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hw4 - ctt253 Homework 4 Sparks(53535 This print-out should...

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ctt253 – Homework 4 – Sparks – (53535) 1 This print-out should have 33 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An element E has the electronic configuration [Ne] 3 s 2 3 p 1 . Write the formula of its com- pound with sulfate. 1. E 2 (SO 4 ) 2. E 2 (SO 4 ) 3 correct 3. E 3 (SO 4 ) 4. E(SO 4 ) 2 5. E 3 (SO 4 ) 2 6. E(SO 4 ) 3 Explanation: E is aluminum; since it has three valence electrons it forms a +3 ion isoelectronic with Ne. 002 10.0 points In the hydrogen chloride molecule HCl the chlorine end of the molecule is more negative than the hydrogen end because 1. chlorine is more electronegative than hy- drogen. correct 2. hydrogen transfers an electron to chlo- rine. 3. hydrogen is more electronegative than chlorine. 4. hydrogen and chlorine have the same elec- tronegativity. Explanation: In a chemical bond the electrons are more strongly attracted toward the more elec- tronegative atom. 003 10.0 points Which atom in the molecule C Br is partially positive? 1. C correct 2. Br Explanation: 004 10.0 points Which pair of bonded atoms has the largest dipole moment? 1. C O 2. C F correct 3. N N 4. C C 5. C N Explanation: Dipole moments result because of the differ- ence in electronegativity (EN) between bond- ing atoms. The bonds with the largest dipole will have the largest difference in EN. EN in- creases from bottom to top and left to right on the periodic table. C C and N N have the same EN, so there is no dipole moment. Between N, O, and F, F is the most EN, and has the largest difference in EN with C. Therefore, the C N bond has the largest dipole. 005 10.0 points Which of the following molecules has the largest dipole moment? 1. F 2 2. HI 3. HCl correct 4. HBr 5. H 2 Explanation:
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ctt253 – Homework 4 – Sparks – (53535) 2 The molecule with the largest dipole mo- ment is the molecule with the most polar bond and the molecule with the largest differ- ence in electronegativities. Out of the choices listed, HCl is the molecule with the largest dipole moment. 006 10.0 points Which of the following pairs of ions would have the greatest coulombic attraction in a solid compound? 1. Mg 2+ , O 2 - correct 2. Mg 2+ , S 2 - 3. Mg 2+ , Se 2 - Explanation: E 1 r , so the ion with the shortest radius will have the greatest coulombic attraction. 007 10.0 points If the interaction energy between a sodium ion and a chloride ion in table salt is 760 kJ/mol, what is the interaction energy between a zinc ion (Zn 2+ ) and a sulfide ion (S 2 - ) in a hy- pothetical structure in which the inter-ionic distances are the same as that of NaCl? 1. 1140 kJ/mol 2. 3040 kJ/mol correct 3. 760 kJ/mol 4. 1520 kJ/mol 5. 1.140 kJ/mol Explanation: q Zn = +2 q S = - 2 q Na = +1 q Cl = - 1 V NaCl = 760 kJ/mol If r is the distance between the two ions (the sum of the ionic radii), the energy interaction between ions is given by Coulomb’s Law: V = q 1 q 2 4 π ǫ 0 r r = q 1 q 2 4 π ǫ 0 V r NaCl = r ZnS q Na q Cl 4 π ǫ 0 V NaCl = q Zn q S 4 π ǫ 0 V ZnS V ZnS = q Zn q S V NaCl q Na q Cl = (+2)( - 2)( - 760 kJ / mol) (+1)( - 1) = - 3040 kJ / mol , the energy released by the interaction.
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