Railway Science (Chemistry-Acid ,Bases and Salt) (Part-IV)

Basic oxide - Metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. Group 1, 2 and lanthanides form basic compounds of oxygen. A large amount of energy is released in its formation.

Common salt (NaCl) is made up of Chlorine and sodium. Strong acid - Acid which is completely ionized in an aqueous solution. Example - HCl (Hydrochloric acid), H₂SO₄ (Sulfuric acid), HNO₃ (Nitric acid).
Strong Base - Compound that has an ability to remove a proton from a very weak acid. Example - KOH (Potassium hydroxide), NaOH (Sodium hydroxide), Rubidium hydroxide (RbOH).

The pH (potential of Hydrogen) value of any solution is a number that simply represents the acidity and basicity. pH scale ranges from 0 to 14. pH of 7 is neutral. pH less than 7 is acidic. pH greater than 7 is basic. pH of 14 is the most basic.

pH - Measurements of acidity and basicity of liquid solution. The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.
pH of some solutions : Concentrated HCl (0), Saliva before meal (7.4), Saliva after meal (5.8), Toothpaste (8.0), Gastric Juice (1.5 - 3.5), Blood (7.4), Lemon Juice (2.5), Vinegar (2 - 3), Coffee (4.85 - 5.10), Tomato juice (4.4).

An acid reacts with a base it neutralises the effect of each other and forms salt and water. Example: NaOH (base) + HCl (acid) → NaCL (salt) + H₂O (water). Hydrolysis means that water (H₂O) is used to break down the chemical bond between two molecules.
Distillation is a process of separation of two miscible liquids which have different boiling points. Electrolysis is the process by which electric current is passed through a substance to effect a chemical change; Example - Produce hydrogen and oxygen from water, Purification (electrorefining) of metals.

A concentrated acid is the one which contains a very large amount of acid than water in the solution; They have a higher mass percentage in the solution; Examples - Concentrated sulphuric acid (98% by mass).
The acid’s proclivity to dissociate into an aqueous solution, regardless of concentration, is classified as strong and weak. Strong acid - completely ionized in an aqueous solution (Hydrogen chloride (HCl)). Weak acid - Ionizes only slightly in an aqueous solution (Acetic acid, found in vinegar).

Base - An element that donates electrons, accepts protons, or releases hydroxide (OH⁻) ions in aqueous solution. Properties of Bases - change the colour of litmus from Red to Blue, bitter in taste, lose their basicity when mixed with acids, react with acids to form salt and water.

Amphoteric Oxide - react with both acids and bases to form salts and water. Equation with Acid - Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l) and Equation with base - Al₂O₃(s) + 2NaOH(aq) → 2NaAlO₂(aq) + H₂O(l). Example: Zinc Oxide (ZnO), Lead oxide (PbO). Chemical name of Compound: Calcium oxide (CaO), Magnesium oxide (MgO), Sodium oxide (Na₂O).

When a strong acid and a strong base react together the resultant is salt and water. NaCl (Sodium Chloride) is obtained by neutralization of Hydrogen chloride and sodium hydroxide. Reaction: HCl (strong acid) + NaOH (strong base) → NaCl + H₂O.

The basic nature of Sodium Hydroxide (NaOH) is due to the presence of Hydroxide (OH⁻) ions in the solution. Sodium hydroxide (NaOH) is also known as caustic soda. Lemon contains citric acid (C₆H₈O₇).
When non-metallic oxides mix with water, it forms an acid that dissociates to give hydrogen ions, thus they are acidic in nature. Phenolphthalein is an acid-base indicator which is colourless in acid solution but turns pink to red as the solution becomes alkaline.