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Unformatted text preview: Experiment 15 STANDARDIZATION OF A SODIUM HYDROXIDE SOLUTION I. Learning Objectives To introduce elementary acid-base reactions and their stoichiometry. To practice quantitative precision in the laboratory. To standardize a solution of sodium hydroxide. II. Background Information A common method for determining the unknown concentration of a chemical in solution is the titration . In a typical titration, a solution of known concentration, the titrant , is added to (reacted with) a solution of unknown concentration in a controlled manner. A chemical reaction between the critical components of the titrant and the solution of unknown concentration is followed using one of several methods: pH dependent colorimetric indicator, pH electrode, reaction temperature, etc. The equivalence point of the reaction is determined, and the volume of titrant required to reach this equivalence point is used to calculate the unknown solution concentration. The setup for a titration of unknown solution B (containing a colorimetric indicator, I) with titrant solution A is shown in Figure 4.1 as an example. When a colorimetric indicator is used in a titration, a noticeable color change in the solution being titrated occurs at or near the equivalence point . Note: The term end point represents the volume of titrant necessary in a titration to affect the desired indicator color change. Ideally, this occurs precisely at the equivalence point , and therefore the terms &quot; end point &quot; and &quot; equivalence point &quot; are often used interchangeably. An unknown amount of an acid in a solution is determined by titration with a standard base solution (of known concentration). Additionally, an unknown amount of base in solution is measured by titration with a standard acid solution. Titrations involving acid/base neutralizations are known as neutralization titrations. Other types of chemical reactions can also form the basis for titrations. Among these other reactions are those 15-2 occurring between oxidizing and reducing agents ( redox titrations) and those occurring between metal ions and complexing agents ( chelometric titrations). Figure 4.1. Titration setup. titrant A solution B of unknown concentration (with indicator I) Solution Concentration A titration experiment has limited value if the concentration of the titrant is not known accurately. The concentration of a solution is usually described as the quantity of dissolved material (the solute) per unit volume of the solution. To determine a solution concentration, the weight of the solute to be dissolved in the solution is first accurately measured using an automatic digital balance. Then, the volume of final solution is accurately measured in a volumetric flask....
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- Spring '07