Chemistry (Part-IX) (Railway)

• The two most important chemicals which are obtained during the process of electrolysis of brine solution are sodium hydroxide and hydrogen.

• Fluorine is the most electronegative element on the periodic table.

• Its electronegativity value is 3.98.

• It lies in period 4.

• Its atomic number is 30.

• Carbon and oxygen can combine to form two gases. In the presence of plenty of air, the product is mainly carbon dioxide (CO₂).

• When combustion of carbon is incomplete, i.e. there is a limited supply of oxygen, carbon monoxide (CO) is formed.

• The washing soda also known as sodium carbonate.

• It is a natural cleaner and a powerful water softener that is used for removing permanent hardness of water.

• The pH of milk is 6.8 and that of lemon is 3.5 due to the presence of citric acid.

• As the pH of the milk drops upon adding lemon, the milk curdles 1.e. the casein protein molecules attract one another forming curdles.

• So. the whole reaction involves precipitation of casein protein.

• It means that the total number of atoms of each element should be equal on both sides of a chemical equation.

• So, in Ca (OH)₂ + CO₂ → CaCO₃ + H₂O, the 4 atoms of Oxygen on the left side are balanced by the same on the right side.

• Carbon atoms linked by a double bond are bound together by two bonds, one s bond and one p bond.

• Ethene. C₂H₄, is the simplest alkene.

• The valence electrons of sulphur are six. Thus, sulphur needs 2 more electrons to achieve the octet.

• Therefore, the valency of sulphur is 2.

• It is produced industrially by treating lime Ca(OH)₂, with chlorine gas.

• 2C1₂, + 2Ca(OH)₂ → Ca(OCl)₂, + CaCl₂ + 2H₂O