CHE113 Exam 2 Solutions PDF

## Solution Key **CHE113** **Exam 2** **14 October 2016** **Name:** **P.O.:** **Score: /90** You will find ten questions included in this exam packet. Each question is worth the points indicated in parentheses. Please answer all questions completely and show your work. Turn in the equations, perio...

## Solution Key **CHE113** **Exam 2** **14 October 2016** **Name:** **P.O.:** **Score: /90** You will find ten questions included in this exam packet. Each question is worth the points indicated in parentheses. Please answer all questions completely and show your work. Turn in the equations, periodic table, and all scratch paper on a separate pile. Save problem 10 for last; this can be turned in next class on a separate sheet of paper. ### 1. (10) Match the words with the best definition or description below. | | Word | Definition | |---|---|---| | A | "shared valence" | | | B | | covalent | | C | | electronegativity | | D | | atomic radius | | E | | partial charge | | F | | formal charge | | G | | ionization energy | | H | | compound | | I | | electron affinity | | J | | octet rule | | K | | ionic | | A | | effective nuclear charge | | B | | predicts nonmetal atoms bond to achieve noble gas e configuration | | C | | The positive charge actually experienced by an electron can be ionic or molecular | | D | | created in polar bonds and denoted with script delta | | E | | indicated with + or - in a circle near the atom | | F | | F has the most energy needed to remove first electron from an atom | | G | | half the distance between neighboring nuclei | ### 2. (6) Indicate the best choice for each question below on the line provided. | | | | | | | |---|---|---|---|---|---| | **D** | The effective nuclear charge for an atom is less than the actual nuclear charge due to: | **A.** Ionic charge | **B.** Penetration | **C.** Lewis bonding | **D.** Shielding | **E.** Pixie dust | | **C** | Which of these elements has the smallest radius? | **A.** Al | **B.** P | **C.** As | **D.** Te | **E.** Na | | **A** | Which of these ions has the largest radius? | **A.** Cl- | **B.** K+ | **C.** S2- | **D.** Na+ | **E.** O2- | | **A** | Which of these elements has the smallest first ionization energy? | **A.** Rb | **B.** Mg | **C.** I | **D.** As | **E.** F | | | Elements with | | | | | | **C** | | first ionization energies and | | electron affinities generally | | | | |  form anions. | | | | | **A.** low, very negative | **B.** high, positive or slightly negative | **C.** low, positive or slightly negative | **D.** high, very negative | **E.** | | **ABCD** | Which of the following is your favorite class you have EVER taken (you must answer to get the point!)? | **A.** Gen Chem I | **B.** CHE113 | **C.** This class | **D.** Chemistry with Dr. Winters | ### 3. (12) Name the following compounds or ions from their formulae | Formula | Name | |---|---| | Cu+2 | Copper (II) | | SnO2 | Tin (IV) Oxide | | C4H9OH | Octanol | | Te-2 | Telluride | | Mg(ClO2)2 | Magnesium Chlorite | | CH3CHCHCOOH | Butenoic Acid | ### 4. (10) Draw the Lewis dot structure of each of the following atoms in their neutral state. Using their respective positions on the periodic table indicate their most common charge on the lines below each. (Note: not all of these actually form ions, predict their most likely charges) * **Mg** : **2+** * **I** : **1-** * **B** : **3+** * **O** : **2-** * **As** : **3-** ### 5. (10) Draw Lewis structures for the following compounds, include formal charges, bond polarities, and molecular polarities. * **NH4+** * Formal Charge: +1 * Bond Polarity: +1 * Total Polarity: Nonpolar * Lewis structure: ``` H | H-N-H | H ``` * **CH3CH2COO-** * Formal Charge: +2 * Bond Polarity: +1 * Total Polarity: +1 * Lewis structure: ``` H H O | | || H-C-C-C-O: | | H H ``` ### 6. (8) Rank the following sets of ionic compounds in order of increasing lattice energy and specify how you ranked each set. * **NaF < MgF2 < MgO** - Based on charge. * **NaBr < NaCl < NaF** - Based on ionic radius. ### 8. (12) Determine the empirical formula of a compound from percent composition or from combustion analysis data and Utilize the empirical formula and molar mass to determine the molecular formula of a compound. You are given the following combustion analysis data from an unknown compound: 40.92% C, 4.58% H, and 54.50 % O by mass. Calculate the empirical formula. Then, you determine using careful laboratory reactions that the molar mass of this compound is 176.12 g; what is the molecular formula of the unknown compound? **Calculations** * Assume 100.0 g of the compound. * **C:** 40.92 g C x (1 mol C / 12.011 g C) = 3.4068 mol C -> 3.4068 / 3.4068 = 1 * **H:** 4.58 g H x (1 mol H / 1.0079 g H) = 4.5441 mol H -> 4.5441 / 3.4068 = 1.33 * **O:** 54.54 g O x (1 mol O / 15.9990 g O) = 3.4109 mol O -> 3.4109 / 3.4068 = 1 **Empirical Formula:** C3H4O3, Molecular Mass = 88 g/mol **Molecular Formula:** (176.12 g / 88 g) = 2 = C6H8O6 ### 9. (10) Use the relationships between Avogadro's number, moles, molar mass, and grams to perform calculations involving compounds. Given 13.8491 g of H3PO4, how many moles are there? How many of each atom are there? **Calculations** * **Moles:** 13.8491 g H3PO4 x (1 mol H3PO4 / 97.99379 g H3PO4) = 0.141326 mol H3PO4 * **H:** 0.141326 mol H3PO4 x (3 mol H / 1 mol H3PO4) x (6.022 x 10^23 atoms / 1 mol) = 2.553 x 10^23 atoms * **P:** 0.141326 mol H3PO4 x (1 mol P / 1 mol H3PO4) x (6.022 x 10^23 atoms / 1 mol) = 8.511 x 10^23 atoms * **O:** 0.141326 mol H3PO4 x (4 mol O / 1 mol H3PO4) x (6.022 x 10^23 atoms / 1 mol) = 3.404 x 10^23 atoms ### 9. (12) I have mentioned in class that valence shell electrons are the most important in terms of chemical reactivity and chemical characteristics. Explain why this is the case. Use an illustration, of your choosing and design, to help answer this question. * **Valence shell electrons are the most important in terms of chemical reactivity and chemical characteristics because they are the ones that participate in bonding.** * **Outer shell electrons determine the atom's tendency to gain, lose, or share electrons to achieve a stable electron configuration ** * **Atoms seek to achieve a noble gas electron configuration, which typically involves eight valence electrons.** * **Therefore, the number and arrangement of valence electrons dictate an atom's reactivity and how it will interact with other atoms.**