B.Sc. 2nd Year Chemistry — Detailed and Examination-Oriented Notes
Inorganic chemistry deals with the study of elements and compounds other than most carbon-based compounds. Inorganic compounds include metals, non-metals, minerals, salts, acids, bases, oxides, coordination compounds and many industrially important substances. These compounds have wide applications in agriculture, medicine, metallurgy, construction, laboratory science and industry.
Some inorganic compounds are particularly important because of their chemical properties, methods of preparation, reactions and practical applications. Compounds such as sodium carbonate, sodium bicarbonate, sodium hydroxide, calcium oxide, calcium hydroxide, calcium carbonate, bleaching powder, alum, hydrogen peroxide and important compounds of transition metals are commonly encountered in chemistry.
The study of these compounds provides an understanding of their preparation, physical properties, chemical reactions, uses and industrial significance. Many of these compounds are also important from an examination point of view because their preparation and characteristic reactions are frequently discussed in inorganic chemistry.
Important inorganic compounds can be broadly classified according to their composition and chemical behaviour.
| Class | Examples | General Characteristics |
|---|---|---|
| Oxides | CaO, MgO, Al₂O₃, Fe₂O₃ | Binary compounds of oxygen with another element. |
| Hydroxides | NaOH, KOH, Ca(OH)₂ | Contain hydroxide ion and are generally basic. |
| Carbonates | Na₂CO₃, CaCO₃ | Contain carbonate ion, CO₃²⁻. |
| Bicarbonates | NaHCO₃, KHCO₃ | Contain hydrogen carbonate ion, HCO₃⁻. |
| Sulfates | Na₂SO₄, CuSO₄, CaSO₄ | Contain sulfate ion, SO₄²⁻. |
| Halides | NaCl, CaCl₂, AgCl | Contain halide ions such as Cl⁻, Br⁻ and I⁻. |
| Coordination compounds | [Cu(NH₃)₄]²⁺, [Fe(CN)₆]³⁻ | Contain a central metal ion bonded to ligands. |
Sodium is an alkali metal belonging to Group 1 of the periodic table. Several sodium compounds are commercially important and are widely used in chemical industries.
Sodium hydroxide is a strong alkali commonly known as caustic soda. It is a white, crystalline solid and is highly soluble in water. Dissolution in water is highly exothermic.
Sodium hydroxide is manufactured industrially by electrolysis of concentrated aqueous sodium chloride solution (brine). This process is known as the chlor-alkali process.
Sodium hydroxide is obtained in solution, while hydrogen is produced at the cathode and chlorine at the anode.
Sodium hydroxide reacts with acids to produce salt and water.
It reacts with acidic oxides such as carbon dioxide.
Sodium hydroxide also reacts with certain metals such as aluminium and zinc to form soluble complexes with evolution of hydrogen.
Sodium carbonate is commonly known as washing soda when present as its decahydrate, Na₂CO₃·10H₂O. It is an important industrial alkali.
Sodium carbonate is commercially manufactured by the Solvay process. The process uses sodium chloride, ammonia, carbon dioxide and water.
An important intermediate is sodium bicarbonate, which precipitates from the ammoniated brine.
Sodium bicarbonate is heated to produce sodium carbonate.
Sodium bicarbonate is commonly called baking soda. It is a white crystalline compound and is less alkaline than sodium carbonate.
It is formed as an intermediate during the Solvay process.
Potassium hydroxide is a strong alkali commonly known as caustic potash. It is a white solid and is highly soluble in water.
It can be prepared by electrolysis of aqueous potassium chloride.
KOH reacts readily with acids and acidic oxides.
Potassium permanganate is a dark purple crystalline compound and is an important oxidizing agent. Its oxidizing behaviour depends on the reaction medium.
Industrial preparation involves conversion of manganese dioxide into manganate followed by oxidation of manganate to permanganate.
In simplified form:
Potassium manganate is subsequently converted into potassium permanganate.
In acidic solution, permanganate ion is reduced to Mn²⁺.
Calcium compounds are widely distributed in nature and have great importance in construction, agriculture and industry.
Calcium oxide is commonly known as quicklime. It is a white, strongly basic solid.
Calcium oxide is prepared by heating limestone strongly.
This process is known as calcination.
The reaction is highly exothermic.
Calcium hydroxide is commonly called slaked lime. It is a white sparingly soluble solid. Its saturated aqueous solution is called lime water, while its suspension in water is called milk of lime.
Lime water becomes milky when carbon dioxide is passed through it because insoluble calcium carbonate is formed.
When excess carbon dioxide is passed, the precipitated calcium carbonate can dissolve because soluble calcium bicarbonate forms.
Calcium carbonate occurs naturally as limestone, marble and chalk. It is an important raw material in many industries.
Bleaching powder is commonly represented as calcium oxychloride, Ca(OCl)Cl, although its commercial composition can be more complex. It is a pale solid with a characteristic chlorine-like odour.
Bleaching powder is manufactured by passing chlorine gas over dry slaked lime.
The exact composition of commercial bleaching powder may vary, but the equation represents the commonly taught overall reaction.
In the presence of carbon dioxide and moisture, chlorine-containing species are released and can produce hypochlorous acid. Hypochlorous acid can generate active oxygen species that oxidize coloured substances.
Hypochlorous acid can produce oxygen under suitable conditions:
Magnesium oxide is a white solid with high melting point and basic character. It is commonly known as magnesia.
It can be prepared by heating magnesium carbonate.
Magnesium hydroxide is a sparingly soluble white solid. It is a weak base compared with soluble alkali hydroxides.
Because of its basic character, magnesium hydroxide has been used in some antacid preparations.
Aluminium oxide is commonly called alumina. It is an important compound of aluminium and occurs naturally in minerals such as corundum. It is amphoteric in nature.
Aluminium hydroxide is a white gelatinous precipitate and is amphoteric.
Its amphoteric nature is an important characteristic of aluminium compounds.
Potash alum is a double salt commonly represented as:
It is also written as potassium aluminium sulfate dodecahydrate. It forms colourless or transparent crystals under suitable crystallization conditions.
Potash alum can be obtained by crystallization from solutions containing appropriate quantities of potassium sulfate and aluminium sulfate.
Copper(II) sulfate pentahydrate is commonly known as blue vitriol. It forms bright blue crystals because of its hydrated copper(II) ions.
It may be prepared by reacting copper(II) oxide or copper(II) carbonate with dilute sulfuric acid.
The solution can be concentrated and crystallized to obtain hydrated copper(II) sulfate.
The hydrated salt is blue, whereas anhydrous copper(II) sulfate is white.
Copper(II) oxide is a black solid and is a basic oxide.
It can also be reduced by hydrogen:
Iron(II) sulfate heptahydrate is commonly called green vitriol. It forms pale green crystals.
It can be prepared by reacting iron with dilute sulfuric acid.
The hydrated salt can crystallize from the resulting solution under suitable conditions.
Iron(III) chloride is an important iron salt and is commonly obtained as a yellow-brown solid or solution depending on its form and concentration.
It can be prepared by direct reaction of iron with chlorine.
Iron(III) chloride is also widely used as a coagulant in water and wastewater treatment.
Silver nitrate (AgNO₃) is a white crystalline compound and an important laboratory reagent.
Silver nitrate can be prepared by reacting silver with nitric acid under suitable conditions.
Silver nitrate is commonly used to test for chloride ions. Addition of silver nitrate to a chloride-containing solution produces a white precipitate of silver chloride.
Silver chloride is photosensitive and can darken on exposure to light.
Hydrogen peroxide is an important inorganic peroxide. It is usually encountered as a colourless liquid in aqueous solution. It acts as both an oxidizing and, under suitable conditions, a reducing agent.
Hydrogen peroxide decomposes into water and oxygen. The decomposition may be accelerated by catalysts such as manganese dioxide and by various enzymes.
In suitable reactions, hydrogen peroxide accepts electrons and is reduced to water.
Ammonia is a colourless gas with a characteristic pungent odour. It is highly soluble in water and forms an alkaline solution.
Ammonia is manufactured by the Haber process. Nitrogen and hydrogen react reversibly to form ammonia.
The industrial process uses elevated pressure, suitable temperature and an iron-based catalyst to obtain an economically useful rate of reaction.
This explains the basic nature of aqueous ammonia.
Nitric acid is a strong mineral acid and an important industrial chemical. It is also a strong oxidizing agent, particularly when concentrated.
Nitric acid is manufactured industrially by the Ostwald process. Ammonia is first oxidized to nitric oxide.
Nitric oxide is oxidized to nitrogen dioxide.
Nitrogen dioxide is absorbed in water to form nitric acid.
Sulfuric acid is one of the most important industrial chemicals. It is a strong diprotic acid and has dehydrating and oxidizing properties under appropriate conditions.
Industrial sulfuric acid is manufactured by the Contact process. Sulfur or sulfide ores are first oxidized to sulfur dioxide.
Sulfur dioxide is then catalytically oxidized to sulfur trioxide.
The oxidation is carried out using a suitable catalyst, commonly vanadium(V) oxide.
Sulfur trioxide is absorbed in concentrated sulfuric acid to form oleum, which is then carefully diluted with water.
Chlorine is a greenish-yellow, reactive halogen gas. It is a strong oxidizing agent and reacts with many substances.
Hypochlorous acid is responsible for much of the oxidizing and disinfecting action of chlorine in water.
With cold dilute sodium hydroxide, chlorine forms chloride and hypochlorite.
With hot concentrated sodium hydroxide, chlorate is formed.
| Compound | Common Name | Main Characteristic | Important Use |
|---|---|---|---|
| NaOH | Caustic soda | Strong alkali | Soap, paper and chemical industries |
| Na₂CO₃·10H₂O | Washing soda | Alkaline salt | Water softening and glass manufacture |
| NaHCO₃ | Baking soda | Releases CO₂ with acid | Baking and antacid formulations |
| CaO | Quicklime | Basic oxide | Cement and metallurgy |
| Ca(OH)₂ | Slaked lime | Basic hydroxide | Whitewashing and water treatment |
| CaCO₃ | Limestone | Carbonate mineral | Cement and construction |
| K₂MnO₄ | Potassium manganate | Mn(VI) compound | Intermediate in permanganate manufacture |
| KMnO₄ | Potassium permanganate | Strong oxidizing agent | Redox reactions and laboratory analysis |
| CuSO₄·5H₂O | Blue vitriol | Blue hydrated salt | Laboratory and industrial applications |
| KAl(SO₄)₂·12H₂O | Potash alum | Double salt | Water purification and dyeing |
The following equations represent important reactions that should be remembered for examination preparation.
Important inorganic compounds have applications in almost every major branch of chemistry and industry.
| Field | Important Compounds | Application |
|---|---|---|
| Construction | CaCO₃, CaO, Ca(OH)₂ | Cement, lime and construction materials |
| Glass industry | Na₂CO₃, CaCO₃ | Glass manufacture |
| Water treatment | Alum, Ca(OH)₂, chlorine compounds | Coagulation, pH adjustment and disinfection |
| Agriculture | Ammonia and nitrogen compounds | Fertilizer production |
| Laboratory | KMnO₄, AgNO₃, CuSO₄ | Reagents and analytical chemistry |
| Metallurgy | CaO, acids and alkalis | Ore treatment and metal processing |
| Chemical industry | H₂SO₄, HNO₃, NaOH, NH₃ | Manufacture of numerous chemicals |
Important inorganic compounds include a wide range of oxides, hydroxides, carbonates, sulfates, halides, acids, bases and coordination-related substances. Sodium compounds such as sodium hydroxide, sodium carbonate and sodium bicarbonate are important in chemical and industrial processes. Calcium compounds such as calcium oxide, calcium hydroxide and calcium carbonate have major applications in construction, metallurgy and water treatment.
Other important compounds include potassium permanganate, bleaching powder, aluminium compounds, alum, copper sulfate, iron salts, silver nitrate and hydrogen peroxide. Industrially important chemicals such as ammonia, nitric acid, sulfuric acid and chlorine are particularly significant because of their large-scale applications.
For examination preparation, special attention should be given to the preparation methods, chemical properties, balanced chemical equations, important reactions, industrial processes and practical applications of these compounds.