Railway Science (Chemistry-Acid ,Bases and Salt)

Litmus paper is used as a visual indicator to distinguish between acidic and basic solutions. It turns red in an acidic solution and blue in a basic solution. Other indicators to test for acids and bases are - Methyl orange, Phenolphthalein, Turmeric, etc.

NH4OH (Ammonium Hydroxide) + HCl (Hydrochloric acid) → NH₄Cl (Ammonium Chloride) + H₂O (Water). Here HCl is a strong acid, NH₄OH is a weak base and the salt formed due to the reaction is NH₄Cl.
Example - HNO₃ (Nitric Acid) + NH₄OH (Ammonium Hydroxide) → NH₄NO₃ (Ammonium Nitrate) + H₂O (Water). HNO₃ is an acid, NH₄OH is a base.

When pH of rain water is less than 5.6, it is called acid rain. It includes any form of precipitation with acidic components, such as sulfuric or nitric acid that falls to the ground from the atmosphere in wet or dry forms.
Effects of Acid Rain - It harms trees, crops, and plants by dissolving and washing away nutrients required for growth. It causes respiratory problems in both animals and humans. Buildings and other structures composed of stone or metal are harmed by acid rain. Alkalinity is a measure of a river's "buffering capacity," or its ability to neutralize acids.

The concentration of hydronium ions decreases when an acid is diluted because on adding water the H+ ions of the acid and hydroxyl ions of water react to form water molecules and the concentration of hydronium ions decreases. This is because on dilution the overall volume of solution increases and so the number of hydronium ions per unit volume decreases.

purple coloured dye which is used as a visual indicator to identify acids and bases. Natural Indicators - These indicators are obtained from natural sources like plants. Examples - Turmeric, litmus, china rose petals, etc. Man-made indicators - Phenolphthalein, Methyl orange. Some indicators and their color change - Litmus Paper(Acidic - Red, Basic - Blue) ,Turmeric (Acidic - Yellow, Basic - Red), China Rose (Acidic - Dark pink (Magenta), Basic - Green), Methyl Orange (Acidic - Red or Orange, Basic - Yellow), Phenolphthalein (Acidic - colourless, Basic - Light Pink). Lichens are used as bio - indicators for air pollution.

Antacids: Substances which reduce or neutralise acidity level. Antacids are a combination of various compounds with various salts of calcium, magnesium, and aluminum as active ingredients. Example - aluminium hydroxide (Al(OH)₃), magnesium carbonate (MgCO₃), magnesium trisilicate (Mg₂O₂Si₃), magnesium hydroxide (Mg(OH)2), calcium carbonate (CaCO₃).

It has 4 hydrogen atoms, only 1 of them is released as H + ion in solution. Weak Acids - That do not entirely ionise in solution or have a low concentration of the H⁺ ion. Examples - Oxalic acid (C₂H₂O₄), Formic acid (HCOOH), Benzoic acid (C₆H₅COOH). Strong Acids (almost completely ionised in solution) - Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Nitric acid (HNO₃).

In Common salt (Sodium Chloride's - NaCl), there is one Sodium atom and one Chlorine atom. So, the molar mass of Sodium Chloride will be equal to the sum of the molar masses of the two different atoms. Therefore, the molar mass of sodium chloride will be 22.99 + 35.45 = 58.44g/mol.

The effect of the acid caused by ant bites can be neutralized by rubbing moist baking soda or Calamine solution, which contains Zinc carbonate. The sting of an ant contains formic acid. When an ant bites, it injects formic acid into our skin and due to which we feel a burning sensation. A calamine solution contains zinc carbonate which is basic in nature. When we apply it on the skin it neutralizes the effect of formic acid.

Lactic acid (C₃H₆O₃) buildup can result in muscle pain, cramps, and muscular fatigue. It is mainly produced in muscle cells and red blood cells. It forms when the body breaks down carbohydrates to use for energy when oxygen level is low. Curd contains lactic acid. Tartaric acid - fruits like grapes, tamarinds, bananas, and citrus fruits. Formic acid - Ant sting.