EXP 6 CHM421.docx - CHM 421 EXPERIMENT 6A Analysis Of Bleach And Copper(II Unknown NAME AYU NAZIRAH BINTI AMAN STUDENT ID 2019208104 GROUP RAS2451(A

EXP 6 CHM421.docx - CHM 421 EXPERIMENT 6A Analysis Of...

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CHM 421 EXPERIMENT 6A : Analysis Of Bleach And Copper(II) Unknown NAME : AYU NAZIRAH BINTI AMAN STUDENT ID : 2019208104 GROUP : RAS2451(A) LECTURER’S NAME : MR HAFIZ BIN YAAKOB DATE OF EXPERIMENT : 11 th NOVEMBER 2019 DATE OF SUBMISSION : 25 th NOVEMBER 2019
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ABSTRACT The objectives of this experiment are to standardize the sodium thiosulphate solution ,to determine the percentage of NaClO in sample and to determine the percentage of copper in an unknown copper sample. Firstly, in Part A, the sodium thiosulphate solution was standardized to get its actual molarity. Then, for analysis of bleach (Part B), 10.0 mL of the bleach sample was used as sample, and then it was diluted with distilled water into pre-weighed 100 mL volumetric flask. The volumetric flask was reweighed and the density of the bleach solution was calculated. The sample was diluted to the 100 mL mark with distilled water. 10.0 mL aliquot of bleach solution with potassium iodide and hydrochloric acid solution was titrated against the standardized sodium thiosulphate until the amber iodine color fades to light yellow. Then, add some starch solution and the titration was continued until the dark color of starch-iodine complex disappears and turns colorless. The titration procedure from Part B was used in analysis of copper(II) unknown (Part C) by using copper(II) unknown with potassium iodide and sulphuric acid solution in a conical flask. The experiment is very important because reactions of oxidation, reduction, and iodometric were took place together. From the calculation, the percentage of the NaClO in Leo is 3.29 %. The percentage of copper in an unknown copper sample is 31.55 %. This percentage shows that the unknown copper(II) is actually copper(II) acetate monohydrate. OBJECTIVES 1. To standardize the Sodium Thiosulphate solution 2. To determine the percentage of NaClO in bleach sample 3. To determine the percentage of Copper in an Unknown Copper sample INTRODUCTION Household bleach contains an oxidizing agent known as sodium hypochlorite, NaOCl. NaOCl is prepared by bubbling chlorine gas into a sodium hydroxide solution. Part of the chlorine is oxidized to the hypochlorite ion, OCl- , and some is reduced to the chloride ion, Cl - . The excess hydroxide keeps the resulting solution strongly basic. An equation describing this process is: H 2 O(l) + ClO - + 2I - → I 2 (aq) + Cl - + 2OH I2 + I - → I 3 Thus, we can write the net reaction of hypochlorite with iodide as: H 2 O(l) + ClO - + 3I - → I 3 - + Cl - + 2OH The triiodide is then reduced back to iodide by titration with a standardized thiosulphate solution: I 3 - + 2S 2 O 3 2- → 3I - + S 4 O 6 2 - Therefore, from these equations, it shows that iodide ion does not undergo any net change in the process but its presence assures that the correct stoichiometry is followed. Its presence is also provides a visually detectable point. The overall reaction is:
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H 2 O(l) + ClO - + 2S 2 O 3 2- → S 4 O 6 2- + Cl - + 2OH (Mole ratio of hypochlorite to thiosulphate is 1:2) One commonly used method for determining oxidizing agents in solution is termed an “iodometric titration”. Iodide ion is a strong enough a reducing agent that many oxidizing agents can react completely
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