Comprehensive notes, MCQs, and Short Questions for Class 11 Chemistry Chapter 15 'Basic Separation Techniques'. Covers Filtration, Crystallization, Solvent Extraction, Distillation, and Chromatography.
Analytical Chemistry: The branch of chemistry that deals with the separation, identification, and quantitative determination of the composition of different substances.
Types of Analysis:
1. Qualitative Analysis: Identifies the elements or compounds present in a sample (e.g., detecting presence of Carbon in a compound).
2. Quantitative Analysis: Determines the exact amount or mass of each component present in the sample.
Steps in Quantitative Analysis:
1. Sampling
2. Separation of desired component
3. Measurement/Calculation of results
4. Drawing conclusions
Definition: The process of separating insoluble solid particles from a liquid using a filter medium.
Filter Paper Types:
1. Ordinary Filter Paper: Folded twice to form a cone. Rate of filtration is slow.
2. Fluted Filter Paper: Folded multiple times (fan-like arrangement) to increase surface area. Rate of filtration is fast.
Process: The filter paper is placed in a funnel. The stem should keep full of liquid to create a slight suction, aiding filtration. Ideally, the paper should be one-fourth to one-half full of precipitate.
Used for precipitates that need to be ignited at high temperatures or are reactive.
1. Gooch Crucible: Porcelain crucible with a perforated bottom covered with paper pulp or a filter paper cut to size. For reactive solutions (like conc. HCl, KMnO4), an Asbestos Mat is used instead of paper. Useful for high-temperature ignition.
2. Sintered Glass Crucible: Glass crucible with a porous glass disc sealed at the bottom. No preparation required. Convenient and time-saving.
Principle: Based on the difference in solubility of a solute in a solvent at high and low temperatures. The solute should be soluble at high temperature and insoluble (crystallize out) at low temperature.
Choice of Solvent: An ideal solvent should:
- Dissolve a large amount of solute at boiling point.
- Dissolve very small amount at room temperature.
- Not react chemically with the solute.
- Be safe, cheap, and easily removable.
Common Solvents: Water, Rectified Spirit (95% Ethanol), Absolute Alcohol, Carbon Tetrachloride, ether.
1. Preparation of Solution: Saturated solution is prepared at boiling point.
2. Filtration: Hot solution is filtered to remove insoluble impurities. A hot water funnel is often used to prevent premature crystallization.
3. Cooling: Different cooling rates produce different crystal sizes (Slow cooling = Large crystals; Fast cooling = Small crystals).
4. Collecting Crystals: Separated via Gooch crucible using vacuum suction.
5. Drying Crystals:
- Pressing between filter papers (Contamination risk).
- Oven drying (Risk of decomposition).
- Vacuum Desiccator (Best method). Drying agents: CaCl2, Silica gel, P2O5.
6. Decolorization: If colored impurities are present, Animal Charcoal is boiled with the solution to adsorb colors.
Definition: The process in which a solid, upon heating, directly changes into vapors without passing through the liquid phase, and the vapors can be condensed back to solid.
Examples: Ammonium Chloride (NH4Cl), Iodine, Naphthalene, Benzoic Acid.
Use: To purify a volatile solid from non-volatile impurities.
Definition: A technique to separate a solute from a solution by shaking it with an immiscible solvent in which the solute represents more solubility (Distribution Law).
Ether Extraction: Used to separate organic compounds from water. Ether is immiscible with water and organic compounds are often more soluble in it.
Distribution Law: A solute distributes itself between two immiscible liquids in a constant ratio of concentrations, irrespective of the amount of solute added.
Simple Distillation: Used to separate a liquid from a solution (e.g., water from salt water) or two liquids with a large boiling point difference. The liquid boils, vapors condense in a condenser, and the distillate is collected.
Fractional Distillation: Used to separate miscible liquids with close boiling points (e.g., Alcohol and Water).
Principle: Based on differences in boiling points. A Fractionating Column is used to provide a large surface area for repeated vaporization and condensation, improving separation efficiency.
Definition: A method for separation based on the distribution of a solute between a Stationary Phase and a Mobile Phase.
Types:
1. Adsorption Chromatography: Stationary phase is solid (e.g., Alumina, Silica). Solute is adsorbed on it. Example: Thin Layer Chromatography (TLC).
2. Partition Chromatography: Stationary phase is a liquid (supported on an inert solid). Separation is based on partition coefficient. Example: Paper Chromatography.
Stationary Phase: Water adsorbed in cellulose fibers of the paper.
Mobile Phase: Organic solvent (Ethanol, Acetone, etc).
Procedure: A spot of mixture is placed on Whatman filter paper. The paper is dipped in solvent. Solvent rises via capillary action.
Retardation Factor (Rf): Ratio of distance traveled by component to distance traveled by solvent front.
Rf = Distance moved by component / Distance moved by solvent.
It has no units and is always less than 1.
Uses: Separation of amino acids, inks, and purity checking.