12. Separation and Purification Techniques (Lecture Notes - Student)

Separation and Purification Techniques

Lesson Overview

  • Course Title: Separation and Purification Techniques

  • Institution: Republic Polytechnic, Centre for Foundational Studies (CFS)

  • Lesson Focus: Techniques for preparing, separating, and purifying salts.

Learning Outcomes

  • Preparation Techniques:

    • Precipitation and titration.

    • Reactions of acids with metals, insoluble bases, and insoluble carbonates.

  • Application: State a method to prepare a given salt from suitable starting materials.

Common Laboratory Equipment

  • Equipment List:

    • Retort stand and clamp

    • Bunsen burner

    • Beakers

    • Conical flask

    • Filter funnel

    • Measuring cylinder

    • Droppers

    • Test tube rack

    • Safety goggles

    • Burette

    • Pipettes

    • Spatula

    • Evaporating dish

    • Pipette filler

    • Test tubes

    • Tripod stand

    • Thermometer

    • Wire gauze

    • Watch glass

Recap: Elements, Compounds, and Mixtures

Elements

  • Definition: Contains one type of atom.

  • Example: Oxygen gas.

Compounds

  • Definition: Contains two or more types of atoms chemically bonded.

  • Example: Carbon dioxide gas.

Mixtures

  • Definition: Contains two or more different substances physically mixed.

  • Examples:

    • Mixture of elements: Oxygen and helium gas.

    • Mixture of compounds: Alcohol and water.

    • Mixture of elements and compounds: Air.

The Need for Pure Substances

  • Importance:

    • Pure substances are essential for studying properties in chemistry.

    • Used in industries to manufacture useful products (e.g., food and drugs).

  • Examples:

    • Medicines must be pure to prevent side effects.

    • Silicon chips require purity to function effectively.

Pure Substances vs Mixtures

  • Pure Substance: Consists of only one substance, not mixed.

  • Mixtures: Contains two or more substances that do not chemically react, separable by physical methods.

Criteria for Purity

Physical Properties

  • Pure substances exhibit sharp melting and boiling points.

    • Melting Point: Sharp and fixed; impurities lower the freezing point.

    • Boiling Point: Fixed; impurities raise boiling point.

  • Examples:

    • Pure ice freezes at 0°C, while saltwater freezes lower than 0°C.

Testing for Purity

  • To test purity, check the melting and boiling points.

    • A boiling point of 105°C may indicate impurities if tested against pure water.

Mixtures Classification

Types of Mixtures

  • Suspension: Non-homogeneous mixture with two or more phases.

  • Solution: Homogeneous mixture with only one phase.

Solutions

  • Formation: A solute dissolves into a solvent.

  • Examples:

    • Fizzy drinks (gas in water).

    • Alcoholic beverages (ethanol in water).

Separation and Purification Methods

  • Overview: Techniques to separate a mixture into components or remove impurities include:

    • Filtration

    • Heat to dryness and crystallization

    • Simple and fractional distillation

    • Paper chromatography

    • Sublimation

    • Separation funnel

Filtration Method

Description

  • Purpose: Separate solid from liquid (e.g., solid-liquid or solid-solid mixtures).

Procedure

  1. Prepare filter paper in the funnel.

  2. Pour the mixture into the funnel.

  3. Collect the filtrate and wash the residue.

Daily Applications

  • Used in:

    • Vacuum cleaners

    • Tea bags

    • Water treatment processes.

Heat to Dryness and Crystallisation

Purpose

  • Obtain dissolved solids from liquid solutions (e.g., salt from seawater).

Sample Procedure

  1. Place mixture in an evaporating dish.

  2. Heat until all solvent evaporates.

Crystallisation Method

  1. Heat to create a hot saturated solution.

  2. Cool to allow crystals to form.

Importance

  • Used for solids that decompose upon heating (e.g., sugar).

Simple and Fractional Distillation

Purpose

  • Separate miscible liquids with different boiling points.

Process Overview

  1. Vaporization of the more volatile liquid first.

  2. Collection as it condenses.

  3. Fractional distillation uses a fractionating column for better separation.

Differences

  • Simple distillation: Used for mixtures with larger boiling point differences.

  • Fractional distillation: Used for mixtures with smaller boiling point differences.

Paper Chromatography

Description

  • Technique for separating colors/dyes in mixtures.

Procedure

  1. Apply concentrated spot on chromatography paper.

  2. Suspend in solvent for separation.

Applications

  • Used in forensics and food dye analysis.

Sublimation

Definition

  • Process where solids turn into gas without passing through the liquid state (e.g., iodine).

Use

  • Separate solids that sublime from those that do not.

Procedure

  1. Heat mixture in evaporation dish.

Separating Funnel

Description

  • Used for separating immiscible liquids.

Procedure

  1. Place mixture in funnel.

  2. Open tap to collect denser liquid.

Discussion Scenarios

  • Example Discussion 1: Testing an unknown solution's boiling point.

  • Example Discussion 2: Separation method for NaCl and sand mixtures.