HW5S - Gauthier, Joseph Homework 5 Due: Oct 2 2007,...

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Unformatted text preview: Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout 1 3. None of these 3. Mg2+ , S2- " I E Explanation: 1. Ca + I - Ca gives up two electrons to form the Ca2+ GG F F F F Ca + I F F 3+ F F E 003 (part 1 of 1) 10 points Use electron-dot notation to demonstrate the formation of ionic compounds involving the elements Ca and I. 10. Ca + I - 3- C C + E I CC CC E E BB B B BB Ca2+ + D D D C C - A A @ @ B B Explanation: E is aluminum; since it has three valence electrons it forms a +3 ion isoelectronic with Ne. A A @ @ 9. Ca + 9 I + I A A A @ @ @ 6. E(SO4 )2 9 - - - CaI2 correct 8 8 7 7 6 6 5. E3 (SO4 ) Ca + I + I + I Ca2 I3 - CaI 88 88 77 77 66 66 3+ 8 8 7 7 6 6 4. E2 (SO4 ) - - 5 5 5 5 4 4 4 4 3 3 3 3 8. Ca + I + I + I 5 5 5 4 4 4 3 3 3 2 2 2 3. E3 (SO4 )2 1 1 1 1 Ca + Ca + Ca + I 1 1 + + + 1 1 2. E(SO4 )3 0 0 7. Ca + Ca + Ca + I 0 ) ( ' 1. E2 (SO4 )3 correct & & Ca + 0 0 I - 3- && && 2+ & & % % 6. Ca + I %% % % $$ 002 (part 1 of 1) 10 points An element E has the electronic configuration [Ne] 3s2 3p1 . Write the formula of its compound with sulfate. - 2- # # Ca + Ca + I ## ## + + # # " 5. Ca + Ca + I "" " " ! Explanation: 1 E , so the ion with the shortest radius r will have the greatest coulombic attraction. - 2- - Ca2 I - CaI - Ca3 I - - I + I 2. Mg2+ , O2- correct Ca2+ + Ca2+ + Ca2+ + 3- 3- 4. Ca + Ca + Ca + I + I Ca3 I2 1. Mg2+ , Se2- 001 (part 1 of 1) 10 points Which of the following pairs of ions would have the greatest coulombic attraction in a solid compound? Ca +Ca + I + I + I 3+ 3+ 2- 2- 2- Ca2 I3 2. Ca + Ca + I + I + I Ca + I + This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. - - CaI - - - - - Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout H H 2 - II Two iodine anions combine with one calcium cation to form an electrically neutral compound: R R R Q Q Q Ca + I + 2+ I SS 004 (part 1 of 1) 10 points Which of the compounds below has bonds with the most covalent character? 1. CaCl2 2. BeCl2 correct 3. LiCl 4. NaCl 5. MgCl2 Explanation: EN is min for BeCl2 . 005 (part 1 of 1) 10 points The lattice enthalpy of calcium bromide is the energy change for the reaction 1. Ca(s) + Br2 ( ) CaBr2 (s) 2. CaBr2 (s) Ca(g) + 2 Br(g) 3. Ca(g) + 2 Br(g) CaBr2 (g) 4. CaBr2 (s) Ca2+ (g) + 2 Br- (g) correct 5. CaBr2 (s) Ca(g) + Br2 (g) Explanation: 006 (part 1 of 1) 10 points How many valence electrons are in a S atom? 1. 2 2. 17; 8 3. 15; 5 4. 16; 5 5. 18; 8 6. 16; 6 7. 17; 7 correct 8. 15; 6 9. 17; 6 10. 15; 7 Explanation: P2- has gained 2 electrons to give it a total of 17. In its valence, it has 3s2 3p5 , giving it a total of 7 valence electrons. 008 (part 1 of 1) 10 points What total number of valence electrons T T S S Ca + I + I TT T T TT SS S S RR R R QQ Q Q I I the I anion. H H cation, and I I II I H H H PP acquires an electron to form 2. 4 3. 16 4. 6 correct 5. 8 Explanation: Valence electrons are electrons that are found in the outermost energy levels of an atom. For S, Atomic number : 16 Electronic configuration : [Ne] 3s2 3p4 Shell Structure : 2 - 8 - 6 Therefore, S has 6 valence electrons. 007 (part 1 of 1) 10 points The P2- anion has how many total electrons and how many valence electrons? 1. 16; 7 - - - - CaI2 Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout should appear in the dot formula for the chlorate ion ClO- ? 3 1. 32 2. 28 3. 24 4. 30 3 Which of the following is the correct Lewis formula for oxygen (O2 )? O O O y y yy x w w x x x x x x x ww ww yy 1. 2. 3. 4. 5. 6. O O O O O O O O O O y y 7. 8. 009 (part 1 of 1) 10 points Which of the following is the best representation of the compound calcium sulfide? - U U X X 1. Ca , 2. Ca 2+ + S c c Y Y - ` ` , 2 g g S d d e e 4. None is appropriate because calcium sulfide is a covalent compound. 2- i i q q 011 (part 1 of 1) 10 points Which of the following is the correct Lewis formula for acetylene (ethyne, C2 H2 )? 010 (part 1 of 1) 10 points H 3. H C C H W Explanation: The metal loses all of its outer (valence) electrons; the non-metal gains sufficient electrons to form an octet. The ratio of the negative and positive ions is chosen so there is no overall charge. 2. H C s S v v u H s u 6. 3 Ca2+ , 2 C W 3- 1. H C C S r r W W 5. 2 Ca+ , S h h correct O 3. Ca2+ , O 2- Explanation: N = 8 2 = 16 A = 6 2 = 12 S = N - A = 16 - 12 = 4 There are 4 shared electrons. The remaining electrons are placed around the oxygen atoms such that each has an octet. The Lewis dot formula for oxygen (O2 ) is O O Explanation: Chlorine has 7 valence electrons and oxygen 6. The overall -1 charge indicates that there is 1 extra electron. The total number of valence electrons is 1 7 e- (from Cl) + 3 6 e- (from O) +1 e- (from -1 charge) = 26 e- 5. 26 correct x O yy x w w correct t bt a ba p bp f bf V WV Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout 4. one; six 4 C H 4. H C 5. H H C C C C 10. H g g C g H g g Explanation: The Lewis formula for acetylene (ethyne, C2 H2 ) is H C C H 012 (part 1 of 1) 10 points How many unshared electrons and bonding electrons exist around the central atom in ozone, O3 ? 1. two; six correct 2. four; three 3. one; three f f H f C g ff g hg f d Wd d d 9. H C e C e H e e W 8. H C C H W H 7. 013 (part 1 of 1) 10 points Which of the following contains exactly one unshared pair of valence electrons? 1. SiH4 2. NaCl 3. PH3 correct 4. C2 H4 5. H2 S Explanation: The PH3 molecule contains exactly 1 unshared pair of valence electrons: H H P H You can check this structure for correctness by verifying that each atom has the correct number of electrons around it (8 for most elements, 2 for hydrogen) and that the structure shows the correct total number of valence electrons (calculated by adding up the available valence electrons from each atom). The C2 H4 molecule contains no unshared pairs; SiH4 contains no unshared pairs; NaCl (an ionic compound) contains 4 unshared pairs; and H2 S contains 2 unshared pairs. 014 (part 1 of 1) 10 points r r t t o o l l C C q O j O O O O O q s hs p Wp u hu m nm i Wi k hk j H 6. d Wd 5. two; two 6. three; six H correct 7. none; two 8. four; four 9. zero; eight Explanation: Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout How many double bonds are present in the "best" resonance structure of the phosphate ion? 1. 0 2. 1 correct 3. 2 4. 3 Explanation: O 0 -1 O P O 0 -1 -1 O | | ~ h~ } } { { y y z z w hw x x v v 5 1. 2. F Cl F Cl F Cl F Cl F Cl F Cl F Cl F Cl 3- is the most plausible 7. 8. F Cl F Cl 2. ten 3. none 4. thirteen 017 (part 1 of 1) 10 points Which of the following is the correct Lewis formula for boron trichloride (BCl3 )? Cl 6. twenty 7. four 8. one correct N 2. Cl B Cl B Cl W 016 (part 1 of 1) 10 points Which of the following is the correct Lewis formula for chlorine fluoride (ClF)? 4. Cl B Cl W W F The Lewis structure is Cl F F W 3. Cl Cl Explanation: W Cl W 5. two 1. B Cl Cl 1. three Explanation: The Lewis formula for chlorine fluoride (ClF) is F Cl W 015 (part 1 of 1) 10 points How many lone pairs of electrons are on nitrogen in NF3 ? 10. structure. 9. 6. 5. 4. 3. correct correct Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout 5. 4. 4 5. It does not exhibit resonance. 6. 6 Cl Cl B Cl Cl Cl B Cl Explanation: B contributes 3 valence e- and each Cl contributes 7 valence e- for a total of 24 e- . B is a known exception to the octet rule and can form stable with 6 valence e- : Cl h B Cl Cl 018 (part 1 of 1) 10 points The CO2- ion has how many resonance con3 figurations? 1. 5 2. 2 3. 3 correct h Cl Cl 10. Cl B Cl 9. Cl B Cl Cl h W 8. Cl B Cl Cl 7. Cl B Cl Explanation: C 4 valence e- O 3 6 valence e- 2- 2 e- Total = 24 valence e- One structure is C O O O which can also be drawn as or O O C O C O W O O for a total of 3 resonance structures. 019 (part 1 of 1) 10 points Resonance is a concept that describes the bonding in molecules 1. where there is more than one choice of location for a double bond as deduced from Lewis dot structures. The true bonding is the average over all possible double-bond locations. correct 2. by asserting that double bonds "flip" or resonate between two locations in the molecule. 3. by asserting that electrons in a double bond can delocalize (spill over) onto adjacent single bonds to make a bond and a half. Explanation: In resonance, although the arrangement of all possible double bond locations may sometimes mean that a bond has a bond order of 1.5, other possibilities can occur such as 1.333 (1 and a third bonds). 020 (part 1 of 1) 10 points Which of the three Lewis structures is the most important? Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout A) -2 C B) -1 C C) -3 C W n 7 +1 N +1 N +1 N 0 -1 N W +1 O acceptable range. 022 (part 1 of 1) 10 points Calculate the formal charge on N in the molecule NH3 . 1. 3 2. 0 correct 3. 1 4. 4 5. 2 Explanation: The Lewis structure is 0 -1 W 1. B only correct 2. C only 3. None of these is important. 4. B and C only 5. A only 6. A and C only 7. All of these are important. 8. A and B only Explanation: -1 is C N O probably the most important as it is the structure with the formal charges of the individual atoms closest to zero. 021 (part 1 of 1) 10 points How many resonance structures can be drawn for N2 O? Disregard any structure with formal charges other than 0, +1, and -1. 1. 2 correct W The Lewis structure +1 023 (part 1 of 1) 10 points Estimate the heat released when 1-butene (CH3 CH2 CH CH2 ) reacts with bromine to give CH3 CH2 CHBrCH2 Br. Bond enthalpies are C H : 412 kJ/mol; C C : 348 kJ/mol; C C : 612 kJ/mol; C Br : 276 kJ/mol; Br Br : 193 kJ/mol. 1. 95 kJ/mol correct 2. 317 kJ/mol 2. 0 3. 507 kJ/mol 3. 1 4. 181 kJ/mol 4. 3 5. 288 kJ/mol Explanation: Explanation: O N O has formal charges out of the 0 0 H N H 0 H N N O N N O h n n O W h Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout H H C H H C H H C H C H H H C H H = = (C Ebreak - C) + (Br H C H Br H C H C H Br 025 (part 1 of 1) 10 points Consider the reaction CH4 (g) + I2 CH3 I(g) + HI(g) . + Br Br 8 off energy). In a reaction, the bonds in the reactants are broken; the ones in the products are formed. The net energy flow determines if the overall reaction is exothermic or endothermic. Emake Br) C) - 2 (C Br) + (C = 612 kJ/mol + 193 kJ/mol - 2 (276 kJ/mol) + 348 kJ/mol = -95 kJ/mol , which means 95 kJ/mol of heat was released. 024 (part 1 of 1) 10 points The heat energy released or absorbed by a chemical reaction is generally determined by the difference between 1. the energy that must be put in to break the bonds in the reactants and the energy that must be put in to make the bonds in the products. 2. the energy that must be put in to break the bonds in the reactants and the energy that is released upon making the bonds in the products. correct 3. the energy that is released upon breaking the bonds in the reactants and the energy that is released upon making the bonds in the products. 4. the energy that is released upon breaking the bonds in the reactants and the energy that must be put in to make the bonds in the products. Explanation: Bond breaking is endothermic (takes in energy) and bond creation is exothermic (gives Bond energy tables give the following values: C H : 411 kJ/mol I I : 149 kJ/mol H I : 295 kJ/mol C I : 213 kJ/mol The change in enthalpy for this reaction is: 1. -52 kJ/mol 2. +463 kJ/mol 3. +52 kJ/mol correct 4. There is no way to tell. 5. -97 kJ/mol Explanation: H H C H I H C H H + H I H + I I -- -- H = BEreactants - BEproducts H) + (I I) = 4 (C - 3 (C H) - (C I) - (H I) = (C H) + (I I) I) - (H I) - (C = 411 kJ/mol + 149 kJ/mol - 213 kJ/mol - 295 kJ/mol = 52 kJ/mol Gauthier, Joseph Homework 5 Due: Oct 2 2007, midnight Inst: Vandenbout 026 (part 1 of 1) 10 points Bond energies are approximate because 1. they depend upon the physical state of the molecule, gas, liquid, or solid. 2. not all molecules burn in oxygen, making calorimetry difficult. 3. they are averages over a number of molecules. correct 4. we cannot measure them accurately. 5. we cannot calculate them accurately. Explanation: Bond energies are averages over a number of molecules. The C H bonds in CH4 and CH3 OH are not the same and require different amounts of energy to break. 9 ...
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This note was uploaded on 03/19/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas at Austin.

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