Analchem Post lab 5.docx - Lab 5 Iodometric Volumetric...

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Lab 5: Iodometric, Volumetric determination of Sodium Thiosulfate (Na 2 S 2 O 3 ) By: Issac Chung Lab partner: Jingjie Yu CHM3120C.002 Introduction
This week we will also be handling titration. In this lab, titration will used to determine the concentration of a compound. The process we will be using this week is the same as last weeks. We will titrate the solution until we see the endpoint. he experimental point at which the completion of the reaction is marked by some signal is called the end point (1). The endpoint is usually indicated with a change of color. In this lab, there are two points in where this happens. The second one is the try endpoint however. Titration is also very helpful when dealing with issues in the food industry. 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 (2). Titration is also used to tell if cheeses and wines have aged enough for distribution to supermarkets and shops (2). It is also useful in waste water analysis. Titration is a key mechanism in this analysis. Often, more specialized titration equipment is used in this application that can measure ammonia levels in combination with other reactants to quantify other chemicals present (3). In this lab we will be using sodium thiosulfate solution to titrate a known concentration of potassium iodate solution. The purpose of this lab is to determine the concentration of the sodium thiosulfate solution based on the moles of potassium iodate and the volume of sodium thiosulfate used. IO 3 - + 5I - + 6H + → 3I 2 + 3H 2 O (1) I 2 + 2S 2 O 3 2- → 2I - + S 4 O 6 2- (2) (Reaction for this lab) Procedures Materials: minimum 20 g of dried KIO3 (potassium iodate), minimum 120 g of KI (potassium
iodide), minimum 150 mL of 6 M HCl, 1 g of starch (for 500 mL starch indicator solution), minimum 30 g of sodium thiosulfate (Na2S2O35H2O) (for 1 L of ~ 0.1 M unknown solution) and 0.1 g of Na2CO3.

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