complexometric titration

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.