Editing Titration (section)

==Titration curves==
{{main|Titration curve}}

[[Image:Oxalic acid titration grid.svg|thumb|A typical titration curve of a [[diprotic acid]] titrated with a strong base. Shown here is [[oxalic acid]] titrated with [[sodium hydroxide]]. Both equivalence points are visible.]]

A titration curve is a curve in the graph the ''x''-coordinate of which represents the volume of [[titrant]] added since the beginning of the titration, and the ''y''-coordinate of which represents the concentration of the analyte at the corresponding stage of the titration (in an acid–base titration, the ''y''-coordinate usually represents the pH of the solution).<ref>
{{Cite book |last=Reger |first=D.L. |title=Chemistry: Principles and Practice |author2=S.R. Goode |author3=D.W. Ball |publisher=Cengage Learning |year=2009 |isbn=978-0-534-42012-3 |edition=3}}</ref>

In an [[acid]]–[[base (chemistry)|base]] titration, the titration curve represents the strength of the corresponding acid and base. For a strong acid and a strong base, the curve will be relatively smooth and very steep near the equivalence point. Because of this, a small change in titrant volume near the equivalence point results in a large pH change, and many indicators would be appropriate (for instance [[litmus]], [[phenolphthalein]] or [[bromothymol blue]]).

If one reagent is a weak acid or base and the other is a strong acid or base, the titration curve is irregular and the pH shifts less with small additions of titrant near the [[equivalence point]]. For example, the titration curve for the titration between [[oxalic acid]] (a weak acid) and [[sodium hydroxide]] (a strong base) is pictured. The equivalence point occurs between pH 8-10, indicating the solution is basic at the equivalence point and an indicator such as [[phenolphthalein]] would be appropriate. Titration curves corresponding to weak bases and strong acids are similarly behaved, with the solution being acidic at the equivalence point and indicators such as [[methyl orange]] and [[bromothymol blue]] being most appropriate.

Titrations between a weak acid and a weak base have titration curves which are very irregular. Because of this, no definite indicator may be appropriate, and a [[pH meter]] is often used to monitor the reaction.<ref>
{{Cite book
  | last = Bewick
  | first = S.
  |author2=J. Edge |author3=T. Forsythe |author4=R. Parsons
   | title = CK12 Chemistry
  | publisher = CK-12 Foundation
  | year = 2009
  | pages = 794–797
}}</ref>

The type of function that can be used to describe the curve is termed a [[sigmoid function]].