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UNIT 1

Bio-inorganic chemistry

It is defined as the study of the structure and function of inorganic ions in biological systems.

Many elements are essential for biological functions in the body. Depending upon the

abundance in the body they are classified as follows:

1. Macro minerals

2. Trace elements.

1. Macro minerals

There are about 7 elements such as Ca, P, K, S, Cl, Na and Mg.

These elements constitute about 0.7% of the atoms in the human body.

They perform variety of biological functions in the body.

Absence of these elements in the body results in disease and sometimes may result in death.

2. Trace elements

There are about 14 elements which are present in the body in small concentrations.

The trace elements are Fe, I, F, Mn, Zn, Mo, Cu, Co, Cr, Se, As, Ni, Si, and B.

The deficiency of these elements causes diseases and even death can result.

The excess concentration of these elements in body produces toxic effect.

Biologically important coordination compounds

A number of coordination compounds have biological importance of which chlorophyll and

hemoglobin are discussed here.

Chlorophyll

1. Chlorophyll is a magnesium porphyrin complex.

2. It is present in all green plants.

3. It consists of two distinct but chemically related substances. They are,

i) Chlorophyll – a (blue colour)

ii) Chlorophyll – b (yellow green colour)

4. The most abundant one is chlorophyll – a.

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Structure of Chlorophyll

Biological importance

1. Its presence is essential for photosynthesis in plants.

2. Chlorophyll causes the combination of CO2 and H2O in presence of sunlight to form starch.

3. CO2 and H2O being colourless and do not absorb any visible light.

4. But chlorophyll, the green colouring matter of the plants can capture and transmit the light

energy for the chemical reaction taking place in photosynthesis.

5. Mg2+ ions acts as a source of phosphorescence and responsible for making the light energy

available for photosynthesis.

6. Free porphyrins show only fluorescent emission.

Hemoglobin

1. It is a conjugated protein.

2. The protein part is globin and the prosthetic group is heme.

3. It is present in the red blood cells of blood.

Structure of Hemoglobin

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4. Each molecule of hemoglobin contains four heme groups.

5. Heme is an iron(II) porphyrin complex.

6. In hemoglobin the hemes are bound via imidazole ring of histidine molecules.

Biological importance

Hemoglobin forms the main constituent of blood.

Metal carbonyls

Carbonyls are the compounds in which the CO group is attached to a metal.

The carbonyls may be classified into two types. They are,

i) Mono nuclear carbonyls

ii) Poly nuclear carbonyls.

i) Mono nuclear carbonyls

They have the general formula M(CO)x.

They contain only one atom of a metal per molecule of CO.

Generally mono nuclear carbonyls are formed by metals which possess even atomic numbers.

ii) Poly nuclear metal carbonyls

They have the general formula Mx(CO)y.

They contain more than one metal atom per molecule of CO.

If they contain two atoms of the metal per molecule, they are called binuclear carbonyls and

they have the general formula M2(CO)y.

Note:

Since mono nuclear carbonyls are formed by metals with even atomic numbers, they have no

unpaired electrons.

The odd electron in each atom is utilized for the formation of metal – metal bond. Thus

binuclear carbonyls are also diamagnetic.

Thus in general carbonyls are diamagnetic.

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Bonding in Carbonyls

1. Carbon monoxide (CO) bonds to transition metals using synergistic π back-bonding.

2. The bonding has three components, giving rise to a partial triple bond.

3. A sigma bond arises from overlap of nonbonding sp-hybridized electron pair on carbon with a

blend of d, s and p orbitals on the metal.

4. A pair of π bonds arises from overlap of filled d orbitals on the metal with a pair of π anti-

bonding orbitals projecting from the carbon of the CO.

Formation of metal ← carbon σ-bond using an unshared pair on the carbon atom

Formation of metal → carbon π-bond

5. As electrons from the metal fill the π anti-bonding orbital of CO, they weaken the carbon-oxygen

bond compared with free carbon monoxide, while the metal-carbon bond is strengthened.

6. Several canonical forms can be drawn to describe the approximate metal carbonyl bonding

modes.

Nickel Carbonyls

Nickel forms only mono nuclear carbonyl i.e., Ni(CO)4.

Binuclear carbonyls are formed by metals with odd atomic numbers. The atomic number of

nickel is 28. So it does not form a binuclear carbonyl.

Mono nuclear carbonyls of Nickel

Nickel tetracarbonyl, Ni(CO)4 (also called nickel carbonyl)

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Preparation

1. Nickel carbonyl can be obtained by passing carbon monoxide over nickel at a temperature of about

60oC.

2. When nickel iodide is heated with carbon monoxide in the presence of halogen, nickel carbonyl is

formed.

Properties

1. Action of Heat: Nickel carbonyl is decomposed when heated to 180 – 200 oC.

2. Action of Acids: Sulphuric acid reacts with nickel carbonyl and evolve carbon monoxide.

3. Action of Bases: It reacts with barium hydroxide.

4. Action of Halogens: It reacts with gaseous chlorine to form nickel chloride. Similarly it reacts with

bromine.

5. Displacement reaction: The CO group in carbonyls can be displaced by reagents such as PCl3, PF3 and

NO2 etc.,

6. With HI: It reacts rapidly with dry hydriodic acid.

7. Action of nitric oxide: It reacts with nitric oxide to give a compound of intense blue colour

Ni(NO)(OH).

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Structure

1. The vapour density of nickel carbonyl and the freeing point of its solution in benzene indicate

the molecular formula to be Ni(CO)4.

2. The electron diffraction studies on nickel carbonyl show that the configuration is tetrahedral

(sp3 hybridization) and the Ni-C-O bonding is linear.

3. Raman spectral studies have revealed that the oxygen atom is triply bonded to carbon atom in

the CO group.

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4. The electronic configuration Ni28 is 1s2 2s22p6 3s23p6 4s2 3d8 4p0.

5. Since the energy of the 3d and 4s electrons is not vary very much, the 4s electrons easily go to

fill the 3d orbitals, there by vacating 4s orbitals.

6. Thus four orbitals (one 4s and three 4p) are now available for chemical bonding with four CO

molecules to give Ni(CO)4.

7. Since the hybridization is sp3 the geometry would be tetrahedral.

Uses

1. The formation of nickel carbonyl is utilized in the purification of nickel.

2. It is used for the preparation of metal mirrors and plates.

3. It is used in glass plating.

4. It is used as a catalyst in many organic reactions.

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Iron Carbonyls

Mono nuclear carbonyl of Iron

Iron pentacarbonyl, Fe(CO)5

Preparation

1. It is prepared by the action of carbon monoxide on iron powder at 200 atm and 100 – 200 oC.

2. Recently it has been prepared by the action of carbon monoxide on ferrous iodide.

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Properties

1. Action of Heat: When it is heated above 1300 oC it decomposes to give iron and carbon monoxide.

2. Action of Acids: It is hydrolysed by sulphuric acid to give ferrous sulphate.

3. Action of Base: It is hydrolysed by weak bases.

4. Reducing action: It behaves as a reducing agent. The iron atom becomes divalent and either CO or

CO2 is liberated.

5. With uv-light: When Fe(CO)5 is irradiated by ultraviolet light, Fe2(CO)9 is formed.

6. With Cyclo pentadiene: When Fe(CO)5 is heated with cyclo pentadiene at 300 oC, it gives the π-

complex ferrocene.

7. With Halogens: It reacts with halogens to give stable tetracarbonyl halide, Fe(CO)4X2.

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Structure

1. The vapour density of iron pentacarbonyl and the freeing point of its solution in benzene

indicate the molecular formula to be Fe(CO)5.

2. The electron diffraction and X – ray studies on iron pentacarbonyl revealed that Fe(CO)5 possess

regular trigonal bipyramid structure.

3. The molecule is diamagnetic and the distance of Fe-C is 1.84 Å.

4. Raman spectral studies have revealed that the oxygen atom is triply bonded to carbon atom in

the CO group.

5. The electronic configuration of Fe26 is 1s2 2s22p6 3s23p6 4s2 3d5 4p0.

6. The five unoccupied orbitals (dsp3) in the valency shell can accept five CO molecules to form

Fe(CO)5.

7. Each CO group giving 2 electrons for the coordinate link.

Uses

1. It is used as antiknock in petrol (,bg;G vjpu;g;G ngl;Nuhy;).

2. It is useful for the preparation of metal powders containing spherical particles.

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Binuclear carbonyl of Iron

Iron ennea carbonyl, Fe2(CO)9

Iron ennea carbonyl, Fe2(CO)9 is a π-nuclear carbonyl.

Preparation

Iron pentacarbonyl is dissolved in glacial acetic acid and is exposed to ultraviolet light for six

hours, Fe2(CO)9 is formed. On cooling golden crystals of the ennea carbonyl separates.

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Properties

1. Action of Heat:

(a) When heated to 50 oC it decomposes to give Fe(CO)5 and some Fe3(CO)12.

(b) When heated to 100 oC, it decomposes to form iron, carbon monoxide, Fe(CO)5 and Fe3(CO)12.

2. With nitric oxide: When heated with nitric oxide at 75 – 100 oC it forms Fe(CO)2NO2.

Structure

1. The structure of binuclear carbonyl of iron is still incomplete.

2. The diamagnetism of poly nuclear carbonyl is accounted for the assumption that metal – metal

bonds are formed.

3. The crystallographic studies of iron ennea carbonyl, Fe2(CO)9 have shown that the two iron

atoms are joined by three ketonic bridges >c=O.

4. The other six CO groups are joined in three each to iron by coordinate bond as shown in the fig.

5. Thus in iron ennea carbonyl the iron atoms are octahedrally coordinate with three CO bridge

groups.

Uses

It is useful for the preparation of metal powders containing spherical particles.

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Chromium Carbonyls

Chromium forms only mono nuclear carbonyl i.e., Cr(CO)6.

Binuclear carbonyls are formed by metals with odd atomic numbers. The atomic number of

chromium is 24. So it does not form a binuclear carbonyl.

Mono nuclear carbonyl of chromium

Chromium hexacarbonyl, Cr(CO)6

Preparation

1. Job’s method: Carbon monoxide at 50 atmospheric pressure and at room temperature is heated with

Grignard reagent (phenyl magnesium bromide) in the presence of anhydrous chromic chloride, we get

chromium hexacarbonyl.

2. Chromium hexacarbonyl can be prepared by treating a solution of a chromic salt dissolved in ether

with triethyl aluminium, Al(C2H5)3 and carbon monoxide at high temperature and pressure.

Properties

1. It is decomposed by chlorine or by conc.HNO3.

2. It reacts with an alkali metal in liquid ammonia.

3. It reacts with pyridine at temperatures above 140 oC.

4. It reacts with potassium hydroxide in methyl alcohol at 100 oC to give a red solution.

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Structure

1. The molecular formula is Cr(CO)6. This makes us infer that it may possess octahedral

configuration.

2. The octahedral configuration of Cr(CO)6 is confirmed by the results of electron diffraction

studies.

3. The electronic configuration of Cr24 is 1s2 2s22p6 3s23p6 4s1 3d5 4p0.

The six unoccupied orbitals (d2sp3) in the valency shell can accept six CO molecules to form Cr(CO)6.

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Thus we have two types of bonds. They are,

Uses

It is used in the preparation of metal mirrors and plates.

Cobalt Carbonyls

Cobalt does not give mono nuclear carbonyls because mono nuclear carbonyls are given by

elements with even atomic numbers.

Since, cobalt’s atomic number is 27 which is odd, it does not give mono nuclear carbonyls.

Binuclear carbonyl of Cobalt

Cobalt octacarbonyl, Co2(CO)8

Preparation

1. It is prepared by the action of carbon monoxide on finely divided cobalt at 1 – 200 atm and at 50 –

200 oC.

2. It is also prepared by the action of carbon monoxide on cobalt sulphate or cobalt iodide in the

presence of copper.

3. When a solution of cobalt carbonyl hydride is treated with an acid, Co2(CO)8 is obtained with the

liberation of hydrogen.

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Properties

1. Action of Heat: When heated to 51 oC it decomposes to give Co4(CO)12. When the temperature is

above 60 oC, Co4(CO)12 further decomposes to give carbon monoxide and metallic cobalt.

2. With Halogens: The halogens decompose cobalt octacarbonyl.

3. Action of Water: It is hydrolysed by water to give a mixture of cobalt carbonyl hydride and cobaltous

hydroxide.

4. Action of Hydrogen: It reacts with hydrogen at 165 oC and 120 atm to form cobalt carbonyl hydride.

5. Action of Ammonia: It reacts with gaseous ammonia to give [Co(NH3)6][Co(CO)4]2.

6. Action of Base: Strong bases like barium hydroxide hydrolyse it to a mixture of cobalt carbonyl

hydride and cobalt carbonate.

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Structure

1. It exists in two isomeric forms. One of these forms has a bridged structure in which two CO

groups bridge two Co atoms which are also linked with each other by a bond.

2. The other form has a non-bridged structure with one Co-Co bond (σ-bond) linking two Co(CO)4

groups.

3. The electronic configuration of Co27 is 1s2 2s22p6 3s23p6 4s2 3d7 4p0.

4. The Co – Co bond is a bent bond which arises due to the unusual overlapping of two singly filled

d2sp3 hybrid orbitals.

5. Each of the Co atoms is in a state of d2sp3 hybridization.

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Manganese Carbonyls

Manganese does not give mono nuclear carbonyls because mono nuclear carbonyls are given by

elements with even atomic numbers.

Since, manganese has atomic number of 25 which is odd, it does not give mono nuclear

carbonyls.

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Binuclear carbonyls of Manganese

Manganese carbonyl, Mn2(CO)10

Preparation

It is prepared by treating manganese iodide and magnesium with carbon monoxide under high

pressure.

Properties

1. Action of Air: It is slowly oxidized by air.

2. Action of Halogens: It reacts with halogens giving manganese carbonyl halides of the type Mn(CO)5X.

3. Action of Sodium: It reacts with sodium in liquid ammonia to yield Na+[Mn(CO)5]-.

4. Action of Diazomethane: It reacts with diazomethane to give a colourless, stable diamagnetic

compound of formula Mn(CO)5CH3.

Structure

1. Mn2(CO)10 has octahedrally coordinated Mn atoms. Each Mn atom is linked to five CO groups

and is also directly bonded to the other Mn atom.Thus Mn2(CO)10 contains ten CO groups.

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2. The CO – Mn – Mn – CO chain is linear. The two square planes each containing four CO groups

and one Mn atom are staggered at angle of 45o.

3. The electronic confiduration of Mn25 is 1s2 2s22p6 3s23p6 4s2 3d5 4p0.

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SILICATES

A group of substances containing negative ions composed of silicon and oxygen are called

silicates.

(OR)

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A set of compounds in which silicon is coordinated tetrahedrally by four oxygen atoms to give

[SiO4]4- units are called silicates.

e.g.,

Sodium silicate, Na2SiO3

Bonding in Silicates

1. The basic unit of all silicates is [SiO4]4- anions.

2. In [SiO4]4- anion, silicon is in sp3 hybridization and tetrahedral in shape.

3. The electronic configuration of Si14 is 1s2 2s22p6 3s23p2.

4. Mutual sharing of electrons between silicon and oxygen atom gives sp3 hybridization.

5. Silicon and oxygen forms a covalent bond.

Structure of [SiO4]4- ion

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Classification of Silicates

Silicates are classified into different types depending upon the number of corners of [SiO4]4-

tetrahedron shared with other tetrahedron.

The different types of silicates are,

1. Ortho silicates

2. Pyro silicates

3. Chain silicates

a) Single chain silicates

b) Double chain silicates

4. Cyclic silicates (or) Ring silicates

5. Two dimensional sheet silicates

6. Three dimensional silicates

1. Ortho silicates

Ortho silicates have discrete (njhlu;gw;w, jdpj;jdpahd) tetrahedral [SiO4]4- units. No oxygen

atom is shared between adjacent tetrahedron.

e.g.,

Zircon, ZrSiO4

Olivine, Mg2SiO4.

Structure

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2. Pyro silicates

When two tetrahedral units share one oxygen atom between them, an anion [Si2O7]6- is

obtained. Such type of silicates are known as pyro silicates. This type of structure is known as island

structure.

e.g.,

Hemimorphite, Zn3(Si2O7).Zn(OH2).H2O

Thorteveitite, Sc2(Si2O7)

Structure

3. Chain silicates

Sharing of two oxygen atoms per tetrahedron gives chain silicates. The chain silicates are

classified into two types. They are,

i) Single chain silicates (Pyroxenes)

ii) Double chain silicates (Amphiboles)

i) Single chain silicates

Single chain silicates have the anion [SiO3]n2n-.

e.g.,

Spodimene, LiAl(SiO3)2

Enstatite, MgSiO3

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Structure

ii) Double chain silicates

Double chain silicates have the anion [Si4O11]n6n-

e.g.,

Tremolite, Ca2Mg5(Si4O11)2(OH)2

Structure

4. Cyclic silicates

Such silicates contain the cyclic or ring anions like [Si3O9]6- or [Si6O18]12-.

These anions are obtained when each SiO4 tetrahedral unit shares an oxygen atom with each of

the two neighboring SiO4 units.

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e.g.,

Benitotite, BaTiSi3O9

Wollastonite, Ca3Si3O9

Structure

5. Two dimensional sheet silicates

When three oxygen atoms of each SiO4 tetrahedron are shared with adjacent SiO4 tetrahedra,

an infinite two dimensional sheet structure of the composition [Si2O5]n2n- results.

e.g.,

Talc, Mg2(Si2O5)2.Mg(OH)2

Kaolin, Al2(OH)4(Si2O5)

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Structure

6. Three dimensional silicates

When all the four oxygens of a SiO4 tetrahedron are shared with adjacent tetrahedral and the

process is repeated, an infinite three dimensional structure results.

Since all the oxygens are the bridge atoms, the silicate is neutral.

e.g.,

Quartz

Crystobalite.

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Beryl

Composition

The anion of this silicate contains a ring of tetrahedral in which an oxygen is shared by one

silicon, one aluminium and one beryllium.

In beryl the rings are arranged in sheets with the metal ions between the sheets are binding

them together.

It has the composition, 3BeO.Al2O3.6SiO2-

Properties

Beryl occurs in hexagonal prismatic crystals.

The gem (gl;iljPl;lg;gl;l kzpf;fy;) varieties of beryl are emerald (kufjk;) and aquamarine

(ePyg;gr;ire epw fy;).

Emerald is grass-green in colour and aquamarine is a pale green, yellowish green, bluish green

or deep blue in colour.

Uses

It is used for,

1. the extraction of beryllium and beryllium oxide.

2. the manufacture of beryllium – copper alloys used in U.S.A.

3. the production of refractories (vjw;Fk; tise;J nfhLf;fhj nghUl;fs; jahupf;Fk;

ciyf;fyd;), abrasives (rhizg; nghUs;) and ceramic (kl;ghz;lj;njhopYf;Fupa) glasses.

Asbestos

Composition

The composition of asbestos is CaMg3(SiO2)4.

Asbestos is available in three varieties namely,

i) Anthophyllite

ii) Amphibole

iii) Serpentine

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Anthophyllite is a magnesium iron silicate.

The best grade amphibole has the composition Ca2Mg5(OH)2Si8O22. It has double chain anions.

Properties

Asbestos is noted for its property of splitting (gpsj;jy;) into fibres.

The fibres of Indian asbestos though often of considerable length are usually weak and brittle. It

possesses good insulating and acid resisting qualities.

In India it is available in Bihar, Orissa, Cuddapah and Chennai.

The amphibole asbestos has high resistance to attack by acids. It can withstand ignition to

temperature near 1000 oC.

Uses

1. The longer fibre can be spun (E}w;fg;gLjy;) into yarn (E}y; Gup) and woven (nea;ag;gl;l) to

cloth either alone or with fibre materials like cotton or copper wire.

2. It is used for brake lining, heavy packings and gaskets and as electrical insulating material.

3. It is used for fire proof wall linings and boiler pipe lining.

4. Asbestos belts convey (nfhz;L Ngh, mDg;G) cement (R+lhd fl;b) and other hot products.

5. Asbestos sheets are used for roofings.

Talc

Composition

Talc is a hydrated magnesium silicate with the composition Mg3Si4O10(OH)4.

Chemical analysis shows the presence of calcium oxide (CaO), aluminium oxide (Al2O3) and other

oxides in talc.

The structure of talc is closely related to that of the mica.

Properties

Talc is extremely soft.

The atoms within the layers are strongly bonded so that the mineral is highly stable both to

acids and to heat.

The hardness of the mineral is greatly increased by the action of heat.

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Uses

1. It is mainly used in ceramics, paints and insecticides.

2. It is used as a filler for paper and rubber.

3. In the cosmetic industry it is used in toilet powder, soaps and creams.

4. Massive talc is cut into slabs and used for laboratory tables, sinks, acid tanks, electrical switch

boards etc.,

5. A fine granular variety known as ‘French chalk’ or ‘Spanish chalk’ is used by tailors for marking

cloth.

6. Slate pencils are made of a variety of talc.

Mica

Composition

The mica of economic importance are muscovite and phlogopite.

Muscovite has the composition H2KAl3(SiO4)3.

Properties

Micas are flexible, elastic, tough and translucent (xsp frpAk;) to transparent (xsp CLUTk;).

They have low electrical and heat conductivity.

The mica structure is based on sheets of linked (Si,Al)O4 tetrahedron.

Commercial mica is of two main types:

1. Sheet and Punch

2. Scrap and flake.

Uses

1. High quality mica is used as dielectric mica in radio and radar circuit capacitors.

2. Muscovite of lower quality called as electric mica is used as insulator elements in hot plates, toasters,

irons and other electrical home equipment.

3. Scrap and flake mica is ground and used in paints, decorative inks, rubber filler and coating on roofing

materials and water-proof fabrics (nea;ag;gl;l Jzp).

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4. Large quantities of ground mica is used in the manufacture of wallpaper.

5. As a protective coating for pictures and historical documents.

6. It is also used in various optical instruments.

Feldspar

Composition

Feldspars are the most important rock forming minerals.

Feldspars are divided into two groups according to the symmetry of their structures. They are,

i) Orthoclase feldspars

ii) Plagioclase feldspars

Orthoclase feldspars

These include,

Orthoclase, KAlSi3O8

Celsian, BaAl2Si2O8

Orthoclases are more symmetrical than plagioclases.

Plagioclase feldspars

These include,

Albite, NaAlSi3O8

Anorthite, CaAl2Si2O8.

The structures of these minerals are based on the three dimensional linked frame work of SiO4

and AlO4 tetrahedra with the cations like Na+, K+, Ca2+ and Be2+ situated in the interstices.

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Properties

They have no colour of their own but are frequently coloured (yellow, reddish brown or dirty

green) by impurities.

They are less hard than quartz.

They are brittle.

Uses

1. Feldspar is used industrially in the manufacture of porcelain (gPq;fhd;) and it is also important

constituent of many ceramic glasses.

2. It is also used as a gemstone.

Zeolite

Composition

Zeolites are hydrated aluminium silicates and have three dimensional structure.

They may be either naturally occurring or artificially synthesized substances.

These can be represented by the general formula, [ ]

where,

z = number of moles of water of hydration

x and y = 1, 2, 3, …….

n = oxidation state of the metal.

e.g.,

Enonite, M2+[(AlO2)2(SiO2)6].6 H2O

‘M’ may be Ca2+ or Mg2+

Zemalinite, Ca[(AlO2)2(SiO2)6].6 H2O

Permutit, Na2[(AlO2)2(SiO2)6].6 H2O

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Properties

Zeolites possess a much more open structure than feldspars.

They contain cavities into which the gases like CO2, NH3 etc., and liquids like water, ethyl alcohol

etc., can enter and be absorbed. Thus they act as molecular sieves.

Sodium ions in zeolite can be exchanged for calcium ions in hard water.

Zeolites are colourless. All zeolites are decomposed by HCl.

Uses

1. Zeolites are used in ion exchange processes.

2. The zeolite permutit can be used in softening of water.

Ultramarines

Composition

These are alumino silicates but do not contain water of hydration.

Some extra anions like Cl-, SO42- and S2- may also be present in the cavity.

e.g.,

Sodalite, Na8[(AlO2)2(SiO2)6].Cl2

Ultramarine, Na8[(AlO2)2(SiO2)6].S2

Uses

1. Many ultramarines are coloured substances. Therefore ultramarines are used as pigments.

2. It is also used in the manufacture of coloured glasses in glass industry.