Acid- Base Chemistry

Titration

With the help of computer-interfaced pH probes, you will investigate the qualitative and quantitative aspects of acid-base reactions. Such reactions are in a class known as neutralization reactions. Determining the molarities and/or volumes involved in a neutralization reaction involves the technique called titration (a titer refers to a known or fixed volume).

Terms

For our purpose the operative definition of an acid is that of Lowry-Bronsted:

An acid is a proton (H+ ) donor and a base is a proton acceptor. In donating its proton, an acid produces a base, called its conjugate base. The converse is true of a base.

 

Therefore every acid-base neutralization reaction involves acid-base pairs. In fact, the act of dissolving an acid in water is an acid-base reaction as shown to the left.

Neutralization reactions take the general form shown below: an acid plus a base yield a salt and water. The heart of this type of reaction is the combination of proton and proton receiver to form water.

There are several factors which describe acids as well as bases - strong, weak, mono-, di-, triprotic/basic. If an acid is effectively 100% dissociated in water, it is considered strong; less than 100%, weak. A monoprotic acid dissociates one mol of H+ per mol of acid, while a diprotic acid produces two mols of H+, triprotic three, etc. We can investigate these factors using titration since this process produces graphs (titration curves) which have distinguishing characteristics.

Dissociation of Weak Acids

The relative strength of weak acids can be found by comparing their pKas. The Ka is the special equilibrium constant for acids, called the acid dissociation constant.

The pKa can be found experimentally from the data accumulated during a titration. pKa is equal to the pH halfway to neutralization. The mathematical justification for this determination follows.

When [A- ] = [HA], log10 = 0 and the pH = pKa.


EXPERIMENTAL PROCEDURE

Part I: The Process of Titration (Qualitative Analysis)

Part II: Titration (Quantitative Analysis)

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