Edexcel Chemistry Topic 19: Modern Analytical Techniques -

Introduction

• Presenter: Chris Harris from Alawis Chemistry
• Focus: Information relevant for Edexcel A-Level Chemistry exams
• Includes a series of free videos, exam techniques, and whiteboard tutorials on Alawis Chemistry YouTube channel
• Videos range from Topic 1 to Topic 19 (this video being the last in the series)
• Option to purchase the videos for personal use

Main Topics Covered

1. Mass Spectrometry
2. Nuclear Magnetic Resonance (NMR)
3. Chromatography

Mass Spectrometry

• Purpose: Used to find the molecular mass of a compound
• M/Z Ratio: Fragment mass divided by charge
• M+ Peak: Shows the mass of the original molecule
• High Resolution Mass Spectrometry: Helps distinguish molecules with the same molecular mass using atomic mass data to several decimal places

Nuclear Magnetic Resonance (NMR) Spectroscopy

Carbon-13 and Proton NMR

• NMR Basics: Utilizes nuclear spin and external magnetic fields
• Types of NMR:
  • Carbon-13 NMR (info on carbon atoms)
  • High-resolution Proton NMR (info on hydrogen atoms)
• NMR Machine: Detects weak magnetic fields from nuclear spins
• Chemical Shifts: Peaks in NMR spectrum showing different environments

Tetramethylsilane (TMS)

• Used as a standard for chemical shifts in NMR
• Provides a reference point at 0 ppm

Interpreting NMR Spectra

• Carbon-13 NMR: Identifies carbon environments
• Proton NMR: Identifies hydrogen environments and splitting patterns
• N+1 Rule: Helps interpret splitting patterns in Proton NMR

Chromatography

Thin Layer Chromatography (TLC)

• Separates and identifies compounds using silica/alumina plates
• Rf Values: Used to identify compounds

Gas Chromatography (GC)

• Separates volatile mixtures
• Retention Time: Time taken for a substance to travel through the column

High-Performance Liquid Chromatography (HPLC)

• Used for substances with high boiling points or that decompose upon heating
• Utilizes pressure and a polar liquid as the mobile phase

Gas Chromatography-Mass Spectrometry (GC-MS)

• Combines GC and mass spectrometry for comprehensive analysis
• Separates mixtures and identifies compounds using a library of known substances

Combined Techniques

• Utilizes multiple techniques to identify unknown substances
• Example problem: Identifying a compound using MS, IR, and NMR spectra

Conclusion

• Emphasis on practice and understanding through examples
• Encouragement to utilize available resources and practice problems for mastery
• Overview of related topics in the video series, available on the Alawis Chemistry YouTube channel

Note: The lecture emphasizes the importance of understanding the mechanics of these techniques as well as their practical applications in identifying chemical structures.