Bromophenol Blue Yellow Purple Methyl Orange Red Orange Methyl Red Red Yellow Bromothymol Blue Yellow Blue

Transcription

1 Titration is a laboratory method used to determine the unknown concentration of a reactant. This is a delicate procedure that requires patience and a good observation skills. Usually, an indicator is used in titration to determine the endpoint of the reaction. Once the endpoint volume is found, mathematics can be used to determine the concentration of the unknown. This procedure is commonly used in the field of analytical chemistry. Indicators must be chosen carefully, or else they will not be helpful in a titration. They must be chosen on the basis of ph at the equivalence point of the two reagents. Common Indicators Indicator Color in Acid Color in Base ph at color change Bromophenol Blue Yellow Purple Methyl Orange Red Orange Methyl Red Red Yellow Bromothymol Blue Yellow Blue Phenolphthalein Colorless Pink Bromocresol Green Yellow Blue Litmus Red Blue History Explore the discoverer's biography, including general facts about his life and anecdotes regarding how he made this particular 1 / 6

2 discovery. Also see other significant scientific discoveries built largely on this concept and other real-world applications in history that may not still be relevant. Discoverer/Developer Titration can be traced to the origins of volumetric analysis, which began in the late eighteenth century. Study of analytical chemistry began in France and the first burette was made by Francois Antoine Henri Descroizilles. The field began to spread to neighboring countries. The first book containing titration was titled Lehrbuch der chemisch-analytischen Titrirmethode (Instructional Book of Titration Methods in Analytical Chemistry) and was published in 1855 in Germany. The author of this book, Karl Freiderich Mohr, is also responsible for advancing the burette from a graduated cylinder- type instrument to a tool with a clamp at the bottom that is still used today. Concept Definition Study the primary definition of this concept, broken into general, basic, and advanced English definitions. Also see the mathematical definition and any requisite background information, such as conditions or previous definitions. General Science The gradual addition of one solution to another until the chemical amount of one reactant being added matches stoichiometrically the amount of another reactant in the solution initially present. Advanced An operation, used in volumetric analysis, in which a measured amount of one solution is added to a known quantity of another solution until the reaction between the two is complete. If the concentration of one solution is known, that of the other can be calculated. 2 / 6

3 Real World Application Discover processes or disciplines in the natural or man-made worlds that employ the concept. Titration is used in laboratory medicine to determine unknown concentrations of chemicals of interest in blood and urine. Pharmacists also use titration in the development of new pharmaceuticals. Titration may also be used to determine the amount of a certain chemical in food. Often, titration is used to determine fat content, water content, and concentrations of vitamins. Titration is also used to tell if cheeses and wines have aged enough for distribution to supermarkets and shops. Of course, the main use of titration is in the laboratory. However, titrations are not limited to the field of chemistry. Scientists of different disciplines use titrations for a variety of different reasons. Vocabulary Learn important vocabulary for this concept, including words that might appear in assessments (tests, quizzes, homework, etc.) that indicate the use of this concept. Important Vocabulary Term Context Analyte - The analyte is NaOH. Back Titration - By using back titration, we determined the chemical oxygen demand of this compound. End Point - The end point has been reached when the solution turns from green to blue. Equivalence Point - The equivalence point is when 3 moles of NaOH has been added. Indicator 3 / 6

4 - The indicator used here is methyl red. Primary Standard - The primary standard we are using is benzoic acid. Standardization - The NaOH was determined to be 0.1M by standardization. Titrant - The titrant used in today's titration is 0.5M HCl. Titration Curve - This titration curve is in the shape of an "s". Videos Browse relevant videos from the Journal of Chemical Education's (JCE) Chemistry Comes Alive! library and other video sources. Endpoint of Titration This video shows the procedure near and at the endpoint of a titration. Titration Curve Animation This quick animation allows the teacher to narrate about different points of the titration curve as a reaction runs. Rough Titration This video shows an example of a rough titration, that would be perfect for introducint titration. HCl + NaOH Titration 4 / 6

5 This video shows the titration of hydrochloric acid and sodium hydroxide. It is a great video for beginning a titration lesson. Reaction: NaOH + HCl NaCl + H 2 O Titration Animation During this animated titration, the narrator explains precisely what is occurring during the titration. Titration Procedure This video shows a complete titration, explaining the steps along the way. It is good to show to students before they attempt their first titration. Some Common Acid/Base Indicators This video shows the colors expected when various indicators are placed in acidic solution and basic solution. Computer Animations Experience computer simulators or animations that illustrate the concept discussed here. Many simulators or animations come with worksheets for use in class / 6

6 Summary Read a summary of the concept, indicating the enduring understanding students should retain after class. Summary Titration is widely used when the concentration of a reagent or certain chemical in a solution is unknown. Students should know how to determine the concentration of the unknown after a titration as well as the reactions involved. Indicators are often used to determine the endpoint of the reaction. Sample Problems Explore sample problems from the JCE QBank and other sources. Sample Problems 6 / 6