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StudentLecture_13

# StudentLecture_13 - CHM 11600 Wed Announcements Exam II two...

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CHM 11600 Wed. 2/23/11 Announcements Exam II two weeks away: Monday March 7, 6:30 pm Covers equilibrium (Ch. 16); organic acids & bases and the lectures on acids/bases from Ch. 17, and Labs Chapters 7 & 8. Ch. 18 (Buffers/titrations) will not be on the exam. Review session on Friday, March 4 Some posted exams have questions struck out. Lab this week: LeChatelier’s Principle, Chapter 6 HW due as usual

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NH 3 + H 2 O NH 4 + + OH - [ ] i 0.010 - 0 ~1 x 10 -7 change - [ ] eq 0.010 - + 1 x 10 -7 = ___________________ = 4.2 x 10 -4 M, [NH 3 ] = 0.010 M Calculate the pH of 0.010 M NH 3 . K b = 1.8 x 10 -5 K b = 1.8 x 10 -5 = [NH 4 + ][OH - ] [NH 3 ] = 2 0.010 (4.2 x 10 -4 / 0.010) x 100 = 4.2%. OK to neglect pOH = - log[OH - ] = ____ . pH = _______________ = 10.63 For _________ : pH > 7
Base Acid + Acid Base + Conjugate Pair Conjugate Pair Reaction 1 HF H 2 O + F - H 3 O + + Reaction 2 HCOOH CN - + HCOO - HCN + The Conjugate Pairs in Some Acid-Base Reactions We can predict where equilibrium lies (K > 1, K < 1) in these acid-base reactions Stronger _____ + stronger _____ weaker _____ + weaker _____ The stronger base “wins” the tug of war for the proton.

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Strength of an acid is judged by degree of ______________ in H 2 O, ie ___________ or magnitude of __________ Generic HA( aq ) + H 2 O( l ) H 3 O + ( aq ) + A - ( aq ) HF( aq ) + H 2 O( l ) H 3 O + ( aq ) + F - ( aq ) Generic :B( aq ) + H 2 O( l ) BH + ( aq ) + OH - ( aq ) :NH 3 ( aq ) + H 2 O( l ) NH 4 + ( aq ) + OH - ( aq ) K b = BH + [ ] OH - [ ] B [ ] Strength of a base is judged by _______ generated in H 2 O, _______ or _________ K a = H 3 O + [ ] A - [ ] HA [ ]
Stronger acid weaker _____________ base Stronger base weaker conjugate ___________ Therefore, a _____________ ACID — a good H + donor — has a WEAK CONJUGATE ___________ — a poor H + acceptor. Reason an acid is strong is that its conjugate base is stable (ie, weak)!

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Ionization Constants for Acids/Bases Acids Conjugate Bases Increasing strength Increasing strength NOTE: For these pairs: _______________________ or ________________________
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StudentLecture_13 - CHM 11600 Wed Announcements Exam II two...

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