L18_AcidBase5_115b08

L18_AcidBase5_115b08 - L18: pH of Salts Made of Acids and...

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? Weak Weak <7 Weak Strong >7 Strong Weak 7 Strong Strong Salt’s pH Base Acid L18: pH of Salts Made of Acids and Bases All equilibria are maintained simultaneously
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What is the pH of a 0.1 M solution of NH 4 Cl? The K b of NH 3 = 1.8*10 -5 . Weak base NH 3 strong conjugate acid NH 4 + : NH 4 + ( aq ) + H 2 O( l ) NH 3 ( aq ) + H + ( aq ) – solution will be acidic (pH<7) K a = [NH 3 ] [H + ][OH - ] = K w [NH 4 + ][ O H - ] K b Equilibrium: NH 4 + (aq) + H 2 O(l) NH 3 (aq) + H + (aq) Initial []: 0.1 0 0 Change: - x + x + x Equilibrium: 0.1- xx x K a = K w / K b = x 2 /0.1 = 1.0*10- 14 /1.8*10 -5 = 5.6*10 -10 x=7.5*10 -6 M=[H + ] pH = 5.13 (acidic) Notes: 1. x – small relative to 0.1M and large relative to 10 -7 2. In the solution all reactions take place at the same time.
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Buffers Ready-to-use buffers for chemistry and biology
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Acid-base simultaneous equilibria: ] [ ] ][ [ HA A H K a + = ) ( ) ( ) ( aq A aq H aq HA + + ) ( ) ( ) ( aq OH aq B aq BOH + + ] [ ] ][ [ BOH OH B K b + = ) ( ) ( ) ( 2 aq OH aq H aq O H + + 14 10 01 . 1 ] ][ [ + = = OH H K w ] log[ + = H pH ] log[ = OH pOH pH + pOH = -log[ K w ]=14 @ 25 o C K w = K a K b
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Suppose 0.1 M of acetic acid is added to the 0.1 M solution of NaAc (pH=8.89). Determine the pH of the solution.
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L18_AcidBase5_115b08 - L18: pH of Salts Made of Acids and...

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