Exam2_v4_with_answers-21

Exam2_v4_with_answers-21 - EXAM 2 CHEMISTRY 224 March 5,...

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EXAM 2 CHEMISTRY 224 March 5, 2008 1. Read the following instructions carefully 2. Write your name and Purdue ID number on the answer sheet 3. Write your Graduate Instructor’s name on the line for “Instructor” on the answer sheet 4. Use a #2 pencil to code all information on the answer sheet. 5. Code your name and Purdue ID number on the answer sheet 6. Code 0224 as the “Section number” on the answer sheet. 7. Code the one best answer to each question on the answer sheet. THERE ARE 20 QUESTIONS. CHECK NOW TO BE SURE THAT YOUR EXAM INCLUDES ALL 20 QUESTIONS. EACH QUESTION IS WORTH TEN (10) POINTS (200 POINTS TOTAL) YOU ARE SUPPOSED TO KNOW (REMEMBER) A NUMBER OF BASIC EQUATIONS. ADDITIONAL FORMULAS AND REFERENCE TABLES ARE INCLUDED AT THE END OF THE EXAM MANY PROBLEMS CAN BE SOLVED ONLY USING THE REFERENCE MATERIALS – IN EACH CASE IT IS YOUR RESPONSIBILITY TO CONSULT THE REFERENCE SECTION AT THE END OF THE EXAM. IF IT SEEMS THAT YOU NEED A CERTAIN COMPLICATED FORMULA WHICH IS NOT GIVEN IN THE TEXT OF THE EXAM WE SUGGEST THAT YOU HAVE A CLOSER LOOK AT THE PROBLEM – PERHAPS, IT CAN BE SOLVED WITHOUT USING THE FORMULA!
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1. The expression for intensity of electric field in a propagating EM wave reads: E 0 sin( ) E Ek x t ω =− . Determine the intensity of the electric field at the point with coordinate at the moment in time 0 x = 0 t = . a. 0 E E = b. 0 /2 EE = c. E =∞ d. / E k = e. 0 E = Answer. e. sin(0)=0 2. What is the mechanism responsible for generation of X-rays? a. change in orientation of nuclear magnetic moment µ b. vibrations of the C-H bond c. transition of the electron from the outer shell to the inner shell d. dissociation of molecular hydrogen e. conspiracy by evil mutant squirrels Answer: c. 3. What is the pH of 0.1 M solution of NaOH in water at room temperature? a. 1.0 b. 7.0 c. 9.2 d. 13.0 e. 14.0 Answer. d. NaOH fully dissociates, with pOH=-log(0.1). To determine pH recall that pH+pOH=14. 4. A hypothetic buffer solution is prepared by mixing a weak acid HA ( , ), and its salt, NaA ( 4 1.80 10 M a K =⋅ 0.0954 M HA c = 0.1797 M NaA c = ). What is the pH of this buffer? a. 2.93 b. 3.47 c. 4.02 d. 5.11 e. 6.34 Answer: c. Henderson-Hasselbalch equation.
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5. Consider a list of acids: 1-Butanoic acid (CH 3 CH 2 CH 2 COOH), hypochlorous acid (HOCl), carbonic acid (H 2 CO 3 ), and bicarbonate (HCO 3 ¯). Order this list according to acid’s ability to donate a proton (begin with an acid least likely to donate a proton). a. CH 3 CH 2 CH 2 COOH, HOCl, H 2 CO 3 , HCO 3 ¯ b. HCO 3 ¯, HOCl, H 2 CO 3 , CH 3 CH 2 CH 2 COOH c. CH 3 CH 2 CH 2 COOH, H 2 CO 3 , HOCl, HCO 3 ¯ d. CH 3 CH 2 CH 2 COOH, HCO 3 ¯, HOCl, H 2 CO 3 , e. HOCl, H 2 CO 3 , HCO 3 ¯, CH 3 CH 2 CH 2 COOH Answer: b. Ordered according to Appendix 3; for H 2 CO 3 and HCO 3 ¯ we have to consider K a1 and K a2 , respectively, as a measure of their ability to donate a proton.
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Exam2_v4_with_answers-21 - EXAM 2 CHEMISTRY 224 March 5,...

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