Understanding Chemical Reactions and Properties of Elements

Posted on Aug 27, 2024 in Chemistry

Nascent Hydrogen

Nascent Hydrogen is a more energetic and powerful reductant than molecular hydrogen. Here’s why:

a. Reduction of Potassium Permanganate: Nascent Hydrogen reduces acidified potassium permanganate, decolorizing it, while ordinary hydrogen cannot.

Reaction: 2H₂SO₄ + 3KMnO₄ + 10[H] → K₂SO₄ + 2MnSO₄ + 8H₂O

AND H₂SO₄ + KMnO₄ + H₂ → No Reaction

b. Reduction of Potassium Dichromate: Nascent hydrogen reduces acidified Potassium Dichromate solution, changing its color from orange to green, while molecular hydrogen cannot.

Reaction: H₂SO₄ + K₂Cr₂O₇ + [H] → K₂SO₄ + Cr(SO₄)₃ + H₂O

c. Reduction of Ferric Chloride: Nascent hydrogen reduces ferric chloride solution to ferrous chloride, while ordinary hydrogen cannot.

Reaction: FeCl₃ + [H] → FeCl₂ + HCl

Ortho and Para Hydrogen

Hydrogen molecules exist in two nuclear spin isomers: ortho and para hydrogen.

• Ortho Hydrogen: Nuclei spin in the same direction (parallel spin).
• Para Hydrogen: Nuclei spin in opposite directions (anti-parallel spin).

At ordinary temperatures, hydrogen is a mixture of 75% ortho and 25% para hydrogen. Cooling increases the percentage of para hydrogen. These isomers have similar chemical properties but differ in internal energy, band spectrum, and specific heat acceptor properties. Para hydrogen is prepared by passing hydrogen through a tube packed with activated charcoal cooled to liquid air temperature.

Oxides

Oxygen, a reactive element, forms oxides by combining with metals and nonmetals.

1. Basic/Metallic Oxides: Formed with most metals (except noble metals like Au, Pt). These are basic and react with acids to form salt and water. Examples: K₂O, Na₂O, CaO.

2. Acidic/Nonmetallic Oxides: Formed with nonmetals. These are acidic and also called acid anhydrides as they form acids with water. Examples: CO₂, SO₂, SO₃, N₂O₅.

3. Neutral Oxides: Neither acidic nor basic. Examples: NO₃, CO, H₂O, N₂O.

4. Peroxides: Contain O₂^— ion, with oxygen exhibiting a -1 oxidation state. Examples: H₂O₂, Na₂O₂.

5. Superoxides: Contain O₂^– ion, with oxygen exhibiting a -1/2 oxidation state. Examples: KO₂, RbO₂, CsO₂.

6. Suboxides: Contain fewer oxygen atoms. Examples: C₃O₂, Ag₄O₂.

7. Mixed Oxides: Mixtures of different oxides. Examples: Fe₃O₄ (FeO + Fe₂O₃), Pb₂O₃ (PbO + PbO₂).

8. Amphoteric Oxides: Behave as both acidic and basic oxides. Examples: ZnO, Al₂O₃.

Dissolution of NaCl in Water

When NaCl is placed in water, the high dielectric constant of water weakens and breaks the inter-ionic forces of attraction. This process requires energy. The free ions are then surrounded by water dipoles (solvation), releasing energy called solvation energy. If the solvation energy is greater than the lattice energy, the compound dissolves in water.

Ammonia (Haber’s Process)

Ammonia is commercially produced through the Haber’s process.

Principle: Nitrogen and hydrogen (1:3 ratio) react at 450°C under 200-500 atmospheres pressure in the presence of an iron catalyst supported by molybdenum to form ammonia.

Reaction: N₂ + 3H₂ → 2NH₃ + 92.6 KJ/mole

Conditions for Maximum Yield:

• High Pressure: Favors the forward reaction due to a decrease in volume.
• Low Temperature: Favors the exothermic reaction.
• High Concentration of Reactants: Increases the reaction rate.
• Use of Catalyst: Increases the reaction rate.

Nitric Acid (Ostwald’s Process)

Nitric acid is produced through the Ostwald’s process.

Steps:

1. Catalytic Chamber: Ammonia and air react over a platinum gauze catalyst at 800°C to form nitric oxide (NO).
2. Oxidation Tower: Nitric oxide is oxidized to nitrogen dioxide (NO₂) at 200-250°C.
3. Absorption Tower: Nitrogen dioxide reacts with water in the presence of oxygen to form nitric acid (HNO₃).

Isomerism

Isomerism: Compounds with the same molecular formula but different structural formulas and properties.

Structural Isomerism: Isomerism due to differences in the arrangement of atoms within the molecule.

Types of Structural Isomerism:

• Chain Isomers
• Position Isomers
• Functional Isomers
• Metamerism
• Tautomerism

Ozone Layer Depletion

Chlorofluorocarbons (CFCs) catalyze the breakdown of ozone (O₃) into oxygen (O₂). UV radiation breaks a carbon-chlorine bond in CFCs, forming chlorine radicals. These radicals react with ozone, depleting it.

Homologous Series

Homologous Series: A series of organic compounds with the same functional group, represented by a general formula, and prepared by similar methods. Consecutive members differ by a -CH₂ unit.

Characteristics:

1. Same functional group.
2. Consecutive members differ by -CH₂.
3. Represented by a general formula.
4. Similar chemical properties.
5. Gradual change in physical properties with increasing molecular mass.
6. Prepared by similar methods.
7. First member may show different chemical behavior.

Stoichiometry

Stoichiometry: Deals with weight relationships in chemical reactions and compounds.

Key Concepts:

• Dalton’s Atomic Theory
• Law of Conservation of Mass
• Law of Constant Composition
• Law of Multiple Proportions
• Law of Reciprocal Proportions
• Gay-Lussac’s Law of Combining Volumes

Charles’s Law

Charles’s Law: At constant pressure, the volume of a gas is directly proportional to its absolute temperature.

Froth Flotation Process

Used to concentrate sulfide ores. The process exploits the difference in wettability between the ore and gangue particles.

Goldschmidt Thermite Process

Used to reduce metal oxides to metals using aluminum powder. The reaction is highly exothermic, producing molten metal.

Difference Between Roasting and Calcination

Roasting: Heating sulfide ores in the presence of air, releasing sulfur dioxide.

Calcination: Heating carbonate ores in the absence of air, releasing carbon dioxide.

Key Differences: