BMI_Lab3PH Buffers

BMI_Lab3PH Buffers - Laboratory # III Topic: pH, Buffers,...

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Laboratory # III Topic : pH, Buffers, and Titration Principle: A buffer is a solution that resists pH changes when strong acids or bases are added to the solution. pH is the negative log of H+ ion concentration . Bronsted-Lowry acid-base theory describes acid as a proton (H+) donor and a base as a proton (H+) acceptor) Most buffer solutions consist of a weak acid and its conjugate base (salt of the weak acid). The buffer equation pKa - pH = log weak acid/salt is useful to calculate ratio of acid/salt needed to give required pH . pKa is the negative logarithm of the acid dissociation constant, Ka . Buffers are effective in resisting a change in pH within a range of about 1pH unit above and below their pK a . Buffers of different pH are prepared by mixing stock solutions of the weak acid and a salt of the acid ( refer lab2 activity1 ). The buffer works best when the pH is close to the pKa of the weak acid. pH of blood is maintained by a combination of phosphate and carbonate buffering system Phosphate buffer pH ranges 5.7 to 8 prepared using varying ratios of 0.2M Sodium monobasic phosphate (NaH 2 PO 4 ) and 0.2M Sodium dibasic phosphate (Na 2 HPO 4 ) We will use pH 7.2 (prepared using a ratio of 1:2.6) Carbonate buffer (pH ranges 9.2 to 10.7) prepared using varying ratios of 0.2M Sodium carbonate (Na 2 CO 3 ) and 0.2M Sodium bicarbonate (NaHCO 3 ). We will use pH 10.0 (prepared using a ratio of 1: 1.2). (Refer lab 2 activity 1 for carbonate buffer prep) Buffer systems Example: Carbonate buffer
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This note was uploaded on 04/24/2008 for the course PHS 2301 taught by Professor Carvalho during the Spring '08 term at St. Johns Duplicate.

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BMI_Lab3PH Buffers - Laboratory # III Topic: pH, Buffers,...

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