CHEMISTRY (Part-IV) (Railway)

An oxidation-reduction or redox reaction is a reaction that involves the transfer of electrons between chemical species (the atoms, ions, or molecules involved in the reaction).

• In Redox reaction, one species is reduced, and another is oxidized.

• AgNO₃ + NaCl → AgCl + NaNO₃ is not a redox reaction since nothing is oxidised or reduced.

Soda-acid fire extinguishers comprise sodium bicarbonate or sodium hydrogen carbonate and sulphuric acid (H₂SO₄).

• The reaction of sodium bicarbonate (NaHCO3) and acid produces a fountain of carbon dioxide with great pressure which extinguishes the fire.

The term 'precipitation reaction' can be defined as "a chemical reaction occurring in an aqueous solution where two ionic bonds combine, resulting in the formation of an insoluble salt". These insoluble salts formed in precipitation reactions are called precipitates.

• One of the best examples of precipitation reactions is the chemical reaction between potassium chloride and silver nitrate, in which solid silver chloride is precipitated out.

• AgNO₃ (aqueous) + KCl (aque-ous) → AgCl (precipitate) + KNO₃ (aqueous)

According to the Reactivity series, Potassium (K) > Sodium (Na) > Zinc (Zn) > Copper (Cu) > Mercury (Hg) > Silver (Ag)

Group 16 of the periodic table consists of 5 elements: oxygen, sulphur, selentum, tellurium and polonium.

• Among them, Oxygen and Sul-phur are non-metals, selenium and Tellurium are metalloids and polonium is a metal under typical conditions.

• The metallic properties increase in the order oxygen, sulphur, selenium, tellurium, or polonium.

• So, Oxygen is the most non-metallic among the five elements of group 16.

When ammonia solution 1.e.. ammonium hydroxide (NH₄OH), is added to aqueous solution of aluminium chloride (AlCl₃), a white precipitate of aluminium hydroxide [Al(OH)₃] is formed.

• AlCl₃ + NH₄  → Al(OH)₃ + NH₄CI

Potassium Bromide (KBr) reacts with Silver Nitrate (AgNO₃) to form Silver Bromide and Potassium Nitrate.

• KBr + AgNO₃ → AgBr + KNO₃

• It is an example of double displacement reaction as well as Precipitation reaction.

Sodium bicarbonate (NaHCO₂), also known as baking soda, is primarily used in cooking (baking), as a leavening agent.

• It reacts with acidic components in batters, releasing car-bon dioxide, which forms the characteristic texture and grain in pancakes, cakes, quick breads, etc.

• Bleaching powder or Calcium hypochlorite Ca(OCI)₂ is used as disinfectant and germicide especially in the sterilization of drinking water.

• It is used as an oxidising agent in many chemical industries to obtain various chemical products.

Barium sulphate reacts with aluminum chloride to produce barium chloride as a precipitate and aluminum sulphate.

• Balancing barium, aluminum, chlorine, and sulfur atoms we get, 3BaSO₄ + 2AICI → 3BaCl₁₂ + Al₂(SO₄)₃

Newland's Law of Octaves states that when elements are arranged in increasing order of Atomic Mass, the properties of every eighth Element starting from any Element are a repetition of the properties of the starting Element.

• Thus, the properties of lithium and sodium were found to be same because sodium is the eighth element, after lithium.