• Hydrogen is a gas at room temperature. 
• Hydrogen is an odourless and colorless gas. 
• Hydrogen is the lightest gas that is insoluble in water. 
• The vapour density of hydrogen is 1.
• Hydrogen is inflammable and reacts with blue flame, which forms water.

• Hydrogen gas is neutral in nature. 
• Hydrogen gas is highly combustible, but it does not support combustion. 
• Hydrogen has a molecular weight of 2.01594 grams and relative density, when compared to air, is 0.0695. 
• Under suitable conditions, hydrogen reacts with metals, non-metals, organic compounds, and metal oxides.

Hydrogen gas is insoluble in water. But if you would want to collect it by downward displacement of air, then an explosive mixture with air will be formed. So, the best way to prepare hydrogen is to collect by displacement of water.

Hydrocarbons are one of the major sources of hydrogen gas. You can get hydrocarbons by reforming fossil fuel, natural gas as well as biomass. But the hydrogen produced this way is not pure; what is produced is a mixture of gases which is also known as reformate. 

Some of the typical gases in this mixture are – hydrogen, water, nitrogen, carbon monoxide, and carbon dioxide. Other impurities in this mixture include – sulfur dioxide, nitrogen dioxide, carbon dioxide, hydrogen sulfide, hydrogen oxide, phosphine, arsine. 

Some of the significant methods which are used to filter out the impurities from Hydrogen element are – 

• Metal Hydrides 
• Pressure Swing Absorption 
• Partial Condensation 
• Absorption Separation 
• Adsorption Separation 
• Palladium Membrane Process 
• Polymer Membrane Process 
• Membrane Separation

When it comes to commercial production, then there are four major ways to produce Hydrogen – 

• Natural Gas 
• Oil 
• Coal 
• Electrolysis 

Natural gas takes a maximum percentage of 48%, with oil taking 30% and coal occupies 18%. Electrolysis is the least used method, which takes only 4% of the entire hydrogen commercial production.

Here the hydrogen is manufactured when the water is passed through the heat catalyst with twice the steam. Here catalyst is the Fe2O3 which is treated in the presence of Cr2O3 at 773 K when CO2 and H2 are obtained as a result of the chemical reaction. CO2 is eliminated under pressure (20-25 atm) and then dissolved in water, as a result of which H2 is collected. 

CuCl + CO + 2H2O → CuCl.CO.2H2O

Hydrogen is manufactured for commercial purposes through acidulated water, and this process is known as electrolysis. In this process, a small amount of sulphuric acid is added to pure water. Since pure water is a poor conductor of electricity, thus adding a less volatile acid makes it a perfect conductor. 

Electric current is passed through the acidulated water, and then the water gets disassociated. 

→ H⁺ + OH⁻

H+ is positive and moves towards the cathode, which is negatively charged. 

H⁺ + e⁻ → H

H + H → H2

As a result, hydrogen is formed at the cathode.

Hydrogen gas reacts with electropositive metals such as potassium, sodium, and calcium. Hydrogen gas gets combined with water and forms hydrides. 

2K + H2 High-Temperature → 2K+H–

2Na + H2 High-Temperature → 2Na+H–

Ca + H2 High-Temperature → Ca+H2–

Hybrides, as a result, react with water and form hydrogen. 

CaH2 + 2H2O → Ca(OH)2 + 2H2

Hydrogen combines with fluorine and chlorine. 

               H2 + F2 ==> 2 HF       

When exposed to sunlight, hydrogen and chlorine react violently, and hydrogen burns in chlorine gas. 

               H2 + Cl2 ==> 2 Hcl     

Hydrogen gets combined with nitrogen forming ammonia. 

               N2 + 3 H2 ==> 2 NH3

• Hydrogen easily catches fire and can explode easily if it is brought near fire. 
• The container where the hydrogen will be collected must be air-tight. Make sure that no burning flame comes near the container. 
• Also, the container end must have some funnel so that the gas will escape, and then the hydrogen will be collected. 
• Zinc is one of the preferred metals which is used in the preparation of hydrogen. Sodium, potassium, calcium, and magnesium can lead to explosive reactions and even cause accidents.

Oxidation and reduction can be defined both in terms of oxygen and hydrogen. 

In terms of oxygen, oxidation means adding oxygen, whereas reduction means reducing the oxygen content. 

In terms of hydrogen, oxidation means loss of hydrogen, whereas reduction means a gain of hydrogen. 

For Example, When magnesium is burnt in the presence of oxygen, then it is termed as magnesium oxide. 

2Mg + O2 → 2MgO

When both chlorine and hydrogen are together exposed in bright sunlight, an explosion occurs, which is termed as hydrogen chloride. 

H2 + Cl2 → 2HCl

As a result of this reduction reaction, hydrogen is added to the chlorine.

The Ph Scale is used to measure the degree of acidity or alkalinity of a solution. Ph scale runs from 0 to 14. 0 indicates an acidic solution, which indicates a negative Ph, whereas 14 indicates alkaline solutions with a higher Ph value. Pure water has a Ph value of 7. The Ph value is linked to the concentration of hydrogen ions inside the solution. Whenever an acid or alkali is diluted towards the solution, then the concentration of H+ ions and thus the Ph value also gets affected.

In this chapter, we have covered all about hydrogen. The major impurities in hydrogen, the manufacturing process of hydrogen, and the major precautions must be taken while manufacturing hydrogen. Oxidation and reduced reactions have also been covered, which will help the students in getting conceptual clarity. All this has been covered under the hydrogen chapter.

1. How can you justify the placement of hydrogen in the periodic table?
2. Hydrogen belongs to atomic number 1, and it falls in the first group of the periodic table. This is the reason why hydrogen is the very first element in the periodic table.
3. Does hydrogen have a dual nature?
4. Hydrogen belongs to the alkali group of metals IA, and it also belongs to halogen group VII-A. Thus, proven hydrogen shows both alkali and halogen nature.
5. How is hydrogen different from alkali metals?
6. When it comes to oxides of alkali metal, then it is basic, whereas oxides of hydrogen are neutral oxide.
7. Why is hydrogen called “Inflammable air”?
8. Hydrogen is one of the highly combustible gases, and thus it is also called inflammable air.
9. What are the major sources of hydrogen?
10. Hydrogen is found in many places, like in the earth’s crust and also in the atmosphere as a free state. It is found in organic compounds as a combined matter too.
11. Which metal should you choose for the preparation of hydrogen?
12. For the preparation of hydrogen, several wide varieties of metals are used. Water-reactive metals such as potassium, sodium, and calcium are used. You can also produce hydrogen from acid-reactive metals like magnesium, aluminum, zinc, and iron.