Infra Red (IR) Spectroscopy | A-level Chemistry | OCR, AQA, Edexcel

Infra Red (IR) Spectroscopy in a Snap!

Unlock the full A-level Chemistry course at http://bit.ly/2m2sMVx created by Ella Buluwela, Chemistry expert at SnapRevise.

SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks.

Sign up today and together, let’s make A-level Chemistry a walk in the park!

The key points covered in this video include:
1. Vibration and IR - Global Warming
2. Making an IR Spectrum
3. Application of IR
4. The Fingerprint Region

Vibration and Infrared Radiation

A pair of atoms constantly vibrates. Infrared Radiation can be absorbed by molecules, causing them to vibrate more. This causes their covalent bonds to vibrate. These bonds can either: Stretch, Bend. The bonds vibrates at their own frequency. This is usually between 300 and 4000cm^-1. This is the IR region of the electromagnetic spectrum. The degree of vibration depends on: Bond Strength: Stronger bonds vibrate at a higher frequency. Bond Length. Mass of Atoms: Heavier atoms vibrate at a lower frequency.

Vibration and IR Radiation: Global Warming

The bonds present in Greenhouse Gases absorbs Infrared Radiation well. These gases absorbed IR that is given off by the Earth’s surface. This heat would otherwise be lost to Space. This contributes to the increasing temperature of our planet. Increasing levels of Greenhouse gases may result in further Global Warming.

Making an IR Spectrum

Process. 1. A beam of infrared radiation is passed through the sample. This beam will have a frequency in the infrared region of the electromagnetic spectrum. 2. Molecules of our sample will absorb some of these frequencies. 3. The beam that passes through is analysed. 4. We can plot a graph of transmittance against frequency. This is the infrared spectrum of the molecule. We can analyse the spectra that are formed. The peaks in the spectrum represent the vibration caused by the absorbance of IR radiation by a specific bond in the molecule.

Applications of IR Spectroscopy

Breathalysers. IR spectroscopy can be used to identify the -OH functional group that is indicative of alcohol. The level of absorption that is observed on the spectrum is related to the concentration of alcohol in the blood. England/Wales: 80mg/100ml. More sensitive methods of testing are used in addition to ensure that tests are specific. Other chemicals may produce similar spectra. Air Quality. IR spectroscopy can be used to monitor the levels of pollutants. The levels of CO and NO can be measured. Forensics. IR spectroscopy can be used to identify the chemicals that are present at crime scenes. Fuels, Accelerants, Plastics.

The Fingerprint Region

This is the region between 500cm^-1 and 1500cm^-1. The absorptions within this range are interesting. They are caused mainly from bending, Together, they are largely unique to the specific molecule. This region can be used to identify the chemical.

Summary

IR Radiation is absorbed by molecules
Covalent bonds stretch and bend
The amount of vibration depends on:
a. Bond strength
b. Bond length
c. Mass of each atom
Most bonds vibrate between 300 and 4000cm^-1
IR beam is passed through the sample and emerging beam is analysed and a graph plotted
Each different functional group has a typical range and shape of absorption
a. These can be found in the data booklet