⚗️ Analytical Chemistry Overview
Definition
Analytical Chemistry is the science of chemical characterization. A complete chemical characterization of a compound must include both qualitative and quantitative analysis.
Qualitative vs Quantitative Analysis
| Type | Purpose | Question Answered |
|---|---|---|
| Qualitative | Detection/identification of elements in a compound | “What is present?” |
| Quantitative | Determination of relative amounts of elements | “How much is present?” |
🌟 Key Point: A complete quantitative analysis involves four major steps: (1) Sampling, (2) Separation, (3) Measurement & Calculation, (4) Drawing Conclusions.
🔍 Filtration Techniques
Definition & Purpose
Filtration is the process used to separate one component of a two-component heterogeneous mixture from a solution.
Example: Separating sand from salt water. Salt dissolves, sand remains insoluble and can be filtered.
Filter Media Types
| Type | Description | When to Use |
|---|---|---|
| Ordinary Filter Paper | Standard paper with various porosities | General laboratory filtrations |
| Fluted Filter Paper | Fan-like folded paper | When faster filtration is needed |
| Gooch Crucible | Porcelain with perforated bottom | High-temperature ignition needed |
| Sintered Glass Crucible | Glass with porous disc | Reactive solutions, no preparation needed |
💡 Tip: Use asbestos mat with Gooch crucible for filtering reactive solutions like concentrated HCl and KMnO₄.
💎 Crystallization Process
Basic Principle
The solute should be soluble in a suitable solvent at high temperature, with excess solute crystallizing out when cooled.
Ideal Solvent Features
- Dissolves large amount at boiling point, small amount at room temperature
- Does not react chemically with solute
- Does not dissolve impurities or allow them to crystallize with solute
- Produces well-formed crystals on cooling
- Inexpensive, safe, and easily removable
Steps of Crystallization
- Prepare saturated solution in suitable solvent
- Filter hot solution to remove insoluble impurities
- Cool filtered solution at moderate rate
- Filter crystals from mother liquor
- Dry crystals (air, oven, or vacuum desiccator)
- Use animal charcoal to remove colored impurities if needed
🌡️ Distillation Methods
Simple Distillation
Purpose: Separate solvent from solution
Example: Making seawater drinkable by distilling pure water
- Uses distillation flask, condenser, and receiving flask
- Add boiling chips to prevent bumping
- Cool water circulates in condenser to condense vapors
Fractional Distillation
Purpose: Separate miscible liquids with different boiling points
Condition: Boiling point difference should be ~25°C or more
Example: Separating ethanol (78°C) from water (100°C)
Apparatus: Includes fractionating column with glass beads to increase surface area
🌍 Real-world Application: Petroleum refining uses fractional distillation to separate components like petrol, diesel, and kerosene.
📊 Chromatography Techniques
Basic Principle
Distribution of solute between a stationary phase and a mobile phase.
| Type | Stationary Phase | Mobile Phase | Examples |
|---|---|---|---|
| Adsorption | Solid | Liquid or Gas | TLC, Column Chromatography |
| Partition | Liquid | Liquid or Gas | Paper Chromatography, GLC |
Paper Chromatography
Stationary Phase: Water entrapped in cellulose fibers of paper
Mobile Phase: Organic liquid (ascending, descending, or radial)
Rf Value: Distance traveled by substance ÷ Distance traveled by solvent front
Applications: Checking purity, identifying substances, separating complex mixtures
Locating Agents
- UV Light: Visualize colorless compounds
- Chemical Agents: Ninhydrin for amino acids
- Purpose: Make colorless spots visible
🧪 Checking Purity of Products
Melting Point Determination
Pure solids have sharp, specific melting points. Example: Pure aspirin melts sharply at 136°C. Impure substances melt over a temperature range.
Mixed Melting Point
Mix sample with pure compound. If melting point remains sharp, sample is pure. If depressed, sample is impure.
Paper Chromatography
Pure compounds produce single spots. Compare Rf values with known standards. Multiple spots indicate impurities.
Boiling Point (for liquids)
Compare with literature values. Pure liquids boil at constant temperature. Fractional distillation can indicate purity.