Symbol : O

Molecular formula : O₂

Atomic number : 8

Atomic weight : 15.999 amu

Molecular weight : 32

Electronic configuration: 1s²2s²2p⁴

Isotopes : ₈O¹⁶, ₈O¹⁷, ₈O¹⁸

Discovered by : Joseph Priestly

→ Most abundant element in earth crust, about 41%.

→ Discovered by English scientist, Joseph Priestley who obtained oxygen by focusing the sun-rays with the help of a lens on mercuric oxide.

→Lavoisier investigated its properties in detail.

→ Exist in diatomic gaseous molecule (O2)

Position of oxygen in the periodic table

The electronic configuration of oxygen is 1s22s22p4. So this element is placed in the p-block in the group VIA or group 16 along with sulphur(S), selenium(Se), Tellurium(Te) and Polonium(Po).Polonium is radioactive and metalloid, while others are non-metals. Gr VIA elements together are called chalcogens (ore forming) because their metallic compounds occur in nature in the form of oxides, sulphides, selenides and tellurides as ores. Only oxygen exists in gaseous state in its group.

Uses of oxygen

1. It is used for artificial respiration in hospital.
2. It is used in rocket fuel. { A mixture of fuel and liq. Oxygen is used to obtain a high speed in high altitude rockets, jets and missiles.}
3. It is used for the preparation of compounds like H₂SO₄, HNO₃, CO₂, etc.
4. It is used as an oxidizing agent in chemical reactions.

Allotropes of oxygen

Allotropes are two or more forms of the same element in the same physical state (solid, liquid, or gas) that differ from each other in their physical, and sometimes chemical properties.

There are two main allotropes of oxygen:

1. A diatomic molecule made up of 2 oxygen atoms with the moelcular formula O₂ commonly referred to as molecular oxygen or dioxygen.
2. A triatomic molecule made up of 3 atoms of oxygen with the molecular formula O₃ referred to as ozone.

Note : Other allotropes are O₄, O₈, etc.

Oxides

Oxides are binary compounds of oxygen with other elements which are less electronegative than oxygen . eg. CO₂, CO, Fe₂O₃, CaO, Na₂O, H₂O, etc.

Note : Binary compounds means compounds having only two types of elements. Binary compounds of oxygen like OF₂, O₂F₂, etc are not oxides, they are fluorides.

Classification of oxides

A. On the basis of acidic and basic behavior :

1. Basic oxides :

Oxides of metals which dissolve in water to form base( alkali) and react with acids to form salt and water are called basic oxides. Eg. Na₂O, H₂O, MgO, CaO, BaO, Li₂O, {CuO, MnO, FeO} etc.

Generally, oxides of group IA metals are basic. {except BeO which is amphoteric.}Eg.

Oxides of d-block elements in the lower oxidation states are basic. They are not soluble in water but react with acid to form salt and water. Eg.

2. Acidic Oxides :

Oxides of non-metals which dissolve in water to form acids and react with bases to form salt and water are called acidic oxides. Eg. SO₂, CO₂, SO₃, NO₂, N₂O₃, N₂O₅, etc.

3. Neutral oxides :

Oxides which neither react with acids nor with bases are called neutral oxides. Eg H₂O, CO, NO, N₂O, etc.

4. Amphoteric oxides :

Oxides which react with acids as well as with base to form salt and water are called amphoteric oxides. Eg. ZnO, SnO, PbO, Al₂O₃, {BeO,} etc.

Trend in the periodic table :

On moving from left to right in a period, metallic character decreases and basic character decreases.

On moving from top to bottom in a group, metallic character increases and basic character increases. Eg. Oxides of group 13 elements:

In oxides of the same element, acidic character increases with increase in oxidation number or number of oxygen atoms. Eg.

Acidic order : N₂O < NO < N₂O₃ < NO₂ < N₂O₅

B. On the basis of structural considerations:

1. Normal oxides :

Oxides formed by normal valency rule are called normal oxides. Eg. Na₂O, MgO, ZnO, Al₂O₃, etc. where valency of O = 2 .

2. Peroxides :

Oxides which contain peroxide ion O₂^2- or (O-O)^2- in which the oxidation number of oxygen is -1 and produce hydrogen peroxide with acid are called peroxides. Eg. H₂O₂ { i.e. H-O-O-H} , Na₂O₂, K₂O₂, BaO₂, etc.

BaO₂ : {i.e. Ba-O-O}

Alkali metals form peroxides of type M₂O₂ and alkaline earth metals form peroxide of type MO₂.

Note : PbO2(lead peroxide) and MnO2 are not true peroxide as they do not produce H2O2 with dil. acid.

3. Super Oxides :

Oxides which contain superoxide ion O₂^– in which the oxidation number of oxygen is -1/2 are called superoxides. Eg. KO₂{potassium superoxide}, RbO₂, CsO₂, etc.

i.e. oxides containing more oxygen atoms than required by the normal valency rule are called superoxides.

4. Suboxides :

Oxides which contain less oxygen atoms than required by the normal valency rule are called suboxides. Eg. N₂O(nitrogen suboxide}, Pb₂O, C₃O₂, etc.

5. Mixed oxides :

Those oxides which are a mixture of two similar oxides of the same element in different valency are called mixed oxides. Eg.

Uses of hydrogen peroxide

1. It is used as an antiseptic for washing wounds, animal bites, etc.
2. It may also be used as a mouth rinse to help remove mucus or to relieve minor mouth irritation.
3. It is used as bleaching agent for hair, wool, silk, etc.
4. It is used to remove stains.
5. It is used as good oxidizing agent in the laboratory.

Questions and answers

1.Which of the following is not a oxide ?

a. CO₂     c. H₂O

b. OF₂     d. BaO₂

2. Which of the following is amphoteric oxide?

a. PbO      c. O₂

b. N₂O₃    d. K₂O

3. Which of the following is peroxide?

a. Na₂O      c. MgO

b. Al₂O₃      d. BaO₂

4. Which of the following is most acidic oxide?

a. Na₂O      c. P₂O₅

b. Al₂O₃      d. SO₃

5. Which of the following is most basic oxide ?

a. Al₂O₃       c. In₂O₃

b. Ga₂O₃      d. Tl₂O₃

6. Which of the following is most acidic oxide?

a. N₂O      c. NO₂

b. NO       d. N₂O₃

Answer :

1.- b ; 2.- a ; 3.- d ; 4.- d ; 5.- d ; 6. – c

References

• Sthapit, M.K., Pradhananga, R.R., Foundations of Chemistry, Vol 1 and 2, Fourth edition, Taleju Prakashan, 2005.
• Day, C.M., Selbin, J., Theoritical inorganic Chemistry, second edition, Affiliated East-West Press Pvt. Ltd., New Delhi, 2002.
• https://www.thealternativedaily.com/hydrogen-peroxide-for-teeth-whitening-and-more/
• https://www.sciencedirect.com/topics/chemical-engineering/oxide

The post Oxygen – Types of oxides and Uses of hydrogen peroxide. appeared first on Online Chemistry notes.

Atomic Number : 1

Atomic weight : 1.008

Electronic configuration : 1s¹

Discovered by : Henry Cavendish

Henry Cavendish discovered hydrogen by passing steam through a red hot gun barrel (mostly iron)

• He called it ‘inflammable air’. It’s name hydrogen was proposed by Lavoiser (Father of modern chem) as it produces water during burning with oxygen( Greek, hydro= water, gen= producer)

• It is the most abundant and lightest element in the universe { and tenth most abundant element in the earth’s crust}

Position of hydrogen in the periodic table

It is the first element in the periodic table. It resembles the alkali metals (group IA) as it can be oxidized to H⁺ ion. On the other hand, it resembles the halogens (group VIIA) as it forms the hydride ion (H^–). Hence ,the position of hydrogen in the periodic table is controversial or anomalous. Hence, it has been given a separate and distinct place unassociated with any particular group as the first element on left side of the periodic table on the top of the alkali metals (gr.IA).

Different forms of hydrogen

1. Molecular hydrogen
2. Atomic hydrogen
3. Nascent hydrogen
4. {Occluded hydrogen}

1. Molecular hydrogen 

Ordinary hydrogen gas which consists of diatomic molecules in which two H atoms are combined together by a covalent bond is known as molecular hydrogen. Due to high H-H bond energy ( 104 KCalmol^-1), molecules of hydrogen is very stable. It does not reacts under ordinary conditions.

2. Nascent hydrogen 

(nascent=newly born) : The atomic hydrogen which is produced during the chemical reaction is called nascent hydrogen.

It is more reactive than ordinary hydrogen molecule. Thus nascent hydrogen is powerful reducing agent than ordinary hydrogen. Following reactions support this statement:

i. Reduction of potassium permanganate:

When molecular hydrogen gas is passed through acidified KMnO₄, the pink colour of KMnO₄ does not change.

But when a piece of zinc is treated with acidified KMnO₄, it’s pink colour is discharged. This is because nascent hydrogen produced from the reaction between zinc and H₂SO₄ reduces KMnO₄ into MnSO₄ salt.

ii.Reduction of potassium dichromate:

When molecular hydrogen gas is passed through acidified K₂Cr₂O₇, the orange colour of K₂Cr₂O₇ does not change.

But when a piece of zinc is treated with acidified K₂Cr₂O₇, it’s orange colour changes to light green. This is because nascent hydrogen produced from the reaction between zinc and H₂SO₄ reduces K₂Cr₂O₇ into Cr₂(SO₄)₃ salt.

iii.Reduction of ferric chloride:

When molecular hydrogen gas is passed through ferric chloride, the yellowish brown(orange) colour of ferric chloride does not change.

But when a piece of zinc is treated with acidified FeCl₃, its colour changes to pale green.

Uses : It is used as reducing agent.

3. Atomic hydrogen 

It is hydrogen atom formed by dissociation of molecular hydrogen at about 1000 to 2000^oC at low pressure. {This can be done by passing hydrogen gas through an electric arcstruck between two tungsten electrodes}

It has very short half life time of 0.3 second. Thus it is unstable.

It is more powerful reducing agent than molecular hydrogen and nascent hydrogen. It can reduce oxides and chlorides of metals like copper, silver, mercury to metallic form.

Uses of atomic hydrogen:

i. It is used as reducing agent.

ii. It is used as atomic hydrogen torch for welding metals of very high melting point.

Differences between nascent and atomic hydrogen :

Nascent hydrogen	Atomic hydrogen
1. Nascent hydrogen is formed in the reaction mixture at room temperature.	1. Atomic hydrogen is produced at very high temperature of about 2000oC by dissociating molecular hydrogen.
2. Nascent hydrogen is formed in situ but not been isolated yet.	2. Atomic hydrogen can be isolated and has a half life of 0.3 seconds.
3. It is weaker reducing agent than atomic hydrogen . It can not reduce certain metallic salts like AgCl, CuO, etc.	3. It is stronger reducing agent than nascent hydrogen. It can reduce such metallic salts. Eg.

4. Occluded hydrogen :

Adsorption of any gas on metal surface is known as occlusion. When molecular hydrogen is adsorbed on a metal surface (such as Fe, Au, Pt and Pd) , then this hydrogen is known as occluded hydrogen. In the powdered state, Pd can occlude approximately 1000 times its own volume of hydrogen. The occluded gas interacts with the metal to form a solid solution; or sometimes a part of the gas combines with the metal to yield other chemical compounds, for example, hydrides.

Ortho and Para hydrogen

Hydrogen molecule in which two hydrogen atoms have same nuclear spin (parallel nucleus spin) is called ortho hydrogen and hydrogen molecule in which two hydrogen atoms have opposite nuclear spin( anti-parallel nucleus spin) is called para hydrogen.

Therefore, in ortho hydrogen two nuclei spin in the same direction and resultant nuclear spin is high but in para hydrogen, two nuclei spin in opposite direction and the resultant nuclear spin is zero. Hence, para hydrogen has lower internal energy than the ortho hydrogen.

• Due to difference in internal energy, the two forms of hydrogen have different physical properties like boiling point, specific heat, thermal conductivity, etc.

• Since, para hydrogen has lower energy, at absolute zero, there is 100% para hydrogen and with increase in temp., proportion of para form decreases. At room temperature, hydrogen gas is mixture of 25% of para and 75% of ortho hydrogen.

Differences between ortho and para hydrogen :

Isotopes of Hydrogen

Isotopes are the atoms of the same element having same atomic number but different mass number. There are three isotopes of hydrogen:

1. Protium or ordinary hydrogen
2. Deuterium or heavy hydrogen
3. Tritium or radioactive hydrogen.

Naturally occurring hydrogen contains about 99.985% of protium, 0.014% of deuterium and 0.001 % of tritium.

• Isotopes have different physical properties since they differ in their mass number.

• They have same chemical properties since their electronic configuration is same. However, they differ in the rate of chemical reaction. For example, D2 reacts with Cl2 about 13 times slower than H2 does. The different in rate of reaction due to difference in mass of the atoms of the same element is called isotope effect.

Uses of protium :

• It is used in filling {toy} balloons.
• It is used in synthesis of ammonia by Haber’s process.
• It is used as rocket fuel.
• It is used for the hydrogenation of vegetable oil to form vanaspati ghee. 

Uses of deuterium :

• It is used in nuclear fusion reaction to liberate large amount of heat which is used in hydrogen bomb.

• It { and its compounds } is used as tracer to determine the mechanism of reactions.
• It is used to prepare heavy water.

Uses of tritium :

• It is used in nuclear fusion reaction to liberate large amount of heat which is used in hydrogen bomb.

• It is used as radioactive tracer { in absorption of water by plant roots.}
• It is used as radioactive substance in cancer therapy.

Heavy water and its applications

• Chemically heavy water is deuterium oxide (D₂O).
• Its molecular weight is 20 amu.
• Heavy water is colorless, odorless and tasteless.
• The ordinary water contains small quantity of heavy water.
• Heavy water is obtained by prolonged or repeatedly electrolysis of water.
• Boiling point = 101.42⁰C and freezing point = 3.8⁰C.

Uses of heavy water:

• It is used as a moderator in nuclear reactors because it slows down the fast moving neutrons and thus helps in controlling nuclear reactions.
• It is used as a tracer to study the mechanism of metabolic processes and many organic reactions.
• It is used to prepare heavy hydrogen.
• It is used in NMR (nuclear magnetic resonance) spectroscopy.

Application of hydrogen as fuel

Hydrogen is an excellent substitute for fossil fuels such as coal, petrol, diesel, etc. Hydrogen fuel cells are growing technology offering significant economic, environmental and energy efficiency benefits.

The operation of hydrogen fuel cells is similar to that of a battery.

The hydrogen fuel cell has two electrods- an anode and a cathode, which are separated by a membrane. Oxygen passes over the cathode and hydrogen passes over the anode. The hydrogen reacts with a catalyst on the anode which converts hydrogen into positively charged ions (H⁺) and negatively charged electrons (e^–). The electrons flowing out of the cell are used as electrical energy to power an electric motor. The hydrogen ions then pass through the membrane to the cathode and combine with oxygen and the electrons to yield water.

2H₂ (g) + O₂ (g) → 2 H₂O (l) + energy

Advantages of hydrogen fuel cells:

• It is pollution-free source of energy. Unlike gasoline and diesel powered vehicles, hydrogen fuel cells do not produce air pollutants.
• It reduces the dependence on petroleum imports as hydrogen can be demostically produced from various sources.
• Fuel cell vehicles powered by hydrogen do not produce greenhouse gas emissions.

Uses of hydrogen fuel cells:

NASA (National Aeronautics and Space Administration) is the primary user of hydrogen resources for its space program. NASA fuels the booster rockets of the space shuttle using liquid hydrogen and employs hydrogen batteries for electrical sources.

• Hydrogen fuel cells can power any portable devices like video recorder, cellular phone, laptop, etc. that uses batteries.
• Hydrogen fuel cells can be used in vehicles such as buses, cars etc. to replace combustion engines or even large batteries.
• Hydrogen fuel cells can be a clean and reliable source of power to cities and buildings.

Questions and their answers :

1. Which of the following is most reactive form of hydrogen?

a. Nascent hydrogen    c. Ortho hydrogen

b. Atomic hydrogen     d. Para hydrogen

2. Water gas is a mixture of :

a. H₂O and CO₂    c. H₂O and CO

b. H₂ and SO₂       d. H₂ and CO.

3. Which of the following is known as heavy hydrogen?

a. Protium       c. tritium

b. Deuterium  d. para hydrogen

4. Which of the following is known as radioactive hydrogen?

a. Protium        c. tritium

b. Deuterium   d. para hydrogen

5. At room temperature, ordinary hydrogen is the mixture of ortho and para hydrogen in the ratio of :

a. 1:3     c. 2:3

b. 3:1     d. 1:2

6. When a piece of zinc is added to acidified potassium dichromate solution, the color changes to:

a. Yellow    c. sky blue

b. Pink       d. light green

7. Least abundant isotope of hydrogen is:

a. Protium      c. tritium

b. Deuterium d. Heavy hydrogen

8. The adsorption of hydrogen by metals is called:

a. Dehydrogenation   c. Occlusion

b. Hydrogenation       d. Absorption

9. Molecular mass of heavy water in amu is:

a. 14     c. 18

b. 16     d. 20

Answers :

1. b     2. d

3. b     4. c

5. a     6. d

7. c     8. c

9. d

Note : 8. The adsorption of hydrogen by metals (such as Fe,Au,Pt and Pd) is called occlusion. In the powdered state, Pd can occlude approximately 1000 times its own volume of hydrogen. 

Q) Give a reaction which shows that water contains hydrogen.

→ When steam is passed through red hot iron, hydrogen gas is obtained.

Since, iron does not contain hydrogen, it must come from water. This reaction shows that water contains hydrogen.

Q) When seam is passed through red hot coke, a mixture of two gases is obtained. Name the gases and write the reaction involved.

→ When steam is passed through red hot coke, a mixture of CO and H₂ gas is obtained.

These gases CO and H₂ together are called water gas.

References

• Sthapit, M.K., Pradhananga, R.R., Foundations of Chemistry, Vol 1 and 2, Fourth edition, Taleju Prakashan, 2005.
• https://www.energy.gov/eere/fuelcells/hydrogen-fuel-basics
• https://www2.lbl.gov/abc/wallchart/chapters/02/3.html

The post Hydrogen – Different forms, Ortho and para; Isotopes and uses. appeared first on Online Chemistry notes.

Manufacture of nitric acid by Ostwald’s process

Principle :

 1. Catalytic oxidation of NH₃ to NO : When ammonia is oxidized with oxygen in presence of catalyst platinum and rhodium in 9 : 1 ratio at about 800⁰C and 5 atmospheric pressure, nitric oxide is formed.

 2. Oxidation of NO to NO₂ : Nitric oxide is cooled to about 50⁰C to 100⁰C and air oxidized to nitrogen dioxide.

 3. Oxidation of nitrogen dioxide(NO₂) to nitric acid in presence of air and water.

Working of the plant or process :

The working of the plant involves following steps :

 1. Catalyst converter : Ammonia gas and air in the ratio of 1:8 by volume is first compressed and passed through converter where ammonia is oxidized into nitric oxide in the presence of platinum as catalyst at temperature 800⁰C.

 2. Cooler : The nitric oxide formed is cooled using refrigerator. The cooled nitric oxide is passed in oxidation chamber.

 3. Oxidation chamber : In this chamber, nitric oxide combines with oxygen to form nitrogen dioxide.

 4. Absorption tower : In absorption tower water is sprayed from its roof and tower is packed with acid proof(resistant) flint (stone). Here, nitrogen dioxide and oxygen {present in air} react with water to form nitric acid.

Thus obtained nitric acid is about 60% concentrated. On distillation, {nitric acid vaporize first, i.e. b.pt. 86⁰C)} the concentration of nitric acid can be increased upto 68%. This is the commercial nitric acid available.

{68% nitric acid forms azeotropic mixture(constant boiling mixture) with water. }

Preparation of 98% nitric acid : For the preparation of conc. HNO₃, it is treated with conc. H₂SO₄, which acts as dehydrating agent. So it absorbs water molecules strongly. The resulting mixture is distilled where nitric acid vaporizes first{ b.pt. 86⁰C}. The vapour is condensed to form 98% nitric acid.{ This form of nitric acid is further crystallized at -42⁰C which is separated and melted to get conc. HNO₃.}

Fuming nitric acid : when some starch solution is kept in conc. (98%) HNO3, conc. HNO3 decomposes into nitrogen dioxide (NO2) forming fume. This form of nitric acid is fuming nitric acid. Fuming nitric acid is stronger oxidizing agent than conc. HNO3.

Physical properties of nitric acid :

 1. It is colourless and odourless liquid. But on long storage, sometimes yellowish colour is seen due to slight decomposition into NO₂ ( and O₂).

 2. It is soluble in water. { 68% nitric acid forms a constant boiling mixture which is termed as azeotropic mixture.}

 3. Nitric acid is corrosive to skin.

 4. Melting point of nitric acid is -42⁰C and its boiling point is 86⁰C.

Chemical Properties of nitric acid (HNO₃)

 1. Decomposition (dissociation) of nitric acid :

In presence of sunlight, nitric acid slightly decomposes and solution turns slightly to yellow or brown due to formation of NO₂ (nitrogen dioxide) .

Concentrated nitric acid decomposes on heating. At higher temperature, the decomposition is rapid.

 2. Acidic nature :

{It changes : blue litmus to red, phenolphthalein- colourless, methyl orange- pink}

• Nitric acid is monobasic acid. It completely dissociates in water:

• It reacts with basic hydroxides, oxides,{ carbonates, ammonia,} etc to give salt and water.

• Mg and Mn reacts with very dilute nitric acid to produce hydrogen gas.

 3. Oxidizing property of nitric acid :

Nitric acid acts as strong oxidizing agent at it’s all concentration. The reactivity and products in chemical reaction involving acid depends upon the following factors:

 i. Concentration of nitric acid

 ii. Reactivity of metal

 iii. Temperature

i.  Concentration of acid : Higher the concentration of nitric acid, higher will be the oxidation state of product formed. These reduced products are formed in general :

 ii. Reactivity of metals : Metals which are more electropositive than hydrogen react with HNO3 to produce nascent hydrogen and metals which are less electropositive than hydrogen react with HNO3 to produce nascent oxygen.

Electrochemical series : The series of various elements obtained by arranging the elements in their increasing order of standard reduction potential in the vertical column is called electrochemical series.

Nascent hydrogen formation theory :

Nascent oxygen formation theory :

 iii. Temperature : The increase in temperature of the reactant increases the rate of the reaction .

A. Oxidation of metals more electropositive than hydrogen :-

→ According to nascent hydrogen formation theory.

 1. Action with zinc :

• With conc. HNO₃ :

• With moderately conc (1:1) HNO₃ :

• With dilute HNO₃ :

• With very dilute HNO₃ :

 2. Action with magnesium :

• With conc. HNO₃ :

• With moderately conc and dilute HNO₃ :

• With very dilute HNO₃ :

 3. Action with iron :

• With hot and conc. HNO₃ : When a highly conc. HNO₃ is added on Fe, a protective layer of ferrosoferric oxide (Fe₃O₄) is formed and the iron becomes passive i.e. prevents the further action of acid on the iron metal.

• With moderately conc.(1:1) HNO₃ : Fe gives ferric salt and NO₂ gas.

• With very dilute HNO₃ : Fe gives ferrous salt and NH₄NO₃

B. Oxidation of metals less electropositive than hydrogen :

→ According to nascent oxygen formation theory.

 1. Action with copper :

• With conc. HNO₃ :

• With moderately conc. or dilute HNO₃ :

 2. Action with mercury :

• With conc. HNO₃ : Hg gives mercuric salt and NO₂

• With moderately conc. or dilute HNO₃ : Hg gives mercurous salt and NO.

C. Reaction of HNO₃ with non-metals :

Dilute HNO₃ has no action with non-metals and metalloids {eg. As, Sb, etc}. Conc. HNO₃ oxidizes non-metals like carbon, sulphur, phosphorus, iodine, etc into their oxides or oxyacids and itself gets reduced to NO₂.

 1. With carbon : Carbon is oxidized to CO₂.

 2. With sulphur : sulphur is oxidized to sulphuric acid.

 3. With phosphorus : Phosphorus is oxidized to phosphoric acid.

 4. With iodine : Iodine is oxidized to iodic acid.

D. Reaction of HNO₃ with inorganic compounds (reducing agents) like H₂S, SO₂, HI, HBr, FeSO₄, etc.

 1. Conc. HNO₃ oxidizes H₂S to S.

 2. Conc. HNO₃ oxidizes KI to I₂ .

 3. Conc. HNO₃ oxidizes SO₂ to H₂SO₄ .

Action with FeSO₄ : ( Test for nitric acid or nitrate ion (NO₃^– ) :

Presence of nitric acid ( or nitrate ion ) in solution can be detected by ring test in wet test analysis. In laboratory, about 1 ml of sample solution is taken and its double volume of concentrated sulphuric acid is added (cautiously). The solution is cooled and few ml of freshly prepared ferrous sulphate solution is added from the side of test tube. Formation of brown ring between two layers of liquid indicates the presence of nitric acid ( or nitrate ).

Here, nitric acid (or nitrate ) reacts with conc. H₂SO₄ and ferrous sulphate to form ferric sulphate. Some ferrous sulphate molecules absorb nitric oxide from the solution and form nitrosyl ferrous sulphate which forms brown ring between two layers of liquid.

Chemical reaction of nitric acid with noble metals in presence of conc. HCl :

Noble metals like gold (Au), platinum (Pt), palladium (Pd), etc. neither react with conc. nitric acid nor with conc. hydrochloric acid. But these noble metals get dissolved in a mixture of conc. HNO₃ and conc. HCl in 1 : 3 ratio by volume. This mixture is called aqua- regia { Aqua= water, regia = king,i.e. kingly water} .

Aqua- regia dissolves such metals due to formation of highly reactive nascent chlorine.

Eg. reaction of gold:

Structure of nitric acid (HNO₃)

Uses of nitric acid :

• It is used in the manufacture of fertilizers, dyes and drugs.
• Used to manufacture explosive like TNT ( trinitro toluene),nitro glycerin etc.
• Used in the purification of gold and silver.
• Used as oxidizing and nitrating reagent in the laboratory.

References :

• Lee, j. D., Concise Inorganic Chemistry, Fifth Edition, Joh, Wiley and Sons, Inc., 2007.
• Sarkar, R., General and Inorganic Chemistry, Second Edition, New Central Book Agency(P) Ltd., India, 2007.
• Shriver, D. F., Atkins, P. W., Inorganic Chemistry, Fifth Edition, Oxford university Press, 2010.
• Agrawal, S. K., Lal, K., Advanced Inorganic Chemistry, Fifth Revised Edition, Pragati Prakashan, Meerut, 2001.
• Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, Fifth edition, John Wily and Sons, Singapore, 1995.
• https://www.tandfonline.com/doi/pdf/10.1080/00022470.1964.10468252
• https://doubtnut.com/question-answer-chemistry/draw-the-lewis-structure-of-nitric-acid-hno3-12973480
• https://en.wikipedia.org/wiki/Ostwald_process

The post Nitric acid (HNO3) : Manufacture by Ostwald’s process,Reactions, Test, Structure and Uses appeared first on Online Chemistry notes.

Preparation of carbon monoxide (CO) :

 1. Carbon monoxide can be prepared by burning carbon with oxygen in limited supply of air.

2. It can also be prepared by reduction of metallic oxide with carbon ( i.e. coal or coke)

3. By passing steam over red hot coke.

Laboratory preparation of carbon monoxide(CO) gas :

Carbon monoxide gas can be prepared in lab by heating formic acid or oxalic acid with conc. H₂SO₄.

Procedure: Small amount of oxalic acid crystal is taken in a round- bottomed flask and all the apparatus are fitted as shown in figure. When conc. H₂SO₄ is poured in the flask through thistle funnel and heated then a mixture of CO and CO₂ gas is formed. The mixture of gas is passed through a bottle containing NaOH solution where the CO₂ gas is absorbed by NaOH.

2NaOH + CO₂ → Na₂CO₃ + H₂O

The pure CO gas is then collected in a gas jar by downward displacement of water.

Physical properties :

1. It is colourless and poisonous gas (with faint smell).
2. It is lighter than air.
3. It is slightly soluble in water.

Chemical Properties of carbon monoxide(CO):

1. It is neutral to litmus.

2. Combustibility (Reaction with oxygen) : It is combustible but not a supporter of combustion. It burns in air to form carbon dioxide.

3. Formation of addition products :

• Action with hydrogen : When carbon monoxide gas is heated with hydrogen in presence of ZnO and Cu at 300⁰C then methanol is formed.

• Action with NaOH ( caustic soda): When carbon monoxide is heated with sodium hydroxide then sodium formate is formed.

   {note: CO2  + NaOH → Na2CO3 + H2O}

• Action with chlorine: Carbon monoxide reacts with chlorine in presence of sunlight to produce phosgene ( carbonyl chloride) which is a poisonous gas.

• Action with sulphur : When a mixture of carbon monoxide and sulphur vapour is heated, then carbonyl sulphide is formed.

         CO + S → COS (carbonyl sulphide)

• Action with ammonical cuprous chloride (solution) : When carbon monoxide gas is passed into ammonical cuprous chloride solution, an addition product i.e. cuprous carbonyl chloride is obtained.

 4. Reaction with transition metals ( i.e. Formation of carbonyl compound) :

Carbon monoxide reacts with transition metals like nickel, iron, cobalt, etc. under suitable conditions to form addition compound called metal carbonyls.

Eg. When CO gas is passed into finely divided nickel at 80⁰C, then nickel tetracarbonyl is formed.

Similarly,

{Carbonyl compound formation takes place due to presence of lone pair of electron in carbon atom of CO molecule, i.e. a Lewis base}

5. Reducing character : Carbon monoxide acts as reducing agent.

• It is used to reduce metallic oxide to metal in metallurgical process. Eg.

• It can reduce iodine oxide to iodine.

• Reduction of Tollen’s reagent( i.e. ammonical silver nitrate solution) : It reduces Tollen’s reagent to metallic silver.

• Reduction of Fehling’s solution : {Basic copper sulphate solution in presence of sodium potassium tartarate is called Fehling’s solution.} It reduces Fehling’s solution to red ppt. of cuprous oxide.

Uses of CO :

1. It is used as reducing agent in metallurgical process.
2. It is used to prepare carbonyl compounds.
3. It is used to prepare poisonous gas.

Structure of carbon monoxide(CO)

Carbon monoxide toxicity :

Q) Why carbon monoxide gas is extremely poisonous( toxic) ?

→ Carbon monoxide combines with haemoglobin to form carboxy haemoglobin. This makes haemoglobin unable to carry oxygen from lungs to the different parts of the body and causes suffocation and even death. Thus CO gas is highly toxic.

{ Therefore, it is adviced that a room being heated by burning coal or other carbon rich fuel should be well ventilated.}

Some questions and answers :

Q) Carbon monoxide is used as a reducing agent in metallurgy but not carbon dioxide, why?

→ CO reduces other substance and itself oxidizes to form CO₂ but CO₂ already is oxidized form and can not further reduce other species. So, CO is used as reducing agent but not CO₂.

Q) How would you convert CO into CO₂ and vice versa ?

→ CO can be converted into CO₂ by heating in the presenc of excess of air.

CO₂ can be converted into CO by passing through red hot coke.

Q) Write down balanced chemical equations giving proper products for the following statements :

i. Water gas is heated over ZnO + Cu.

ii. Carbon monoxide is passed over heated caustic soda.

→ i.

   ii)

Additional Questions from carbon :

Q) What is dry ice? Why it is called so?

→ Solid CO₂ is called dry ice because its structure is similar to that of ice. When it is kept for some time then it gets evaporated without wetting the place where it is kept.

Q) How can you prove that all the allotropes of carbon contain same element?

Q) Show that diamond and graphite consist of carbon only.

→ To prove it first of all 1 gm sample of each allotropes of carbon is taken in a combustion tube and burnt with oxygen to form carbondioxide . The carbondioxide formed is passed into calculated amount of NaOH solution. In all cases the weight of NaOH solution increases. This proves all the allotropes of carbon contains same element.

References :

• Shriver, D. F., Atkins, P. W., Inorganic Chemistry, Fifth Edition, Oxford university Press, 2010.
• Agrawal, S. K., Lal, K., Advanced Inorganic Chemistry, Fifth Revised Edition, Pragati Prakashan, Meerut, 2001.
• Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, Fifth edition, John Wily and Sons, Singapore, 1995.
• Day, C.M., Selbin, J., Theoritical inorganic Chemistry, second edition, Affiliated East-West Press Pvt. Ltd., New Delhi, 2002.
• https://www.medicalnewstoday.com/articles/171876
• https://www.simply.science/images/content/chemistry/metals_and_non_metals/carbon_family/conceptmap/Carbon_Monoxide.html

The post Carbon monoxide (CO) : Preparation, Properties, Structure and Poisoning. appeared first on Online Chemistry notes.

Hydrogen sulphide (H₂S) gas is prepared in the laboratory by treating iron sulphide with dil. H₂SO₄.

Procedure : Iron sulphide (FeS) pieces are kept in woulf’s bottle. Then a thistle funnel and delivery tube is fitted as shown in fig. When dilute H₂SO₄ is poured in woulf ’s bottle, reaction between FeS and dil. H₂SO₄ takes place and H₂S gas is evolved which is collected in the gas jar by upward displacement of air.

Test of H₂S : When a lead acetate paper is dipped in the jar containing H₂S gas, it turns to black due to formation of lead sulphide.

Intermittent supply of H₂S gas by Kipp’s apparatus :

(Working principle of Kipp’s apparatus )

{Intermittent = Stopping and starting at irregular intervals}

H₂S gas is frequently required for salt analysis in the laboratory. The special apparatus which is used for the preparation of H₂S is called Kipp’s apparatus.

Kipp’s apparatus consist of three bulbs A, B and C. The bulbs are interconnected with each other. The upper bulb C contains a long stem which reaches upto bulb A. When dil. H₂SO₄ is poured from bulb C, liquid level rises in bulb A and reaches upto bulb B just to cover iron sulphide. Then the reaction between iron sulphide and H₂SO₄ takes place to form H₂S gas. As H₂S gas is formed, the pressure inside bulb B increases and forces the dil. H₂SO₄ up into the upper bulb C. Then the contact between FeS and dil. H₂SO₄ breaks and the formation of gas is stopped (ceased). When the tap is opened H₂S comes out and the pressure decreases. As a result liquid level again rises at bulb B and H₂S gas start to evolve again. In this way H₂S gas is prepared intermittently by Kipp’s apparatus.

Physical Properties of H₂S :

1. It is colourless gas with rotten egg smell.
2. It is soluble in water.
3. It is poisonous gas.

   {In its low concentration it causes nausea, dizziness and headache. At high concentration it is fatal (i.e. deadly poisonous). Conc. of H2S in air 1 part in 1000 parts of air may be fatal.}

4. It is heavier than air{with vapour density 17}

Chemical Properties of H₂S :

 1. Acidic character of H₂S :

It acts as a weak diprotic (dibasic) acid. It ionizes in two steps to give two protons.

• H₂S reacts with base to form two series of salts. Eg.

• H₂S reacts with basic oxides to give salt.

2. H₂S as reducing agent :-

Sulphur in H₂S bears -2 oxidation state which in minimum oxidation state of sulphur. In chemical reaction, H₂S tends to get oxidized . So H₂S acts as reducing agent.

• It reduces halogens into halogen acids.

• It reduces sulphur dioxide to sulphur.

• It reduces ferric salt to ferrous salt.

• It reduces conc. HNO₃ to NO_2.

• It reduces conc. H₂SO₄ to SO₂.

• It reduces acidified potassium permanganate solution and pink colour of KMnO₄ is discharged.

• It reduces acidified K₂Cr₂O₇ solution and orange color of K₂Cr₂O₇ changes to green.

3. H₂S as analytical reagent in salt analysis ( Precipitation of metal sulphide) :

H₂S gas is used as analytical agent to detect group II basic radicals in acidic medium i.e. HCl and group IIIB basic radicals in in alkaline medium i.e. NH₄Cl and NH₄OH.

Group II basic radicals : Group II basic radicals consists of Cu ⁺⁺ , Hg ⁺⁺, Pb⁺⁺, Cd⁺⁺, Sn⁺⁺, As⁺⁺⁺, Sb⁺⁺⁺, Bi⁺⁺⁺. In qualitative salt analysis this group II radicals are precipitated in the form of their sulphide in acidic medium. By noting the colour of ppt., we can identify the metal cations.

Group IIIB basic radicals : Group IIIB basic radicals consist of Zn⁺⁺, Co⁺⁺, Ni⁺⁺, Mn⁺⁺. These are precipitated by passing H₂S in alkaline medium ( i.e. NH₄Cl + NH₄OH).

Structure of H₂S :

Uses of Hydrogen sulphide (H₂S) :

• It is used as analytical reagent in laboratory.
• It is used as reducing agent.
• It is used to prepare metallic sulphide, which can be used as pigment.

References :

• Shriver, D. F., Atkins, P. W., Inorganic Chemistry, Fifth Edition, Oxford university Press, 2010.
• Agrawal, S. K., Lal, K., Advanced Inorganic Chemistry, Fifth Revised Edition, Pragati Prakashan, Meerut, 2001.
• Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, Fifth edition, John Wily and Sons, Singapore, 1995.
• Day, C.M., Selbin, J., Theoritical inorganic Chemistry, second edition, Affiliated East-West Press Pvt. Ltd., New Delhi, 2002.
• Mitra, L.A. , A Text Book of Inorganic Chemistry, Ghos and Company, 61^st edition, 1996.
• https://en.wikipedia.org/wiki/Kipp%27s_apparatus
• https://www2.humboldt.edu/scimus/HSC.54-70/Descriptions/Kipp%27sGasApp.htm

The post Hydrogen sulphide (H2S): Lab preparation, Kipp’s apparatus, Properties and Uses. appeared first on Online Chemistry notes.

Preparation of Sulphur dioxide:

• By burning sulphur in air.

• By roasting metal sulphide : When metal sulphides (sulphide ores) are heated in excess of air at high temperature, then SO₂ gas is produced.

Laboratory preparation of sulphur dioxide (SO₂) :

Sulphur dioxide gas is prepared in laboratory by heating copper turnings with conc. H₂SO₄.

Procedure: Copper turnings are taken in a round bottom flask fitted with thistle funnel and delivery tube as shown in figure. When conc. H₂SO₄ is poured through thistle funnel and mixture is heated sulphur dioxide gas is evolved, which is collected in the gas jar by upward displacement of air.

Drying of SO₂:  If sulphur dioxide gas is to be dried, the gas obtained is passed through conc. Sulphuric acid . The moisture is absorbed by conc. H₂SO₄.

Chemical Properties of sulphur dioxide (SO₂)

1. Weak acidic nature of SO₂ :

It dissolves in water to give sulphurous acid, a weak diprotic (dibasic) acid.

Sulphurous acid ionizes in two steps:

It produces two series of salts if reacted with base.Eg.

2. SO₂ as a reducing agent :

Aqueous sulphurdioxide shows reducing character and SO₂ itself gets oxidized to H₂SO₄.

• It reduces halogens (Cl₂, Br₂, I₂) in aq. Solution to respective halides. Eg.

• It reduces acidified potassium permanganate solution and pink colour of KMnO₄ is discharged.

• It reduces acidified K₂Cr₂O₇ solution and orange color of K₂Cr₂O₇ changes to light green.

• It reduces ferric salt to ferrous salt and colour changes from yellow to light green.

• It reduces potassium iodate(KIO₃) solution to iodine.

3. SO₂ as an oxidizing agent :

SO₂ oxidizes powerful reducing agents like H₂S, HI, Mg, Fe, etc and itself get reduced to sulphur or sulphide.

4. SO₂ as a bleaching agent:

Formation of colourless product from coloured substance is called bleaching. Chemical substances such as SO2, H2O2, CaOCl2, Cl2, etc. show bleaching action.

SO₂ can act a a bleaching agent in presence of moisture. It can bleach coloured wool, silk, flower, hair, etc. The bleaching action of sulphur dioxide is due to the formation of nascent hydrogen in presence of moisture, which reduces colouring substance to colourless reduced product.

In some cases, bleaching action of SO₂ is due to formation of colourless addition product.

→ The bleaching action of SO₂ is temporary. The bleached colourless compound will regain its original colour slowly on standing in air due to oxidation by air.

Comparison of bleaching action of SO₂ and Cl₂:

Test for sulphur dioxide (SO₂) :

• Odour : Sulphur dioxide has typical suffocating smell of burning sulphur.
• Potassium dichromate paper test : When SO₂ comes in contact with acidified potassium dichromate paper, the orange coloured paper turns to green due to formation of chromium sulphate.

Uses of SO₂

• It is used as bleaching agent.
• It is used in the manufacture of sulphuric acid.
• It can be used as disinfectant, fungicide and food preservative.

References :

• Sarkar, R., General and Inorganic Chemistry, Second Edition, New Central Book Agency(P) Ltd., India, 2007.
• Shriver, D. F., Atkins, P. W., Inorganic Chemistry, Fifth Edition, Oxford university Press, 2010.
• Agrawal, S. K., Lal, K., Advanced Inorganic Chemistry, Fifth Revised Edition, Pragati Prakashan, Meerut, 2001.
• Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, Fifth edition, John Wily and Sons, Singapore, 1995.
• https://www.environment.gov.au/protection/publications/factsheet-sulfur-dioxide-so2
• https://en.wikipedia.org/wiki/Sulfur_dioxide

The post Sulphur dioxide (SO2) : Preparation, Properties and Uses. appeared first on Online Chemistry notes.

Sulphuric acid is widely used chemical in industries. It is used in the manufacture of fertilizers, drugs, dyes, polymers, etc. thousands of tons of sulphuric acid is manufactured every year worldwide. So it is called king of chemicals.

Manufacture of sulphuric acid(H₂SO₄) by contact process

• In early days, sulphuric acid used to be maniufactured by lead chamber process.

• Contact process is modern method. The acid obtained is pure( free from impurities) and is quite concentrated (96-99%). The contact process, it’s name is mainly from the fact that the conversion of sulphur dioxide into sulphur trioxide is carried out in contact with surface of catalyst.

Principle :

 1. Production of sulphur dioxide : Sulphur dioxide gas can be prepared either by burning sulphur or roasting of iron pyrites.

 2. Catalytic oxidation of sulphur dioxide : Sulphur dioxide is oxidized to sulphur trioxide in presence of catalyst vanadium pentoxide at about 450⁰C temperature and 2 atm pressure.

 3. Conversion of SO₃ into H₂SO₄ : sulphur trioxide obtained is absorbed in 98% H₂SO₄ to produce oleum or fuming sulphuric acid. The oleum is diluted with calculated amount of water to get desired concentration of H₂SO₄.

Conditions for optimum yield of H₂SO₄ :

Formation of SO₂ to SO₃ is one of the must important steps in the manufacture of sulphuric acid. The production of H₂SO₄ entirely depends on the amount of SO₃ formed. As reaction is reversible, exothermic and proceeds with decrease in volume, Le- Chatelier’s principle can be applied for the maximum yield of sulphur trioxide.

• Low temperature : This reaction is exothermic . So, low temperature is required for maximum yield. But too low temperature is too slow to attain equilibrium. So an optimum temperature of about 450⁰C is supplied.
• High concentration of reactants : High concentration of SO₂ and O₂ is used for more production of SO₃ .
• High pressure : High pressure favours the reaction because the product formed has less volume than reactant . But the acid resistant tower which are able to withstand high pressure are difficult to build. Hence, an optimum pressure of about 2 atm is applied.
• Use of catalyst : Rate of reaction is increased by the use of positive catalyst . So, vanadium pentoxide is used as catalyst for higher yield of H₂SO₄.

Details of the plant or process :

 [I] Sulphur or pyrite burner : SO₂ gas is obtained by burning sulphur or iron pyrite with air in sulphur or pyrite burner.

 [II] Purification unit : The impure SO2 gas obtained is purified by the purification unit.

1. Electrical dust precipitator : Dust particles present in sulphur dioxide gas is precipitated in electrical dust precipitator by the influence of high potential difference applied between the metallic conductors fitted in the chamber.
2. Steam chamber : The lighter dust particles are settled down by using steam in steam chamber.
3. Cooler : The gases coming out from the steam chamber are passed through cooler. The gases get cooled down to about 100⁰C.
4. Washing tower(scrubber) : The cooled SO₂ gas is then passed into a tower called scrubber which is packed with quartz and water is sprayed from the top. The water soluble impurities are washed away.
5. Drying tower : The moisture present in sulphur dioxide is absorbed by the spray of conc.H₂SO₄ in drying tower.
6. Arsenic purifier : arsenous oxide ( As₂O₃) present in gas is absorbed by ferric hydroxide( because it may causes catalytic poisoning).

 [III] Testing box : The purity of sulphur dioxide is checked in testing box by passing through a darkened box.

 [IV] Preheater : The purified mixture of SO₂ and O₂ is heated upto 450⁰C.

 [V] Contact chamber : The SO₂ gas is catalytically oxidized to sulphur trioxide (SO₃) in the presence of V₂O₅ as catalyst at 450⁰C temperature and 2 atm pressure.

 [VI] Absorption tower : This tower is packed with quartz (or acid proof stone) in which 98% H₂SO₄ is sprayed from the top of the tower. Concentrated H₂SO₄ absorbs sulphur trioxide to form oleum( or pyrosulphuric acid). Oleum is then treated with calculated amount of water to form sulphuric acid of desired concentration.

Physical Properties of H₂SO₄:

• It is colourless, hygroscopic, syrupy liquid.
• It is highly soluble in water (due to formation of intermolecular hydrogen bond). It dissolves in water with the liberation of large quantity of heat(19Kcal/mol) which may causes the explosion or spurt the acid out of the container.

      H₂SO₄ + nH₂O → H₂SO₄.nH₂O + Heat

Therefore, sulphuric acid is diluted by adding the acid slowly to water with constant stirring and not by adding water to the acid.

• It’s melting point is 10⁰C and boiling point is 338⁰C.
• Pure H₂SO₄ is covalent compound and bad conductor of electricity. However aqueous H₂SO₄ conducts electricity.
• Litmus test : Sulphuric acid is covalent compound. In pure state it does not change the colour of the blue litmus paper. However, aqueous acid gets ionized and produces hydrogen(or hydronium) ion into solution. Due to which it can change the colour of blue litmus paper to red.

Chemical properties of H₂SO₄ :

 1. Decomposition of H₂SO₄ :

On heating H₂SO₄ decomposes into SO₂, H₂O and O₂.

 2. Acidic nature of H₂SO₄:

H₂SO₄ is a strong dibasic (diprotic) acid and ionizes in two steps.

It gives two series of salts like bisulphate and sulphate when reacted with base.Eg.

 3. H₂SO₄ as an oxidizing agent :

 i. Action with metals : More electropositive metals ( i.e. metals lying above hydrogen in electrochemical series) like Zn, Fe, Mg, Al, etc. react with dil H₂SO₄ to produce hydrogen gas. Here H₂SO₄ reduces to H₂ and metals oxidize to metal sulphates.

Conc. H₂SO₄ oxidizes Zn, Cu, Ag, Hg, etc. to respective metal sulphates and H₂SO₄ gets reduced to SO₂.

 ii. Action with non metals :

• Carbon is oxidized to carbondioxide.

• Sulphur is oxidized to sulphurdioxide.

• Phosphorus is oxidized to phosphoric acid.

 iii. Action with some other reducing agents :

• H₂SO₄ oxidizes H₂S to S and itself reduces to SO₂.

• HBr and HI are oxidized to Br₂ and I₂ respectively.

{Note : HCl can not be oxidized to Cl₂ because of strong bond.}

 4. Sulphuric acid as dehydrating agent :

H₂SO₄ is a good dehydrating agent. It absorbs water molecules from sugar, cellulose, copper sulphate crystals, etc.

• With sugar (charring action) : When conc. H₂SO₄ is treated with sugar, wood, paper, etc. it absorbs water and a black mass of carbon is formed. This process is called charring.

• With copper sulphate crystals : It removes water of crystallization from hydrated salts.

• With oxalic acid crystals and formic acid:

Structure : Lewis structure of H₂SO₄

Uses of sulphuric acid :

• It is used for the manufacture of fertilizers.
• It is used in manufacture of HCl, HNO₃, H₃PO₄, etc.
• It is used as an oxidizing agent.
• It is used as a drying and dehydrating agent.

Test of H₂SO₄ :

Sulphuric acid gives H+ ions and SO₄^{– –} ions in aqueous solution. The presence of H⁺ ion can be detected by litmus paper. The presence of SO₄^{– –} can be detected by BaCl₂ solution which gives white precipitate.

Sodium thiosulphate(hypo) :

Molecular formula : Na₂S₂O₃. 5H₂O

It is commonly called hypo.

Uses of sodium thiosulphate(hypo) :

• It is used as a fixer in photography. { i.e. for fixing silver bromide in photographic plate}
• It is used in (iodometric) titration for the estimation of iodine.
• It is used as an antichlor agent to remove excess of chlorine from bleached textiles/fibers.

REFERENCES :

• Lee, j. D., Concise Inorganic Chemistry, Fifth Edition, Joh, Wiley and Sons, Inc., 2007.
• Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, Fifth edition, John Wily and Sons, Singapore, 1995.
• Day, C.M., Selbin, J., Theoritical inorganic Chemistry, second edition, Affiliated East-West Press Pvt. Ltd., New Delhi, 2002.
• Mitra, L.A. , A Text Book of Inorganic Chemistry, Ghos and Company, 61^st edition, 1996.
• https://pubchem.ncbi.nlm.nih.gov/compound/Sulfuric-acid
• https://www.sciencedirect.com/topics/earth-and-planetary-sciences/sulphuric-acid
• https://www.britannica.com/technology/contact-process

The post Sulphuric acid (H2SO4) : Manufacture by contact process, properties, uses, test and structure. appeared first on Online Chemistry notes.

Allotropes of phosphorus :

Phosphorus exists on following allotropic forms :

1. White or yellow phosphorus
2. Red phosphorus
3. Black phosphorus
4. Violet phosphorus
5. Scarlet phosphorus

Among them white and red phosphorus are more common.

        1. White Phosphorus :

      Chemical properties of (white) phosphorus:

• Action with air (O₂) : Phosphorescence : Phosphorus is highly reactive and it burns(oxidize) in air giving yellow-green flame forming phosphorus pentoxide and trioxide. This phenomenon is called phosphorescence.

Q) why is phosphorus stored in water?

→ Phosphorus is highly reactive and it easily oxidized in the presence of oxygen at room temperature and burns with yellow- green flame. This phenomenon is called phosphorescence. Due to this reason phosphorus is stored in water.

• Action with chlorine : Phosphorus forms trichloride and pentachloride with chlorine

Note: similar reaction for bromine and iodine too.

• Action with metal : phosphorus combines with metals like Na, K, Mg, Ca, etc to form metal phosphide.

• Reducing property : Phosphorus is reducing agent. It reduces conc. HNO₃ to NO₂ and conc. H₂SO₄ to SO₂.

• Action with caustic alkali (i.e. Caustic soda or caustic potash) :

When phosphorus is boiled with aqueous solution of caustic soda(NaOH) or caustic potash(KOH), phosphine gas is formed.

Structure of white phosphorus :

    2. Red Phosphorus :

When white phosphorus is heated at about 250⁰C in an inert atmosphere( of nitrogen or carbondioxide or coal gas) for several hours then it is converted into red phosphorus.

Structure of red phosphorus:

Uses of phosphorus :

• It is to prepare poison for killing rats.
• It is used in match industries.
• It is used in manufacture of phosphate fertilizer.
• It is used to prepare phosphine gas, phosphoric acid, etc.

Phosphorus hydride (Phosphine) (PH₃) :

Laboratory Preparation of phosphine :

Phosphine gas is prepared in laboratory by heating white phosphorus with caustic soda or caustic potash in an inert atmosphere.

During the preparation of phosphine, some quantity of diphosphine(P₂H₄) is formed. Due to presence of highly inflammable diphosphine, PH₃ gas burns with air as it comes out of water and forms vertex rings of phosphorus pentoxide.

Hence, during the preparation of phosphine gas all air inside the reaction flask is replaced by inert gas like CO₂ to minimize the risk of explosion. The phosphine gas evolved should be first passed through freezing mixture where diphosphine is condenced but phosphine is not condensed. Then the pure phosphine gas is collected in a gas jar by downward displacement of water.

Chemical Properties of Phosphine :

• Decomposition : Phosphine gas dissociates at 4400C to give red phosphorus and hydrogen.

• Combustion ( action of air) : Phosphine is non-supporter of combustion. But when phosphine is heated with air phosphorus pentoxide or phosphoric acid is formed.

• Reducing properties :
• Reduction of AgNO₃ solution : When PH3 gas is passed through AgNO3 solution then metallic silver along with phosphorus acid and nitric acid is formed.

Q) What happens when the gas produced by the action of white phosphorus with sodium hydroxide is passed through silver nitrate solution?

• With CuSO₄ solution : Phosphine gives black ppt. of copper phosphide with CuSO₄ solution. This is test reaction of phosphine.

Uses of phosphine :

• It is used to the formation of smoke screen during wars.
• It can be used as reducing agent.

Structure of Phosphine gas :

Oxides of phosphorus:

Phosphorus trioxide (P₂O₃) :

Uses : It is used to prepare Phosphorous acid and Phosphoric acid.

Structure of P₂O₃ : It exists in dimer form i.e. P₄O₆.

Phosphorus Pentoxide (P₂O₅) :

Uses :

• It is used as dehydrating agent in organic reactions.
• It is used for preparing phosphoric acid.

Structure of P₂O₅ :

Oxyacids of phosphorus :

Orthophosphoric acid (H₃PO₄) :

Preparation :

In laboratory, phosphoric acid is prepared by heating red phosphorus with concentrated HNO3 in presence of iodine as catalyst.

       P₄ + conc. 20 HNO₃      →    4H₃PO₄ + 4H₂O + 20 NO₂

Chemical Properties :

• Action of heat :   When orthophosphoric acid is heated, it produces pyrophosphoric acid at 250⁰-260⁰C and metaphosphoric acid at 300⁰C with removal of water molecule.

• Acidic nature :It is tribasic( triprotic )acid. It ionizes in three steps and forms three series of salts with alkali.

Uses of phosphoric acid :

• It is used in the manufacture of phosphate fertilizers.
• It is used as rust removal agent, household cleaning agent, sanitizing agent, etc.

Structure of orthophosphoric acid and phosphate ion :

                           BORON :

Occurance : it is not found in free state in nature. It is found in combined states as boric acid, borax, etc.

Uses of boron :

• It is used in the steel industry for increasing hardness of steel.
• Small amount of boron compound is essential for plant growth.
• It is used as semiconductor for making electronic devices.

Boric acid (Ortho boric acid) :

Molecular formula : H₃BO₃ or B(OH)₃

Uses :

• It is used as an antiseptic. Its aqueous solution is used in washing eyes, nose, ear,etc.
• It is used as a preservative for milk and food stuffs.

Borax :

Molecular formula : Na₂B₄O₇. 10H₂O

Uses :

• It is used to detect basic radicals in salt analysis (borax bead test).
• is used as a preservative for food stuffs.
• It is used in manufacture of soaps, washing powder, etc.

                                  SILICON :

Uses of silicon :

• It is used to make chips used in electric devices.
• It is used to make carborundum which is used as an abrasive.
• Silica (SiO2) is used as building material in making cement.

Carborunbum : Silicon carbide (SiC).

Use : It is used as abrasive.

Silica : SiO₂

Uses :

• Used as building material in making cement.
• Used for preparing glass.
• Used for making silica gel which is used for absorbing moisture.

Silica gel : i.e hydrated silica : SiO₂. xH₂O

Use : It is used for absorbing moisture and as an adsorbent in chromatography.

Sodium silicate : Na₂SiO₃

Uses :

• It is used for making glass.
• It is used for making silica gel.

                         Noble Gases

The elements which are present in zero group or 18 group of Modern periodic table are known as noble gases. Helium, neon, argon, krypton, xenon and radon constitute the noble gas family. They are very less reactive at normal temperature and pressure.

Uses of noble gases :

• Helium is used for filling ballons.
• Argon is used in electric bulb.
• Radon is used for the treatment of cancer i.e. in radiography.

Q. what are noble gases? Why are they chemically inert?

→ The elements which are present in zero group or 18 group of Modern periodic table are known as noble gases. They are chemically inert because of stable valence shell with octet electrons except in helium( duplet).

Eg. He : 1s² Ne : 1s²2s²2p⁶

They have high ionization energy so transfer and share of electrons is very difficult. Hence, noble gases are chemically inert.

Q) The first ionization energy of noble gases is higher than that of halogens, explain.

→ The electronic configuration of noble gases is very stable due to presence of fulfilled electrons in the outermost orbital. So, very high amount of energy is required to remove electrons from the outermost orbital and the value of ionization energy is very high. But in case of holegens, there are seven electrons in outermost orbital, i.e. not fulfilled . Hence, I.E. of noble gases is higher than that of halogens.

          Environmental Pollution :

Air Pollution : The contamination of air with harmful gases, dust, smoke , etc. is known as air. The pollutants like CO, NO, NO₂, SO₂, O₃, smoke, dust, etc. which pollute the air are called air pollutants.

Smog : It is the combination of smoke and fog.

• Chemical smog : Sulphur dioxide (SO₂) and particular matter present in air form this type of smog during cold and humid climate. When SO₂ combines with water vapour, it forms sulphurous acid which condenses on smoke, dust particles etc. and form a mixture called chemical smog.

→ It causes respiratory problems such as bronchitis, pneumonia, etc.

• Photochemical smog : The smog which is formed by the reaction of automobile exhaust in the presence of sunlight is called photochemical smog.

The major components of photochemical smog are NO, CO, NO₂, hydrocarbons, etc.

→ The photochemical smog causes headache, eye problem, skin problem, etc.

→ it reduces visibility and affects the air and road traffic.

Acid Rain :

Generally rain water is slightly acidic having pH about 5.6 due to dissolved CO₂ in water. However, pH of the rain water is decreased below pH 5.6 if the acidic oxides like oxides of sulphur and nitrogen get dissolved in it. Such rain water is called acid rain.

→ It can destroy the life of aquatic animals.

→ It causes damage of buildings and rocks.

→ It increases the acidity of soil and decreases the fertility of soil.

Green house effect :

The green house effect is a natural process that warms the earth. When the energy from sun reaches the earth’s atmosphere, some of it is reflected back to space and the rest is absorbed by greenhouse gases.

Greenhouse gases include water vapour, carbondioxide, methane, nitrous oxide, ozone and some artificial chemicals such as chlorofluorocarbon (CFCs).

The absorbed energy warms the atmosphere and the surface of the earth. This process maintains the temperature of our earth due to which the life is possible in earth.

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Manufacture of ammonia by Haber’s process:

1. Low temperature : Since the reaction is exothermic, low temperature is favourable for the formation of ammonia. If the temperature is below 450⁰C, N₂ and H₂ react too slowly to attain equilibrium state. Thus an optimum temperature of about 450-500⁰C is maintained.
2. High pressure : The total volume of product is lower than total volume of reactant so, equilibrium shifts in forward direction with the increase in pressure. In practice, 200 to 900 atmospheric pressure is applied.
3. High concentration of reactants : Since reaction proceeds in forward direction with decrease in volume, so either one or both reactants( H₂ and N₂) should be used in excess amount for high yield of NH₃.
4. Catalyst : Presence of the catalyst speeds up the rate of reaction. Finely divided Iron catalyst and Molybdenum promoter is used.
5. Purity of hydrogen and nitrogen : The nitrogen and hydrogen gas should be very pure, otherwise the catalyst is poisoned and decreases catalytic activity.

Physical Properties of Ammonia :

1. It is a colourless and pungent smelling gas.
2. It is lighter than air.
3. It is easily liquefiable gas. It can also be solidified. Melting point of solid ammonia is -78⁰C and boiling point of liquid ammonia is -33.4⁰C.
4. It is neither combustible nor a supporter of combustion.
5. It is highly soluble in water as it forms intermolecular hydrogen bond with water.

Chemical Properties (reactions) of Ammonia :

1. Basic nature:

• Ammonia changes the colour of moist litmus paper into blue.
• It dissolves in water to give OH^– ions.
• It reacts with acid to give salt.

• Due to presence of lone pair of electrons on the nitrogen atom, ammonia acts as a Lewis base,

• Action with oxygen : When ammonia is heated with oxygen, it gets oxidized to nitrogen gas. Here ammonia acts as reducing agent.

•  Action with metal oxides : when ammonia gas is passed over heated copper oxide or lead oxide, metal oxide is reduced to respective metals.

•  Action with bleaching powder : When ammonia gas is heated with bleaching powder, it reduces CaOCl₂ into CaCl₂.

• Action with fluorine :

• Action with chlorine :

• Action with bromine :

 

• Action with iodine :

         

• Action with copper sulphate solution :

Uses of ammonia :

1. It is used for the manufacture of urea.
2. It is used as cooling agent in refrigerator.
3. It is used for reducing metal oxide.
4. It is used to manufacture nitric acid by Ostwald’s process

Structure of ammonia :

REFERENCES :

• Agrawal, S. K., Lal, K., Advanced Inorganic Chemistry, Fifth Revised Edition, Pragati Prakashan, Meerut, 2001.
• Cotton, F. A., and Wilkinson, G., Advanced Inorganic Chemistry, Fifth edition, John Wily and Sons, Singapore, 1995.
• Day, C.M., Selbin, J., Theoritical inorganic Chemistry, second edition, Affiliated East-West Press Pvt. Ltd., New Delhi, 2002.
• Lee, j. D., Concise Inorganic Chemistry, Fifth Edition, Joh, Wiley and Sons, Inc., 2007.
• Sarkar, R., General and Inorganic Chemistry, Second Edition, New Central Book Agency(P) Ltd., India, 2007.
• Shriver, D. F., Atkins, P. W., Inorganic Chemistry, Fifth Edition, Oxford university Press, 2010.
• Mitra, L.A. , A Text Book of Inorganic Chemistry, Ghos and Company, 61^st edition, 1996.
• https://www.aiche.org/resources/publications/cep/2016/september/introduction-ammonia-production
• https://pubchem.ncbi.nlm.nih.gov/compound/Ammonia
• https://en.wikipedia.org/wiki/Ammonia

The post Ammonia : Manufacture by Haber’s Process, Properties, Uses And Structure. appeared first on Online Chemistry notes.