Hydrogen
Hydrogen is the first element in the periodic table which exists as a diatomic molecule in the environment with an atomic mass of 1 amu. Hydrogen has two isotopes: deuterium and tritium. The mass 2 isotope, deuterium, or heavy hydrogen (symbol D, or 2H), has a nucleus of one proton and one neutron and makes up 0.0156 percent of the conventional hydrogen mixture. Tritium (symbol T, or 3H) is the mass 3 isotope, having one proton and two neutrons in each nucleus, and makes up around 10-15 to 10-16 percent of hydrogen. It is abundant in the universe. In the periodic table, the position of hydrogen is not justified because it resembles both alkali metals as well as halogens. Hydrogen has one electron in its outer shell with configuration 1s1. In this topic, we’ll study the physical and chemical properties of hydrogen
What are the Properties of hydrogen?
Hydrogen is a colourless, odourless, and tasteless gas. It is lighter than air having a density of 0.08988 g/L at and 1 atm. Hydrogen is very slightly soluble in water. It has an atomic mass of 1.008 amu and an ionisation enthalpy of 1312 KJ mol-1. It is abundant in the universe and non-toxic and can be used as a clean fuel in the future.
The chemical properties of hydrogen depend on the reactivity of hydrogen. Hydrogen is unreactive and quite stable due to the strong H-H bond.
Combustion:
When hydrogen is burned it gives a pale blue flame in oxygen .$2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}$
Reaction with Metals: Hydrogen reacts with electropositive metal at high temperatures to give metal hydrides.
$\mathrm{H}_{2}+2 \mathrm{Na} \rightarrow 2 \mathrm{NaH}$
Hydrogen reacts with sodium metal to form sodium hydride.
Reaction with non-metals: Hydrogen reacts with fluorine in the dark to produce hydrogen fluoride and in sunlight with chlorine to produce hydrogen chloride.
$\mathrm{H}_{2}+\mathrm{F}_{2} \stackrel{\text { Dark }}{\rightarrow} 2 \mathrm{HF} \\$
$\mathrm{H}_{2}+\mathrm{Cl}_{2} \stackrel{\text { sunlight }}{\rightarrow} 2 \mathrm{HCl}$
Reaction with nitrogen: Nitrogen reacts with hydrogen in 1:3 to produce Ammonia. When this reaction occurs at 673K and 200 atm pressure in the presence of Fe as catalyst and Mo as a promoter it is known as Haber’s process.
$\mathrm{N}_{2}+\mathrm{H}_{2} \rightleftharpoons 2 \mathrm{NH}_{3}$
Uses of hydrogen
Some important uses and properties of hydrogen are Hydrogen acts as a reducing agent
Hydrogen is used in the hydrogenation or hardening of vegetable oil.
$\text{Vegetable oil} +\mathrm{H}_{2} \stackrel{\text{Ni}~473 \mathrm{~K}}{\rightarrow}~\text{Fat}$
It is also used as rocket fuel in the form of liquid. It is also used to manufacture liquid compounds such as ammonia, urea, and synthetic petrol.
Water (H2O)
Hydrogen burns with oxygen to produce water H2O. Water is a tasteless, colourless liquid. Water molecules have strong hydrogen bonding, which gives strange qualities when it is condensed. Water has a higher specific heat, thermal conductivity, surface tension, dipole moment, and high melting and boiling points.
The chemical properties of water include that it is amphoteric in nature. Water is reduced to a hydrogen molecule by electropositive elements. As a result, water is an excellent source of hydrogen. Water reacts with sodium metal to give sodium hydroxide and hydrogen. $\mathrm{H}_{2} \mathrm{O}(1)+\mathrm{Na}(\mathrm{s}) \rightarrow \mathrm{NaOH}(1)+\mathrm{H}_{2}(\mathrm{~g})$. Water has a very strong tendency to hydrolyse due to its dielectric constant.
Heavy Water
Water is known by the formula H2O that heavy water is made up of oxygen and deuterium. Deuterium is the isotope of hydrogen having an atomic mass of 2 amu. Hence, heavy water is denoted by D2O.
Physical Properties
Heavy water appears colourless at STP.
It is an odourless gas at room temperature.
The density of heavy water is greater than that of water as the mass of deuterium is greater than that of hydrogen.
Heavy water forms a homogeneous solution when mixed with normal water.
Chemical Properties
Normal water dissociates more than heavy water
Reaction with Metals: Heavy water reacts with alkali and alkaline earth metals to form heavy hydrogen.
$\mathrm{D}_{2} \mathrm{O}+2 \mathrm{Na} \rightarrow 2 \mathrm{NaOD}+\mathrm{D}_{2}$
Reaction with Metal oxides: Heavy water reacts slowly with a metal oxide to form heavy alkalies.
$\mathrm{Na}_{2} \mathrm{O}+\mathrm{D}_{2} \mathrm{O} \rightarrow 2 \mathrm{NaOD}$
Reaction with non-metallic oxide
$\mathrm{D}_{2} \mathrm{O}+\mathrm{N}_{2} \mathrm{O}_{5} \rightarrow 2 \mathrm{DNO}_{3}$
Hydrogen Peroxide
Structure
Hydrogen peroxide (H2O2) is a non-linear, non-planar molecule. It has an open book structure. The −O−O− linkage is called peroxy linkage.
Structure of hydrogen peroxide
Preparation
In the laboratory, hydrogen peroxide is prepared by adding calculated amounts of sodium peroxide to an ice-cold dilute (20%) solution H2SO4.
$\mathrm{Na}_{2} \mathrm{O}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}_{2}$
Properties and Reactions
Hydrogen peroxide is a pale blue syrupy liquid that freezes at - 0.5°C and has a density of 1.4 in a pure state. Hydrogen peroxide is diamagnetic and has more hydrogen bonding than water. These are some physical properties of hydrogen peroxide. On heating, hydrogen peroxide decomposes to water and oxygen. It shows oxidising as well as reducing nature. Used for bleaching delicate articles like wool, hair, feather, ivory, etc. it is also used as an antichlor and oxidant for rocket fuel.
Hydrogen peroxide is an unstable liquid and decomposes into water and oxygen either upon standing or upon heating $2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}$. It is a powerful oxidizer as well as a reducing agent in neutral acidic or basic medium.
$2 \mathrm{KI}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{KOH}+\mathrm{I}_{2}$
$2 \mathrm{FeSO}_{4}+\mathrm{H}_{2} \mathrm{SO}_{4}+\mathrm{H}_{2} \mathrm{O}_{2} \rightarrow \mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)+2 \mathrm{H}_{2} \mathrm{O}$ (as an oxidising agent )
$\mathrm{H}_{2} \mathrm{O}_{2}+\mathrm{O} \rightarrow \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}$ (as reducing agent )
Hydrides of Hydrogen
Hydrides are hydrogen compounds that contain less electronegative elements. When hydrogen combines with another element, the resulting product is known as a hydride. Hydrides are classified into three broad classes or kinds. The categories are determined by the elements with which hydrogen forms bonds, or by chemical bonding alone. Ionic, covalent, and metallic hydrides are the three types of hydrides.
Ionic hydrides
When a hydrogen molecule combines with highly electropositive s-block components, they produce (Alkali Metals and Alkaline Earth Metals). Ionic hydrides are crystalline, non-conducting, and non-volatile in their solid-state. Example: NaH, KH, CaH2.
Covalent Hydrides
When hydrogen combines with other electronegative elements such as Si, C, and others, covalent hydrides are created. CH4 and NH3 are the most common examples.
Metallic Hydrides
A metal hydride is a hydrogen compound that forms a bond with another metal element. The bonds are primarily covalent, however, ionic bonds are occasionally used to generate hydrides.
Properties of Hydrogen Chloride
HCl is a diatomic molecule consisting of hydrogen and chlorine atoms connected by a single covalent bond. The bond is polar as chlorine is more electronegative than hydrogen. HCl exists as a colourless, pungent gas at room temperature. Acts as a strong monobasic acid that dissociates completely on dissolving in water. HCl gas is highly soluble in water, the presence of ions turns blue litmus red.
Summary
Hydrogen has an atomic number one with three isotopes, hydrogen-deuterium and tritium. Hydrogen generally exists as a diatomic gas in the environment. Hydrogen is found in a variety of compound water, Hydrogen peroxide, Hydrogen Chloride, etc. Hydrogen in gaseous form can be used as a clean alternative for fuel in the coming years. Hydrogen as an ion decreases the pH of the solution.
FAQs on Properties of Hydrogen for JEE
1. Why is hydrogen used as a fuel in rockets?
Liquid hydrogen is used as a fuel in rockets and various spaceships. It is a light and extremely powerful rocket propellant, has the lowest molecular weight, and burns to give a large amount of energy. The reaction is highly exothermic thus it acts as a driving force to be used in rockets. Hydrogen can also work as fuel for internal combustion engines. Hydrogen fuel is a clean fuel that is produced when oxygen and hydrogen are burned together. it is not widely used at the moment but there are chances of its large-scale usage.
2. Explain the bleaching action of hydrogen peroxide?
The bleaching action of H2O2 is due to nascent oxygen formed which reacts with organic material and breaks the bond present. This is due to the oxidising nature of hydrogen peroxide. Thus, the bleaching action of hydrogen peroxide is due to oxidation and its oxidising properties. Hydrogen peroxide oxidises the colouring matter to a colourless product
$\text{colouring matter}+O\rightarrow\text{colourless matter}$
Materials like ivory, silk, wool, leather, etc. are bleached by it, hydrogen peroxide gives nascent oxygen.
$H_{2}O_{2}\rightarrow H_{2}O+O$
3. What is the cheapest way to produce hydrogen?
The group of industrial processes for producing hydrogen gas is known as hydrogen production. Coal gasification, partial oxidation of heavier hydrocarbons, steam reforming of natural gas and other light hydrocarbons, and coal combustion all contribute to the production of the vast majority (95%) of hydrogen from fossil fuels. Other techniques of producing hydrogen include electrolysis of water, methane pyrolysis with no CO2 emissions, and biomass gasification. The later procedures, methane pyrolysis, and water electrolysis can be carried out instantly using any electricity source, including solar power.