Third Exam CHEM 1A Spring 2017 Name: Instructions: Last First Read every problem carefully so that you can understand the question and the information given. You have to gauge your time. If a problem is too challenging, move on. Keep track of significant figures and use scientific notation (if requested or needed). Points will be deducted if you give an impossible answer(s), so, check your answers. If you need me to clarify what I am asking, let me know. DO NOT ask me if your answer is ok or if you are solving a problem correctly, unless you are ready to turn in the exam. Write your final answer in the box provided for every problem, and show your work clearly for partial/full credit. Useful Information Equations: ΔTb = Kbm ΔTf = Kfm 1
1. (8) What mass of water is needed to dissolve 292.50 g of NaCl to produce a 0.2503 m aqueous solution? m(kg) = 2. (12) By looking at the diagram below, answer the following: a. Give and describe the state at 850 C and 1.75 atm? b. Give the conditions at the triple point (T and P)? c. Give the conditions at the critical point (T and P)? d. Identify (give the name) of the following processes and state if the process is exo or endothermic. Briefly explain. At 300 C, increase P from 0.25 to 1.25 atm: At 0.25 atm, decrease T from 100 C to 50 C: e. If this substance was at a pressure of 1.75 atm, at what temperature would it boil? 3. (8) Give the structures of the following compound. Include lone pairs and multiple bonds. a. CH2CHCOOCONHCH2CH2CCH Circle all sp 2 atoms. 28 2
4. (12) a. Define the term lattice energy. To which equation is it related? (Show the expression!) b. Which factors increase the lattice energy? c. KBr and CsCl lattice energies are nearly equal. What can you conclude from this observation? d. Arrange the following substances according to their expected lattice energies, from lowest to highest: ScN, KBr, MgO, NaF. Briefly explain. 5. (6) Which of the following in each pair is likely to be more soluble in C6H14 (hexane)? Explain briefly. a. CCl4 or CaCl2 b. C6H6 (benzene) or CH2(OH)CH(OH)CH2(OH) (glycerol) c. CH3CH2CH2CH2CH2CH2CH2COOH (octanoic acid) or CH3COOH (acetic acid) 6. (10) a. Which of these two solutions will have a higher B.P.: 0.10 m NaCl or 0.10 m C6H12O6? Explain. b. Calculate the B.P. of the NaCl solution (Kb for water is 0.51 C/m). c. The experimental B.P. of the NaCl solution is lower than the calculated assuming total dissociation. Why? d. Which solution will have the higher M.P.? 28 3
7. (14) a. Draw the Lewis structures and orbital overlap of N2 and N2H4 (Hydrazine). b. Give the hybridization of the N atoms in each molecule and the box diagram with the ground state and hybridized configurations. 8. (8) Draw the Lewis structure for the thiocyanate ion: SCN. If more than one structure can be drawn, circle the one that you think is the dominant structure and explain your choice clearly. 9. (8) a. Draw the Lewis Structure for the phosphate ion. b. Hybridization on P? 30 4
10. (8) An aqueous solution of sulfuric acid (H2SO4) has a concentration of 3.39 m. The density of this solution is 1.18 g/ml. Calculate the molarity of sulfuric acid in this solution. M = 11. (10) Between KrF 2 and SeF 2, which one would be more soluble in CH 3 OH? Analyze the molecules and explain your reasoning thoroughly. 12. (6) a. Which of the following bonds is more polar: S Cl, S Br, Se Cl, or Se Br? Explain your reasoning thoroughly. b. The substance PbCl4 is a yellow, oily liquid at room temperature that decomposes at 50 C. Why is this unexpected? Clearly explain. 24 5
13. (18) a. Draw the heating and cooling curve for benzene. Identify the M.P. and B.P. b. What temperature will a sample of 12.00 g of benzene reach if the initial temperature is 10.0 and you provide it with 2.10 kj of energy? T f = c. Why is the plateau of vaporization always larger than the one for fusion? 14. (5) Look at the molecules and their normal B.P. Explain this situation thoroughly. MM: 142.28 g/mol MM: 74.12 g/mol 23 6
15. (8) Clearly define each of the following properties and explain how intermolecular interactions affect them: a. Vapor pressure: b. Capillarity: 16. (4) Which of the following compounds is more volatile? Explain your reasoning thoroughly. O H 3 C C CH 3 Acetone MM: 58.08 g/mol CH 3 CH 2 CH 2 OH Propanol MM: 60.1 g/mol 17. (5) The three molecules below have the formula C5H12 (they are known as structural isomers). pentane isopentane neopentane a. Which one has the lowest boiling point and why? b. Which one would have the highest viscosity and why? 17 7