Principles Related to Practical Chemistry – JEE Mains Chemistry
1. Detection of Extra Elements in Organic Compounds
In practical chemistry, the detection of extra elements like nitrogen, sulfur, and halogens in organic compounds is a fundamental task. Various methods such as the Lassaigne’s test are used for this purpose.
- Nitrogen Detection: The presence of nitrogen is confirmed by heating the organic compound with sodium metal, forming sodium cyanide, which can be identified by its reaction with ferric chloride.
- Sulfur Detection: Sulfur is detected by the formation of a yellow precipitate when sodium fusion extract is treated with lead acetate.
- Halogen Detection: Halogens are identified through reactions with silver nitrate to form precipitates like silver chloride, silver bromide, or silver iodide.
2. Detection of Functional Groups in Organic Compounds
The detection of functional groups like hydroxyl, carbonyl, carboxyl, and amino groups is vital in organic chemistry.
- Hydroxyl Group: The presence of alcohols or phenols can be confirmed using Lucas reagent or phenolphthalein in neutral conditions.
- Carbonyl Group: Aldehydes and ketones can be detected by reactions such as the Tollen’s test or Fehling’s test.
- Carboxyl Group: Carboxylic acids are detected by their reaction with sodium bicarbonate to release carbon dioxide.
- Amino Group: Amines are detected through reactions like the ninhydrin test, where they form a blue or purple color.
3. Chemistry Involved in the Preparation of Organic and Inorganic Compounds
Practical chemistry often involves the preparation of various compounds. Below are some key examples.
- Inorganic Compounds: Mohr’s salt and potash alum are prepared by specific reactions involving salts and acids.
- Organic Compounds: Acetanilide, p-nitro acetanilide, aniline yellow, and iodoform are synthesized using reactions like nitration, condensation, and halogenation.
4. Titrimetric Exercises and Indicators
Titrimetric exercises are a cornerstone in practical chemistry, particularly in acid-base titrations and redox reactions.
- Acids and Bases: The titration of acids and bases is performed using indicators like phenolphthalein for strong acid-strong base titrations.
- Oxalic Acid vs KMnO₄: Oxalic acid is titrated against potassium permanganate (KMnO₄) to determine its concentration.
- Mohr’s Salt vs KMnO₄: Mohr’s salt is used in redox titrations with KMnO₄ to study oxidation-reduction reactions.
5. Qualitative Salt Analysis
Qualitative salt analysis is a practical technique used to identify cations and anions in a given salt sample. Below are the major ions studied in this analysis.
- Cations: Pb²⁺, Cu²⁺, Al³⁺, Fe³⁺, Zn²⁺, Ni²⁺, Ca²⁺, Ba²⁺, Mg²⁺, NH₄⁺
- Anions: CO₃²⁻, S²⁻, SO₄²⁻, NO₃⁻, NO₂⁻, Cl⁻, Br⁻, I⁻ (Insoluble salts excluded)
6. Chemical Principles in Experimental Studies
Several experiments in practical chemistry help understand thermodynamics, kinetics, and other principles.
- Enthalpy of Solution of CuSO₄: The enthalpy change when copper sulfate dissolves in water can be measured to understand the heat involved in the process.
- Enthalpy of Neutralization: The enthalpy change during the neutralization of a strong acid with a strong base can be measured to study the energy change in acid-base reactions.
- Preparation of Lyophilic and Lyophobic Sols: The preparation of sols involves dispersion of solid particles in liquids, with lyophilic sols being more stable than lyophobic sols.
- Kinetic Study of the Reaction of Iodide Ions with Hydrogen Peroxide: The reaction between iodide ions and hydrogen peroxide at room temperature can be studied to understand the rate of reaction and its dependence on concentration.