CHEMISTRY 362 Descriptive Inorganic Chemistry. M. Y. Darensbourg. Examination II March 29, Name:

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1 CHEMISTRY 362 Descriptive Inorganic Chemistry M. Y. Darensbourg Examination II March 29, 2017 Name: An Aggie does not lie, cheat or steal or tolerate those who do. Signed: Point Group Assignment S = Σm s Spin multiplicity = 2S + 1 μ(s. o. ) = 2 S (S + 1)

2 pg. 1 CHEMISTRY 362 Descriptive Inorganic Chemistry M. Y. Darensbourg Examination II March 29, 2017 Question Points possible Points received I 25 II 25 III 20 IV 12 V 18 Bonus (20) Total 100 (120) Useless Conversion Factors Ratio of an igloo's circumference to its diameter: Eskimo Pi 2000 pounds of Chinese soup: Won ton 1 millionth of a mouthwash: 1 microscope Time between slipping on a peel and smacking the pavement: 1 bananosecond 8 nickels: 2 paradigms

3 I. Acids and Bases A. Fill in the blanks in the following table, using Pauling s rule (pk a = 8-5n) to predict the pk a. Note some answers are given to you. Predicted pk a Ox. State of central atom Formula of acid anhydride pg. 2 H 2 SO 4-2 H 2 SO 3 H 3 PO 4 P 4 O 10 H 3 PO 3 +3 B. Whereas H 3 PO 4 is a triprotic acid, H 3 PO 3 is only diprotic. Give the Lewis structures of each and account for this difference. C. Give equations for the successive ionization equilibria for H 3 PO 4 ; i.e., define K a1, K a2, and K a3. K a1 : K a2 : K a3 : D. Rank or order the basicity of the conjugate bases of the oxoacids of chlorine. OCl - ; ClO 2 - ; ClO3 - ; ClO4 - E. Your answer in D. means that which HClO x acid is the strongest? F. Circle the more stable Lewis acid-base adduct in the following pairs and briefly explain your choice. i) Me 3 N: BF 3 or H 3 N: BF 3 ii) Me 3 N: BMe 3 or Et 3 N: BEt 3 iii) iv) Me 3 B :CO or F 3 B :CO AgCl or AgI

II. Molecular Orbital Bonding Approach for Diatomics: O 2, O 2 +, O 2 -, O2 2-1.

4 II. Molecular Orbital Bonding Approach for Diatomics: O 2, O 2 +, O 2 -, O Dioxygen can lose an electron to form O 2 +, and it also exists as super-oxide, O 2 - and as the peroxide dianion, O Give the electronic configuration of each of these, using the following horizontal form of the MO energy level diagram: [KK] σ 2s σ* 2s σ 2pz π 2p(x,y) π* 2p(x,y) σ* 2pz. Also give the spin and ground state term symbol for each. pg. 3 Bond order S Term symbol O 2 O 2 + O 2 - O Sketch the σ 2pz and the π* 2px molecular orbitals of O 2 - on the following coordinate systems. σ 2pz π * 2px x x x x O O z O O z y y y y 3. The O 2 has a bond distance of 1.21 Å. Is the bond distance of the O 2 + species smaller or larger than 1.21 Å? Why? 4. Which dioxygen species is isoelectronic (same no. of electrons) with nitric oxide, NO? 5. The HOMO of NO is a combination of N and O orbitals as noted below: (circle the correct answer.) a) ψ(π*) = a N 2px - b O 2px (with a > b) b) ψ(π*) = a N 2px - b O 2px (with a < b) c) ψ(π*) = a N 2px - b O 2px (with a = b) d) none of the above

5 III. Short answer questions mainly from localized bonding or Valence Bond, approach to electron distribution and geometries in molecules. pg. 4 1) Of the molecules below, only is nonpolar. a) CO 2 b) HO 2 c) NH 3 d) HCl e) TeCl 2 2) PCl 3 has lone pairs on P, a geometry, and belongs to the point group. 3) PCl 4 Br has lone pairs on P, a geometry, and belongs to the point group. 4) The central iodine atom in the ICl 4 ion has non-bonded or lone electron pairs and bonded electron pairs in its valence shell. Its symmetry point group is. The lone pairs are in hybrid orbitals; the bonded pairs are in hybrid orbitals. 5) The H-E-H bond angles in NH 3 are 107 while in PH 3 they are 93. Thus the lone pairs in NH 3 and in PH 3 are in? and? orbitals, respectively. (Circle the correct answer) a) s and sp 3 b) sp 3 and s c) p and sp 3 d) sp 3 and p 6) On the coordinate system provided, give a sketch of a) a single sp 3 d 2 hybrid orbital and b) a single sp 3 hybrid orbital. Give the % s-character in each. a) b) 7) Give a sketch of the orbital overlap which leads to the coordinate covalent bond between B and N in the amine-borane, H 3 B :NH 3, Lewis Acid/Base adduct. Identify the hybrid orbital character on each atom.

6 IV. Acetonitrile is the chemical compound with the formula CH 3 CN. This colorless liquid is the organic analogue of HCN. In the laboratory, it is used as a medium-polarity solvent that is miscible (mixes well) with water and a range of organic solvents, but not so well with saturated hydrocarbons. pg. 5 a) Contrast the Lewis structures of CH 3 CN and HCN. Give the symmetry point group of each. b) Which has the greater dipole moment? Rationalize your answer. c) In water, one of these has a pka of 9.3 and the other has a pka of 25. Complete the ionization equilibria equations below and assign the pka values. CH 3 CN + H 2 O pka = HCN + H 2 O pka = d) Both HCN and benzene dissolve in acetonitrile. Which intermolecular force accounts for the solubility of HCN in acetonitrile? Which accounts for the solubility of benzene in acetonitrile?

V Consider the textbook figures A, B, C, and D and answer the questions that relate to the figures. pg. 6 A B C D A. A is a unit cell of an alloy of copper and gold.

i) What ions and how many occupy 2 nd -nearest neighbor positions of the central Cs + ion? ; b) What is the radius ratio predicted structure of LiCl?

Predict the effect on the melting point of LiCl, if it were in the Cs

7 V Consider the textbook figures A, B, C, and D and answer the questions that relate to the figures. pg. 6 A B C D A. A is a unit cell of an alloy of copper and gold. What is the composition (copper to gold ratio) of this alloy? Show how you derived this formula. B. a) B is the unit cell of cesium chloride. i) What ions and how many occupy 2 nd -nearest neighbor positions of the central Cs + ion? ; b) What is the radius ratio predicted structure of LiCl? Note: the radii of ions involved in these questions are: Cs + = 1.88 Å; Li + = 0.73Å ; Cl = 1.67 Å. c) Assume all Cs + ions were replaced by Li + ions. Predict the effect on the melting point of LiCl, if it were in the CsCl structure form? Give a reason for your answer. C. Place labels (metal, semi-conductor, or super-conductor) on Figure C that describes the variation of electrical conductivity with temperature. Give a rationale for the temperature dependence of metals vs. semi-conductors. D. Figure 3.73 of your text is reproduced here as D. It displays band structures of doped semiconductors. a) Which is of n-type and which is of p-type? b) Which describes silicon doped with arsenic? a) right (a) ; left (b) b) right side (a) or left (b)

8 Bonus Question: pg. 7 a) The Born-Mayer Equation given below right is a theoretical approach to the lattice energy of an ionic salt. Define the following terms and describe their significance to the calculation of lattice energies. N = Z = A = r e = b) The lattice energy of NaCl is calculated by this approach to be 756 kj/mol whereas the experimental, measured value is 787 kj/mol. As with NaCl, magnesium oxide crystallizes in the rock salt lattice. The factor in the Born equation that most influences the lattice energy of MgO is. The estimated Lattice Energy of MgO is. (Fill in the blanks.) c) Based on the Born equation, the lattice energy of BaO is expected to be (greater or less) than that of MgO. Circle your choice and give a rationale for your choice. d) The Born-Haber cycle is an experimental, thermodynamic approach to determining lattice energy of an ionic salt. Consider the B-H cycle as presented in Figure 3.48 of your text. From this diagram, select (or calculate) the values (in kj/mol) of the following: Example: Ionization energy of _K 0 _ = 425 kj/mol Electron affinity energy of = Enthalpy of sublimation of = Bond Dissociation Energy of = Enthalpy of Formation of = Lattice Energy of =

CHEMISTRY 362 Descriptive Inorganic Chemistry. M. Y. Darensbourg. Examination III. April 19, Name:

CHEMISTRY 362 Descriptive Inorganic Chemistry M. Y. Darensbourg Examination III April 19, 2017 Name: An Aggie does not lie, cheat or steal or tolerate (and BTHO) those who do. Signed: Point Group Assignment