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StudentLecture_15

# StudentLecture_15 - CHM 11600 Lab Acid-Base Equilibria(Part...

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CHM 11600 3/3/2010 Lab: Acid-Base Equilibria (Part I) Monday Lecture: Read Section 6.1 – 6.4 HW this week only due Saturday (OWL down last Sunday) Exam 2: Tues. 3/9/10 6:30 PM Hall of Music Equilibrium (Ch 16), Acid-Base Chemistry (Ch 17 and sections 3.7 and 4.6), and lab manual chapters 5, 6 and 7 Review session: Friday 3/5/2010 during the lecture time.

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Buffers & Titration Curves The math equations you will need: Equilibrium equation (for K a , K b , & K w ) For pH, pOH, & pK: pX = -log X X = 10 -pX X = [H 3 O + ], [OH - ], or K PK w = pH + pOH Henderson-Hasselbalch equation: This equation relates pH, pK a , and the concentrations of a mixture of an acid and its conjugate base (a buffer). But remember blind use of equations without understanding the chemistry behind them can lead to mistakes, as we saw in the last lecture.
Henderson-Hasselbalch equation Calculates pH K a = [H 3 O + ][A - ] [HA] log K a = log _______ + log (________________) ______ [H 3 O + ] = ________ K a + log ([A - ]/[HA]) log (K a ) = log = log [H 3 O + ] x [H 3 O + ][A - ] [HA] [A - ] [HA] pH = pK a + log [A - ] [HA]

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Buffers Buffer: __________ of a weak acid and its conjugate base or of a weak base and its conjugate acid that __________________________ (constant [H 3 O + ]) upon dilution or addition of small amounts of acid or base. Acidic buffer: Weak acid / _______ conjugate base CH 3 CO 2 H / NaCH 3 CO 2 Basic buffer: weak base / ________ conjugate acid NH 3 / NH 4 +

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Buffers The pH of our blood is about 7.4 . If it rises above about _______ or falls below ______ irreversible brain damage and death can occur. CO 2 + H 2 O H + + HCO 3 Buffer: H 2 CO 3 /HCO 3 - Where have you used a buffer? Demo: CO 2 + water with indicator and CO 2 + buffer with indicator
Buffers Test Tube Number 1 2 3 4 5 6 7 8 9 Volume of CH 3 CO 2 H 24.00 mL 21.00 mL 18.00 mL 15.00 mL 12.00 mL 9.00 mL 6.00 mL 3.00 mL 1.00 mL Volume of NaCH 3

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StudentLecture_15 - CHM 11600 Lab Acid-Base Equilibria(Part...

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