Iodometry Lab Report

The purpose of this experiment was to determine the weight percentage of copper in brass. This was achieved by performing a redox titration known as iodometry. Copper, which was obtained from the brass, was used to react with iodide to produce iodine. Iodine was then titrated with thiosulfate. In this experiment, the amount of titrant dispensed correlates with the amount of copper; therefore, the amount of copper in brass was calculated by using the data recorded.
In this experiment, the analyte is copper and the sample is brass. The concentration range of copper in brass is 50-95%. When copper reacts with iodide it forms a precipitate (CuI) along with iodine. As shown in this reaction: 2Cu2++ 4I- 2CuI(s) + I2. Iodine is formed because copper
To prepare the titrant solution, a liter of distilled water was heated until it boiled. After boiling the water, about 25 grams of sodium thiosulfate was added into the water while stirring. The solution was then allowed to cool down to room temperature with the aid of an ice bath. Once the solution temperature decreased, about 0.1 grams of sodium carbonate was added into the solution. When the solution was complete, it was transferred into a 1 liter plastic bottle. The plastic bottle was wrapped around with aluminum in order to block the light from the solution because light catalyzes the thiosulfate to decompose. Before standardizing the thiosulfate, a blank determination of KI was performed. Potassium iodide may sometimes contain iodate ions; therefore, this part was performed to detect any iodate ions. In the blank determination experiment, exactly 2.00 grams of KI was dissolved in 50 mL of distilled water and then acidify with 5 mL of 3M sulfuric acid. After the acid, 5 mL of starch was immediately added into the solution. The solution didn't turn into a blue color, so a blank correction was not needed for the standardization and analyzes volumes. After determining that a black correction is not needed, the standardization of thiosulfate was performed. To standardize the thiosulfate, about 2.00 grams of potassium iodate was dried in an oven. After drying the potassium iodate for an hour, it was taken out and in three 250 Erlenmeyer flasks about 0.12 grams of potassium iodate was placed in each flask. The KIO3 was dissolved with 75 mL of distilled water. After rinsing the buret for titration with 10 mL aliquots of thiosulfate three times, 10 mL of 1M HCl was added into each flask containing the KIO3 solution. When the acid was added into the iodate solution, it turned into a dark brown color. When this color appeared, it was immediately titrated until the color became a pale yellow color. Once the