sept_9_pdf_3_slides_per_page - Announcements Date of First...

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1 Announcements Date of First Mid-term: October 7th. Forum on Website for people who wish to change lab sections, to find a match. Corrected Lab Schedule posted. Please check Moodle website for information required for laboratories Ionization of Water H 2 0 + H 2 0 H 3 O + + OH - or H 2 0 H + + OH - Keq= [H + ][OH - ]/[H 2 0] Since Keq is 1.8 x 10 -16 M (at STP) and [H 2 0] is 55.5 M (1000gL -1 /18gmol -1 ) Then, [H + ][OH - ] = 1 x 10 -14 M 2 and [H + ] = [OH - ] = 1 x 10 -7 M Definition of pH [H+] = [OH-] = 1 x 10 -7 M simplify: pH , pH = - log [H + ] e.g. (i) [H + ] = 1 x 10 -4 M ; pH = 4 (ii) pH = 5; then [H + ] is 1 x 10 -5 (iii) pH = 6.6, [H + ] is 1 x 10 -6.6 or more correctly 2.5 x 10 -7 M
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2 pH, Acid and Base H + + Base = Conjugate acid of Base + Acid = H + + Conjugate base of Acid - For example: NH 3 + H 2 O = NH 4 + + OH - CH 3 COOH + OH - = H 3 0 + + CH 3 COO - Acid strength: measured by dissociation constant Ka and pKa HA (aq) H + + A - Ka = [H + ][A - ]/[HA] pKa = -log [Ka] Strong acids: extremely high Ka and low pKa ( infinity for HCl - why??) Weak acids have more easily measurable Ka
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3 pH of 0.1 M acetic acid? (Ka = 1.8 x 10 -5 ) Ka = [CH 3 COO - ][H + ]/[CH 3 COOH] Ka= (x) (x)/0.1 - (x) If Ka is LESS than 10 -2 ... then x < 0.1 Ka = (x) 2 /0.1 Therefore: x 2 = 1.8 x 10 -6 x = 1.34 x 10
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This note was uploaded on 11/12/2008 for the course BIOLOGY BIOCHEM 25 taught by Professor Mrs.lawery during the Spring '08 term at Indian Institute of Technology, Chennai.

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sept_9_pdf_3_slides_per_page - Announcements Date of First...

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