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lab 9

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Alferid Hussin ShifaCHM (Course 124) (Section 01)Lab (9)Nov 21/2019Lab 9: Redox Titration Analysis of Commercial BleachObjective: The purpose of this experiment is to perform a redox titration and determine the amount of hypochlorite ion present in commercial bleach. List of chemicals, & hazard:- Commercial Bleach- Potassium Iodide - KI- 3 M Hydrochloric acid - HCl (highly hazards)- 0.100 M sodium thiosulfate - C3H6OList of Chemicals with Safety Hazard: There are Hazards chemicals in this experiment.I. Safety Precautions:- Be cation when handling the HCl solutionII. Handling Equipment:- Be careful when handling the auto titratorIII. Waste Disposal:- Disposal the mixtures in the sink, or into the appropriate waste beaker.List of Equipment:Erlenmeyer flask (100 mL) Pipet aid & disposable pipet’s (Three of 10 mL)Beaker (three of 50 mL) Scale Distilled water volumetric flask (100 mL) Auto titrator 1Pre-Lab Questions:NoneProcedure in short: 1. Dilute the concentrated bleach by mixing 5.00 mL of a commercial bleach with enough distilled water to reach the 100-mL volumetric flask. 2. Weigh out approximately 2 g of solid KI and mix it with about 25 mL of distilled water into Erlenmeyer flask. Swirl to dissolve the KI, then add 25 mL of the dilute bleach. Swirl to mix it.3. Add exact 2 mL of 3 HCl. slowly into the mixture in the Erlenmeyer flask. As you add the HCl, swirl the mixture. Finale result should have a dark yellow solution.4. Program your auto titrator to initiate the trituration. Then add enough sodium thiosulfate solution into a beaker for the titrant solution.5. Initiate the trituration with two wash cycles of the titrant solution. Then begin the trituration.6. Repeat this process if needed. Result 2Mole ratio: 2:1Molarity dilute (diluted by a factor of 20) −¿ :3.89−3CI O¿ M Molarity undiluted bleach: 7.78−2Calculated percent by mass NaClO: 21.45 %Original Commercial bleach percent by mass NaClO: 5.25 %Percent error: 308.57 %Cycle No.Initial mVConc. Result(% w/w)Endpoint VolmL1 -367.9 0.00720 1.944Post lab 1. a. −¿+ H2O−¿+Cl¿−¿← ClO❑¿Cl2+ 2OH¿ O: −¿−¿+e¿−¿ → I2¿2 I¿ iodide is being oxidized R: −¿+ H2O−¿→ Cl¿−¿+e¿+¿+ClO¿2 H¿ hypochlorite ions are being reducedb. 2−¿−¿+ S4O6¿2−¿ → 3 I¿−¿+ 2 S2O3¿I3¿O: − ¿2−¿+2 e¿2−¿ → S4O6¿2 S2O3¿ thiosulfate ions are being oxidizedR: −¿−¿→ I¿−¿+ I2❑+2e¿I¿ iodine is being reduced2. (a) Too lowThe calculated percentage will be less than the expected value because the distilled water in the pipet will dilute the commercial bleach solution to anextent. Therefore, the number of moles will also seem to decrease, and when divided by the total mass of the bleach, a smaller percent of NaClO in the bleach is calculated(b) No changesAdding an extra gram of KI will not exhibit any change in the calculated percentage of NaClO. This is because KI is already added in excess in the procedure, and any more will not affect the calculation of the percentage.(c) Too lowsince less solid iodine is present, the reaction with sodium thiosulfate will decrease and a smaller number of moles of NaClO will be determined. Hence a decrees in the percentage.Any specific observations:- No specific observations were madeConclusion:- In the experiment, a redox titration was performed in order to determine the percent of sodium hypochlorite in commercial bleach. This is done by reacting the bleach with sodium thiosulfate in the presence of iodide ions. The concentration of sodium thiosulfate is already known, and calculations can be done in order to calculate the percent by mass of NaClO in commercial bleach. According to the calculated result from the auto titrator, 1.944 mL of sodium thiosulfate was used in the titration procedure, which amounts to a percent of 21.45%. Because 5.25% of the commercial bleach is sodium hypochlorite, the percent error was found to exceed 300%; which suggest a huge error with our results- There was the potential of many errors in this experiment. Mainly, these errors are focused on contamination. A total of four different solutions (with varying degrees of molarity) were used, and any difference between could have resulted in different solutions and concentrations. Also, since the auto titer could not account for those error, any changes will alter the calculation by huge


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