CHAPTER19CHEM

CHAPTER19CHEM - Ch 19 Equilibria of Acid-Base Buffer Systems 19.1 Equilibria of Acid-Base Buffer Systems Acid-base buffer a solution that lessens

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Ch. 19 Equilibria of Acid-Base Buffer Systems 19.1 Equilibria of Acid-Base Buffer Systems Acid-base buffer: a solution that lessens the impact on pH from the addition of acid or base. i. To withstand the addition of a strong acid or strong base w/out significantly changing its pH, a buffer must contain an acidic component that can react with the added OH- and a basic component that can react w/ added H3O+ ion. (cannot be just any acid or base b/c would neutralize each other) ii. The components of a buffer are the conjugate acid-base pair of a weak acid (or base). Buffers work through the common-ion effect : occurs when a given ion is added to an equilibrium mixture that already contains that ion, and the position of equilibrium shifts away from the forming more of it (shifts to opp. Direction of it). Lowers dissociation of acid [H3O+] or base [OH-], thereby lowering Ka less acidic or basic higher pH. A buffer consists of high concentrations of a weak conjugate acid-base pair [ex. Weak Acetic acid CH3OOH (conj acid) and acetate ion CH3COOH - (conj base)] A buffer consists of high concentrations of the acidic (HA) and basic (A - ) components. -when small amounts of (strong acids or bases) H3O+ or OH- ions are added to the buffer, they cause a small amount of one buffer component to convert into the other , which changes the relative concentrations of the two components. As long as amount added is much smaller than amount of HA or A- (weak acids and bases) originally present, the added ions have little effect on the pH b/c they are consumed by one or the other buffer component: a large excess of A- reacts with any added H 3 O + , and a large excess of HA reacts with any added OH-. Solving for [H 3 O + ] Ka= [CH3COO-][H 3 O + ] / [CH3COOH] [H 3 O + ] = Ka x [CH3COOH]/[CH3COO-] -b/c Ka is constant, the [H 3 O + ] of the solution depends directly on the buffer-component concentration ratio [CH3COOH]/[CH3COO-] 1. If the ratio [HA]/[A-] goes up, [H 3 O + ] goes up 2. If the ratio [HA]/[A-] goes down, [H 3 O + ] goes down When add a small amount of strong acid, the increased amount of H 3 O + ion reacts w/ a stoichiometric amount of acetate ion from the buffer to form more acetic acid: H 3 O + (aq,added) + CH3COO- (aq, from buffer)  CH3COOH (aq) + H2O (l) As result, [CH3COO-] goes down by same amount of H 3 O + added [as it combines w/ H 3 O + ] (equilibrium shifts to the right) and [CH3COOH] goes up by that amount, which increases buffer- component ratio, increasing [H 3 O + ] slightly. However changes in concentration ratio are small, so pH is also small. If OH- is added to the right, that amount of CH3COOH combines with it and decreases, (equilibrium shift to the left) which increases amount of CH3COO- . Decreases buffer-component ratio, decreasing [H 3 O + ], but again very small change. The Henderson-Hasselbalch Equation
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/14/2010 for the course CHEM 1A taught by Professor Okamura during the Fall '08 term at UC Riverside.

Page1 / 4

CHAPTER19CHEM - Ch 19 Equilibria of Acid-Base Buffer Systems 19.1 Equilibria of Acid-Base Buffer Systems Acid-base buffer a solution that lessens

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online