Lecture of B.Sc (II) on Analytical Chemistry (a)

By Dr. Sheerin Masroor Assistant Professor of Chemistry A.N.College Patliputra University Patna Bihar EDTA

 Ethylenediaminetetraacetic acid .

 Abbreviations: EDTA, H4EDTA.

 Chemical formula: C10H16N2O8.  IUPAC NAME: 2,2′,2″,2‴-(Ethane-1,2-diyldinitrilo)tetraacetic acid.  Other Names: EthyleneDiamineTetraAcetic acid, N,N′-Ethane-1,2-diylbis[N- (carboxymethyl)glycine], Diaminoethane-tetraacetic acid.  It was synthesised for the first time in 1935 by Ferdinand Münz.  It is aminopolycarboxylic acid.  Conjugate base is ethylenediaminetetraacetate. Structure Synthesis  It was first explained in 1935 by Ferdinand Münz, who was able to prepare the compound from ethylenediamine and chloroacetic acid.  Nowadays EDTA can mainly be synthesized from ethylenediamine (1,2-diaminoethane), formaldehyde, and sodium cyanide leading to formation of tetrasodium EDTA, which further is converted in a subsequent product into the acid forms by reacting with HCl:

 H2NCH2CH2NH2+4CH2O+4NaCN+4H2O→(NaO2CCH2)2NCH2CH2N(CH2CO2Na)2+4NH3 .

(NaO2CCH2)2NCH2CH2N(CH2CO2Na)2+4HCl→(HO2CCH2)2NCH2CH2N(CH2CO2H)2+4NaCl Binding of EDTA

 Ethylenediaminetetraacetic acid (H4EDTA or H4Y).  Ethylenediaminetetraacetate anion (EDTA-4 or Y-4).  In coordination chemistry, EDTA4− usually binds to a metal cation through its two amines and four carboxylates.  This hexadentate ligand forms very stable complexes (usually octahedral structures) with most of the transition metals. 2+  EDTA is a hexaprotic system (H6Y ) with 4 carboxylic acids and 2 ammoniums  The donor atoms in EDTA4- are the two N atoms, and the four, negatively charged O atoms. Effect of pH 2+  At very low pH (very acidic conditions) the fully protonated H6EDTA form predominates,  Whereas at very high pH or very basic condition, the fully deprotonated EDTA4− form is prevalent.  Some of the complexes of EDTA4− takes more complex structures because of any reason like due to either the formation of an additional bond to water, i.e. seven-coordinate complexes, or the displacement of one carboxylate arm by water.  EDTA can able to forms especially strong complexes with Mn(II), Cu(II), Fe(III), Pb(II) and Co(III).  The iron(III) complex of EDTA is seven- coordinate in figure. EDTA COMPLEX  It can be seen that EDTA makes 1:1 complexes with most metals but not with Group 1A metals of periodic table.

 EDTA complexes are usually form water soluble complexes with high formation constants.

 Formation constant, Kf, (or stability constant) can be given as: Hard Water  Hardness of water can be defined as the content of minerals present in it which may be added when water percolates through deposits of limestone, chalk or gypsum which are mostly made up of calcium and magnesium carbonates, bicarbonates and sulfates.  Water hardness is mostly seen to degrades boilers, cooling towers, and other equipment that handles water.  For domestic usage, hard water is often indicated by: a. Lack of foam formation when soap is agitated in water, and b. By the formation of limescale in kettles and water heaters. Water hardness can be treated, by water softening to reduce adverse effects. The units are as follows: 1. Parts per million (ppm) and can be defined as

1 mg/L CaCO3.It is equivalent to mg/L without chemical compound specified, and to American degree. 2. Grains per Gallon (gpg) can be defined as 1 grain (64.8 mg) of calcium carbonate per U.S. gallon (3.79 litres), or 17.118 ppm.

3. a mmol/L is equivalent to 100.09 mg/L CaCO3 or 40.08 mg/L Ca2+. 4. A degree of General Hardness (dGH or 'German degree (°dH, deutsche Härte))‘ can be defined as 10 mg/L CaO or 17.848 ppm. 5. Clark degree (°Clark) or English degrees (°e or e) is defined as one grain (64.8 mg) of CaCO3 per Imperial gallon (4.55 litres) of water, equivalent to 14.254 ppm. 6. A French degree (°fH or °f) is defined as 10 mg/L

CaCO3, equivalent to 10 ppm. Cause of Hardness  It may be caused by the presence of concentration of multivalent cations in the water, which are positively charged metal complexes with a charge greater than 1+.  Mostly, the cations have the charge of 2+, like Ca2+ and Mg2+.  Some of these metallic ions can enter a water supply by leaching from different minerals such as calcite, dolomite and gypsum.  Ca2+ and Mg2+ form insoluble salts with soaps causing precipitation of the soap scum.  A major component of such scum is calcium stearate, which arises from sodium stearate, the main component of soap: − 2+  2 C17H35COO (aq) + Ca (aq) → (C17H35COO)2Ca (s) Types of Hardness  Temporary hardness  It is a kind of water hardness and can be caused by the presence of dissolved bicarbonate minerals such as calciumbicarbonate and magnesium bicarbonate.  In dissolved form, these type of minerals can give calcium and magnesium cations (Ca2+, 2+ 2− − Mg ) and carbonate and bicarbonate anions (CO3 and HCO3 ).  The presence of these kind of metal cations makes the water hard and is Temporary in nature.  This type of "temporary" hardness can be reduced either by boiling the water,  Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling. Removing Temporary Hardness

Boiling Clarks Method  Permanent Hardness  Permanent hardness (mineral content) are generally difficult to remove by boiling.

 It is caused by the presence of calcium sulfate/calcium chloride and/or magnesium sulfate/magnesium chloride in the water, which do not precipitate out if the temperature increases.  Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column. Removing Permanent Hardness

By use of Chemicals By IonExchangers  Aim: To estimate the amount of total hardness present in the given sample of water by EDTA titration method.  Apparatus required: 50 ml Burette, 20 ml Pipette, 250 ml Conical flask, 100 ml Beaker, 250 ml beaker, Glass funnel.

 Chemicals required: EDTA solution, Standard CaCO3 solution, Eriochrome Black–T indicator, Buffer solution.  Theory: EDTA (Ethylenediamine tetra acetic acid) forms colorless stable complexes with Ca2+ and Mg2+ ions present in water at pH = 9-10.

 To maintain the pH of the solution at 9-10, buffer solution (NH4Cl + NH4OH) is used. Eriochrome Black-T (E.B.T) is used as an indicator.  The sample of hard water must be treated with buffer solution and EBT indicator which forms unstable, wine-red colored complex s with Ca2+ and Mg2+ present in water.  If Eriochrome Black T dye is added to the hard water which have to be analysed at high pH of approx10 it will gives wine red coloured unstable complex with Ca+2 and Mg+2 ions of the sample water.  Now when this wine red-coloured complex is titrated against EDTA solution with known strength the colour of the complex changes wine red to original blue colour showing the endpoint.  Disodium salt of ehtylenediamine tetraacetic acid: (Na2H2Y)  where Y = deprotonated agent.  In aqueous solution EDTA ionises to give 2Na+ ions and act as a strong chelating agent.  The indicator used is Eriochrome Black T (EBT) is a complex organic compound (sodium – 1 – (1-hydroxy 2-naphthylazo)-6- nitro-2-naphthol-4-sutphonate).  It has two ionisable phenolic hydrogen atoms and for simplicity + –. it is represented as Na H2In  Eriochrome Black-T(EBT) is the metal ion indicator used in the determination of hardness by complexometric titration with EDTA.  The EBT tends to polymerize in strongly acidic solutions to a red brown product, and hence the indicator is generally used in EDTA titration with solutions having pH greater than 6.5.  The sulphuric acid groups loses its proton much before the pH range of 7-12, which is of interest for metal ion indicator use.  The dissociation of the two hydrogen atoms of the phenolic groups only should therefore be considered and hence the dye – stuff may be represented by the formula H2D . As acid-base indicator of EBT with two colour changes as follows:

For the pH range 8-10, the blue form of the indicator HD2– gives a wine red complex with Mg2+ :

2– After that EDTA (H2Y ) is added to such a solution containing Mg2+ ions preferentially it will make complexes with EDTA (since the metal EDTA complex is more stable than the metal- indicator complex) and liberates the free indicator HD2– at the end point, and produces a sharp colour change from wine red to blue. The ongoing reactions in the EDTA titration may be summarized as follows: Dimethylglyoxime.

IUPAC name:N,N′-Dihydroxy-2,3-butanediimine

Chemical formula:CH3C(NOH)C(NOH)CH3.

Abbreviation is dmgH2 for neutral form, and dmgH for anionic form, where H stands for hydrogen. dmgH2 is used in the analysis of palladium or nickel.  Preparation Divided into two steps: a. Butanone first reacts with ethyl nitrite to give biacetyl monoxime. b. The second oxime is made on reaction with sodium hydroxylamine monosulfonate.  Uses  It is use to separate metals from complexes forms complexes such as Nickel, Palladium, and Cobalt.  It is also used in precious metals refining to precipitate palladium from solutions of palladium chloride.  Cupferron  Cupferron is word used for the ammonium salt of the conjugate base derived from N- nitroso-N-phenylhydroxylamine.

 Its formula is NH4[C6H5N(O)NO].  It can acts as common reagent for the complexation of metal ions, which has to be seperated in the area of qualitative inorganic analysis.  Here the anion binds to metal cations through the two oxygen atoms, forming five- membered chelate rings.  Synthesis  Cupferron can be prepared from phenylhydroxylamine and an NO+source such as butyl nitrite in the presence of ammonia.

C6H5NHOH + C4H9ONO + NH3 → NH4[C6H5N(O)NO] + C4H9OH

Uses  It is used to separate tin from zinc.  Also seperates copper and iron from other metals in the laboratory.  It also finds application as a quantitative reagent for vanadates and titanium; and for the colorimetric determination of aluminum. Thiosalicylic acid

Other Names: 2-Sulfanylbenzoic acid. 2-Mercaptobenzoic acid. o-Thiosalicylic acid. ortho-Thiosalicylic acid.

Chemical Formula: C6H4(SH)(CO2H). Synthesis of Thiosalicylic Acid •50 g of 2-chlorbenzoic acid if mixed with a little water and then 13.5 g of sodium hydroxide dissolved in 25 ml water, 100 g of sodium hydrosulfide, and 0.5 g of crystallised copper sulphate also mixed in. •The whole is then heated with continous stirring at temperature 150-200° C. •The mass soon becomes dark red and melts. •The temperature is then raised to 250° C, when the mass becomes thick, heats spontaneously, and gradually . •The cooled melt is dissolved in a litre of water and the thiosalicylic acid precipitated from the filtered solution with hydrochloric acid. •Can be explained by the reaction given below: Uses  It is an analgesic and anti-inflammatory agent.  Can be used (in form of sodium salt) to relieve symptoms of acute gout, painful musculoskeletal conditions, osteoarthritis and rheumatic fever.  in the form of drug can exerts its action by inhibiting prostaglandin synthesis.