HourEx4 Practice Chapt 8 & 9 Kotz

Transcription

1 HourEx4 Practice Chapt 8 & 9 Kotz Multiple Choice 5 pts apiece Identify the letter of the choice that best completes the statement or answers the question. PUT YOUR ANSWER ON THE BUBBLE SHEET PROVIDED.You are envcouraged to show your work on these pages for your own benefit. However, marks in this section of the exam booklet will not be graded. (If the answer on these pages is correct, and the incorrect circle is filled in on the bubble sheet, the question will be graded incorrect. Therefore, please double-check your bubble sheet before handing it in!) Do not leave blanks! 1. A selenium atom has valence electrons. a. 2 b. 6 c. 16 d. 28 e How many lone pairs of electrons are assigned to the carbon atom in carbon monoxide? a. 0 b. 1 c. 2 d. 3 e One resonance structure for OCN ion is drawn below. What is the formal charge on each atom? a. O atom = 0, C atom = 0, and N atom = 0 b. O atom = 0, C atom = 0, and N atom = 1 c. O atom = 1, C atom = 0, and N atom = 0 d. O atom = 1, C atom = 1, and N atom = +1 e. O atom = +1, C atom = 0, and N atom = 2 4. Which of the following are resonance structures for formate ion, HCO 2? a. 1 and 2 b. 2 and 3 c. 3 and 4 d. 1, 3, and 4 e. 2, 3, and 4

2 5. The central atom in the triiodide ion, I 3, is surrounded by a. two single bonds and no lone pairs of electrons. b. two single bonds and two lone pairs of electrons. c. two single bonds and three lone pairs of electrons. d. one single bond, one double bond, and one lone pair of electrons. e. two double bonds and one lone pair of electrons. 6. Which of the following molecules has the smallest bond angle between any two hydrogen atoms? a. CH 4 b. H 2 O c. BH 3 d. BeH 2 e. SiH 4 7. Use VSEPR theory to predict the molecular geometry of BrF 5. a. tetrahedral b. see-saw c. trigonal-bipyramidal d. square-pyramidal e. octahedral 8. Which of the following compounds has polar covalent bonds: NaBr, Br 2, HBr, and CBr 4? a. NaBr only b. Br 2 only c. HBr only d. Br 2 and HBr e. HBr and CBr 4

3 9. How many sigma (σ) bonds and pi (π) bonds are in carbon monoxide? a. three σ, zero π b. two σ, one π c. two σ, two π d. one σ, two π e. zero σ, three π 10. Which of the underlined atoms (C 1, C 2, N, and O) are sp 2 hybridized? a. C 1 and C 2 b. C 1, N, and O c. N and O d. O and C 2 e. O only 11. Which of the following statements is/are CORRECT? 1. The overlap between an s orbital and a p orbital is called a pi-bond. 2. The overlap of two s orbitals in H 2 is called a sigma bond. 3. HF is formed from the overlap of a hydrogen 1s orbital with a fluorine 2s orbital. a. 1 only b. 2 only c. 3 only d. 2 and 3 e. 1, 2, and 3

4 12. Nitric acid, HNO 3, dissociates in water to form nitrate ions and hydronium ions. What change in hybridization of the nitrogen atom occurs in this dissociation? a. sp 2 to sp 3 b. sp 2 to sp c. sp 3 to sp d. sp to sp 3 e. no change 13. A molecular orbital that decreases the electron density between two nuclei is said to be. a. hybridized b. bonding c. antibonding d. pi-bonding e. nonpolar Diagram 9-1 The molecular orbital diagram below may be used for the following problem(s). For oxygen and fluorine, the σ 2p orbital should be lower in energy than the π 2p. However, the diagram will still yield correct bond order and magnetic behavior for these molecules. Energy σ* 2p π* 2p σ 2p π 2p σ* 2s σ 2s σ* 1s σ 1s 14. Refer to Diagram 9-1. According to molecular orbital theory, which of the following species is least likely to exist? a. Be 2 b. F 2 2+ c. C 2 2 d. Li 2 e. B 2 2

5 15. Refer to Diagram 9-1. According to molecular orbital theory, which of the following species has the highest bond order? a. F 2 b. F 2 2+ c. C 2 2 d. Li 2 e. B In the NO 2 ion, each atom can be viewed as sp 2 hybridized. Thus, each atom has one remaining unhybridized p orbital. How many π 2p molecular orbitals (including both bonding and antibonding orbitals) are formed using the unhybridized p orbitals? a. 1 b. 3 c. 4 d. 6 e. 12

6 Part II. 10 points per question For full credit, you must show all conversion factors and the final answer with complete units, use the correct number of significant figures, and round off correctly. WRITE CLEARLY: if the grader cannot read your writing, no credit will be assigned. Question 17. When heated, azomethane decomposes into nitrogen gas and ethane gas CH 3 N=NCH 3 (g) N 2 (g) + C 2 H 6 (g) Calculate H for this reaction using the data shown below: Bond Bond Enthalpy (kj/mol) Bond Bond Enthalpy (kj/mol) C H 413 N N 163 C N 305 N=N 418 C C 346 N N 945

7 Question 18 (a) Draw a correct Lewis formula for the oxalate dianion (C 2 O 4 2- ). In this ion, the C atoms are bonded to each other, and each C has two O s. There are no O-O bonds. Include resonance forms if necessary. (b). This ion contains one or more multi-atom π-bonds. Illustrate one of these using your best artistic skills. Represent the opposite signs of the wavefunction using + and/or - symbols.