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

The pH value of a solution is equal to the logarithm of the inverse of hydrogen ion (H⁺) concentration. The p in pH stands for potenz in German which means power.
pH = - log [H⁺], pH = - log [10⁻⁵ ],
pH = 5 log [10]
Hence, the pH of the solution is 5.

A blue litmus paper turns red in acidic conditions but has no effect in basic condition and this shows that the pH will be less than 7. A red litmus paper turns blue under basic conditions and has no effect under acidic conditions and this shows that the pH is greater than 7. The material is neutral if neither the red nor the blue paper changes colour.

Non-metallic oxides - It forms an acidic solution when dissolved in water, turning litmus solution to red color. Non-metal oxides like CO₂ and SO₂ react with water and produce acids. Amphoteric substance is one that can act as either an acid or a base, depending on the medium. Metal oxides are basic because they react with dilute acids to form salt and water.

It is an organic compound of the phthalein family that is widely used as an acid-base indicator. As an indicator phenolphthalein is colorless below pH 8.5 and attains pink to deep red hue above pH 9.0. Methyl orange has the property to color alkaline and neutral water yellow. If the water becomes acidic, it turns red immediately. Eosin shows the cytoplasm, collagen, connective tissue, and other structures of the cell as an orange-pink-red color.

An amphoteric compound is one that can react with both acids and bases. Amphoteric behavior applies to acids and bases defined in the Bronsted-Lowry sense and in the wider Lewis sense. Example: Zinc oxide reacts with water. ZnO (Zinc oxide) + 2HCl (Hydrochloric acid) ZnCl₂ → (Zinc chloride) + H₂O (Water) and Zinc oxide react with base.
ZnO + 2NaOH (Sodium Hydroxide) → Na₂ZnO₂ (Sodium zincate) + H₂O. Water reacts with acid. H₂O + HCl ⇌ H₃O (Hydronium) + Cl and Water reacts with base. H₂O + NH₃ ⇌ NH₄ (Ammonium) + OH. Nitrous oxide (N₂O) is a colorless, sweet-tasting gas. It is also known as laughing gas.

It is a white, crystalline solid that is soluble in water and has a slightly acidic pH. Acidic Salts : Those salts which form an acidic solution on dissolving in water are called acidic salts. Example : ammonium chloride and ammonium sulfate. Basic Salts : Those salts which form a basic solution on dissolving in water are called basic salts. Example : sodium carbonate and sodium hydrogen carbonate.

An oxide that can act as either an acid or base in a reaction to produce salt and water. Example - Zinc oxide (ZnO) , Aluminium oxide (Al₂O₃), Sodium oxide (Na₂O) , Gallium oxide (Ga₂O₃) .
Basic Oxide - An oxide that gives a base in water. Magnesium oxide (MgO), Calcium Oxide (CaO), Potassium Oxide (K₂O), Sodium Oxide (Na₂O).
Neutral Oxide - that neither has an acidic characteristic nor a basic one. Example Nitric acid (HNO₃), Carbon monoxide (CO). Acidic oxides - an oxide that when combined with water gives off an acid. Example - Nitrogen Dioxide , Sulphur trioxide.

It is a mixture of different types of indicators that exhibits different coloration at different levels. It is used to detect the acidic or basic nature of a substance or a solution. Unlike litmus, universal indicators tell how acidic or basic a solution is. Phenolphthalein has the chemical formula C₂₀H₁₄O₄ . It is written as “phph” or “HIn”. It is used in acid-base titration as an indicator. A Litmus test is used to find out if a solution is an acid or a base.

An amphoteric compound is one that can react with both acids and bases. Examples - Copper (Cu), Zinc (Zn), Aluminum (Al), and Beryllium (Be). Neutral oxide: It is an oxide which neither reacts with acids nor with bases. Examples - Nitrous oxide (N₂O), Nitric oxide (NO), Carbon monoxide (CO).
A Basic oxide reacts with water to give a base. Examples - the oxide of most metals, such as Na₂O, CaO, BaO. Acidic oxide reacts with water and produces an acid. Usually, it is the oxide of non-metals. Examples - SO₂ , CO₂ , SO₃ , Cl₂O₇ , P₂O₅ , and N₂O₅ .

7 represents a neutral pH. Neutral solutions are neither acidic nor alkaline. pH level below 7 - acidic solution. pH above 7 - alkaline solution. Alkaline solutions include sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium carbonate.