Determination of Water Hardness

Complexometric Determination of Water Hardness

Lab Report

Introduction:
In this lab the use of disodium salt of EDTA is used to determine the concentration of M^2+ metal ion impurities in hard water by chelometric titration. The indicator Eriochrome Black T will help detect when you EDTA has completely chelated the metal impurities.
Chemical Principle:
A complex ion consists of a metal ion with Lewis bases attached to it. These Bases form strong covalent bonds with the central complex ion in which both electrons of the bond are donated by the Lewis base. The Lewis bases that form this complex are referred to as ligands and they are typically either neutral molecules or anions. The stability of the resulting complex, or chelate, enables it to be used as a solvent to strip metal ions from various substances. Through chelometric titration, EDTA can be used to gauge the concentration of metal wastes found within hard water. The chemical equations that are to calculate a measure called the relative average absolute deviation which will be used to estimate the precision, and to calculate the water hardness of the substance.
Procedure:
Part 1
Prepared a 0.004 M disodium EDTA solution by adding .7207g of Na2EDTA to 500 mil of deionized water in plastic bottle.
Standardized the Na2EDTA solution using a stock calcium ion solution as a primary standard.
Followed procedure 2.a-g as instructed in lab manual.

Part 2
Choose one prepared unknown water sample as provided (unknown #107)
Followed procedure 3.a-f
Observation and Calculations:
Standardized calcium ion solution (1.000 g CaCO3/L solution)
First Titration
Initial burette reading
0.0mL
Final burette reading
26.6mL
Ammonia
3.0mL
Na2EDTA= .0037M

Second Titration
Initial burette reading
0.1mL
Final burette reading
28.0mL
Ammonia
3.1mL
Na2EDTA=.0036M
Third Titration
Initial burette reading
0.0mL
Final burette reading
26.6mL
Ammonia
3.1mL
Na2EDTA=.0037M