Oxidation-Reduction Titration with Potassium Dichromate Lab

Abstract:
In this lab an oxidation-reduction titration was performed to complete a volumetric analysis of iron. Potassium dichromate was titrated with a solution of water, an organic redox indicator, and a mix of concentrated phosphoric/sulfuric acid that was combined with an unknown substance. The solution was titrated with the potassium dichromate until the solution reached a deep purple, indicating the iron ions had been oxidized. The procedure was repeated three times with three different masses of unknown and the same molarity of potassium dichromate was used. The volume of potassium dichromate was recorded, and the mass of iron in the unknown substance was determined. The percent of Iron(II) in the unknown substance was found. The average mass of iron in the substance was 0.280 g, and the average percent of iron in the unknown substance was 23.2%. All objectives of this procedure were met.

Introduction:
In this experiment an oxidation-reduction reaction was used to complete a volumetric analysis of iron. A solution of was used as an oxidizing agent in order to determine the oxidation of an unknown amount of to . Potassium dichromate is used to oxidize alcohols and convert primary alcohols to aldehydes and sometimes carboxylic acids. The chemical is potentially harmful to human health and is a crystalline ionic solid that is a bright red-orange bright color. When it is used in an aqueous solution, the color change determines whether there is a ketone or aldehyde present. When aldehydes are in the mixture, the solution will change colors from red-orange to green. Keytones will not change color in the presence of potassium dichromate since they can no longer be oxidized. Other industries use potassium chromate to help prepare chromic acid which is used for etching materials and cleaning glassware. The chemical is also used in cement to improve its texture and density, to tan leather, and screen print (Potassium Dichromate ).

Procedure:
Approximately 1.2 g of was weighed on a top-loading balance, and its mass was recorded to 0.001 g in the data table. The weighed amount of was transferred to a clean 250-mL volumetric flask and dissolved in tap water, diluting the solution exactly to the etched line. Next, three samples of approximately 1.000-1.400 g of the unknown sample was weighed. Each sample was placed into its own 250-mL Erlenmeyer flask. To the lowest weight sample of unknown 75 mL of tap water, 8 drops of redox indicator, and 15 mL of concentrated sulfuric/phosphoric acid mixture was added. Then several mL of the solution was transferred to a clean buret and rinsed with several small portions of the solution. This process ensures that the standard solution will not be diluted when the buret is filled. The buret was filled and zeroed it using a waste beaker. Using a white piece of paper or paper towel as a background, the lowest weight flask was titrated to a deep purple endpoint. The solution will pass through a green color on the way to the endpoint. It was made certain to obtain a definite purple color. The volume was recorded to the nearest 0.01 mL of needed to reach the endpoint in the data table. The two remaining samples of unknown were covered with Parafilm until day two of this experiment. 75 mL of tap water, 8 drops of redox indicator, and 15 mL of the concentrated sulfuric/ phosphoric acid mixture was added to the second weight sample of unknown. Several mL of were placed into a clean buret and rinsed with several small portions of the solution. The buret was filled and zeroed using a waste beaker. The flask was then titrated to the purple