation below with products, phases, and balancing: H2CO3 (aq) + 2 LiOH(aq)  Li2CO3(aq) + 2H2O(l) You begin a titration with 1.012 M of base in a buret. From the buret, you deliver 14.53 mL of the base to a flask containing 30.00 mL of acid in order to reach a nice, light pink end point. Based on your data, what is the concentration of the acid? (1.012 mol/L)(0.01453 L) = 0.014704 mol LiOH * (1 mol H2CO3 / 2 mol LiOH) = 0.0735218 mol H2CO3 0.0735218 mol H2CO3 / 0.03000 L = 0.2451 M H2CO3 15. (7 pts) Find the empirical formula of pentane (a major component of a fuel mixtures) if it contains 85.62% Carbon and 14.37% Hydrogen. 85.62% C  85.62 g C * (1 mol / 12.011 g) = 7.1285 mol C / 7.1285 = 1 14.37% H  14.37 g H * (1 mol / 1.008 g) = 14.256 mol H / 7.1285 = 2 empirical formula: CH2 What is the molecular formula of pentane if its actual molar mass is 70.135 g/mol? CH2 = 14.027 g/mol 70.135 / 14.027 = 5 (CH2)5  C5H10 (molecular formula) page 3 of 3