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Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The interplay of acids and bases and their conjugates is at the heart of the topics covered in this section.
Think of them as a love square. These topics are critical for understanding the properties of a whole mess of biological and environmental solutions. We'll start with building a qualitative understanding of what a buffer is and then get into some titrations. This provides a buffer against changes in the pH of the solution. You can think of a buffer solution as a burly tough guy that won't budge when someone tries to push him around. He's sort of like a bouncer at a party. A buffer solution won't budge much from its pH even when we add in an acid or base.
How did these buffer solutions get so buff? It's all about the equilibrium between the acids and conjugate bases in the solution. Now let's suppose you added some strong base to this solution, say NaOH. This would result in an increase in [OH - ] and the pH would shoot up. But wait. There's more. This is Le Chatlier's principle , which tells us when an equilibrium is stressed by a change in the concentration of just one of the equilibrium species, the equilibrium will shift to alleviate the stress.
This is how a buffer solution of a weak acid is able to absorb OH - molecules and buffer against the addition of a strong base. You can imagine that if we had a very dilute buffer solution of a weak acid or base and we added bucket loads of strong acid or base, the pH would eventually change significantly. At this point, the buffer loses its buffer quality.
The Henderson-Hasselbalch equation is a handy relationship to use when dealing with buffers and their capacities. This equation tells us that the pH of a buffer solution has a value close to the p K a - logK a of the weak acid or base. We can derive this equation starting with our favorite equilibrium:. Two of these terms we have seen before. This equation is also useful in determining how extensively dissociated a weak acid solution is based on the pH of the solution. This is also known as the half-equivalence point, which we'll get to later.
A titration consists of adding incremental amounts of base to an acid or vice versa in order to determine properties of the acid or base making up the solution like concentration and pK a. Titration of a weak acid with a strong base Opens a modal.
Titration of a weak acid with a strong base continued Opens a modal. Titration of a weak base with a strong acid Opens a modal. Titration of a weak base with a strong acid continued Opens a modal. Titration curves and acid-base indicators Opens a modal. Redox titrations Opens a modal. Introduction to titration.
Solubility equilibria. Dissolution and precipitation Opens a modal. Common polyatomic ions Opens a modal.
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