Precautions :-

• The bottom end of the thistle funnel should be immersed in dilute sulfuric acid, otherwise hydrogen gas will escape from the thistle funnel.
• The equipment must be airtight otherwise the gas will leak out.
• Initially, some amount of gas is released from the water, then only after that the gas should be collected in the gas jar, because water vapor is found in the hydrogen gas that comes out in the beginning.
• Do not bring any burning object near the equipment, as there is a risk of explosion.

Other method :-

Hydrogen gas can also be prepared with the help of water, acids and bases.

From water : –

By the reaction of water on different metals at ordinary temperature, metals like sodium, potessium and calcium etc.

2Na + 2H2O → 2NaOH + H2

2K + 2H2O → 2KOH + H2

Ca + 2H2O → Ca(OH)2 + H2

By the reaction of water vapor on metals:

Metals like magnesium, zinc, iron, etc., after decomposition of hot water vapor give hydrogen gas.

Mg + H2O → MgO + H2

Zn + H2O → ZnO + H2

Precautions :-

First of all, take water in a round bottom flask and heat it. Iron powder is heated in a hard glass tube and the vapor formed in the flask is passed over the hot iron powder through the glass tube. In this way hydrogen gas is obtained –

3Fe + 4H2O ⇌ Fe3O4 + 4H2

By electrolysis of water :-

First of all, by adding a few drops of acid and alkali to water, make it a conductor of electricity. By the electrolysis of water, hydrogen is collected at the cathode and oxygen is collected at the anode.

H2O ⇌ H+ OH–

H+ + e– → H

H + H → H2

OH– – e– → OH

4OH → 2H2O + O2

By the reaction of metal hydrates :-

Calcium hydrates (Hydrolith) decomposes water at ordinary temperature to generate hydrogen –

CaH2 + 2H2O → Ca(OH)2 + 2H2

From Acids :-

Zinc magnesium, iron and tin etc. react with dilute hydrochloric acid or dilute sulfuric acid at ordinary temperature to produce hydrogen gas –

Zn + 2HCl → ZnCl2 + H2

Zn + H2SO4 → ZnSO4 + H2

Mg + 2HCl → MgCl2 + H2

Mg + H2SO4 → MgSO4 + H2

Fe + H2SO4 → FeSO4 + H2

From Alkalies :-

Metals like zinc, lead, aluminum and tin etc. produce hydrogen gas by decomposition of boiling concentrated aqueous solution of sodium hydroxide and potessium hydroxide –

Zn + 2NaOH → Na2ZnO2 + H2

2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2

Pb + 2NaOH → Na2PbO

Sn + 2NaOH + H2O → Na2SnO3 + 2H2

Purification of Hydrogen :-

In hydrogen gas prepared with suitable methods, phosphine (PH3), arsine (AsH3), hydrogen sulfide (H2S), nitrogen dioxide (NO2), sulfure dioxide (SO), carbon dioxide (CO2) etc. are found as impure. To remove these impurities, hydrogen gas is passed through the following substances –

Silver nitrate solution – This solution separates sedentary (AsH3), phosphine (PH3) hydrogen sulphide (H2S).

Lead nitrate solution – This solution absorbs the remaining hydrogen sulphide (H2O).

Caustic potash solution – SO2, CO2 and NO2 are separated by this solution.

Phosphorus Pentaoxide – it absorbs the moisture of the gas.

Dissolution of Hydrogen :

By Electrolysis of Water: Where electricity is cheap, it is used there. Hydrogen gas in excess of acid or base mixed water is collected by the method of electrolysis at the cathode.

By lanes Process :- In this process hydrogen is obtained by passing steam over hot iron.

3Fe + 4H2O ⇌ Fe3O4 + 4H2

After all the iron is reduced, the flow of steam is stopped and water gas (CO + H2) is passed, as a result of which iron is again obtained from ioran oxide.

Fe3O4 + 4CO → 3Fe + 4CO2

Fe3O4 + 4H2 → 3Fe + 4H2O

From water gas: – Water gas is obtained when water vapor is passed over blood-heated carbon. Nowadays hydrogen is obtained in large quantities through water gas –

C + H2O → CO + H2

Liquification of water gas: – Bioling temperature of carbon monoxide is – 2525 C, so on cooling water gas (CO + H2), carbon monoxide (CO) liquefies and remains in hydrogen gasic state –

Basch process: – When a mixture of water gas and water vapor is passed over a hot catalyst (Fe2O3 and Cr2O3), carbon dioxide and hydrogen gas are obtained. This process is called Basch process.

At high pressure, CO2 is dissolved in water and separated, due to which pure hydrogen gas is obtained –

CO + H2 + H2O –(Fe2O3+Cr2O3)→ CO2 + 2H2

Hydrogen Test :-

• The mixture of hydrogen and air burns with a loud sound.
• When a piece of burning wood is taken in a hydrogen jar, it gets extinguished, because this gas is not helpful in burning.
• It burns in oxygen or air with a blue flame.

Hydrogen Properties :-

Physical properties :-

• It is soluble in water in very small amounts.
• It is absorbed by metals like platinum and palladium.
• It is a good conductor of heat.
• It is a lighter gas than all other gases and the mass of 1 ml hydrogen gas at S.T.P. is 0.00009 grams.
• Hydrogen gas can be liquefied at low temperature (-253°C) and high pressure.
• Hydrogen gas burns by itself, but does not help in the burning of other things.
• Its relative density is 0.0695.
• Hydrogen gas is colourless, odourless, tasteless and transparent.

Chemical properties :-

Reaction with litmus :- Hydrogen gas has no effect on litmus. Hence this gas is neither acidic nor alkaline.

Reaction with metals :- Hydrogen gas reacts with metals like sodium, calcium etc. to form their hydrides.

2Na + H2 → 2NaH

Ca + H2 → CaH2

Reaction with sulfure – By passing this gas into hot boiling sulfure solution, hydrogen sulfide gas is formed –

H2 + S → H2S

Reaction with nitrogen – In the presence of iron (Fe) and Molibdenum (Mo), it combines with nitrogen at 450°C and 200 atmospheric pressure to produce ammonia gas –

N2 + 3H2 → 2NH3

Reaction with Chlorine :- In sunlight it reacts with chlorine to form hydrogen chloride gas –

H2 + Cl2 → 2HCl

Reaction with oxygen :- Hydrogen gas burns in oxygen with a blue flame, as a result of which water is formed –

H2 + Cl2 → 2HCl

Reducing properties :- When hydrogen gas is passed over hot oxides of lead, copper etc., these oxides get reduced to their metals –

PbO + H2 → Pb + H2O

CuO + H2 → Cu + H2O

Hydrogenation :- When hydrogen gas is passed at 120°C to 180°C temperature in the presence of nickel powder, vegetable oil becomes vegetable oil (Ghee). This process is called Hydrogenation of oils.

vegetable oil + H2 → vegetable oil (Ghee)

Additive reactions with unsaturated organic compounds

CH2 = CH2 → CH3 – CH3

CH≡CH + H2 → CH2 = CH2 → CH3 – CH3

Uses of Hydrogen :-

Hydrogen is used by Haber method to obtain ammonia.

It is used in making hydrochloric acid and vegetable ghee.

It is used for joining and cutting metals by generating oxyhydrogen flame (2800°C temperature).

It is also used as a reducing agent.

Earlier it was used in balloons, but now a mixture of helium and hydrogen is used in its place.

Used in the synthesis of mthenol.

CO + H2 + H2 → CH3OH

Hydrogen gas is used to make water gas (CO + H2).

With the help of hydrogen coal, it is used to make artificial petrol.