CHEM 1A: Exam 2 Practice Problems:

Transcription

1 CHEM 1A: Exam 2 Practice Problems: These practice problems are not a comprehensive list of all questions to be asked on the exam. Refer to the suggested textbook HW, other practice problems on the review page, iclicker questions, quiz 2 questions & challenge problem sets for a more comprehensive review. 1. Which ion below would require the MOST energy to remove an electron? Which ion would require the LEAST amount of energy to remove an electron? Explain your reasoning. A. K + B. Ca 2+ C. Ca 3+ D. Se - E. Se 2-2. Rank these bonds from LONGEST to SHORTEST: C O, C P, Si P, C N, C=O (double bond) 3. Rank these ions from LARGEST to SMALLEST: I -, Li +, K +, Se 2-, Te 2-, Te 3-4. The 3 curves below represent the C C single bond, C=C double bond, and the C C triple bond. Label each curve based on the corresponding bond lengths and bond strengths. 5. Which substance below would be the MOST polar? Explain your reasoning. A. F 2 B. Br 2 C. BrCl D. CH 3F E. CF 4 6. Which substance from the question above would most likely be a gas?

2 7. Which substance below would have the highest vapor pressure and highest flammability? Explain your reasoning. 8. Which substance below would be the LEAST water soluble and best for use in Rain-X? Explain your reasoning.

3 9. For each atom below, label the HYBRIDIZATION & bond angles. How many pi bonds are present in this molecule? 10. Circle the Lewis dot structures below that are INCORRECT. 11. Draw the Lewis dot structure for the molecule: CH 3-SO-CH 3. Hint: Sulfur is the central atom with a C S C sequence. 12. Draw the lowest energy the Lewis dot structure for selenite, SeO Include all resonance structures & calculate the bond order of the Se O bonds. Based on the Lewis dot structure above, predict 1) the electron geometry, 2) the molecular geometry, 3) the bond angles.

4 13. Sulfur hexafluoride has a boiling point of -63 oc, but sulfur tetrafluoride has a boiling point of -38 oc. Explain this difference using Lewis dot structures, intermolecular forces, and VSEPR theory. 14. Consider the Lewis dot structure for the arsenate anion shown below. a. First assign formal charges to all atoms within the structure. Use this information to predict the overall charge on arsenate. b. Based on part a, try to minimize the formal charge in the arsenate ion to reach the LOWEST energy Lewis dot structure. DRAW ALL RESONANCE STRCUTURES. c. Considering the resonance structures you wrote above, what is the bond order of an Arsenic Oxygen bond in the arsenate anion? 15. Circle the preferable molecular geometry for SF4O based on VSEPR theory. Explain your reasoning.

5 16. Consider the three Lewis dot structures for triiodide shown below. PROPOSED STRUCTURE: i. ii. iii. a. Assign formal charges to each atom in each structure above. What is the overall charge of triiodide? b. Each structure above would predict a DIFFERENT molecular geometry for the central iodine atom. Use VSEPR theory to predict the I I I bond angle that would be expected BASED ON EACH INDIVIDUAL STRCUTURE. Hint: First count bonding and nonbonding regions on the central atom to determine the electron geometry. PROPOSED STRUCTURE Predicted I I I Bond Angle ( o ) i. ii. iii. c. The triiodide anion, I 3-, has been found experimentally to have a linear molecular geometry. Which proposed Lewis dot structure would be consistent with a linear geometry for triiodide? 17. A sample of an unknown hydrocarbon (C XH Y) is burned completely in oxygen to give g of carbon dioxide and g of water. What is the empirical formula of the compound? 18. Write the balanced chemical equation for mixing aqueous ammonium sulfate with aqueous barium chloride. Be sure to write the phases of the products based on general solubility rules.

6 19. Using the observed results from the reactions below, predict the products for the reaction between aqueous silver perchlorate and aqueous calcium bromide. Complete the BALANCED molecular equation in the box provided. BE SURE TO LABEL THE PHASES OF THE PRODUCTS. AgClO4(aq) + NaBr(aq) yields precipitate CaBr2(aq) + KClO4(aq) no reaction AgClO4(aq) + CaBr2(aq) 20. What is the limiting reactant if 5 moles of calcium phosphide is mixed with 20. moles of water and allowed to react according to the equation below? What is the theoretical yield of PH3? Ca3P2 + 6 H2O 2 PH3 + 3 Ca(OH)2 21. What is the limiting reactant if 10.0 grams of tetraphosphorus decoxide is mixed with 20.0 g of water and allowed to react according to the equation below? What is the theoretical yield? P4O H2O 4 H3PO4 22. If 50.0 grams of tetraphosphorus decoxide is mixed with 120. grams of nitric acid to produce only 2.50 grams of dinitrogen pentoxide according to the reaction below, calculate the percent yield of N2O5. P4O HNO3 4 H3PO4 + 6 N2O5