School Science Lessons
2024-06-10
Ligands, EDTA
Contents
(UNChemLigands) 1.0 Ligands
2.0 Reactions of metals with ligands
3.0 EDTA
Paraffin oil
Phenolic compounds by name
Phenyl group
1.0 Ligands
A ligand can be an ion or an atom that can form a co-ordination complex with a central atom, usually a metal.
A ligand is a molecule that selectively binds to another molecule.
Transition metals, (transition elements), can form bonds called dative covalent bonds by accepting pairs of electrons, (shown as :), from other ions or molecules.
Both the shared electrons come from the same atom.
The ion or molecule that forms the bond with the transition metal is called a ligand, e.g. (:Cl-), (:CN-), (H2O:), (:NH3).
More than one ligand can bind to a transition metal ion to form a complex ion.
The number of ligands so bonded is called the co-ordination number, for example:
co-ordination number 4: [CoCl4]2-,
co-ordination number 6: [CO(NH3)6]3+
Experiments
12.5.0 Chromium ions in solution, (See: 6.)
1.1 Copper (II) sulfate solution with ammonia solution, ligand substitution
1.2 Copper (II) sulfate solution with concentrated hydrochloric acid, ligand substitution
1.1 Copper (II) sulfate solution with ammonia solution, ligand substitution
The copper ion, Cu2+ (aq), in aqueous solution, forms a blue complex ion, [Cu(OH2)6]2+, with 6 water molecules.
The blue complex is the cause of the blue colour of copper sulfate solution.
Ammonia solution contains hydroxide ions, OH-, and is alkaline.
Add ammonia solution drop by drop to the pale blue copper sulfate solution.
A pale blue precipitate of insoluble copper hydroxide forms.
Cu2+ (aq) + 2OH- (aq) --> Cu(OH)2 (s)
Add more ammonia solution to dissolve the copper hydroxide to form the deep blue complex ion, [Cu(NH3)4(OH2)2]2+.
Four of the 6 water molecules in the blue complex ion, [Cu(OH2)6]2+ have been replaced by ammonia ions, leaving 2 water molecules still there.
So the number of ligands around the copper ion is still 6.
1.2 Copper (II) sulfate solution with concentrated hydrochloric acid, ligand substitution
The copper ion, Cu2+ (aq), in aqueous solution, forms a blue complex ion, [Cu(OH2)6]2+, with 6 water molecules.
The blue complex is the cause of the blue colour of copper sulfate solution.
Concentrated hydrochloric acid has a high concentration of chloride ions.
Chloride ions are better ligands than water, because they are negatively charged ions and are attracted electronically to the copper ion, Cu2+.
Experiment
Add concentrated hydrochloric acid drop by drop to a pale blue copper sulfate solution.
The solution turn yellow-green as the chloride ion ligands, Cl-, replace water in the complex ion.
Four chloride ions replace the 6 water molecules in the blue complex ion to form the yellow-green [CuCl4]2- complex ion.
So the number of ligands around the copper ion has dropped from 6 to 4.
2.0 Reactions of metals with ligands
See diagram 16.4.4: EDTA molecule
Metals and ligands form co-ordination bonds (co-ordination complexes), with both electrons coming from the ligand.
Ligands have a lone pair of electrons.
Metals do not have enough electrons to form covalent bonds by sharing one electron from the metal ion with one electron from the bonded atom.
The metals involved include Ag+, Al3+, Cu2+ and Fe3+.
Examples of ligands include: -NH3, -OH2, -Cl-, -OCOCH3-, -EDTA-4, -NTA-3.
Complexes include metal carbonyls, metal (CO)4, [Cu(H2O)6]2+, [PtCl4]2-.
Metals usually bond with 4 to 6 ligands.
Chelates are ligands that bind more than one compound.
Copper forms a series of ligands with ammonia.
Cu2+ + NH3 <--> CuNH32+
CuNH32+ + NH3 <--> Cu(NH3)22+
Cu(NH3)22+ + NH3 <--> Cu(NH3)32+
Cu(NH3)32+ + NH3 <--> Cu(NH3)42+

Ammonia is a monodentate (one tooth) ligand, because it forms one co-ordination bond with a metal.
Ethanediamine, (H2NCH2CH2NH2), is a bidentate (two tooth) ligand, because it forms two co-ordination bonds with a metal.
Triethanetetramine (trien) and nitrilotriacetic acid (NTA), are tetradentate ligands, because they form one four co-ordination bonds with a metal.
Ethanediaminetetraacetate (EDTA4-), is a hexadentate ligand, because it forms six co-ordination bonds with a metal.
4.0 EDTA
EDTA, Ethylenediaminetetraacetic acidEdetic acid, C10H16N2O8, ((HOOCCH2)2NCH2)2, colourless crystalline solid, slightly soluble in water.
It is a chelating agent, i.e., it forms stable bonds with metal ions and so it decrease their chemical activity.
It occurs in Perilla frutescens and Apis cerana.
EDTA binds calcium and heavy metal ions, including lead - it can form the calcium complex [Ca(EDTA)]2-.
It is used to treat forming soluble stable complexes to be excreted through the kidneys.
It decreases in serum calcium levels and is used to treat lead poisoning.
It is used in pharmaceutical manufacturing, as a food additive, for water softening, removing scale from kettles.
EDTA deactivates the enzymes containing metal ions that cause food spoilage, loss of colour and loss of flavour.

If a ligand is defined as a small molecule that binds to a larger molecule, then chelates can be said to bring about the complexation of a ligand.
The terms ligand, chelate, chelating agent and sequestering agent are used in slightly different ways in chemistry, medicine, and general industry.
A chelate is a metal ion bound to two or more atoms of a chelating agent (sequestering agent), e.g. the simple chelating agent 1,2-diaminoethane (ethylene diamine), NH2.CH2.CH2.NH2, forms bonds to a metal ion through its nitrogen atoms.
[Diaminoethane, ethylene diamine, C2H4(NH2)2, ligand, chelating agent, Toxic by all routes, Corrosive]
Porphyrin chelates include haeme, in haemoglobin, bonded to iron (II) ion, and chlorophyll bonded to Mg (II) ion.
4.2 Ion exchange resins, deionized water
3.4.7 Prepare nylon polymer:
19.4.6 Sequestrants, food additives Experiments
9.9.18.5 Mineral deficiency experiment, hydroponics, EDTA
12.13.11 Tests for metal ions, using EDTA
12.13.12.0 Tests for water hardness, EDTA titration, Calmagite indicator
12.13.12.1 Tests for water hardness, EDTA titration, Eriochrome Black T indicator
4.2 Ion exchange resins, deionized water
Let RZ = the resin, an organic polymer matrix.
Charged groups are bound to the resin.
Cation exchange resin, H+ form, to remove cations, e.g. Ca2+, from solution.
2RZ-SO3- H+ + Ca2+ <--> RZSO3-)2Ca2+ + 2H+
Anion exchange resin, OH- from, to remove anions, e.g. Cl-, from solution
RZ-N(CH3)3+ OH- + Cl- -->RZ-N(CH3)3+ Cl- + OH-
To "soften" water, usually only a cation exchange resin is used.
If both a cation exchange resin and an anion exchange resin are used with tap water to remove ionic salts by ion exchange, the resulting solution is deionized water, a cheaper alternative to distilled water.
Paraffin oil
Paraffin oil, Kerosene, Highly flammable, toxic by all routes, avoid vapour inhalation, skin irritant
Use kerosene to clean chrome-plated taps, to soak greasy overalls before washing with soap powder.
Use kerosene-soaked cheesecloth left to dry for furniture dusters.
Paraffin, hard paraffin wax (chunks), alkane mixture, CnH2n+2), paraffin wax black 43 / 46.
The term "paraffins" was the former name for "alkanes".
Paraffin (Latin parum little, affinis connected), because of its low chemical activity.
The name invented by German chemist Karl Reichenbach in 1830.
1. Paraffin, FP 60oC (UK paraffin oil) (USA, Australia, kerosene), (also kerosine, "kero"), is a petroleum fraction containing a mixture of about ten different hydrocarbons, 10 to 16 carbon atoms per molecule, depending on the origin of the original petroleum.
Kerosene has a flash point about 25°C, so it is a relatively safe fuel.
Use paraffin oil, kerosene, in a well-ventilated space for kerosene lamps and domestic heaters, but do not use it as a degreaser of engines.
2. Paraffin wax is alkanes C20H42) to C40H82, and is used to make candles, polish, "wax" paper.
3. Liquid paraffin, (petrolatum liquid, paraffin liquid), is a pure mineral white oil emulsion used as a medicine.
It is a colourless, tasteless, liquid form of petroleum jelly, mixture of >C12 alkanes, known as petrolatum jelly ("Vaseline").
White paraffin, is another kind of petroleum jelly.
Paraffin wax, MP. 45 to 65oC (pastillated wax, 52oC), relative density 0.9
Nitroparaffins, nitroalkanes
Paraffin wax, fractional distillation
Kerosene, paraffin oil, distillation
Kerosene, for bath cleaning, Prepare
Temporary emulsions and permanent emulsions
Emulsions
Catalytic cracking of kerosene
Prepare soap
Phenolic compounds, by name
Anethole
Arbutin
Bergenin
Caffeic acid
Capsaicin
Carvacrol
Catechol
Chlorogenic acid
< a href="../topics/topicIndexCarbon.html#CichoricacidH">Cichoric acid
Cinnamaldehyde
Cinnamic acid
Coumaric acid
Coumarin
Cresol
Curcumin
Cyanidin
Emodin
Ethylphenol
Estradiol (oestradiol), C18H24O2
Estragole
Eugenol
Ferulic acid
Furanocoumarins
Gallic acid
Guaiacol, Methyoxyphenol
Juglone
Mangiferin
Methyl salicylate
Myristicin
Nordihydroguaiaretic acid
O-leuropein
Paeonol
Piceatannol
Plumbagin
Quercetin
Raspberry ketone
Resorcinol
Resveratrol Rosmarinic Acid
Salicyclic acid
Sesamol
Shikonin
Shogoal
Silibinin
Sinapinic acid
Tannic acid
Thymol
Tyrosine
Tyrosol
Umbelliferone
Urushiol
Vanillin
Zingerone
Phenyl group
Phenyl group, (C6H5)
1-phenylazo-2-naphthol, sudan I, C.I. Solvent Yellow 14, toxic. skin irritant, purchase solution
3-phenylpropenoate, C11H12O2, (Ethyl cinnamate, 3-phenylpropenoate, toxic, Flammable)
3-phenyl propenoic acid, C9H8O2, C9H10O2, C6H5CH:CHCOOH, cinnamic acid, toxic if ingested
Phenyl benzoate, C13H10O2 (recrystallization experiments, ethanol solvent), benzene substitute, toxic, Irritant, Flammable
Phenyl bromide, Bromobenzene: 12.18.3
Phenyl salicylate, C13H10O3
Phenylalanine, C9H11NO2
Phenylamine, C6H5NH2
, Phenylammonium chloride, C6H5NH2.HCl, aniline hydrochloride
Phenyldimethylamine, C8H11N, dimethylaniline
Phenylethene, C8H8O2, C6H5CH:CH2, Styrenes, 3.8.2
Phenylethene, (C6H5CH,CH2), vinyl benzene, styrene
Phenylethylamine, C6H5CH2CH2NH2
Phenylformic acid, C6H5COOH, benzoic acid, benzene carboxylic acid
Phenylhydrazine, C6H8N2, Highly toxic by all routes
Phenylhydrazine, C6H8N2, Solution / mixture < 1%, Not hazardous
Phenylhydrazine hydrochloride, phenylhydrazinium chloride, Highly toxic by all routes
Phenylhydrozone, C13H12N2, benzaldehyde
Phenylmethyl benzoate, C14H12O2. benzyl benzoate
Phenylthiocarbamide, C7H8N2S, PTC, phenylthiourea, (PTU), tasters: #9.9.2
Phenylthiocarbamide, C7H8N2S, PTC: 1.13
Phenylthiourea, C7H8N2S, phenylthiocarbamide, 1-phenyl-2-thiourea (rat poison), Highly toxic if ingested, asthmatics may be allergic
Phenylthiourea, C7H8N2S, 0.1% solution soaked in paper used for taster / non-taster genetic test, Experiment Not permitted in schools
Phenylurea, C6H5NHCONH2, phenylcarbamate, toxic if ingested