Complexometric Determination of Calcium in Milk Experiment 4

Introduction (Ca) is a mineral that can be found in cereals fruits , vegetables & Dairy products . it is Essential to the proper formation of teeth and bones. increase intake can reduce osteoporosis, a disease that affects millions where bones become fragile (bone thinning)

In this experiment the percentage of calcium present in milk will be determined by using complexometric titration with EDTA. EDTA( ethylenediaminetetraacetic) acid is a hexaprotic ion (chelating agent): meaning that each of the acid oxygen’s and each of the amine nitrogen’s can donate one electron pair, and it works by binding to metal ions (i.e. forms a complex with calcium ions).

Ca2+ + EDTA→ Ca[EDTA]4-

For EDTA, most metal-ligand complex formation reactions are fast, stoichiometric and result in stable compounds. The clinical determination of calcium in milk is done by an EDTA titration. Eriochrome black T (EBT) used as an indicator.

Reagent: Disodium tetracetic acid (Na2 H2 EDTA. 2H2O) Magnesium EDTA solution 0.1 M . Eriochrome Black T (EBT) indicator solution. Buffer solution. Calcium carbonate (CaCO3) standard 0.8 g/L . Sodium cyanide (NaCN). Unknown I (150 ppm) Unknown II (100 ppm).

Procedure: I) Standardization 1- 10 ml CaCO3 2- 3 ml buffer 3- 4 drops Mg-EDTA 4- 1 drop EBT 5- Titrate with EDTA solution until get sky-blue color (end point).

II)Analysis 1- 10 ml sample 2- 3 ml buffer 3- 4 drops Mg-EDTA 4- 1 drop EBT 5- Titrate with EDTA solution until get sky-blue color (end point).

Calculation: I)Standardization Ca titer = (weight of CaCO3mg/ml of EDTA titer) x (volume of CaCO3ml/1000 ml) x (atomic weight of Ca /M.wt of CaCO3) Since: Weight of CaCO3 = 0.8g/L 800mg/1000ml Volume of EDTA (from my reading) =5.8 ml Ca titer = (800/5.8) x (10/1000) x (40.08/100.09) = 137.93 x 0.01 x 0.400 = 0.551 mg/ml

II)Analysis Concentration of Ca in the unknown sample = (Ca titer mg/ml x ml of EDTA for unknown) / volume of sample in liter   Volume of sample = 10 ml 0.01 L Volume of EDTA from my reading = 1.8 ml Ca = (0.551mg/ml x 1.8ml) / 0.01L = 99.18 mg / L