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Exam_3_20061_key

# Exam_3_20061_key - EAS 1600 INTRODUCTION TO ENVIRONMENTAL...

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EAS 1600 - INTRODUCTION TO ENVIRONMENTAL SCIENCES Fall, 2006 Exam 3 - 12/1/06 < Answer all Questions < Show all your work < Place your name on each page < This is a closed-book exam, notes are not allowed; all are expected to comply with the Georgia Tech Honor Code. Please also note that cell phone use or contact with any other person is not allowed. I am aware and in compliance with the Georgia Tech Honor Code Signature: ____________________________________________________________ Print Name: ___________________________________________________________ Lab Section: ___________________ 1

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1. Consider a solution that initially contains carbonic acid (H 2 CO 3) at 2 x 10 -4 mole/l and bicarbonate (HCO 3 - ) at 2 x 10 -3 mole/l. (15 pts). a. What is the pH of the solution? (10 pts) H 2 CO 3 H + HCO 3 - 2x10 -4 0 2x10 -3 -x +x +x 2x10 -4 - x x 2x10 -3 + x 7 3 2 3 10 3 . 4 ] ][ [ + = x CO H HCO H (this could be neglected-very small) 7 4 3 10 3 . 4 10 2 ) 10 2 )( ( = + x x x x x x ) 10 2 ( 10 3 . 4 10 2 4 7 3 x x x x x = 8 10 2 . 4 = x x 37 . 7 ) 10 2 . 4 log( 8 = = pH x pH 4 points for chart set-up 3 pts for correctly using Ka set-up 3 pts for correct answer b. Is this solution buffered against a pH change by the addition of a strong acid? Why or Why Not? (5 pts) Yes – this solution is buffered. If a strong acid is added the conjugate base (HCO 3 -) is protonated and pH is restored. An example of LeChatelier’s principle. 2 pts for correct answer of ‘Yes’ and 3 pts for reason 2. An El Nino event can be described as a disruption of the Walker Circulation in the region of the equatorial Pacific Ocean. Draw a diagram of the Walker Circulation and be sure to indicate wind directions, areas of precipitation, and at least relative temperatures and pressures. (10 pts) 2