# Buffer solutions and the common ion

The Henderson-Hasselbalch Equations In general, for a solution of an acid with added amounts of conjugate base, except at extreme dilution, we can assume the following relationships: Titrations Video transcript - [Voiceover] Let's say we have a solution of acetic acid. And we know what's going to happen in solution. And so there's a concentration of acetate anions in solution.

What would happen now if you added some sodium acetate? Right, so if you added some sodium acetate. Let me go ahead and write this out here. So if you add some sodium acetate to your solution, you now have some more acetate anions. So you're increasing the concentration of one of your products. You're increasing the concentration of your acetate anion.

And according to Le Chatelier's principle, if you increase the concentration of one of your products, the equilibrium shifts to the left. So the equilibrium is going to shift to the left, and that means that some of this acetate anion is going to react with some of your hydronium ion when your equilibrium shifts to the left. This decreases the concentration of hydronium ion, and if you decrease the concentration of hydronium ion, you're going to increase the pH of your resulting solution.

So the acetate anion is the common ion, and this is the common ion effect. So there are two sources for your acetate anion. So one is the ionization of acetic acid, that's one source for your acetate anion. The other source is the sodium acetate that you added in. So we have two sources.

So we'd expect a pH that's higher than just a solution of acetic acid alone. Let's go ahead and do the calculation and see that that is true. So calculate the pH of a solution that is one molar in acetic acid.

And there's the Ka for acetic acid. And one molar for sodium acetate. So we're just gonna start by rewriting our acid-base reaction. And right now let's just for a second pretend like we have only acetic acid.The common ion effect states that in a chemical solution, if the concentration of any one of the ions is increased, then, some of the ions in excess should be removed from solution, by combining with the oppositely charged ions.

Some of the salt will be precipitated until the ion product is equal to the solubility equilibrium|solubility product. In short, the .

The Common Ion Effect and Buffer Solutions If a solution is made in which the same ion is produced by two different compounds the common ion effect is exhibited. Buffer solutions are solutions that resist changes in pH when acids or bases are added to them.

Buffer Solutions A buffer solution is one in which the pH of the solution is "resistant" to small additions of either a strong acid or strong base. Calculations are based on the equation for the ionization of the weak acid in water forming the hydronium ion and the conjugate base of the acid.

the common-ion effect can shift the base solutions containing common ions is for buffering. A buffered solution (or buffer) is an aqueous solution that resists changes in pH. A buffered solution may contain a weak acid and .

Solutions containing weak acids and their conjugate bases (or weak bases and their conjugate acids) are called "buffer solutions" because they resist changes in pH.

Compare the effect of adding HCl to M acetic acid and to the M and M. The buffer solution must remove most of the new hydrogen ions otherwise the pH would drop markedly. Hydrogen ions combine with the ethanoate ions to make ethanoic acid. Although the reaction is reversible, since the ethanoic acid is a weak acid, most of the new hydrogen ions .

 Learning Objectives This page describes simple acidic and alkaline buffer solutions and explains how they work.
Buffer Solutions - Chemistry LibreTexts