Chemistry 100 Final Exam April 21, 2012

Transcription

1 Chemistry 100 Final Exam April 21, 2012 G. Orlova, G. Marangoni, M. Aquino Name: ID: This exam has a three-hour (3 hour) time limit. Read over the entire exam before beginning. Do those questions that you find easiest in the beginning. Proceed through the exam from the easier questions to the harder ones. Ration your time according to the value of each question. There should be 12 different questions. A periodic table and a list of relevant equations are provided. If this exam does not contain 12 questions (14 pages), notify the instructor immediately. Answer all questions on this exam paper. Please use only the back of the exam paper for rough calculations. Read all questions carefully!! Please write legibly!! Question Full Marks Marks Earned Question Full Marks Marks Earned Error! Referen ce source not found

2 Chemistry 100 Final Exam Total Total Have you put your name and ID at the top of this page? 1. Answer 5 out of the following 8 questions (a-f). [Each question is valued at 4 marks for a total of 20 marks]. a) What do we mean by a weak acid? What is the correlation between the strength of a weak acid and its conjugate base? b) Explain the trends of effective nuclear charge, Z eff, across and down the periodic table. c) State the Pauli exclusion principle. How is the Pauli exclusion principle a key to understanding the periodic table? d) Write equations depicting the 1 st, 2 nd, and 3 rd ionization energy of magnesium. How would the 3 rd ionization energy compare to the other two?

3 Chemistry 100 Final Exam e) What do we mean by the primary structure and the secondary structure of a protein?? f) Do catalysts affect the overall enthalpy change for a reaction, the activation energy, or both? Explain. g) Define a condensation reaction. What kind of structures do we obtain from continued condensation of amino acids? h) An unknown solution contains one of the following substances NaCl, NH 4 Br, and NaF. The ph of solution of the salt is measured at Identify the salt.

4 Chemistry 100 Final Exam Two possible skeletal structures for chlorous acid (HClO 2 ) are shown below. [8 marks] O H O Cl O H Cl O A B a) Convert each structure above to a Lewis structure by adding lone-pairs and double bonds as necessary. (2 marks) b) Which structure (A or B) is the more likely? Give a valid reason for your choice. I think structure is more likely because??? (2 marks) c) Compute the formal charge for each atom and enter the values here (4 marks) Structure A H: Cl: O(left): O (right): Structure B H: Cl : O(top): O (right):

5 Chemistry 100 Final Exam For the molecules below, give the geometry of the electron domains, the molecular shapes and the hybridizations at each non-hydrogen atom (please note that you should draw the Lewis structures!). [8 marks] a) N 2 H 4 b) HNCO (the atoms are bonded as shown).

6 Chemistry 100 Final Exam The following data were collected for the rate of disappearance of NO in the reaction [8 marks]: 2 NO (g) + O 2 (g) 2 NO 2 (g) Experiment # [NO] (M) [O 2 ] (M) Initial Rate (M/s) x x x 10-1 a) What is the rate law for this reaction? (2 marks) b) What are the units of the rate constant? (1 marks) c) What is the average value of the rate constant calculated from the three data sets? (3 marks) d) What is the rate of disappearance of NO when [NO] = M and [O 2 ] = M? (2 marks)

7 Chemistry 100 Final Exam A buffer solution contains 0.14 mol of butanoic acid (HC 4 H 7 O 2 ) and 0.11 mol of sodium butanoate (NaC 4 H 7 O 2 ) in 2.50 L. (K a for HC 4 H 7 O 2 = 1.5 x 10-5 ). [8 marks] a) What is the ph of this buffer? (4 marks) b) What is the ph of the buffer after the addition of mol NaOH? (assume that the total volume does not change) (4 marks)

8 Chemistry 100 Final Exam [6 marks] a) The quantum numbers listed below are for four different electrons in the same atom. Arrange them in order of increasing energy (4 marks). i) n = 4; l = 0; m l = 0; m s = +1/2 ii) n = 3; l = 1; m l = 0; m s = +1/2 iii) n = 3; l = 2; m l = 2; m s = +1/2 iv) n = 4; l = 1; m l = -1; m s = +1/2. b) What is the maximum number of electrons in an atom that can have the following quantum numbers (2 marks): i) n =5, l = 3 ii) n = 3, l = 2, m l = 1

9 Chemistry 100 Final Exam The following is the structure of the artificial sweetener aspartame. Circle and name the functional groups in aspartame and indicate with a star any chiral carbon centers. [6 marks] O O O HOCCH 2 CHCNHCHCOCH 3 NH 2 CH 2

10 Chemistry 100 Final Exam Write the structures for the following compounds. [10 marks] a) 5-methyl-3-bromo-trans-2-hexene b) 1,3-dichlorocyclohexane c) Para-dichlorobenzene d) Draw and name the product of the following reactions i) CH 2 = CH 2 + HCl (g) ii) CH 3 CH 2 COOH (l) + (CH 3 ) 2 CHOH

11 Chemistry 100 Final Exam Under aerobic (O 2 present) conditions, the oxidation of glucose in body tissue produces CO 2 and H 2 O with a Gibbs energy change of 2880 kj, whereas anaerobic (no O 2 present) oxidation produces C 2 H 5 OH and CO 2. Using the following data, compare the Gibbs energy change for anaerobic versus aerobic oxidation of glucose and calculate the equilibrium constant for the anaerobic oxidation process. [8 marks] Substance H f (kj/mole) S (J/K mole) C 6 H 12 O 6 (s) CO 2 (g) C 2 H 5 OH (l) H 2 O (l) O 2 (g)

12 Chemistry 100 Final Exam Draw the peptides formed by the reaction of: [6 marks] a) Glycine (NH 2 CH 2 COOH) and cysteine (NH 2 CH(CH 2 SH)COOH). (4 marks) b) How many different tripeptides are formed by serine and phenylalanine (note no structures are necessary, use the abbreviations ser and phe for the amino acids). (2 marks)

13 Chemistry 100 Final Exam DO EITHER A OR B [6 marks] a) What are the main types of intermolecular forces in the following molecules. i) CH 3 OH; ii) CH 2 Br 2 ; iii) NaCl/NH 2 OH. b) When a 3.88 g sample of solid ammonium nitrate (NH 4 NO 3 ) dissolves in 60.0 g of water in a coffee-cup calorimeter, the temperature drops from 23 C to 18.4 C. Calculate H (in kj/mol of NH 4 NO 3 ) for the solution process. (Assume the specific heat (C) of the solution is the same as that of pure water, J/g-K).

14 Chemistry 100 Final Exam The first order rate constant for the decomposition of dinitrogen pentoxide (N 2 O 5 ) is 6.82 x 10-3 s -1 at 70 C. Suppose we start with moles of N 2 O 5 (g) in a volume of 2.0 L. [6marks]. 2 N 2 O 5 (g) 4 NO 2 (g) + O 2 (g) a) How many moles of N 2 O 5 (g) will remain after 5 minutes? (3 marks) b) How many minutes will it take for the quantity of N 2 O 5 (g) to drop to moles? (3 marks)