HYDROGEN

PHYSICAL PROPERTIES

1) Hydrogen is a colorless, odorless, tasteless gas.

2) It is insoluble in water.

3) It is the lightest element .

4) It is neutral to the litmus test.

5) It is highly combustible gas.

6) It is non-toxic gas.

7) Hydrogen has a melting point of -259.14 °C.

8) and a boiling point of -252.87 °C.

Q :-Discuss the position of hydrogen in the periodic table --or--

POSITION OF HYDROGEN

Q:-Why do we call Hydrogen a rogue element?

Hydrogen is the first element in the periodic table .

Its atomic number is one .

Its electronic configuration : 1s1

The position of hydrogen in the periodic table is controversial or anomalous .It does not hold a proper position in the periodic table because:.

In some properties it resembles alkali metals. And in some other properties it resembles halogens.And it still differs from both of them.

1) RESEMBELENCE WITH ALKALI METALS

ELECTRONIC CONFIGURATION :Like alkali metals it has one electron in its valence shell . E.g. hydrogen

2) ELECTROPOSITIVE CHARACTER

Like alkali metals it can lose its only valence electron to acquire positive charge. E.g

H → H+ + e-

Li → Li+ + e-

3) OXIDATION STATE

Just like alkali metals hydrogen shows +1 oxidation state.

4) REDUCING AGENT

Like alkali metals hydrogen is a strong reducing agent. E.g.

Fe3O4 + 4H2 → 3Fe + 4H2O

5) LIBERATION AT CATHODE

During electrolysis of salt solutions of hydrogen and alkali metals both are liberated at cathode. E.g.

2HCl(aq) → H2(g)+ Cl2 (g)

At cathode At anode

2NaCl(l) → 2 Na (s) + Cl2 (g)

COMBINATION WITH NON-METALS

Like alkali metals hydrogen combines with non-metals like oxygen , halogen , sulphur to form oxides , halides and sulphides.

Water → sodium oxide

HCl → sodium chloride

Hydrgen sulphide→ sodium sulphide

RESEMBELENCE WITH HALGENS

1) ELECTRONIC CONFIGURATION :-Just like halogens hydrogen also needs one electron to acquire stable electronic configuration of nearest noble gas. E.g H is one electron less than He and similarly F is one electron less than neon

2) ELECTRONEGATIVE CHARACTER:-Just like halogens hydrogen also have tendency to acquire negative charge by gaining one electron.

3) LIBERATION AT ANODE :-During electrolysis of molten alkali metal hydrides , hydrogen gas is liberated at anode. Similarly during electrolysis of molten alkali metal halides ,the halogens are liberated at anode.

4) OXIDIZING AGENT:- like halogens it can act as oxidizing agent. E.g NaH and NaCl.

5) OXIDATION STATE :- just like halogens h, hydrogen shows an oxidation state of -1.

6) COMBINATION WITH METALS:-Both hydrogen and halogens combine with metals to form hydrides and halides respectivley.

7) IONIZATION ENERGY:-The ionization energy of hydrogen and halogens are quite comparable . E.g H=1312 and Cl=1255

8) ATOMICITY :-Just like halogens, it exists as diatomic molecule.

9) FORMATION OF COVALENT BOND :-like halogens ,hydrogen also combines with non-metals to form covalent compounds. E.g.Methane ,ammonia,carbon tetra chloride ,nitrogen tirchloride, etc.

10) SUBSTITUTION REACTIONS :-In hydrocarbons both elements have the tendency to replace one another.

11) Both are typical non-metals

POINTS OF DIFFERENCES FROM ALKALI METALS

1) It exists as a gas while alkali metals are solids .

2) It is non-metal whereas alkali metals are typical metals.

3) It has very high ionization energy as compared to alkali metals.

4) It forms covalent compounds while compounds of alkali metals are mainly ionic.

5) Its oxide is neutral while oxides of alkali metals are basic.

POINTS OF DIFFERENCE FROM HALOGEN

1) Just like halogens it does not contain any lone pair of electrons in its molecular form.

2) Its oxide is neutral in nature whereas oxides of halogens are acidic in nature.<;p>

3) Size of hydride ion is much smaller than halide ions.

CONCLUSION

In the light of above discussion it is concluded that hydrogen resembles and at the same time differs from alkali metals and halogens .Thus it is difficult to assign it a proper position in the periodic table. Because of its controversial position, it is sometimes referred to as rogue element. However being a special case it is placed separately at the top of the periodic table.

ISOTOPES

Atoms of the same element having different atomic masses are called isotopes. E.g. Hydrogen element has three isotopes:

ISOTOPIC EFFECT

The difference in the properties of isotopes due to their different masses is called isotopic effect. E.g. all the three isotopes of hydrogen have different physical properties like density ,m.pt and b.pt ,rate of adsorption etc.

Q:- What is heavy water?

Ans:- The water which contains deuterium isotope of hydrogen is called heavy water and it is written as D2O.Whereas water containing protium is called ordinary water.It is written as H2O.

What is Allotropy?

Ans:-The phenomenon of existence of an element in two or more forms having similar chemical properties but different physical properties is called allotropy and the various forms of that element are known as allotropic forms or allotropes. E.g. hydrogen molecule exists in two allotropic forms:

1)ortho-hydrogen :- two nuclei spin in the same direction

2) para-hydrogen :- when two nuclei spin in the opposite direction

PREPARATION OF HYDROGEN

Hydrogen gas in laboratory is prepared by the action of dilute sulphuric acid on granulated zinc .The hydrogen gas produced in this way is collected in a gas jar by the downward displacement of water.

The chemical reaction taking place inside the wolf bottle is as follow:

APPARATUS REQUIRED

Q:Why don't we use conc sulfuric acid for preparing hydrogen gas

Ans:Because with zinc it produces sulphur dioxide and water along with zinc sulphate.Sulphur dioxide is poisonous and can cause headache and other health problems.

Q:What is nacent hydrogen ?

Ans :- Nascent hydrogen– Hydrogen formed at the of reaction is known as Nascent hydrogen.

Order of reactivity of different forms of hydrogen

Atomic hydrogen > Nascent hydrogen > Molecular hydrogen

Q: What is Occulusion ?

Ans: The property of metal to adsorb any gas on its surface is called occulusion.E.g. adsorption of hydrogen gas on the surface of palladium.

USES OF HYDRGOEN

It is used as a reducing agent in several redox reactions.
It is used to manufacture vanaspati ghee by hydrogenation of oils
It is used as as a rocket fuel in liquid form.
It is used to manufacture ammonia gas in Haber’s process.
It used in fuel cell to produced electricity.
It is used in oxy-hydrogen torches for cutting and welding.
It is used to prepare synthetic petrol.

TYPES OF HYDROGEN

(i) Molecular hydrogen Ordinary hydrogen gas consists of di-atomic molecules in which two H-atoms unite together by covalent bond. This is known as molecular hydrogen. Due to high bond energy ,molecular hydrogen is very stable .It does not react under ordinary conditions .

(ii) Atomic hydrogen :-Hydrogen obtained by the dissociation of molecular hydrogen is called atomic hydrogen. Atomic hydrogen is very energetic and very reactive .It has a very short life and spontaneously combine to form molecular hydrogen.

NASCENT HYDROGEN:monoatomic hydrogen liberated during a chemical reaction is known as nascent hydrogen or newly born hydrogen. It is very reactive in nature. it is strong reducing agent. E.g. When Zinc is passed through dil H2SO4, nascent hydrogen is produced as:

Zn + dil. H2SO4 → ZnSO4 + 2[H]

This nascent hydrogen reduces the pink potassium permanganate solution into colorless manganite salt. Ordinary hydrogen don’t react with KMnO4 .

2KMnO4 + 3 H2SO4 +10 [H] →K2SO4 + 2MnSO4 + 8H20.

Q:- What is hard water ?

Ans :- The water that does not produce lather with soap solution easily. It contains soluble salts of bicarbonates, sulphates and chlorides of calcium and magnesium .

Q:- what is soft water?

Ans :- The water that produces lather with soap solution easily. It is free from salts of calcium and magnesium (bicarbonates, sulphates and chlorides ).

Q:- what is hardness of water ?

Ans:- It is the property of the water due to which it does not form lather with soap solution.

Q:- what is the cause of hardness of water?

Ans :- hardness of water is due to the presence of soluble bicarbonates,chlorides and sulphates of calcium and magnesium in it.

Q:- What is temporary hardness and permanent hardness of water.--OR--

Q:- What is the cause of temporary hardness and permanent hardness of water

Ans:Hardness of water is two types

1) Temporary hardness :- It is due to the presence of soluble bicarbonates of calcium and magnesium in water. It is called temporary because it can be removed by simply boiling .

2) Permanent hardness :-It is due to the presence of chlorides and sulphates of calcium and magnesium in water. It can not be removed by boiling .That is why it is called permanent hardness.

Q : Write a short note on cleansing action of soap.

Ans :-CLEANSING ACTION OF SOAP:- Soaps are sodium salts of long chain fatty acids .they have a polar head and a non polar tail.For example sodium stearate consists of non polar tail of long hydrocarbon chain and a polar head of carboxylate ion and sodium Ions. The polar head is water soluble whereas the non polar tail is soluble in organic solvents. Due to the presence of grease or fats on the cloth ,the dust particles get stick to the cloth and the cloth becomes dirty. When the aqueous solution of soap is applied on the cloth the non polar end is directed towards the oil or grease present on the cloth and the polar head is directed towards the water. In this way each oil droplet is surrounded by a large number of negatively charged carboxylate ions to form an aggregate called Micelle .A large numbers of micelles are formed during the process of washing. When cloth is rubbed with hands or agitated with washing machine these micelles are dispersed in the soapy water and dirt gets detached from the surface of the cloth.

Q:-Why do soaps not work in hard water?

Ans :- Water which does not produce lather with soap readily is called hard water.Hard water contains salts of calcium and magnesium. These salts are bicarbonates,chlorides and sulphates.When hard water is treated with soap,the ions(Mg2+ and Ca2+) present in it react with anions of fatty acids present in soaps to form scum or curdy white precipitate. As a result of which lather is not formed and a lot of soap gets wasted.

Q:- what is softening of water?

Ans:- The process of removal of hardness of water is called water softening . Following methods can be used to remove hardness of water:-

1)BOILING :- This method is used to remove temporary hardness of water. When water is boiled the soluble bicarbonates are converted into insoluble carbonates which settle down and removed by filtration.

Following methods are used to remove permanent hardness of water:

1) Washing soda method:

In this method chlorides and sulphates of magnesium and calcium react with washing soda to form insoluble carbonates which can be removed by filtration.

CaCl2 + Na2CO3 → CaCO3 + 2NaCl

MgCl2 + Na2CO3 → MgCO3 + 2NaCl

CaSO4 + Na2CO3 → CaCO3 + Na2SO4

MgSO4 + Na2CO3 → MgCO3 + Na2SO4

ION EXCHANGE METHOD

In this method calcium and magnesium ions of hard water are exchanged with other ions present in the ion exchangers. The ion exchangers are the complex substances which act as a medium for exchanging ions. Two types of ion exchangers are used for this purpose :

TYPES OF ION EXCHANGE METHOD

1)Permutit or Inorganic ion exchanger

A porous mass obtained by fusing a mixture of washing soda,silica and alumina is called permutit.It is also called sodium zeolite.It is used to soften hard water. Permutit is loosely packed over layers of sand and gravel in a big tank. Hard water is introduced through an inlet at the bottom of the tank. From the bottom of the tank water rises upward through the layers of gravel and sand. Then water water comes in contact with permutit. Here the calcium and magnesium ions of water get exchanged with sodium ions of permutit. The water that rises above the permutit layer is soft as it is free from calcium and magnesium ions.It can be taken out from the outlet.

Na2Z + Ca2+ → CaZ + 2Na+

Na2Z + Mg2+ → MgZ + 2Na+

REGENERATION OF PERMUTIT

After sometime the whole of permutit gets converted into calcium and magnesium zeolite and does not work. Then it is regenerated by passing 10% solution of sodium chloride through it.

CaZ + 2Na+ → Na2 Z + Ca2+

MgZ + 2Na+ → Na2 Z + Mg2+

The calcium and magnesium ions are washed away with water .The regenerated permutit can be used again for softening of hard water.

2) ORGANIC ION EXCHANGER

An ion-exchange resin is a polymer that acts as a medium for ion exchange. It is an insoluble support structure normally in the form of small microbeads, usually white or yellowish. The ion exchange resins are superior to zeolites since they can remove all types of cations and anions present in the hard water. On the other hand zeolites remove only cations present in the hard water. The resulting water obtained after treating hard water with ion exchange resins is called demineralized or deionized water.

Q :- what is demineralized or deionized water ?

Ans :- water that does not contain any ion is called demineralized water.it is obtained by passing ordinary water through ion exchange resins.

Q :- what is ion exchange resins ?

Ans:- An ion-exchange resin is a polymer that acts as a medium for ion exchange. It is an insoluble support structure normally in the form of micro beads, usually white or yellowish.

Q:What are resins ?

Ans:- resin is a solid or highly viscous substance which can be plant-derived or synthetic in origin. They are often mixtures of organic compounds. Many plants, particularly woody plants produce resin in response to injury. The resin acts as a bandage protecting the plant from invading insects and pathogens.

Q:- what is hydrogen peroxide ?

Ans :- It is a chemical compound with molecular formula H2O2 .

It was discovered by Thenard in 1918. It is an unstable compound .

STRUCTURE

The structure of hydrogen peroxide is non-planar. This structure is also known as open book structure because it gives the appearance of open book. There are two planes in this structure and each plane has one O-H bond. The inter-planar angle is 111.50 in the gaseous phase, but it is reduced to 90.2° in the solid state due to hydrogen bonding. Other difference in the structure of hydrogen peroxide are given in the diagram as follow:

PREPARATION OF H2O2

1) From sodium peroxide :- Hydrogen peroxide can be prepared in the laboratory by the action of ice cold, dilute sulphuric acid(20%) on sodium peroxide.

Na2O2 (s) + H2SO4 → Na2SO4 (s) + H2O2 (l)

Most of the sodium sulphate separates out on cooling as crystals of Na2SO4 . 10H2O, thus a 30 % of hydrogen peroxide containing small amount of sodium sulphate is obtained.

b) Hydrogen peroxide can also be prepared in the laboratory by the action of ice cold, dilute sulphuric acid(20%) on hydrated barium peroxide BaO2. 8H2 O.Barium peroxide is made into a thin paste and added slowly to ice- cold dilute sulphuric acid(20%).

BaO2 (s) + H2SO4 (aq) → BaSO4 (s) + H2O2 (l)

Barium sulphate is allowed to settle down as a precipitate and filtered off. The filtrate obtained is a dilute solution of hydrogen peroxide

c) From barium oxide using Phosphoric acid can be used in place of sulphuric acid .

2 BaO2 (s) + 2H3PO4 (aq) → Ba( PO4) 2 (s) + 3H2O2 (l)

d) From barium oxide by passing carbon dioxide gas:- carbon dioxide gas may be passed through hydrated barium peroxide paste in ice cold water , in a slow stream

BaO2 (s) + CO2 + H2O → BaCO3(s) + H2O2(l)

The precipitated Barium carbonate is filtered off which leaves Hydrogen peroxide.

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