Railways

 

• Substance (or chemical substance):

A "substance" is a kind of matter that can-not be separated into other kinds of matter by any physical process, e.g. gold, silver, iron, sodium chloride, calcium carbonate etc.

• Pure substance:

Is one that is a single substance and has a uniform composition. Such a substance always have the same texture and taste, e.g. water, salt, sugar etc.

• Testing the purity of a substance:

The purity of substance can easily be checked by checking its melting points in case of a solid substance or by checking its boiling points in case of a liquid substance.

• Types of pure substances:

Two different types of pure substances are (i) Element: An element is a substance which can-not be split up into two or more simpler substances by usual chemical methods of more...

• Law of conservation of mass: This law was stated by Lavoisier in 1744. It states that "In all physical and chemical changes, the total mass of readouts is equal to total mass of products."
• Law of constant proportions (or constant composition): This law was first stated by Proust in 1797. According to the law "a chemical compound is always found to be made up of the same elements combined together in the same proportions by weight" e.g. the ratio of hydrogen and oxygen in pure water is always 1: 8 by weight. This law is also called law of definite proportions.
• Law of multiple proportions: This law was given by John Dalton (1803) and states that "when two elements combine to form two or more compounds, the different mass of one of the elements and the fixed mass of the one with which more...

Classification of Elements and Periodicity in Properties  

• Classification means identifying similar species and grouping them together.
• Lavoisier divided elements into two main types known as metals and non-metals.
• Doberiner's Law of triads:

According to this law, "in certain triads (group of three elements) the atomic mass of the central element was the arithmetic mean of the atomic masses of the other two elements.” But in some triads all the three elements possessed nearly the same atomic masses, therefore the law was rejected. e.g., atomic masses of Li, Na and K are respectively 7, 23 and 39, thus the mean of atomic masses of 1st and 3rd element is = 7 + 39 = 23

• Limitations of Doberiner's Triads: He could identify only a few such triads and so the law could not gain importance. In the triad of Fe, Co, Ni, all more...

  Introduction   The term acid, in fact, comes from the Latin term acere, which means “Sour”. In everyday life we come across many compounds that chemists classify as acids. Bases are compounds which taste bitter eg. Milk of magnesia. Salts also have wide applications for example ammonium chloride is used as electrolyte in dry cells, sodium bicarbonote (baking powder) in the manufacture of glass etc.   Properties of acids and bases  

• A. Properties of acids
• Chemical properties:

(i) Action of metals: Metals generally react with dilute acids to form their respective salt and hydrogen. \[Metal+Acid\to Salt+Hydrogen\] (ii) Action with metal oxides (Basic oxides) Metal oxides are generally basic oxides. These oxides get neutralised when they react with acids. These reactions are mostly carried upon heating e.g. \[Basicoxide+Acid\to Salt+Water\] \[\left( Neutralization\text{ }reaction \right)\]   (iii) Action with metal carbonates more...

  Metals and Non-metals  

• Metals and Non-metals: There are more than 114 elements present in the periodic table. These elements can be broadly classified into two categories i.e., metals and non-metals. Out of 114 elements, 22 are non-metals.
• Physical properties of metals:

(i) They are usually shiny i.e. have a metallic luster. (ii) Metals have a high density (iii) Metals are ductile i.e. they can be drawn into wires. (iv) Metals are malleable i.e. they can be founded into thin sheets. (v) Metals are good conductors of electricity. (vi) Metals have high melting point and are generally in solid state at room temperature. (vii) Metals are good conductors of heat and sound.

• Uses of metals:

(i) Metals are very important for modern humans it is not possible to imagine our life without them. (ii) Metals are used in manufacturing of bridges, railways, aeroplanes, more...

  Introduction  

• The pollutants may be inorganic, biological or radiological in nature.

(i) Bio-degradable pollutants are domestic wastes which are rapidly decomposed by micro-organisms. (ii) Non-biodegradable pollutants include chemicals, mercuric salts, lead compounds, pesticides, etc. (iii) Natural pollution is caused by radioactive substances, volcanic eruptions, forests and mines fires floods, etc. (iv) Artificial pollution is caused by industries, thermal plants, automobile, exhausts, sewage, etc.   Environment  

• Environment: The conditions existing around animal or human life.

Atmosphere: The gaseous envelop surrounding the earth. It has been classified into following regions:- (i) Stratosphere: The layer of the earth's atmosphere above the troposphere and below the mesosphere. (ii) Troposphere: The lowest region of the atmosphere extending from earth's surface to the lower boundary of the stratosphere. In this region, human beings along with other organisms live. It contains water vapour and is greatly more...

  Introduction  

• Definition

Chemistry is a branch of science which deals with study of matter and various changes it undergoes. It deals with the preparation, properties, reactions and structures of chemical elements and compounds. For convenience the study of chemistry is sub-divided into various branches such as: (i) Inorganic chemistry                 (ii) Organic chemistry                   (iii) Physical chemistry                 (iv) Analytical chemistry              (v) Industrial chemistry

• Valency

During the formation of molecules of compounds, atoms combine in certain fixed proportions. This is because of the fact that different atoms have different combining capacities. The combining capacity of an atom or radical is known as its valency.

• Ions or radicals

In addition to atoms and molecules, a third type of particles occurs in substances. These particles, called ions, or atoms or group of atoms that carry an electrical charge. An ion is formed when electrons are more...

  Introduction Chemistry has helped significantly in meeting human needs by providing chemical fertilizers, improved varieties of insecticides and pesticides to increase the yield of crops and fruits. It has given us a large number of lifesaving drugs. Also chemical industries manufacturing polymers, soaps, detergents, glass, ceramics etc.   Industrially Important Compounds Glass   It consists of a mixture of two or more silicates.

• Preparation of glass:
• Common glass (or soft glass): It is used to make bottles, glass wares etc. and is obtained by heating together silica (in the form of sand), sodium carbonate or sodium sulphate and chalk or lime stone (calcium carbonate). Some broken glass and a little coke are usually added. The glass so prepared consists of silicates of sodium and calcium.

\[N{{a}_{2}}C{{O}_{3}}(s)+\underset{\left( silica \right)}{\mathop{Si{{O}_{2}}(s)}}\,\to N{{a}_{2}}Si{{O}_{3}}(s)+C{{O}_{2}}(g)\] \[N{{a}_{2}}S{{O}_{4}}(s)+Si{{O}_{2}}(s)\to N{{a}_{2}}Si{{O}_{3}}(s)+S{{O}_{3}}(g)\] \[CaC{{O}_{3}}(s)+Si{{O}_{2}}(s)\to CaSi{{O}_{3}}(s)+C{{O}_{2}}(g)\]

• Hard glass: For more...

  General Organic Chemistry  

• Wohler prepared the first organic compound urea while preparing ammonium cyanate.
• Classification of organic compounds:

  The existence of two or more chemical compounds with the same molecular formula but having different properties owing to different arrangement of atoms within the molecule is termed as isomerism

• Hydrocarbons: All those compounds which contain just carbon and hydrogen are called hydrocarbons.
• Functional group: The atom or group of atoms which determine the properties of a compound is known as functional group. e.g. \[-OH\] (alcohol), -CHO (aldehyde), > C = C < (alkene), \[-C\equiv C-\] (alkyne), etc.
• Homologous Series: A series of compounds in which more...

  Introduction ²

• Biodiversity refers number and types of wide variety of plants and animals present on earth.
• In 1773, Swedish botanist Carolus Linnaeus formulated the system of Binomial Nomenclature in his book 'Species plantarum''. In binomial system, each name is expressed in two parts i.e., generic name and specific name.
• Taxon is the branch of biology that deals with the framing of laws and principles for classifying the organisms on the basis of their characteristics and evolutionary relationships.
• The hierarchial system of classification was introduced by

Kingdom \[\to \] Phylum or Division\[\to \] Class\[\to \] Order\[\to \]Family\[\to \] Genus\[\to \]Species

• Species is defined as "the smallest real basic unit of taxonomy which is reproductively isolated from other group of individuals".
• more...