Table 1. Standardization of 0.01 M EDTA Against the Primary Standard Calcium Carbonate Balanced Chemical Equation: Details Trial 1 A. Preparation of Ca²+ Standard Solution Mass (g) CaCO3 Amount (mmoles) Ca = Amount (mmoles) CaCO3 Volume (mL) of Ca Standard Solution Molarity of Ca Standard Solution B. Determination of the Concentration of EDTA Solution (Molarity) Balanced Chemical Equation Molarity of Ca Standard Solution Volume (mL) of Ca Standard Solution Titrated Amount (mmoles) Ca Amount (mmoles) EDTA reacted Volume (mL) of the EDTA Solution delivered Molarity of EDTA solution Average Molarity EDTA solution Deviation Standard Deviation Coefficient of Variation (%RSD) C. Other Expressions of Concentration of the EDTA Solution Average Molarity of EDTA Standard Solution Ca titer (mg Ca/ml of EDTA solution) 21.70 Trial 2 0.2473 21.60 Trial 3 21.40

Please write and show the balanced chemical reactions (on the upper part (above letter A) and under determination of the concentration EDTA solution). 

Hint: 

Experimental Procedure:

A. Preparation of 0.01M EDTA solution

Transfer about 2-g of disodium dihydrogen EDTA dihydrate and 0.1-g of MgCl2•6H2O into a clean 400-mL beaker and dissolve the solids in water.  If the solution appears turbid, add NaOH solution until the solution is clear.  Transfer the solution into an amber bottle, add enough distilled water to make about 0.500 L and mix thoroughly.   Label the contents of the bottle as 0.01 M EDTA.

B. Standardization of 0.01M EDTA solution using CaCO3 as Primary Standard

You should prepare the Ca2+ standard solution as follows:  accurately weigh about 0.2-0.4-g of primary standard CaCO3 that has been previously dried at 100oC.  Transfer the solid to a 250-ml volumetric flask, using about 100-mL water.  Slowly add 1:1 HCl dropwise until effervescence ceases and the solution is clear.  Dilute with water to the mark and mix solution thoroughly. Pipet a 25-mL portion of the Ca2+ standard solution and transfer it into a 250-mL Erlenmeyer flask.  Add 5-mL of the NH3-NH4Cl buffer solution and 5 drops of Eriochrome Black T (EBT) indicator.  Titrate carefully with the EDTA solution to the point where the color changes from wine-red to pure blue. No tinge of red should remain in the solution.  Repeat the titration with two other aliquots of Ca2+ standard solution.

Report the molar concentration of the EDTA solution.

C. Determination of Ca in Drugs

The Lab Instructor will provide you with an OTC drug sample that contains calcium lactate only and some information regarding the composition of the drug.  From this data, make the detailed procedure for the determination of Ca in the drug sample.  Always remember that the desired volume of the titrant that will be consumed for each analysis must lie within the range of 10 to 40 mL.  Show the calculations to your Lab Instructor before proceeding.

Measure about 50 mL of distilled water into a 250-mL beaker and dissolve one or more tablets.  If the sample is not very soluble in distilled H2O, add about 5 mL of 0.5 M HCl and this will improve its solubility.  Transfer the dissolved tablet into a volumetric flask and dilute to the mark.  Label the mixture as dilute tablet solution (DTS).  Determine the volume of the aliquot portion of the DTS that must be measured so that the volume of the titrant needed to reach the end point will lie within the range of 10 to 40 mL.

With the use of a volumetric pipet, obtain an aliquot portion of the DTS and transfer it into a 250-mL Erlenmeyer flask.  Add 1.0 mL of the buffer solution and 5 drops of the indicator solution.  Titrate with the standard EDTA solution to a color change of wine-red to pure-blue.  Perform the titration in triplicate measurements.