Chemistry 1A Dr. Stanton Fall 2014 Final

Transcription

1 PLEASE DRAW VALECE BOD PICTURES O THE BACK OF THIS PAGE! Chemistry 1A ame Dr. Stanton Fall 2014 Final This exam has 8 pages, none of them blank. Show all work. Closed book and notes. Turn your cell phone off. Helpful Information has moved to the top of page 2! If you write your answer anywhere other than below the question, tell me where to find it. 1. (20 points) Fill in the following table. Be sure to show any resonance structures. BE SURE to draw the valence bond pictures on the back of this page! Lewis Dot Structure Electron Pair Molecular Geometry & Valence Bond Picure Polar Yes or o? HSO (4 atoms in ClO 3 - (Cl in middle) CC (4 atoms in a row)

2 p. 2 Helpful Information ame G o = H o - T S o ΔH o f (C 6 H 6(l ) = 48.7 kj/mol K = o C av = 6.02 x A = εl C R = L atm/(mol K) K = o C atm = 760 torr 2. (15 points) Calculate the heat given off when 45.0g of benzene (C 6 H 6(l) ) is burnt. 3. (12 points) a) State the Second Law of Thermodynamics. b) State how many protons, neutrons, and electrons the following atoms or ions have: umber of protons umber of neutrons umber of electrons 108 Pd S c) Explain how two molecules are attracted to each other by London Forces. (A small sketch is helpful here.)

3 Pressure (Pa) p. 3 ame 4. (8 points) Based on the phase diagram for carbon: a) Should diamond exist at 1 atm (1 x 10 5 kpa) pressure and 25 o C? What is the equilibrium form of carbon under these conditions? Diamond Graphite Liquid b) What will happen to a piece of graphite exposed to huge pressures? 10 7 Vapor c) Circle the triple points and state the phases present at each triple point Temp (K) 5. (12 points) I have drawn a 1s orbital and 3d xy orbital for the same atom. For each location, state whether it is likely, unlikely, or impossible to find the electron there. Position A is on the x axis. Position 1s electron 3d xy electron y A B C A B D D C x

4 p. 4 ame 6. (6 points) Calculate G o for the following reaction. Is this reaction spontaneous at 25 o C? 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) 7. (10 points)at what temperatures will each of the following processes be spontaneous? a) ΔH = - 15 kj and ΔS = -51 J/K. b) ΔH = - 15 kj and ΔS = 51 J/K. 8. (11 points) Short Answer: a) Circle the atom with the larger radius: Te or I b) ame the strongest intermolecular force in pure liquids of each of the following three substances: H 3 ICl CCl 4

5 p. 5 ame 9. (20 points) Iron rusts according to the equation: 4 Fe (s) + 3 O 2 (g) 2 Fe 2 O 3 (s) g of iron filings are placed in a 1.05 L box containing (in addition to the iron) pure oxygen at 794 torr and a constant temperature of 25.0 o C. The iron is allowed to rust away. a) If this is the only reaction occurring in the box, and the reaction goes to completion, what is the limiting reagent? b) How many grams of Fe 2 O 3 will be produced?

6 p. 6 ame 10. (12 points) a) Write the ground state electron configuration for Sb: b) Write the ground state electron configuration for Cr 3+ : c) Write all of the possible values for each of the four quantum numbers for an electron in a 7p orbital. 11. (12 points) A nitric acid solution (volume ml) is neutralized by adding ml of M barium hydroxide solution. What is the molarity of the nitric acid solution?

7 12. (16 points) Write balanced equations for the following: p. 7 ame a) A solution of perchloric acid is added to a solution of sodium oxalate. (Write net ionic AD convention equations for this one, please. Oxalate ion: C 2 O 4 2- ) b) I - (aq) + ClO - (aq) I 3 - (aq) + Cl - (aq) (acid) c) 2 H 4 (aq) + Cu(OH) 2 (s) 2 (g) + Cu (s) (basic solution)

8 p. 8 ame Extra Credit #1: Phenolphthalein is bright pink in basic solution, but is colorless in acid solution. We can go from the pink form to the clear form by adding acid: + 2 H + phenolphthalein, basic form PIK phenolphthalein, acidic form CLEAR Since the acidic form is colorless, it does not absorb visible light. The basic form does absorb visible light (thus we see it as colored!) λ max = 555 nm, εl = 2.1 x 10 3 M -1. Solution X contains phenolthalein in its basic form. I measure the absorbance at 555nm to be I take ml of Solution X and add 1.00 ml of 5.00 x 10-3 M HCl. What will be the absorbance now? Extra Credit #2 In 1997, Karl Christe, a chemist at the Air Force Research Lab and USC, announced the discovery of + 5, with 5 nitrogen atoms in a row. (Chemical and Engineering ews, Jan. 25, 1999, p. 7.) a) Draw a Lewis Dot structure for this ion. b) My first attempt to draw a Lewis Dot structure for this ion gave a linear structure. Experimentally, the ion is found to have a V shape. Draw the best Lewis Dot structure consistent with this geometry. What will be the angle of the V? Explain why this is a better structure than the linear structure. 1+