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

It is also used as a fungicide and as an insecticide powder. Boric Acid is a weakly acidic hydrate of boric oxide with mild antiseptic, antifungal, and antiviral properties. Sulphuric acid is a constituent of acid rain which is formed by atmospheric oxidation of sulphur dioxide. The main constituent of Vinegar is acetic acid. Hydrochloric acid is the main component of gastric juice.

Litmus paper is used to test whether a substance is acidic or basic. Acids turn blue litmus paper to red, whereas bases turn red litmus paper to blue. Acids have pH lower than 7, bases have pH more than 7 and pH of neutral compounds is 7. In 1909 Dr. Soren Sorensen (A Danish chemist) introduced the concept of pH (Potential of Hydrogen).

Its pH changes very little when a small amount of strong acid or base is added to it. Example - A solution of acetic acid CH₃COOH and sodium acetate CH₃COONa. Neutral solution has a pH of 7, indicating an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) in the solution.
Example - Pure Water. Highly acidic solution has a pH below 7, indicating a high concentration of hydrogen ions (H⁺). Example - hydrochloric acid (HCl). Basic solution has a pH above 7, indicating a high concentration of hydroxide ions (OH⁻). Example - sodium hydroxide (NaOH).

(HCl, strongly acidic). Muriatic acid :- Used in the production of chlorides, fertilizers, and dyes, in electroplating, and in the photographic, textile, and rubber Industries. Perchloric acid (HClO₄) - It is a mineral acid and is considered stronger than sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Picric acid (C₆H₃N₃O₇): Uses - In medicinal formulations in the treatment of malaria, trichinosis, herpes, smallpox and antiseptics.

The pH scale is a logarithmic scale that measures the acidity or alkalinity of a solution. A pH of 7 is neutral, a pH below 7 is acidic, and a pH above 7 is alkaline. The lower the pH, the higher the concentration of hydrogen ions in the solution.

Ascorbic acid (Vitamin C) - a vitamin found particularly in citrus fruits and green vegetables. Sources - Orange, Tomato, Guava, Lemon, Amla. Tamarind is rich in B vitamins, especially thiamine (B1) and folate (B9).

Universal indicators can be used to identify the pH of a solution by comparing its color to a color chart that shows the pH values associated with each color. The universal indicator will give orange or yellow color if the solution is a weak acid. The pH of the solution will range from 3-6, indicating that the solution is acidic but not strongly. Strong acids have a pH value of 0 to 3 . Strong alkalis have a pH value of 11 to 14. Weak alkalis have a pH value of 8 to 10.

Borax is the common name for the chemical sodium tetraborate decahydrate with formula of (Na₂B₄O₇ ·10H₂O). It is a salt of boric acid. Litmus paper is a natural indicator which is used to distinguish acids from bases. The blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions. The colour of a neutral litmus solution is purple.

Metals readily react with acid and produce hydrogen gas because metals are placed above hydrogen in reactivity series and displace it during a reaction with an acid. Also, as acids have a property of giving H + ions. The general chemical equation for this reaction is: Metal + Acid → Salt + Hydrogen gas. Example - 2HCl (Hydrogen chloride) + Mg (Magnesium) → MgCl₂ (Magnesium chloride) + H₂ (Hydrogen).

When an acid is diluted (exothermic process) with water, the concentration of H⁺ ions decreases and the concentration of OH⁻ increases, and the pH increases and shifts towards 7. For diluting any acids - add acid to the water rather than adding water to the acid. Weak acids - partially ionized in their solutions. Strong acid - completely ionized when dissolved in water. Neutralisation Reaction: Acid + Base → Salt + Water.