Hydrogen
is the lightest and most abundant element in the universe, constituting roughly 75% of its elemental mass. It is the primary building block for the universe since stars primarily consist of hydrogen in its plasma state. Key properties and information about hydrogen include:
Physical State:
At standard temperature and pressure (STP), hydrogen is a colorless, odorless, and tasteless diatomic gas, H
2
.
Occurrence:
While abundant in the universe, on Earth, it's mostly found combined with other elements, especially in water
(H
2
O)
and organic compounds. Isotopes: Hydrogen has three primary isotopes:
protium (1H
1
, no neutrons), deuterium (
1
H
2
, one neutron), and tritium (
1
H
3
, two neutrons).
Preparation of Hydrogen
Electrolysis of Water:
By passing an electric current through water, it decomposes into hydrogen and oxygen gases.
2H
2
O
(l)
→2H
2(g)
+O
2(g)
Reaction of Acids with Metals: Dilute acids react with metals like zinc, iron, and magnesium to release hydrogen gas.
Zn
(s)
+ 2HCl
(aq)
→ZnCl
2(aq)
+H
2(g)
Mg
(s)
+ 2HCl
(aq)
→ MgCl
2(aq)
+ H
2(g)
Reaction of Water with Active Metals: Alkali metals (like sodium) and alkaline earth metals (like calcium) react with water to produce hydrogen.
2Na
(s)
+2H
2
O
(l)
→2NaOH
(aq)
+H
2(g)
Ca
(s)
+2H
2
O
(l)
→Ca(OH)
2(aq)+
H
2(g)
Steam on Hot Metals: When steam passes over red-hot coke or iron, hydrogen gas is produced.
C
(s)
+ H
2
O
(g)
→ CO
(g)
+ H
2(g)
3Fe
(s)
+ 4H
2
O
(g)
→ Fe
3
O
4(s)
+ 4H
2(g)
Steam Methane Reforming (SMR): This industrial method involves reacting methane with steam in the presence of a catalyst to produce hydrogen.
CH
4(g)
+ H
2
O
(g)
→ CO
(g)
+ 3H
2(g)
Chemical Properties of Hydrogen
Combustion: Hydrogen burns in air or oxygen to form water.
2H
2(g)
+ O
2(g)
→ 2H
2
O
(l)
Reaction with Halogens: Hydrogen reacts with halogens to form halides.
H
2(g)
+ Cl
2(g)
→ 2HCl
(g)
H
2(g)
+ Br
2(l)
→ 2HBr
(g)
Reduction: Hydrogen acts as a reducing agent. For instance, when heated with copper (II) oxide, it reduces it to copper.
CuO
(s)
+ H
2(g)
→ Cu
(s)
+H
2
O
(g)
Formation of Hydrides: Hydrogen reacts with many elements to form compounds
called hydrides. For example, with sodium, it forms sodium hydride.
2Na
(s)
+ H
2(g)
→ 2NaH
(s)
Reaction with Nitrogen (Haber Process): Hydrogen reacts with nitrogen to form ammonia in the Haber process.
N
2(g)
+ 3H
2(g)
→ 2NH
3(g)
Reaction with Organic Compounds: Hydrogen adds across double and triple bonds in unsaturated hydrocarbons in a reaction called hydrogenation. This is used to turn vegetable oils into solid fats.
C
2
H
4(g)
+ H
2(g)
→ C
2
H
6(g)
Hard and Soft Water
Soft Water:
Water that produces lather with soap readily. It doesn't contain significant amounts of dissolved calcium and magnesium ions.
Hard Water:
Water that doesn't produce lather easily with soap because it contains dissolved calcium and magnesium ions. Hardness can be temporary or permanent.
Temporary Hardness:
Caused by the presence of bicarbonates of calcium and magnesium. It can be removed by boiling.
Ca(HCO
3
)
2
→ CaCO
3
↓+ CO
2
+ H
2
O
Permanent Hardness: Due to the presence of chlorides and sulfates of calcium and magnesium. Boiling doesn't remove it.
Removal of Permanent Hardness: Using Washing Soda (Sodium carbonate): It precipitates the calcium and magnesium ions.
Ca
2+
+ Na
2
CO
3
→ CaCO
3
↓ + 2Na
+
Ion exchange resins are polymers that can swap specific ions with ions in a solution that passes through them. They are commonly used to soften water by replacing calcium and magnesium ions with sodium ions. Here's how it works, explained through equations:
Download PDF Hydrogen Formula
-
Cation Exchange Resin (for removing cations like Ca
2+
and Mg
2+
): The resin, initially loaded with sodium ions (Na+), is represented as RNa, where R is the resin matrix. When hard water passes through the cation exchange resin:
RNa + Ca
2+
→ RCa
+2
+ Na
+
RNa + Mg
2+
→ RMg + 2Na
+
Here, the calcium and magnesium ions from the water are replaced by sodium ions. Thus, the hardness-causing cations are removed from the water, and sodium ions are released instead.
-
Anion Exchange Resin (for removing anions, if needed): Anion exchange resins work on a similar principle but remove anions from the water. Suppose the resin is initially loaded with chloride ions (Cl-), represented as RCl:
RCl + SO
4
2−
→ RSO
4
+ Cl
–
RCl + 2HCO
3
−
→ R(HCO
3
)
2
+ Cl
–
Also Check –
Discovery of Proton Formula
Preparation and Properties of Water
Preparation: Naturally from rivers, lakes, and underground reservoirs. Also from the combustion of hydrogen:
2H
2(g)
+ O
2(g)
→ 2H
2
O
(l)
Properties:
It has high heat capacity and heat of vaporization.
It acts as a universal solvent due to its polarity.
It can form hydrogen bonds leading to its high boiling and melting points relative to its molecular weight.
Also Check –
Bond Order Formula
Heavy Water (D₂O)
Preparation:
By the electrolysis of ordinary water; the fraction of heavy water increases as electrolysis proceeds.
Properties:
Chemically similar to ordinary water but has different physical properties (e.g., higher density, boiling point, melting point). It doesn't support life as efficiently as ordinary water. Used as a moderator in nuclear reactors.
Also Check –
Charles Law Formula
Hydrogen Peroxide (H₂O₂)
Preparation:
By the electrolysis of an aqueous solution of sulfuric acid or from peroxydisulfates.
2HSO
4
−
→ H
2
S
2
O
8
+ H
2
O
H
2
S
2
O
8
+ 2H
2
O→ 2H
2
O
2
+ H
2
SO
4
Properties:
Pale blue liquid in pure form.
It acts as a powerful oxidizing as well as a reducing agent.
Decomposes in the presence of light to give oxygen:
2H
2
O
2
→
2H
2
O
+
O
2
Used as a bleaching agent and in pollution control.
