17.2 - Infrared Spectroscopy Flashcards Preview

OCR A Chemistry A Level - Chapter 17 > 17.2 - Infrared Spectroscopy > Flashcards

Flashcards in 17.2 - Infrared Spectroscopy Deck (9)
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1

What happens when covalent bonds absorb IR radiation?

- Covalent bonds contain energy and naturally vibrate
- Absorption of IR makes them vibrate in 2 ways - bending or stretching.

2

What happens during bending or stretching of bonds?

Stretch - rhythmic movement that increases or decreases the distance between the 2 atomic centres

Bending - change in bond angle

3

What does the amount a bond bends or stretches depend on?

- Atom's mass in bond - heavier=more vibration
- Bond strength - the stronger the bond the fast the vibration

4

How much radiation can a bond absorb?

Any bond can absorb as much radiation that has the same frequency as its natural frequency.

5

How do chemists measure the absorption of IR?

Frequency values are too large, so the reciprocal is used which is = to wave number

6

How are IR and atmospheric gases linked?

- Sun's IR is absorbed by Earth
- Some IR is re-emitted in the form of longer wavelengths
- H2O, CH4, CO2 (greenhouse gases) absorb these wavelengths and re-emit this energy as radiation > cause for global warming as it heats up the Earth.

7

What is the purpose and process of Infrared Spectroscopy (for organic molecules)?

- Used to identify functional groups
1. Place sample in IR spectrometer
2. Fire IR beam at 200-4000cm^-1 at sample
3. Molecule absorbs some of IR and re-emits that beam - it is analysed to identify the absorbed frequencies
4. Graphs plotted of transmittance against wavenumber.

8

What is the fingerprint region?

<1500cm^-1 on an infrared spectrum is known as the fingerprint region
- It contains unique peaks that are used to identify a particular molecules by comparing to a booklet of published spectrums or by a computer.

9

What are the applications of IR radiation?

- Pollutants can be identified by checking published IR fingerprint regions
- IR-based breathalysers pass a beam of IR through the breath sample to detect IR-absorbance - characteristic ethanol bonds identified