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Exam_3_2008_B_key

# Exam_3_2008_B_key - EAS 1600 INTRODUCTION TO ENVIRONMENTAL...

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EAS 1600 - INTRODUCTION TO ENVIRONMENTAL SCIENCES Fall, 2008 Exam 3 - 11/24//08 < 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 and I agree to abide by the grading policies of this class. Signature: ____________________________________________________________ Print Name: ___________________________________________________________ Lab Section: ___________________ B 1

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1. An aqueous solutions has a pH of 11.5. What is the H + concentration in the solution? (5 pts) pH = -log[H + ] 11.5 = -log[H + ] [H + ] = 10 -11.5 = 3 x 10 -12 2. a. A solution contains carbonic acid (H 2 CO 3 ) and bicarbonate (HCO 3 - ). The carbonic acid has a concentration of 0.1 mole/l and bicarbonate is 10 times larger. What is the pH of the solution? (10 pts) H 2 CO 3 H + HCO 3 - 0.1 0 1 -x +x +x 0.1 - x x 1 + x 7 3 2 3 10 3 . 4 ] ][ [ + = x CO H HCO H (this could be neglected-very small) 7 10 3 . 4 1 . 0 ) 1 )( ( = + x x x x 8 10 3 . 4 = x x 37 . 7 ) 10 3 . 4 log( 8 = = pH x pH b. Is the solution above buffered? Why? (5 pts) yes, it contains a weak acid and its conjugate base i.e. carbonic acid and bicarbonate 2