ACEE219_Week8_new

ACEE219_Week8_new - ACEE ACEE 219 Environmental Chemistry...

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ACEE 219 Environmental Chemistry Week 8 April 20, 2010 novation Hall 127 ACEE 219 Spring 2010 HDP 1 Innovation Hall 127
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pen System Open System ttp://www advancedaquarist com/2009/2/chemistry album/image003 jpg ACEE 219 Spring 2010 HDP 2 http://www.advancedaquarist.com/2009/2/chemistry_album/image003.jpg
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arbonate System Carbonate System •CO 2(g) , CO 2(aq) , H 2 CO 3 , HCO 3 - , CO 3 2- , carbonate containing solids (e.g., CaCO 3 ) • Major acid-conjugate base systems in natural waters CO 2(g) CO 2(aq) ; K = K H = 10 -1.5 CO 2(aq) + H 2 O H 2 CO 3 ; K m = 10 -2.8 H 2 CO 3 H + + HCO 3 - ; K 1 ’ = 10 -3.5 H 2 CO 3 * H + + HCO 3 - ; K a,1 = 10 -6.3 HCO 3 - H + + CO 3 2- ; K a,2 = 10 -10.3 [H 2 CO 3 *] = [H 2 CO 3 ] + [CO 2 (aq)] [CO 2 (aq)] ACEE 219 Spring 2010 HDP 3
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arbonic Acid Carbonic Acid Closed system H C T,CO3 =10 -5 M 0 0 2 4 6 8 10 12 14 pH 2 , pC O 4 6 ntration [H 2 CO 3 *] pC = 5 8 10 og Conce [HCO 3 - ] 12 lo [H + ] [OH - ] [CO 3 2- ] ACEE 219 Spring 2010 HDP 4 14 pK a1 = 6.3 pK a2 = 10.3
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arbonic Acid Carbonic Acid Open system (P CO2 = 10 -3.5 atm) -log[CO 3 2- ] = - 2pH + 21.6 0 02468 1 0 1 2 1 4 pH -log[HCO 3 - ] = - pH + 11.3 2 4 n, pC O * pC T,CO3 6 entratio n [H 2 CO 3 ] 8 10 og Conc e [HCO 3 - ] 12 lo [H + ] [OH - ] [CO 3 2- ] 14 ACEE 219 Spring 2010 HDP 5 pK a1 = 6.3 pK a2 = 10.3
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arbonic Acid Carbonic Acid Open system (P CO2 = 10 -3.5 atm) 0 02468 1 0 1 2 1 4 pH 2 4 n, pC O * pC T,CO3 6 entratio n [H 2 CO 3 ] 8 10 og Conc e [HCO 3 - ] 12 lo [H + ] [OH - ] [CO 3 2- ] 14 ACEE 219 Spring 2010 HDP 6 5.7 6.3 6.6
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xample 4 32 Example 4.32 Calculate pH for 10 -4 M HCl addition to 10 -3 M C CO3 solution (pH=7.0) • Assuming added HCl reacts with the most abundant base (i.e., HCO 3 - ) the solution. p T,CO3 (p ) in the solution. HCO 3 - + H + H 2 CO 3 * • Final [HCO - ] = initial [HCO - ] – [H + ] added We neglect the reactions with OH - and CO 3 2- due to their low concentrations 3 3 = 8.3 x 10 -4 –10 -4 = 7.3 x 10 -4 M • Final [H 2 CO 3 *] = initial [H 2 CO 3 *] + [H + ] added = 1.7 x 10 -4 + 10 -4 = 2.7 x 10 -4 M • From K a,1 [H + ] = 10 -6.3 x 2.7 x 10 -4 / 7.3 x 10 -4 =10 -6.73 pH = 6.73 ACEE 219 Spring 2010 HDP 7 Snoeyink & Jenkins Example 4-32
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xample 4 32 Example 4.32 Calculate pH for 3 x 10 -4 M NaOH addition to 10 -3 M C CO3 solution (pH=7.0) p T,CO3 (p ) • Assuming added NaOH reacts firstly with the strongest acid (i.e., H
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ACEE219_Week8_new - ACEE ACEE 219 Environmental Chemistry...

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