Chapt17A_B10th_ed_stu_07

# Chapt17A_B10th_ed_stu_07 - COMMON-ION EFFECT when the salt...

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COMMON -ION EFFECT when the salt of the conjugate base of a weak acid or the conjugate acid of a weak base is added to the weak acid or base it suppresses the dissociation of the acid or base. HF H 1+ + F 1- adding a salt like NaF will drive the equilibrium toward the side of the undissociated HF NH 3 + H 2 O NH 4 1+ + OH 1- adding a salt such as NH 4 Cl will shift the equilibrium toward the formation of the undissociated NH 3 .

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Calculate the pH of a solution that is 0.50 M in HF and 0.30 M in NaF. (K a for HF = 7.2x10 –4 )
Calculate the pH of a solution that is 0.25 M in NH 4 Cl and 0.50 M in NH 3 . (K b for NH 3 = 1.8x10 –5 )

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BUFFERS- solutions that undergo little change in pH on the addition of added H 1+ or OH 1- . Common example: blood a buffer consists of a conjugate acid - base pair both components must be present in large excess usually a weak acid & the salt of its conjugate base a weak base and the salt of it conjugate acid
Lets look at how a buffer works by looking at an HF-NaF buffer. HF H 1+ + F 1- <--- from NaF (acid component) (base component) add H 1+ : reacts with base F 1- : F 1- + H 1+ C HF add OH 1- : reacts with acid HF: HF + OH 1- C F 1- + H 2 O

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Similarly lets look at an NH 3 - NH 4 Cl buffer

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## This note was uploaded on 04/03/2008 for the course CHEM 114 taught by Professor Martin during the Spring '08 term at Moravian.

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Chapt17A_B10th_ed_stu_07 - COMMON-ION EFFECT when the salt...

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