Volumetric Analysis

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\Chem 4\Volumetric analysis\R. Pau\p.1 Topic : Volumetric analysis A. INTRODUCTION Volumetric analysis is a method used to measure the concentration of a solution. The technique involved is called titration. During titration, 1. 2. 3. A fixed volume of a solution is measured into a conical flask with a An is added to the solution. until the indicator just changes . Another solution is added from a colour. At that moment, the two reactants have JUST completely reacted is called the of titration. Apparatus for volumetric analysis : 1. † Volumetric flask this is used to prepare a solution of known concentration. ( ) 2. † Pipette this is used to transfer exactly the known volume of solution (usually 25.0 cm3) to conical flask. 3. † Burette this is used to hold solution going to react with the solution in the conical flask. The greatest capacity is 50.0 cm3. Before transferring a solution to the burette, wash the burette first with distilled water and then rinse the burette with the solution transferred. Fill the burette and make sure that the tip of the burette is filled. ** 4. † Conical flask this is used to receive the solution from the burette and for the reaction to take place. \Chem 4\Volumetric analysis\R. Pau\p.2 B. ACID-ALKALI TITRATIONS In acid-alkali titration, the pH changes remarkably at the end point. Hence, the indicator would give a sharp colour change at the end point. Colour change of some common indicators are listed below : Indicator Methyl orange Phenolphthalein Note : Litmus is NOT used in titration because the colour change is not easily observed. The choice of indicator depends on the strengths of the acid and alkali used in titration : Titration strong acid + strong alkali strong acid + weak alkali weak acid + strong alkali weak acid + weak alkali Indicator Phenolphthalein, methyl orange
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