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BCHM 426 Lecture 1: Biochem Lab Notes

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31 Jan 2017

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Binghamton University

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Within 1 ph unit of the pka unit because its equally effective at buffering with conj base and conj acid. Little conj base to absorve the protons, meaning a buffer would be useless. If you choose a/b pair that pka near ph, then youll be able to buffer in both directions. The higeher conc of the bugger, the better it resists ph changes (stronger buffering capacity) bc you have more buffer molecules. Buffer = conj acid con + base conc. If you have to do a solution, telling you acetic acid and acetate, the buffer strength is the total of both. Buffers have some salts in it, so ionic strength can sometimes be important. Salts may form precipitation, but more often it can change the pka. Salts can change the equilibrium, so the ionic strength can affect the equilibrium. Ex: making your solution (58. 44 g/mol) (. 1l)(1mol/l) = 5. 844g.

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Related Questions

Experiment 18: Buffers Purpose In this experiment you will prepare several buffers and investigate their properties. Discussion A solution of a weak acid and one of its salts, in approximately equal concentrations, resists changes in pH when acid or base is added to it. (Note: The pH of a solution is a measure of the concentration of free H3Ot ion; it does not indicate concentration of combined acid such as HA.) The same is true for a solution of a weak base and one of its salts. A solution with this property is called a buffer (see illustration next page). Bufter systems are extremely important in many chemical and biological systems. For example, your blood contains a buffer system utilizing carbonic acid and bicarbonate ion. The important equilibrium in an acidic buffer is HA (aq) H20 ) A (a)0 () acid conjugate base in which the concentrations of acid and conjugate base are approximately equal. If a small amount of free acid (H30) is added to this solution, it reacts with the conjugate base A (reaction 1 in reverse). The equilibrium constant for this reaction is very large, so the reaction proceeds to near completion, absorbing the added acid. Similarly, added base (OH-) reacts with the acid HA as shown below: 2. HA (aq) + OH-(aq) ATaq) + H2O (1) This reaction also proceeds to completion, effectively absorbing any added base. Since the H30 and OH- concentrations are kept constant, the solution thus resists pH changes when an acid or base is added to it. A similar argument can be made for a basic buffer The actual pH of a buffer can be determined from the value of the Ka and the concentrations of the acid and conjugate base obtained from an initial-change- equilibrium table. However, a shortcut for buffers is available, and is shown below. We begin by writing and rearranging the equilibrium constant expression for the acid dissociation. If the -log of both sides of equation (3) is taken, a relationship involving pH is then obtained. H30IA] HA] 3. HA HAI -loglH30'1- -log Ka A- 141