Standardization of Potassium Permanganate Solution by an Iron (II) Salt, Lab Reports of Chemistry

Download Standardization of Potassium Permanganate Solution by an Iron (II) Salt and more Lab Reports Chemistry in PDF only on Docsity! UNIVERSITI TUNKU ABDUL RAHMAN FACULTY OF SCIENCE BACHELOR OF SCIENCE (HONS) CHEMISTRY YEAR 1 TRIMESTER 1 UDEC1224 CHEMISTRY LABORATORY II Name Chan Yong Li Student ID No. 19ADB04214 Name of Lab Partners 1. Foo Yu Cheng (18ADB02613) 2. Loo Xin Tong (19ADB02955) Practical Group P3 Practical Sub-group G3 No. of Experiment Experiment 1 Title of Experiment Standardization of Potassium Permanganate Solution by an Iron (II) Salt Date of Experiment 10th June 2019 Date of Submission 17th June 2019 Name of Lecturer Dr Ooi Zhong Xian 1.0 Title Standardization of Potassium Permanganate Solution by an Iron (II) Salt 2.0 Objectives 1. To standardize potassium permanganate solution by an iron (II) salt. 2. To calculate the molarity of the ammonium iron (II) sulphate solution prepared. 3. To determine the molarity of the potassium permanganate solution, KMnO4. 4. To understand the definition of primary standard. 5. To define redox titration. 3.0 Results Part A: Preparation of a Standard Ammonium Iron (II) Sulphate Solution (0.1M) Mass of ammonium iron (II) sulphate used = 3.9010 g Part B: Standardization of Potassium Permanganate Solution Titration number 1 2 3 Initial volume of burette (cm3) 0.00 21.80 20.00 Final volume of burette (cm3) 21.80 43.60 41.60 Total volume of KMnO4 used (cm3) 21.80 21.80 21.60 Average volume of KMnO4 required for titration = (21.80+21.80+21.60 ) cm3 3 = 21.73 cm3 4.0 Calculations 2015). Unlike sulphuric acid, nitric acid and hydrochloric acid may involve in competing for the oxidation-reduction reactions, which in turn results in reducing the accuracy of the titration. If the titration was done in a neutral- or alkaline-conditioned solution, instead of reducing the purple-coloured MnO4 - ions to colourless Mn2+ ions, brown precipitate would form (Chemistry Stack Exchange, 2018). The brown precipitate formed will be MnO2 due to the presence of brown-coloured Mn4+ ions. The equation is as follows: MnO4 - + 4 H+ + 3 e- → MnO2 + 2 H2O In this experiment, the primary standard solution, ammonium iron (II) sulphate solution was prepared and titrated with potassium permanganate solution to determine the concentration of the potassium permanganate solution. The molarity of the ammonium iron (II) sulphate solution prepared from this experiment was 0.09948 M and was approximate to 0.1 M while the molarity of the potassium permanganate solution determined from this experiment was 0.02289 M and was approximate to 0.02 M . Iron (II) sulphate crystals, FeSO4 .7H2O cannot be used for standardization because the salt is rendered impure by efflorescence and by atmospheric oxidation to form a brown basic sulphate result of a reaction of the following type: 12 FeSO4 + 3 O2 + 6 H2O → 4 [Fe(OH)3 .Fe2(SO4)3] The salt, ammonium iron (II) sulphate, Fe(NH4)2(SO4)2 .6H2O, is free from these disadvantages and can be obtained in a high state of purity. In solution, it reacts freely as iron (II) ion, sulphate ion and ammonium ion while only the iron (II) ion reacts with the permanganate ion, MnO4 -. In addition, ammonium iron (II) sulphate solution was used as a primary standard due to its stability and its availability in a highly pure form. Unlike ammonium iron (II) sulphate, potassium permanganate solution cannot be obtained in a very pure form as it reacts readily with any reducing substances or even with any organic compounds. Moreover, it is a photosensitive compound (Ullah, 2017). Hence, potassium permanganate is not suitable to be used as a primary standard. Questions 1. Calculate the molarity of the potassium permanganate, KMnO4. Considering the equation of the reaction: MnO4 - + 8 H+ + 5 Fe2+ → Mn2+ + 5 Fe3+ + 4 H2O From this equation, 1 mole of MnO4 - reacts with 5 moles of Fe2+. Number of moles of Fe2+ present in the conical flask = Molarity × Volume = 0.09948 M × 0.025 L = 0.002487 mol Ratio of MnO4 - to Fe2+ (according to the equation) 1 mol :5 mol Ratio of MnO4 - to Fe2+ (according to the experiment) x mol :0.002487 mol Let: x = Number of moles of MnO4 - Number of moles of MnO4 -, x = (0.002487 mol)(1 mol) 5 mol = 0.0004974 mol ∴ Molarity of potassium permanganate = Number of moles Volume = 0.0004974 mol 0.02173 L = 0.02289 M ≈ 0.02 M 2. What is a primary standard? A primary standard is made from a solid which can be obtained 100% (almost) pure. For instance, a solution of approximately known concentration is made and used as a primary standard against a solution which will be standardized. The solution made from a primary standard is called a standard solution (Ramsden, 2000) . 3. Define ‘redox’ titration. Redox titration is a type of titration that determines the concentration of an unknown solution (analyte) that contains either an oxidizing or reducing agent. It is based on a redox reaction between the analyte and titrant, where the analyte is the substance to be analysed and the titrant is the standardized solution (Lumen, n.d.) . 6.0 Precaution steps 1. Sulphuric acid (strong acid) must be added into the conical flask instead of hydrochloric acid or nitric acid so that the results obtained will be more accurate. 2. Fill in the burette with distilled water and test for absence of leaks from the tip and stopcock. 3. Rinse the burette with small portions of the titrant solution before the experiment to prevent dilution of the titrant solution. 4. When setting up the burette, place the burette to a vertical position to reduce parallax error and make the reading more accurate. 5. Wash the sides (walls) of the conical flask (during the titration) with distilled water to ensure all of the potassium permanganate solution (added from the burette) has reacted with the ammonium iron (II) sulphate solution. 7.0 Conclusion The molarity of the ammonium iron (II) sulphate solution prepared from this experiment was 0.09948 M and was approximate to 0.1 M while the molarity of the