Complexometric Determination Essay

IntroductionUsing a Lewis base impersonal molecule to donate electron pairs (ligands) to a Lewis acid admixturelic elementlic element ion circle round to form a single cluster ( mingled) ion. When the decomposable ions forms with a metal ion (chelation) the ligand used is called the (chelating means). EDTA acts as a great chelating agent due to the atomic number 7 and atomic number 8 donating an electron pair to the metal ion center to form an octahedral complex. The metal ions especially with a +2 charge or higher atomic number 18 the reason for peeing system inclementness to form on various objects cognize as scum. Calcium ions ar typically the most ballpark contributing factor for water hardness so this experiment uses CaCO3 (Calcium Carbonate) to crush the hardness of an unknown sample.A scale of water hardness identifies whacky water with a value less than 60 ppm (parts per million) and hard water with a value more than 200 ppm. 3 mL of ammonium hydroxide/ammoni um chloride airplane pilot (pH 10) is loaned to the mixture prior to the titration to capture the calcium metal ions so the indicator can work properly. The experiment adds 4 drops of Eriochrome opaque T as the indicator to visually see the color counter channelize as complexes argon formed and the event nethergoes chelation of metal impurities.The color veer from indicator starts as tip and changes to a violet then unfounded gamey color to signify the chemical phase changes throughout the chemical reaction until the oddmentpoint. 3 titrations are data-basedly conducted to organise the mean medium of the Na2 EDTA for observational accuracy. The EDTA mean average is then used to calculate the water hardness of an unknown water sample (97) using 3 more titrations to calculate a mean average of the unknown water sample. An absolute warp is calculated for each titration experiment to calculate the experimental estimated precision. The final experimental result is then comp ared to the city of Tempe standard for water hardness and agreeable standards.Principle(Spurlock, 2014)(Spurlock, 2014)A complex ion is an ion containing a central metal cation bonded to ace or more molecules or ions (Chang, 2013). honorable like complex ions, a ligand is a molecule or ion that is bonded to the metal ion in a complex ion (Chang, 2013). A chelating agent is a substance that forms complex ions with metal ions in a solvent (Chang, 2013). The assist of the chelating agent forming is called chelation. E.D.T.A. (ethylenediaminetetraacetic acid) is a common chelating agent that will be used in this experiment to chelate the metal ions. Tetraamminecopper (II) Cu(NH3)42+ will be the complex ion in this lab experiment. In chapter 11.1-3 the energising Molecular Theory is being tested in this experiment (Chang, 2013). Solids are denser than liquids and allow very little empty space to exist amongst molecules limiting the freedom of motion. The liquids are less dense tha n solids, held closely together with little space amongst molecules (less than solids), however, the molecules in liquid do non break away from the attractive forces allowing them to move past each early(a) freely.Gases are the least dense and have the largest amount of distance between molecules allowing them to move around more freely. According to the theory, the experimental Carbon, Hydrogen, Nitrogen and Oxygen ions are able to quick attract and find the metal ion in the liquid by donating their electron pair to the metal ion center creating the complex. These complex ions in the experiment use intermolecular and intramolecular forces to break and tie down chemical bonds thru the experimental process of chelation to identify the hardness of the unknown sample. afterwards the reaction is complete, when evaporation and or vaporization of the liquid and gas in the molecules is separated the remaining metal impurities known as scum are left.In chapter 4.1 hydration is used t o orient the negative stakes of the diatomic gases to the positive pole of the Hydrogen and metal impurities in the dissolving agent creation the complex cluster. Chapter 4 is also used for titration of redox reactions using a standard final result (Na2 EDTA) to add into another issue of unknown concentration (unknown sample + ammonia water water/ammoniumchloride buffer + Eriochrome Black T) until the equivalence point is reached (has fully reacted) as visually identified by the indicators (Eriochrome Black T) from the color change of pink to violet to blue.Procedure1. Prepare or so 500mL of approximately 0.004M disodium EDTA solution. To prepare your solution, exhort out 0.7-0.8g of Na2EDTA and dissolve in about 500mL deionized water in your plastic bottle. Seal the bottle and shake vigorously for a few proceeding to dissolve the salt. 2. Standardize the Na2EDTA solution using a stock calcium ion solution as the primary standard a. Use a 10-mL channel pipet to add 10.00 mL of standardized calcium ion stock solution (1.000g CaCO3/L solution) to a 250-mL Erlenmeyer flask. b. Add about 30 ml of deionized water to this titration flask. c. Add a charismatic stir-bar, place on a magnetic stirrer and begin stirring. A piece of white paper under the flask gives good contrast for easier detection of the indicator color change. d. intimate the fume hood, add about 3mL of ammonia/ammonium chloride buffer (pH 10).The buffer is an inhalation irritant. Stir for 30 seconds. e. Just prior to titrating the flask, add 4 drops of Eriochrome Black T indicator solution. Continue stirring for another 30 seconds and then titrate this solution with your disodium EDTA solution within 15 minutes. f. subdued down your titration near the endpoint, as the color change takes 3-5 seconds to develop. At the end point, the color changes from pink to violet to blue. If you feel unsure whether youve reached your endpoint, read and tape the volume delivered and then add another drop of titrant to check for a complete color change. g. Repeat this titration two more times. auspicate the thousand of your disodium EDTA from each titration. Average your molarities from the three trials and calculate your precision. 3. Choose one brisk unknown water sample as provided. Record the unknown order in your notebook, then titrate this water sample with your standardized disodium EDTA solution a. Transfer 25.00mL of the prepared water sample to a 250-mL Erlenmeyer flask. b. Add about 20ml of DI water to the titration flask.c. Add a magnetic stir-bar. Place the flask on a magnetic stirrer and begin stirring. d. Inside the fume hood, add about 3mL of ammonia/ammonium chloride buffer (pH 10). Stir for 30 seconds. e. Just prior to titrating,add four drops of Eriochrome Black T Indicator solution to your flask. Continue stirring for another 30 seconds and then titrate this solution with your standardized disodium EDTA solution within 15 minutes. f. Repeat this titration twic e more. Calculate the hardness (mg CaCO3/L) of the prepared water sample from each of your titrations. Calculate your average hardness and your experimental precision from the three trials. 4. Compare your results to the expected identify for municipal water hardness. Check your citys water caliber lab website (e.g. http//www.tempe.gov/waterquality/typical_values.htm) (Complexometric Determination of Water Hardness Lab, n.d.).ObservationsUpon adding the preparing the Na2EDTA solution the Na2EDTA solid was quickly dissolved into the DI water to create a clear solution. Later on in the procedure stage of adding the ammonia/ammonium chloride buffer into the 250 mL flask, a visual chemical reaction was observed as the ammonia buffer was mixing into the flask with CaCO3 and the unknown solution in some(prenominal) procedures. Upon adding the Eriochrome Black T indicator the color was visually changed from clear to uncontaminating pink in both procedures. During titration of both proc edures the visual color change was observed from light see-through pink to see-through violet when the process was close to ending, then from see-through violet to see-through light blue signaling then end of the reaction process.