complexometric titration
DESCRIPTION
Lecture for Complexo titrationTRANSCRIPT
QUIZ What is the molarity of a KSCN solution
if 23.15ml was used to backtitrate a solution containing pure 1.1956 g of Barium Chloride (BaCl2; MW=208.23g/mol) dissolved in 52 ml of 0.4489 M Silver Nitrate?
COMPLEXOMETRIC TITRATION
HISTORY Justus Leigbig (1850) Metal Ligand Complexation Ag and Hg Ions Ligands are Cl and CN ions –
Monodentate However only silver and Hg form stable
complex with these Ligands.
HISTORY Schwarzenbach (1945) Aminocarboxylic acids – multidentate
ligands Forming stable 1:1 complex with metal
ions Analytical Purposes was establish when
metallochromic dyes were introduced. Metallochromic dyes – visual indicators
for complexation reactions
ETHYLENEDIAMINETETRAACETIC ACID (EDTA)
ETHYLENEDIAMINETETRAACETIC ACID (EDTA)
Lewis Acid 6 binding sites Metal-ligand complex – cage like = very
stable All metal Ion complex of EDTA = 1:1
OPTIMUM EDTA – METAL LIGAND FORMATION
pKa1 = 0.0 pKa2 = 1.5 pKa3 = 2.0 pKa4 = 2.68 pKa5 = 6.11 pKa6 = 10.17
All carboxylate ions must be ionized All ammonium ions should be non
ionized Achieved only if pH > 10.17
CONDITIONAL FORMATION CONSTANTS
CONDITIONAL FORMATION CONSTANTS
THE EDTA-METAL COMPLEX To ensure stability of ion
We add buffers to control pH However some buffers are also ligands. So
be careful
STANDARDIZATION OF 0.1 M EDTA Usually EDTA can be obtained in pure form Standardized with Metallic Magnesium,
Calcium Carbonate or Metallic Bismuth Procedure:
Weigh 0.24 g Metallic Mg Dissolve in 25ml 1 M HCl and Dilute to 1L Transfer 25 ml of solution to erlenmeyer flask Ad 2ml of pH 10 ammonia buffer Add Erichrome black T Titrate until the solution change to blue
STANDARDIZATION 0.1 M EDTA solution was standardized using
Metallic Magnesium. 0.2414 g of Mg Metal was weighed and prepared for standardization. The EDTA solution consumed is 25 ml. What is the exact Concentration of EDTA solution?
Mole of EDTA = Mole of MagnesiumM(edta) V(edta) = weight Mg/ MW Mg M(edta) x 0.025 L = 0.2414 g / 24.305
CALCIUM DETERMINATION
MAGNESIUM CONTAINING COMPOUNDS
pH 10 (ammonia buffer) Erichrome Black T
At presence of other metals ---- ?
CALCIUM CONTAINING COMPOUNDS pH 12-13 (0.1 M NaOH) Murexide Indicator
Endpoint : Violet Color
ZINC CONTAINING COMPOUNDS pH 10 (ammonia Buffer) Erichrome Black T
NICKEL CONTAINING pH 8 (10% ammonium Chloride-
ammonia solution) Murexide
ALUMINUM – PICKY pH 5.5 (acetate buffer) *previously neutralized Too slow reaction Residual Titration EDTA as Excess Zinc Sulfate as Backtitrant Indicator (Potassium Ferrocyanide + 3,3’dimethyl
naphthidine) Potassium Ferrocyanide -> Formation of Znferrocyanide Change in redox potential, dimethylnaphthidine is
oxidized = pink
WATER HARDNESS TEST Measure of amount of Mg and Ca in water High Ca and Mg content = hard water procedure
Transfer exactly 50 mL of water to 250 mL Erlenmayer flask. Acidify the solution with hydrochloric acid. Bring to boil, cool down. Alkalize with ammonia. Filter solution through filter paper. Add 1 ml of pH 10 ammonia buffer. Add 3 drops of Eriochrome Black T solution or pinch of
Eriochrome Black T ground with NaCl. Titrate with 0.01M EDTA solution till color changes from violet to
blue.
QUIZ: COMPLETE THE TABLEFor Determination of:
pH of Titration
Buffer Used
Titrant/s used
Indicator and color of Endpoint
Magnesium
1 2 3 4
Calcium 5 6 7Nickel 8 9 10 11Aluminum 12 13 EDTA
Back Titrant:14
15
EXAMPLES You are using EDTA with a molarity
of .0080 for the titration. You titrate 50.00 mL of water sample using 10.68 mL of EDTA.
What is the CONCENTRATION of Ca2+ ion?
EXAMPLES What is the %w/w Ca ion content of a
milf formula if 0.453 g of the powder was titrated with 23.17 ml of 0.1337 M EDTA Solution to a murexide endpoint?
EXAMPLES A 200 mg Aluminum Hydroxide tablet
was dissolved in acetate buffer. What is the actual concentration of Aluminum Ions in the solution if 50 ml of 0.1 M EDTA solution is used as an excess titrant and is backtitrated with 30ml of 0.0983 M Zinc Sulfate to a pink endpoint?
STANDARDIZATION EXAMPLE A 0.0352 g sample of pure calcium
carbonate (100.09 g/mol) was dissolved in acid and titrated to its endpoint with newly made EDTA titrant (~0.010 M) according to the procedure given below. The starting burette volume was 0.10 mL. The ending burette volume was 35.52 mL. Calculate the exact concentration of the EDTA titrant. Show all work.
SAMPLE PROBLEM A 0.0456 g sample of an unknown sample
was titrated using the EDTA titrant from question 1 and the procedure below. The starting burette volume was 0.05 mL. The ending burette volume was 42.35 mL. Calculate the % calcium oxide (CaO; 56.0774 g/mol) by mass in the sample. What is the indicator? What pH should be maitained? What Buffer solution is used?
WATER HARDNESS 100.0 mL of an unknown water sample
was titrated using the EDTA from question 1 and the procedure below. The starting volume was 0.25 mL and the ending volume was 20.53 mL. Calculate the concentration of Ca2+in the tap water. Show all work.