Railway Science (Chemistry-Acid ,Bases and Salt)

Chlor Alkali Process - When electricity is passed through an aqueous solution of NaCl, it decomposes to form sodium hydroxide by electrolysis of aqueous chloride. 2NaCl(aq) + 2𝐻₂𝑂(l)  → 2NaOH 2 𝑂 → (aq)+C𝑙₂ (g) +𝐻₂ .
Products - hydrogen, chlorine, NaOH [ sodium hydroxide]. It is used in the manufacturing of chlorine, hydrogen, and sodium hydroxide (caustic) solutions.

Red cabbage leaves are a natural acid-base indicator and it is red in color. The red cabbage leaves remain red in acidic solutions but turn green on adding to basic solutions. Methyl orange is used as an acid-base indicator (shows color changes in acid, base, and neutral substances). Vanilla, clove, and onion are Olfactory Indicators.

Lemon Juice (pH - 2.2): Source of Vitamin C, it promotes immunity, battles infection, and heals wounds. Gastric Juice (pH - 1.2): used to inactivate swallowed microorganisms, thereby inhibiting infectious agents from reaching the intestine. Milk of magnesia (pH- 10): used to treat occasional constipation. Sodium hydroxide solution (pH- 14 ): used to produce soaps, rayon, paper, products that explode, dyes, and petroleum products.

Acidic strength increases with increasing H⁺ concentration. When pH increases then [H⁺] decreases. In pH scale: 1-3 (strong acid), 4-6 (weak acid), 7- neutral, 8-10 (weak base), 11- 14 (strong base). A - Weak acidic (Example - CH₃COOH). B- Strong acid (Example - HCl). C- Strong base (Example - NaOH). D- Neutral (Example - Saliva) . E- Weak base (Example - NH₃).

Aluminium sulphate, Filter Alum or Dialuminum trisulphate)}. Different plants require soils of different pH. Some need acidic soil while some need basic soil and the extreme of both is harmful to the plants and affects the crop yield. Neutralization of soil is an important factor for crop production. If the soil is too acidic, it should be treated using bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide). Organic matter is added to soil that is too basic by itself.

The stronger the acid, the more readily it donates H⁺  ion. For example, hydrochloric acid and lemon juice are very acidic and readily give up H⁺ ion when added to water. An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid. Acidic substances are usually identified by their sour taste.

An acid will have a higher concentration of protons (H⁺ ) relative to hydroxide ions (OH⁻) . Higher the concentration of protons in the acid, the stronger it will be. A base will have a higher concentration of hydroxide ions (OH⁻) relative to protons (H⁺). In precipitation reactions, two soluble salts in aqueous solutions are combined and form an insoluble precipitate.

Salt: Substance produced by the reaction of an acid with a base; consists of the positive ion (cation) of a base and the negative ion (anion) of an acid. The reaction between an acid and a base is called a neutralization reaction.

Weak acid - ions partially dissociated into an aqueous solution. It contains covalent bonds and possesses low conductivity due to the presence of fewer unpaired atoms. Example - CH₃COOH, H₂CO₃ , H₃PO₄ , C₆H₅COOH, etc. Strong acid - fully dissociates into its ions in an aqueous solution. It contains ionic bonds. It possesses high conductivity due to the presence of the unpaired atoms. Example - HCl, HNO₃ , H₂SO₄ , H₂SO₃ , HBr, etc.

When an acid is heated, its pH value decreases due to increase in ionization, that is the acid decomposes more. Similarly, pH of weak base increases with increase in temperature due to increase in ionization or [OH⁻ ] ion concentration.