Complexometric Titration of Calcium - Lab Report Example

Practical Application Complexmetric titration This experiment is referred to as a Complexmetric titration which is applied in the determination of traces of calcium in milk or water samples. The experiment can also be used to determine the presence of calcium carbonate in solid samples. The experiment has various application both in the laboratory and industrial applications. Drug manufacturing firms for instance use the procedure to test for the presence of anti-acid in drugs. The titration involves complex reactions where molecules or ions are formed when metals ions react with ligands or complexing agents which represents either one or more molecules. The reaction just like any other titration reaction represents the Lewis acid-base reactions. In this type of reaction, the metal ion accepts the extra electron from the molecule which donates the electron to form a covalent bond. Introduction In this experiment, the searchers are trying to perform a complex formation reaction for analytical purposes. The main aim of this titration reaction is to determine the presence of calcium ions in a titrant by a method referred to as titrimetric. The chemists use the common titrant referred to as ethylenediaminetetraacetic acid, (EDTA). This acid is commonly used in complex formation reactions because of its ability to form complexes with most metal ions because of its tetrabasic form. The EDTA acid molecule has a hexadentate ligand structure having four oxygen and two nitrogen molecules which donate atoms simultaneously. One major advantage of using EDTA as a chelating agent is because it forms a stable compound with most metals ions in a reacting ration of 1:1. Secondly, the reaction between EDTA and metal ions forms larger compound structures such that the reaction is product favored making it suitable for the reaction to proceed to full completion. These two major advantages make EDTA to be the preferable titrant in most complex formation reactions. Experimental The purpose of this titration reaction is to determine the presence and concentration of calcium carbonate, (CaCO3) in an unknown solution sample. The known reagents in this reaction include the following: First, there is a known amount of Ammonia buffer solution. Secondly, there is Disodium EDTA dehydrate with an FW of 372.24. Thirdly, there is a calcium carbonate with an FW of 100.87 which is primary standard and dried for a period of about 2 hours at 100 0c. We also have Erichrome Black T indicator solution and lastly, we have magnesium Chloride, (MgCl2). Procedure a) EDTA Preparation and Standardization 1) Weigh about 1.90g of EDTA acid pellets and 50g of Magnesium Chloride pellets. Transfer the mixture into a volumetric flask of about 500 mL and about 3 mL of ammonia solution with a pH of 10. Add water to the mixture and swirl to dissolve the contents of the flask. Dilute the mixture to the mark and swirl the mixture to get a uniform solution. The solution created can be estimated to have a molarity of about 0.01. It is however important to note that the exact molarity of this solution can be determined by standardization of CaCO3. 2) Weigh about 0.3 g of the Calcium Carbonate pellets and transfer the pellets in a clean beaker with a capacity of 250 mL. Add about 50 mL of distilled water to the content in the beaker. Add 6 M HCL acid to the mixture drop by drop to dissolve the CaCO3. Once al the sold has dissolved, add transfer the solution into a 500 mL volumetric flask and add distilled water to the mark. Calculate the concentration of the calcium ions in the solution. 3) Transfer 50 mL of solution prepared above into an Erlenmeyer flask with a capacity of 250 mL followed by adding 5 mL of the ammonia buffer solution. Add a few drops of the Erithchrome black T indicator and titrate the solution against the EDTA acid until the color changes to pure blue from the previous wine red color. Determine the molarity of the EDTA acid. 4) Repeat the procedure above a couple of times to for consistent results. b) Determining Water Hardness through Titration of Tap Water and Bottled Water. 1) Transfer 100 mL of tap water in a 250 mL Erlenmeyer flask using a Pipet. Add about 10mL of ammonia buffer solution and a few drops of Eriochrome Black T Indicator. Titrate the sample of tap water using the EDTA solution prepared in the previous procedure to end point. Determine the Concentration level of the Calcium Carbonate in the tap water. Repeat the procedure a couple of times for consistency. 2) Determine the following: the average, standard deviation of the outcome, RSD (ppt) and lastly, 95% confidence interval of the concentration level of CaCO3. 3) Repeat the first procedure using bottled water in place of tap water. 4) Determine the concentration (ppm) of the CaCO3 in the bottles water. Also determine the following: the average, standard deviation of the outcome, RSD (ppt) and lastly, 95% confidence interval of the concentration level of CaCO3. Results The weight of the EDTA pellets used = 1.9013 g The weight of the MgCl2 used = 0.0594 g The weight of the CaCO3 used was = 0.3051 g Distilled water = 50 mL The values of experiment a): EDTA Preparation and Standardization Volume 1 = 32.56 mL Volume 2 = 32.43 mL Volume 3 = 32.43 mL The values in the Experiment b): Determining Water Hardness through Titration of Tap Water and Bottled Water. Volume 1 = 27.53 mL Volume 2 = 27.34 mL Volume 3 = 27.32 Volume 4 = 26.51 mL Discussion The average volume in experiment a) a) Average = (32.56 + 32.43 + 32.43)/3 = 32.47 b) Standard deviation The mean = 32.47 mL √ {(32.47-32.56)2 + (32.47 -32.43)2 + (32.47 - 32.43)2}/3 =0.4650 c) RDS RDS is the second step of the reaction because it is the slowest at this point. d) 95% confidence interval of concentration of EDTA = (32.43/32.47)100 = 99.87% e) Standardization of the EDTA To find the Molarity of CaCO3= Mass/FW FW = 100.87 Mass = 0.3051 g = 0.3051/100.87 0.003025 moles The Two reagents react in the ratio 1:1 for a complete complex formation reaction Therefore the number of moles of EDNA used is 0.003025 moles 0.003025 moles are contained in 32.47 Concentration = (500 * 0.003025)/32.47 = 0.0465 M Experiment b) a) Average = (27.53 + 27.34+ 27.32 + 26.51)/4 = 27.18 mL b) Standard deviation Mean = 27.18 mL = √ {(27.18 -27.53)2 + (2.18 – 27.34) 2+ (27.18 – 27.32)2 + (27.18 – 26.51)2}/4 = 0.4534 c) RDS RDS is the second step of the reaction because it is the slowest at this point. d) 95% confidence interval of concentration of CaCO3 (27.18/27.53)100 = 98.72% e) The concentration of CaCO3 = 0.003025 M Average Volume of Solution = 27.18mL =1000 mL = 0.003025 moles =27.18 mL = (27.18 * 0.003025)/1000 = 0.0008222 Moles Conclusion The Complexmetric titration reaction has a wide range of industrial and laboratory applications just as noted in the above experiment. Chemist’s use it in a number of analytical chemistry practical’s due to its reliability in giving accurate results. Read More