ULTRAMARINE BLUE

Synthetic ultramarine blue is the most widely used blue pigment in the present time. Ultramarine blue pigment is insoluble in water and dark blue in colour. In 1928, blue ultramarine was first prepared by Guiment and Gamelin. The ultramarine blue pigment is a complex silicate of aluminium and sodium assisted with about 12% sulphur.

Blue, green and white are three varieties of ultramarine. Among these three varieties, blue colour variety is the most popular and this blue ultramarine is used as a pigment. This blue colour variety can be prepared from green or white ultramarine. These ultramarine pigments are affected by acid but stable in alkali and light. Due to liberation of H₂S gas, these pigments are affected by acid. The composition of three types of ultramarine are as follows---

Blue ----- Na₅Al₃Si₂S₃O₁₂

Green ----- Na₅Al₃Si₂S₂O₁₂

White ----- Na₅Al₃Si₃SO₁₂

The ultramarine composition is however not stoichiometric. Because the degree of exchange that takes place depends upon the various factors. These factors are solution concentration, heating time etc.

Preparation of Blue Ultramarine

When a mixture of sodium carbonate (soda ash), kaolin, charcoal, quartz, sulfur and resin is heated blue ultramarine is prepared. [It is very important that iron should not present in the raw materials. If iron present in the raw materials it appreciably dulls the colour and forms a white mass. In presence of air this white mass changes to green.] After heating, the product is cooled and powdered. If sodium carbonate (soda ash) in the raw materials is substituted by sodium sulphate, then darker blue colour is produced.

For the manufactured of ultramarine there are three methods--

 (1) Sulphate process--- In the sulphate process kaolin, sodium sulphate and charcoal are heated together.

(2) Soda sulphate process--- In the soda sulphate process kaolin, sodium carbonate (soda ash), sodium sulphate, sulfur and tar are heated together.

(3) Soda process--- In the soda process kaolin, sodium carbonate (soda ash), sulfur, colophonium and tar heated together.

The depth of the colour of the ultramarine increases with the increase in the amount of sulfur content. In the ultramarine, sulfur present is in the same form as in the polysulphides, is the probable reason for the colour of ultramarine. In the blue ultramarine Na⁺ ion is present. When Na⁺ ion is replaced by other cations such as K⁺ ion or Ag⁺ ion, it is found that the colour of ultramarine changes to various colour, depending on the cations. This indicates that within the alumino silicate skeleton, the cation present, have a potential influence on the colour.

Uses of Ultramarine

(1) Ultramarine blue is widely used for wall painting.

(2) It is used for laundry purpose. It is used for neutralize the yellowish tone in cotton or linen fabrics.

(3) For painting woods ultramarine blue used as a pigment.

(4) For whitening, paper and other products, ultramarine is also used.

Limitation

Ultramarine can not be used as a cooling material or iron articles because in ultramarine large percent of sulfur present. Due to possibility for the formation of PbS, it can not be mixed with lead pigments.

ELECTRON AFFINITY

Electron affinity (EA) of an atom is defined as the energy released when an electron is added to the valance shell of a gaseous atom in its ground state.

In other words, electron affinity of an atom is defined as the energy released when a gaseous atom captures an electron.

X(g) + electron → X^-(g) + EA

The process of addition of an electron to an atom is an exothermic process. Electron affinity is also called enthalpy of electron attachment because electron affinity is the energy involved in addition of an electron to an atom. According to our usual thermodynamic convention, since electron affinity is the energy released it should be represented with a negative sign, but unfortunately electron affinity values are normally represented with a positive sign.

However, negative electron affinity values are also known. Such value indicates that the species does not want to have an extra electron. Subsequent addition of electrons to an atom gives successive electron affinity values such as (EA)₁, (EA)₂, (EA)₃ --- etc. Once an electron is added to an atom, subsequent entry of 2 nd, 3 rd--- etc, electron would involve repulsion between the existing electrons and the entering electrons. In such cases energy would be required to push the electron against the interelectronic repulsion. Hence the 2 nd, 3 rd etc electron affinity values are always negative.

Electron affinity values are expressed in ev/atom, Kcal/mole and KJ/mole.

Electron affinity values can not obtain experimentally. Electron affinity values are obtained indirectly from Born-Haber Cycle.

Periodic Trend of Electron Affinity

(1) Variation Along a Period

On moving from left to right along a period that is from alkali metals to halogens along a period, the radius of atom decreases and nuclear charge increases. As a result of these two factors, the attractive force between the nucleus and the added electrons is increase. Therefore, the atom has greater tendency to captures an electron. So, generally electron affinity values gradually increase from left to right along a period, that is from alkali metals to halogens. Since, each period start with an alkali metal, it lies extreme left in periodic table and it has the lowest value of electron affinity. Halogen lie extreme right in the periodic table, it has the highest value of electron affinity.

(2) Variation Along a Group

On moving from top to bottom along a group that is downwards along a group, the radius of atom increases and the nuclear charge also increases on the same direction. The increase in atomic radius decreases the electron affinity values and increase nuclear charge increases the electron affinity values. Here the effect of atomic radius overcome the effect of nuclear charge. So, the value of electron affinity decreases on going from top to bottom along a group that is downwards along a group.

Factors Affecting the Magnitude of Electron Affinity

(1) Size of the Atom

The smaller is the size of the atom, the greater is the electron affinity value.

Electron Affinity ∝ Atomic Size

For smaller atom the attraction of the nucleus for the added electron is stronger. So, the electron affinity value is greater for smaller atom.

(2) Nuclear Charge

Electron affinity directly proportional to the nuclear charge.

Electron Affinity ∝ Nuclear Charge

With increase in nuclear charge the attraction of the nucleus for the added electron increases. Therefore, the electron affinity value increases with increase in nuclear charge.

(3) Electron Configuration

Atoms with stable electronic configuration, that is with half filled or full filled electronic configuration have little or no tendency to accept any more electron. So, they have low or negative electron affinity values. Tendency to attain stable electronic configuration is reflected by high electron affinity value.

Electron Affinity of Some Cases

(1) The electron affinity values of the noble gases are negative---

The valance shell electronic configurations of noble gases are ns² np⁶ (He has 1s² configuration). So, noble gas atoms have stable electronic configuration. They have no tendency to captures any extra electron. Therefore, electron affinity values of noble gases are negative. That is energy will be required to push the electron in the valance shell of noble gases.

(2) Halogens possess large positive electron affinity values---

The valance shell electron configuration of halogens is ns² np⁵. So, the halogens atoms have one electron short to fulfill their octet and to obtained stable noble gas electronic configuration. So, to attain stable electronic configuration they have very high tendency to captures an electron. Accordingly, halogens possess large positive electron affinity values.

(3) Electron affinity values of Beryllium (Be) Magnesium (Mg) and Nitrogen (N) are negative---

Valance shell electron configurations of Beryllium (Be) and magnesium (Mg) are ns², so they have filled s shell. Valance shell electron configuration of nitrogen (N) is ns² np³, so nitrogen has half filled p shell. According to Hund’s rule a half filled shell or full filled shell attains extra stability. Hence, the atoms such as Be, Mg and N would be much reluctant to captures extra electron. So, the electron affinity values of Be, Mg and N are negative.

(4) The 2 nd electron affinity value of oxygen (O) and sulfur (S) are negative---

When an atom captures an electron an uninegative ion is formed.

O(g) + e^- → O^-(g) + Energy

S(g) + e^- → S^-(g) + Energy

So, the 1 st electron affinity value is positive for oxygen and sulfur, because they have captured an electron readily. In spite of their high tendency to attain stable electronic configuration, entry of the second electron will be difficult. Because entry of the second electron would involve repulsion between the existing electrons and the entering electron. In such situation energy will be required to push the electron against such repulsion. So, the second electron affinity value of oxygen and sulfur are negative.

MAGNESIUM

Symbol --- Mg

Abundance --- 2% in the earth’s crust.

Physical state (STP)--- solid

Elemental category --- alkaline earth metal

Colour --- shiny grey

Discovery --- Joseph Black

Atomic no --- 12

Atomic weight --- 24.305

Period --- 3

Group --- 2 or IIA

Block --- s block

Known isotopes --- ₁₂Mg¹⁹, ₁₂Mg²⁰, ₁₂Mg²¹, ₁₂Mg²², ₁₂Mg²³, ₁₂Mg²⁴, ₁₂Mg²⁵, ₁₂Mg²⁶, ₁₂Mg²⁷, ₁₂Mg²⁸, ₁₂Mg²⁹, ₁₂Mg³⁰, ₁₂Mg³¹, ₁₂Mg³², ₁₂Mg³³, ₁₂Mg³⁴, ₁₂Mg³⁵, ₁₂Mg³⁶, ₁₂Mg³⁷, ₁₂Mg³⁸

Main isotopes --- ₁₂Mg²⁴, ₁₂Mg²⁵, ₁₂Mg²⁶

Isotopic abundance --- ₁₂Mg²⁴(78.99%), ₁₂Mg²⁵(10.005%), ₁₂Mg²⁶(11.005%)

Melting Point --- 650 ⁰C (923.15 K)

Boiling Point --- 1090 ⁰C (1363.15 K)

Heat of Fusion --- 8.47 KJ/mol

Heat of Vaporisation --- 127.5 KJ/mol

Molar heat capacity --- 24.855 J/(mol-K)

Density --- 1.7 g/cm³

Molar volume --- 0.000013

Electron configuration --- [Ne] 3s²

Electrons per shell --- 2 (1 st shell), 8 (2 nd shell), 2 (3 rd shell)

Oxidation state --- +2

Valance --- 2

Electronegativity --- 1.31 (Pauling scale)

Ionisation energy --- 737 KJ/mol (1 st), 1450 KJ/mol (2 nd), 7731 KJ/mol (3 rd), 10542 KJ/mol (4 th)

Covalent radius --- 141 pm

Atomic radius --- 160 pm

Van der Waals radius --- 173 pm

Radius of Mg²⁺ (6-coordinated) --- 72 pm

E⁰(V) for [Mg²⁺(aq)/Mg(s)] --- – 2.37

Natural occurrence --- primordial

Crystal structure --- hexagonal close packed (hcp)

Specific heat --- 1020 J/(Kg K) (solid phase)

Thermal expansion --- 24.9 μm/(m-K) (at 298 K)

Thermal conductivity --- 156 W/(m-K)

Electrical resistivity --- 43.8 nΩ-m (at 293K)

Speed of sound --- 4939 m/s (at 298 K)

Magnetic type --- paramagnetic

Mass magnetic susceptibility --- 6.88 x 10^-9 m³/Kg

Molar magnetic susceptibility --- 1.69 x 10^-10 m³/mol

Volume magnetic susceptibility --- 1.2 x 10^-5

Mohs hardness --- 2.5

Brinell hardness --- 260 MPa

Poisson ratio --- 0.29

Young’s modulus --- 45 Gpa

Shear modulus --- 17 GPa

Bulk modulus --- 35.5 GPa 

Lattice angles --- π/2, π/2, 2π/3

Lattice constants --- 320.88 pm, 320.88 pm, 521.09 pm

Quantum numbers --- ¹S₀

Neutron cross section --- 6.3 x 10^-2

Neutron mass absorption --- 1 x 10^-4 

OILS FATS AND WAXES

Oils--- Oils are esters of higher fatty acids. Oils contain a large proportion of glycerides of unsaturated acid. Melting point of oil is below 20⁰C.

Fats--- Fats are esters of higher fatty acids. Fats contain a large proportion of glycerides of saturated acid. Melting point of fat is above 20⁰C.

Classification of Oils and Fats

(1) Depending on uses oils and fats are two types---

(i) Edible--- Those oils and fats are uses for cooking purpose or eating purpose are known as edible oils or fats.

(ii) Inedible--- Those oils and fats are uses for making soaps, detergents, paintings etc are known as inedible oils or fats.

(2) Depending on nature of the carbon chain, oils and fats are three types---

(i) Non-drying oils or fats--- If the carbon chain present in oil or fat is saturated, then that oil or fat is called non-drying oil or fat.

(ii) Semi-drying oils or fats--- If the carbon chain present in oil or fat have some degree of unsaturation, then that oil or fat is called semi-drying oil or fat.

(iii) Drying oils or fats--- If the carbon chain present in oil or fat is unsaturated, then that oil or fat is called drying oil or fat.

(3) Depending on the source of availabilities oils and fats are three types---

(i) Vegetable oils or fats--- Oils or fats extracted from vegetable source are known as vegetable oils or fats.

(ii) Animal oils or fats--- Oils or fats extracted from animal source are known as animal oils or fats.

(iii) Mineral oils or fats--- Oils or fats extracted from mineral source are known as mineral oils or fats.

Waxes--- Waxes are esters of monohydric alcohols with higher fatty acid. The molecular weight of these alcohols is very large. Waxes are non-crystalline esters.

Depending on the source of availabilities waxes are five types, such as----

(i) Animal waxes

(ii) Vegetable waxes

(iii) Mineral waxes

(iv) Mineralised vegetable waxes

(v) Synthetic waxes

Difference Between Fats and Oils

If we consider the Chemical properties there is no difference between fats and oils, both fats and oils consist of mixed glycerides. The difference between fats and oils is merely physical one of consistency.

(i) Melting point of fat is above 20⁰C, whereas melting point of oil is below 20⁰C. Coconut oil and ghee are fats in winter but oils in summer.

(ii) A large proportion of glycerides of saturated fatty acids are present in fats, whereas a large proportion of glycerides of unsaturated fatty acids are present in oils.

(iii) The iodine value of oils is high due to presence of higher unsaturation in oils, whereas the iodine value of fats is low.

(iv) Due to presence of unsaturation that is double bond in oils, oils can be hydrogenated by using H₂ and Ni catalyst. Since fats contain a large proportion of glycerides of saturated fatty acid, so fats can not be hydrogenated. By heating fats can be converted to oils.

Difference Between Vegetable and Mineral Oils

(i) The vegetable oils have high flash point, and this might be 326⁰C. Whereas flash point is 200⁰C for most mineral oils.

(ii) Mineral oils have zero acid value but vegetable oils have definite acid value.

(iii) Vegetable oils contain a large proportion of glycerides of saturated and unsaturated fatty acids, so they can not be distilled with the steam, and vegetable oils are called fine oils. Mineral oils are mixture of various hydrocarbon such as kerosene, paraffin, petroleum etc. Mineral oils are highly volatile, possess unpleasant smell and can be distilled with steam.

Examples of Animal Oils

(i) Cord-liver oil

(ii) Shark liver oil

(iii) Fish oil

(iv) Whale oil

Examples of Vegetable Oils

(i) Mustard oil

(ii) Coconut oil

(iii) Seed oil

(iv) Linseed oil

(v) Castor oil

Examples of Mineral Oils

(i) Kerosene oil

(ii) Diesel

(iii) Petroleum oil

(iv) Paraffin oil

SODIUM

Symbol --- Na

Abundance --- 28300 ppm (total abundance), 22700 ppm in the earth’s crust. Sodium is fifth most abundant metal (after Al, Fe, Ca and Mg).

Physical state (STP)--- solid

Elemental category --- alkali metal

Colour --- silvery white metallic

Discovery --- Humphry Davy

Atomic no --- 11

Atomic weight --- 22.989

Period --- 3

Group --- 1 or IA

Block --- s block

Known isotopes --- ₁₁Na¹⁸, ₁₁Na¹⁹, ₁₁Na²⁰, ₁₁Na²¹, ₁₁Na²², ₁₁Na²³, ₁₁Na²⁴, ₁₁Na²⁵, ₁₁Na²⁶, ₁₁Na²⁷, ₁₁Na²⁸, ₁₁Na²⁹, ₁₁Na³⁰, ₁₁Na³¹, ₁₁Na³², ₁₁Na³³, ₁₁Na³⁴, ₁₁Na³⁵

Main isotope --- ₁₁Na²³

Isotopic abundance --- ₁₁Na²³ (100%)

Melting Point --- 97.8 ⁰C (370.95 K)

Boiling Point --- 883 ⁰C (1156.15 K)

Critical Temperature --- 2573 K

Critical Pressure --- 35 MPa

Heat of Fusion --- 2.6 KJ/mol

Heat of Vaporisation --- 97.3 KJ/mol

Molar heat capacity --- 28.25 J/(mol-K)

Density --- 0.97 g/cm³

Molar volume --- 0.000023

Electron configuration --- [Ne] 3s¹

Electrons per shell --- 2 (1 st shell), 8 (2 nd shell), 1 (3 rd shell)

Oxidation state --- +1

Valance --- 1

Electronegativity --- 0.93 (Pauling scale)

Electron affinity --- 52.5 KJ/mol

Ionisation energy --- 495.7 KJ/mol (1 st), 4563 KJ/mol (2 nd), 6910 KJ/mol (3 rd), 9542 KJ/mol (4 th)

Covalent radius --- 166 pm

Atomic radius --- 186 pm

Van der Waals radius --- 227 pm

Ionic radius (octahedral) --- 102 pm

Hydrated radii --- 276 pm

E⁰ for [Na⁺(aq) + e = Na(s)] --- – 2.71

Natural occurrence --- primordial

Crystal structure --- body centered cubic (bcc)

Specific heat --- 1230 J/(Kg K) (solid phase)

Thermal expansion --- 71 μm/(m-K)

Thermal conductivity --- 142 W/(m-K)

Electrical resistivity --- 47.5 nΩ-m

Speed of sound --- 3200 m/s (at 20 ⁰C)

Magnetic type --- paramagnetic

Mass magnetic susceptibility --- 8.79 x 10^-9 m³/Kg

Molar magnetic susceptibility --- 1.9 x 10^-10 m³/mol

Volume magnetic susceptibility --- 8.5 x 10^-6

Mohs hardness --- 0.5

Brinell hardness --- 0.68 MPa

Young’s modulus --- 10 Gpa

Shear modulus --- 3.3 GPa

Bulk modulus --- 6.3 GPa 

Lattice angles --- π/2, π/2, π/2

Lattice constants --- 428.9 pm, 428.9 pm, 428.9 pm

Quantum numbers --- ²S_1/2

Neutron cross section --- 5.3 x 10^-1

Neutron mass absorption --- 7 x 10^-4

PREPARATION OF ALKANES

Alkanes can be prepared by various ways. General methods of preparation of alkanes are--

(1) From Unsaturated Hydrocarbons

Alkanes are prepared by the catalytic reduction of unsaturated hydrocarbons such as alkene or alkyne in the presence of a suitable catalyst such as Ni, Pt, Pd, Raney Ni etc. Here hydrogen is added to an unsaturated hydrocarbon (alkene or alkyne) in the presence of a catalyst. This process is known as hydrogenation.

The catalytic hydrogenation reaction takes place at normal temperature and pressure if we use Raney Ni, Pt or Pd as a catalyst.

But if we use Ni as a catalyst, then the catalytic hydrogenation reaction takes place at 200 ⁰C – 300 ⁰C. The catalytic hydrogenation reaction in presence of a Ni catalyst at 200 ⁰C – 300 ⁰C is known as Sabatier-Senderens reduction.

(2) From Alkyl Halides

Alkanes can be prepared from alkyl halides in different ways---

(A) Through Grignard Reagent

When alkyl halide heated with magnesium powder in ether solution, alkyl magnesium halide (R―Mg―X) is produced. This alkyl magnesium halide (R―Mg―X) is known as Grignard reagent.

R―X + Mg → R―Mg―X

C₂H₅―I + Mg → C₂H₅―Mg―I

When Grignard reagent treated with water or dilute acid, alkane is produced.

R―Mg―X + H₂O → RH + Mg(OH)X

C₂H₅―Mg―I + H₂O → C₂H₆ + Mg(OH)I

(B) By Wurtz Reaction

In dry ether solution at normal temperature the reaction of two molecules of alkyl halide (preferably the bromide or iodide) with two molecules of pure and dry metallic sodium produce alkane.

R₁―X + 2Na + R₂―X → R₁―R₂ + 2NaX

CH₃―Br + 2Na + CH₃―Br → CH₃―CH₃ 

+ 2NaBr

If we use two types of alkyl halide, then mixture of alkanes is produced. It is difficult to separate this mixture of alkanes, because their close boiling point.

CH₃―Br + 2Na + C₂H₅―Br → CH₃―CH₃ + C₂H₅―C₂H₅ + CH₃―C₂H₅ + 2NaBr

This Wurth reaction is very useful for the synthesis of symmetrical alkane.

(C) By Corey-House Synthesis

In dry ether solution at normal temperature the reaction of alkyl halide with pure and dry metallic lithium produced alkyl lithium.

RX + 2Li → RLi + LIX

C₂H₅I + 2Li → C₂H₅Li + LiI

Reaction of alkyl lithium (RLi) with cuprous iodide (CuI) produced lithium dialkyl cuprate (R₂CuLi).

2RLi + CuI → R₂CuLi + LiI

2C₂H₅Li + CuI → (C₂H₅)₂CuLi + LiI

Reaction of lithium dialkyl cuprate (R₂CuLi) with another molecule of alkyl halide produced alkane.

R₂CuLi + R'X → R―R' + RCu +LiX

(C₂H₅)₂CuLi + CH₃I → C₂H₅―CH₃ + C₂H₅Cu + LiI

R and R' may be same or different. R group may be primary, secondary or tertiary but R' group always primary.

This Corey-House reaction is very useful for the formation of both symmetrical and unsymmetrical alkane.

(D) Reduction of Alkyl Halides

(i) Alkane is prepared by the reduction of alkyl halide by Zn and HCl.

C₂H₅Cl + Zn + HCl → C₂H₆ + ZnCl₂

(ii) Alkane is prepared by the reduction of alkyl halide by Zn and NaOH.

Zn + 2NaOH → Na₂ZnO₂ + 2[H]

R―X + 2[H] → R―H + HX

(iii) When alkyl halide is reduced by Zn-Cu couple in presence of alcohol alkane is produced.

Zn → Zn²⁺ + 2e

R―X + e → R∙ + X^-

R∙ + e → R:^-

R:^- + C₂H₅OH → R―H + C₂H₅O^-

(iv) When alkyl halide is reduced by LiAlH₄, NaBH₄ or Ph₃SnH alkane is produced.

R―X + H^- → R―H + X^-

(v) When alkyl halide is reduced by H₂ in presence of Pd-C or Raney Ni, alkane is produced.

R―X + H₂ → R―H + HX

(vi) When alkyl iodide is reduced by hydroiodic acid (HI) and red phosphorus at 150 ⁰C, alkane is produced.

C₂H₅―I + HI → C₂H₆ + I₂

(3) From Carbonyl Compounds

Alkane can be prepared from carbonyl compounds such as aldehyde and ketone by Clemensen reduction process and Wolf-Kishner reduction process.

(A) By Clemmensen Reduction

When carbonyl compounds such as aldehydes and ketones are heated with zinc amalgam (Zn/Hg) and concentrated HCl, carbonyl compounds reduced to form alkane.

(B) By Wolff-Kishner Reduction

Carbonyl compounds such as aldehydes and ketones react with hydrazine (H₂N―NH₂) to formed hydrazone. When the resulting hydrazone is heated with sodium ethoxide (NaOC₂H₅) and ethylene glycol (HOH₂C―CH₂OH) at 180 ⁰C, alkane is produced.

(4) From Carboxylic Acid

Alkane can be prepared from carboxylic acid by two methods. One is decarboxylation process and another is Kolbe’s electrolytic method.

(A) By Decarboxylation Process

Alkane is produced when carboxylic acid is heated with soda lime (NaOH + CaO). In this reaction CO₂ is removed, so it is called decarboxylation reaction.

This is a degradation reaction, because in this process the number of carbon atom in the produced alkane is one less than that of the carboxylic acid.

(B) Kolbe’s Electrolytic Method

Electrolysis of a concentrated and cool aqueous solution of sodium or potassium salts of monocarboxylic acid using platinum electrodes produced alkane at the anode.

2R―COOK + 2H₂O → [R―R + 2CO₂(anode)] + [H₂ + 2KOH (cathode)]

2CH₃COOK + 2H₂O → [C₂H₆ + 2CO₂(anode)] + [H₂ + 2KOH (cathode)]

Kolbe’s method of electrolysis is suitable for the preparation of even number of carbon atom alkane, but not suitable for the preparation of odd number of carbon atom alkane.

(5) From Alkyl Borane

Reaction of alkene with borane produced trialkyl borane.

3R―CH=CH₂ + B₂H₆ → (R―CH₂―CH₂)₃B

Alkane is produced by hydrolysis of the resulting trialkyl borane with acid.

(RCH₂CH₂)₃B + 3CH₃COOH → 3RCH₂CH₃ + (CH₃COO)₃B

(6) From Alcohol

When alcohol is reduced by red phosphorus (P) and hydroiodic acid (HI) in a closed vessel at 150 ⁰C, alkane is produced.