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11/25/15 ANSWER KEY CHEM 60 Exam 3 Name: __________________________________ Open-End Questions and Problems Please read the following. To receive full credit for a question or a problem, in addition to the correct answer, you must show a neat, complete, and logical method of solution where each number is labeled with the appropriate unit and the final answer is rounded to the correct number of significant digits. The correct answer without any work shown will generally get zero credit! When an explanation is required, it should be brief, but accurate and complete. There are 7 questions for a total of 42 points. (Exam 3 part with multiple choice questions is worth 58 points. Both parts combined are 100 points total. 1. (6 points) Fill the blanks in the following table. Neon Nitrogen Ammonia The number of molecules in 1.00 mole of none 6.02×1023 6.02×1023 The number of atoms in 1.00 mole of 6.02×1023 1.20×1024 2.41×1024 The number of elements in 1.00 mole of one one two The number of substances in 1.00 mole of one one one The number of compounds in 1.00 mole of none none one The mass in grams of 1.00 mole of 20.18 28.02 17.03 The volume in liters of 1.00 mole of 24.5 24.4 23.3 2. (6 points) Give the chemical formula for each of the following molecules, ions, or formula units. H2SO4 sulfuric acid H2CO3 carbonic acid HNO2 nitrous acid HSO4− hydrogen sulfate ion HCO3− hydrogen carbonate ion NO2− nitrite ion H2SO3 sulfurous acid CO32− carbonate ion N3− nitride ion H2S(aq) hydrosulfuric acid C4− carbide ion NH3 ammonia Al4C3 aluminum carbide NH4NO2 ammonium nitrite barium hydrogen Ba(HSO4)2 sulfate 3. (6 points) Write the full-formula, complete ionic, and net ionic equation (FFE, CIE, and NIE) for each of the two reactions described below. In each equation, indicate physical state of each reactant and product: (s), (l), (g), or (aq). (a) Zinc is added to sulfuric acid. FFE: Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) CIE: Zn(s) + 2 H+(aq) + SO42−(aq) → Zn2+(aq) + SO42−(aq) + H2(g) NIE: Zn(s) + 2 H+(aq) → Zn2+(aq) + H2(g) (b) Hydrobromic acid is mixed with a sodium carbonate solution. FFE: 2 HBr(aq) + Na2CO3(aq) → 2 NaBr(aq) + H2O(l) + CO2(g) CIE: 2H+(aq) + 2Br−(aq) + 2Na+(aq) + CO32−(aq) → 2Na+(aq) + 2Br−(aq) + H2O(l) + CO2(g) NIE: 2 H+(aq) + CO32−(aq) → H2O(l) + CO2(g) 4. (6 points) Examine the following list of chemical substances to answer questions (a), (b), (c) and (d). CH3OH NH4ClO3 Na2O2 Al2S3 SO3 NH2OH KMnO4 (a) Which of the substances contain(s) a polyatomic cation? NH4ClO3 (b) Which of the substances contain(s) a polyatomic anion? NH4ClO3 Na2O2 KMnO4 (c) Which of the substances contain(s) both ionic and covalent bonds? NH4ClO3 Na2O2 KMnO4 (d) Which of the substances contain(s) no ionic bonds? CH3OH SO3 NH2OH HClO4 HClO4 5. (6 points) Fill the blanks. Formula Name Al aluminum atom Ba2+ barium ion Br Electronic Structure Number of Protons per Molecule, Atom or Ion Number of Number of Valence Electrons per Electrons per Molecule, Molecule, Atom or Ion Atom or Ion 13 13 3 56 54 0 bromine atom 35 35 7 Br2 bromine molecule 70 70 14 Br− bromide ion 35 36 8 CF4 carbon tetrafluoride molecule 42 42 32 SO32− sulfite ion 40 42 26 Ba2+ 6. (6 points) What are dispersion forces? How does the strength of dispersion forces relate to molar mass? 5. (6 points) Fill the blanks. Formula Name Electronic Structure Number of Protons per Molecule, Atom or Ion Number of Number of Valence Electrons per Electrons per Molecule, Molecule, Atom or Ion Atom or Ion aluminum atom barium ion bromine atom Br− carbon tetrafluoride molecule 6. (6 points) What are dipole-dipole forces? How can you tell whether a compound has dipoledipole forces? 5. (6 points) Fill the blanks. Formula Name Electronic Structure Number of Protons per Molecule, Atom or Ion Number of Number of Valence Electrons per Electrons per Molecule, Molecule, Atom or Ion Atom or Ion aluminum atom barium ion bromine atom Br− carbon tetrafluoride molecule 6. (6 points) What is hydrogen bonding? How can you tell whether a compound has hydrogen bonding? 7. (6 points) Consider the following three molecules: CO2 (a) BF3 CH4 In which molecule are the bonds most polar? Explain. In BF3 molecule. The difference in electronegativity (∆EN) is the largest between boron and fluorine. The ∆EN’s between carbon and oxygen and between carbon and hydrogen are smaller. (b) Which molecule is the most polar? Explain. None of the 3 molecules is polar. Each of the 3 molecules is highly symmetrical with symmetrical distribution of positive and negative charges. linear trigonal planar tetrahedral