CHEMISTRY (Part-IV) (Railway)

Chemical equations are balanced to satisfy the law of conservation of mass.

• This law states that matter can be changed from one form to another, but the total amount of mass remains constant.

• According to this law, the mass of products in a reaction must be equal to the mass of reactants so that the balancing is done, and this law is obeyed.

In 1869, Mendeleev formulated a law, now known as the periodic law.

• According to it, the properties of elements are periodic functions of their atomic masses This means, if the elements are arranged in order of increasing atomic masses, then those with similar properties are repeated at regular intervals.

• On the basis of the periodic law. Mendeleev presented his periodic table.

• Henery Moseley gave a modern periodic table, who based on atomic number.

Formation of water from hydrogen and oxygen is a combination reaction because hydrogen and oxygen combine to form a single product (water). The reaction occurs as follows: 2H₂ + O₂ → 2H₂O

Combination reoction is a reaction in which A and B combined to give C.

∴ A+B→C

Calcium sulfate dihydrate is a calcium salt and a hydrate with the chemical formula of CaSO₄.₂H₂O.

• Gypsum is a sulfate mineral composed of calcium sulfate dihydrate.

• It appears as white or nearly white, odorless, crystalline solid.

The homologous series is the group of organic compounds that differ from each other by a methylene (-CH₂) group. A homologous series of ketones can include propanone, butanone, and 2-pentanone with chemical formulas of CH₃COCH₃, CH₃CH₂COCH₃, and CH₃CH₂CH₂COCH₃, respectively, where each successive compound differs from the previous one by a group.

An electropositive element is an element with atoms that have a tendency to lose electrons and form positive ions.

• Electropositivity increases down the group and decreases in a period.

• Caesium (Cs) metal is at the last in the group of alkali metals, thus it is the most electropositive element.

Sodium hydroxide, also known as caustic soda, is an inorganic compound with the formula NaOH.

• It is used in many industries; in the manufacture of pulp and paper, textiles, drinking water, soaps, and detergents, and as a drain cleaner.

The homologous series is the group of organic compounds that differ from each other by a methylene (-CH₂) group.

C₃H₈ (propane), C₄H₁₀ (Butane) and C₅H₁₂ (Pentane) belong to the same homologous series (alkane CnH₂n+₂ family).

• They are hydrocarbons with C-C single bond.

The correct matches are as follows:

pH value discovered by Sorenson. It lies between 0 to 14. If pH value is 7 is Neutral, PH value less than 7 is acidic, pH value greater than 7 is alkaline.