The amount of calcium in solution is determined by using Ethylenediaminetetraacetic acid or EDTA. EDTA is a compound that is often used to separate metal ions from aqueous solution. Furthermore, the complexometric indicator Eriochrome Black T is used in this titration because a color change occurs when the reaction has concluded. The indicator is chosen due to the fact that when EDTA reacts with Ca2+ a complex is formed. In order to ensure a complete reaction, a buffer was added to fully deprotonate the EDTA molecule. To determine the concentration of Ca2+ found in the tap water and the unknown, the following reaction was utilized, which include the calculation of moles (Table 2). The reaction that is taking place follows the scheme of M2+…show more content… The average volume of EDTA that was used is .5mL with a standard deviation of .1mL. The average percentage of the volume of EDTA added to the tap water is 4.67%. Table 2: Volume of Solution Required for the Unknown
Unknown Solution Trial 1 Trial 2 Trial 3
The volume of Unknown Solution (mL)
50.00
50.00
50.00
The Volume of EDTA (mL) Added 18.52 19.11 18.90
Table 2 illustrates the concentration of calcium that is found in the unknown. The average volume of EDTA that was used is 18.84mL with a standard deviation of .299mL. The average percentage of the volume of EDTA added to the unknown is 37.68%.
Preparation of EDTA Standard
.6074g disodium EDTA dihydrate÷372.24= Moles Disodium EDTA dihydrate
.00163mol÷.5L= .00326M EDTA standard Concentration of Ca2+ in boiled EasyPure Water
0L standard used *.00326M = 0 moles standard = 0 moles Ca2+ Concentration of Ca2+ in Tap Water from the Center for the Sciences
.000604L of standard used* .00326 = 1.97*10-6 moles EDTA used= moles Ca2+ in tap water
1.97*10-6 moles Ca2+ ÷ .25L = 7.88*10-6 M Ca2+ = corrected molarity
(7.88*10-6 + 5.30*10-6 + 6.57*10-6) ÷ 3 = 6.58*10-6 M with a standard deviation of…show more content… Results