3/17/25, 7:42 AQA A Level Chemistry - Infrared Spectroscopy Flashcards |
AM
AQA A LEVEL CHEMISTRY - INFRARED SPECTROSCOPY EXAM
QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
Terms in this set (16)
Alkenes - shake with bromine water - decolourises
Halogenoalkanes - add aqueous sodium hydroxide (NaOH) and warm, then acidify
with nitric acid (HNO3), then add aqueous sodium nitrite (AgNO3) - precipitate of
silver halide forms
What are the chemical tests for alkenes, Alcohols - add acidified potassium dichromate (VI) (Kr2Cr2O7) - orange to green
halogenoalkanes, alcohols, aldehydes and with primary or secondary alcohols
carboxylic acids? Aldehydes - warm with Fehling's solution or warm with Tollens' reagent - blue to red
precipitate or silver mirror
Carboxylic acids - add aqueous sodium hydrogen carbonate (NaHCO3)
What is infrared spectroscopy used for? To identify bonds and the functional group of organic compounds
1) A beam of infrared radiation with a spread of frequencies is passed
through a sample
2)The radiation emerges missing frequencies absorbed by bonds
How does infrared spectroscopy work?
3) Plots a graph of intensity of radiation (transmittance) against frequency (expressed
as wavelength cm-1)
- A pair of atoms joined by a chemical bond are always vibrating
e.g. stronger bonds vibrate faster at a higher frequency
e.g. heavier atoms vibrate slower at a lower frequency
- Each bond has a unique natural frequency in the infrared region of the EM
spectrum
-Each bond can only absorb photons of IR light of the same frequency as this natural
Why does infrared spectroscopy work? vibration
1) Photons absorbed make the bond vibrate harder than natural frequency
(excited state)
2)Transmittance detected and if 100% then no IR radiation absorbed
Stretch Vibration and Bending Vibration
1/
3
AM
AQA A LEVEL CHEMISTRY - INFRARED SPECTROSCOPY EXAM
QUESTIONS AND ANSWERS WITH COMPLETE SOLUTIONS VERIFIED
Terms in this set (16)
Alkenes - shake with bromine water - decolourises
Halogenoalkanes - add aqueous sodium hydroxide (NaOH) and warm, then acidify
with nitric acid (HNO3), then add aqueous sodium nitrite (AgNO3) - precipitate of
silver halide forms
What are the chemical tests for alkenes, Alcohols - add acidified potassium dichromate (VI) (Kr2Cr2O7) - orange to green
halogenoalkanes, alcohols, aldehydes and with primary or secondary alcohols
carboxylic acids? Aldehydes - warm with Fehling's solution or warm with Tollens' reagent - blue to red
precipitate or silver mirror
Carboxylic acids - add aqueous sodium hydrogen carbonate (NaHCO3)
What is infrared spectroscopy used for? To identify bonds and the functional group of organic compounds
1) A beam of infrared radiation with a spread of frequencies is passed
through a sample
2)The radiation emerges missing frequencies absorbed by bonds
How does infrared spectroscopy work?
3) Plots a graph of intensity of radiation (transmittance) against frequency (expressed
as wavelength cm-1)
- A pair of atoms joined by a chemical bond are always vibrating
e.g. stronger bonds vibrate faster at a higher frequency
e.g. heavier atoms vibrate slower at a lower frequency
- Each bond has a unique natural frequency in the infrared region of the EM
spectrum
-Each bond can only absorb photons of IR light of the same frequency as this natural
Why does infrared spectroscopy work? vibration
1) Photons absorbed make the bond vibrate harder than natural frequency
(excited state)
2)Transmittance detected and if 100% then no IR radiation absorbed
Stretch Vibration and Bending Vibration
1/
3
