Complexometric Determination of Water Hardnesss

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Complexometric Determination of Water Hardness

Mike Monaghan
CHM 152LL
01/27/2013

Abstract: What can be found from this experiment is as follows,

Introduction/Background: This lab was about determining water hardness. Water hardness is the amount of metal ions in the water. The most common found ion in the water is calcium ions and typically with a charge of +2. Water hardness plays a big significance in our daily life because to many metal ions in our drinking water can have adverse effects on our body. You can measure the water hardness by EDTA titrations. EDTA is a disodium salt that stands for ethylenediaminetetraacetic acid and it is a chelating agent. Chelation is the process of a ligand forms a complex with a metal ion. Eriochrome Black T is an indicator you add to the water sample that will turn the water pink if metal ions exist. Through the process of titration, carefully adding EDTA to the water sample with the Eriochrome Black T will cause a chemical reaction to occur, slowly changing the water color from pink to violet and then violet to a light blue which will be the end of the chemical reaction. Once the titration is complete you can calculate your water hardness.

The formula used to calculate the water hardness is as followed: Mg Caco3/1L CaCO3 soln= VmL Na2EDTA soln/0.02500L CaCO3 soln x M mol Na2EDTA/1L Na2EDTA soln x 1 mol CaCO3/1 mol Na2EDTA x 100.1g CaCO3/ 1 mol CaCO3/1 mol Na2EDTA x 100.1 g CaC03/ 1 mol CaCO3 Above in the formula V represents the actual delivered volume of Na2EDTA solution and M is your actual molarity.

Procedures: Start by preparing 500mL of 0.004 disodium EDTA solution. This is what will be added to the buret. Next take a 250-mL Erlenmeyer flask and add 10.00mL of standardized calcium and 30mL of deionized water. Place a magnetic stir-bar in the flask and set on top of a piece of white paper on a magnetic stirrer. After place 3mL of ammonia/ammonium chloride buffer (pH10) inside the flask and let it...
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