3.6 Organic analysis Flashcards
Test for alkenes
Bromine water - colour change from orange to colourless
Test for primary and secondary alcohols
Warm with acidified potassium dichromate - colour change from orange to green
Test for aldehydes
Warm with Tollen’s reagent - silver mirror
OR
Warm with Fehling’s solution - Brick red precipitate forms
(Also react with acidified potassium dichromate)
Test for carboxylic acids
Add sodium carbonate or sodium hydrogencarbonate - effervescence
Test for halogenoalkanes
Warm with aqueous silver nitrate - precipitate of silver halide
What is infra-red spectroscopy used to identify?
Specific covalent bonds
Axis for IR spectroscopy graphs
% transmittance against wave number (cm⁻¹)
Fingerprint region of an IR spectroscopy graph
- Below 1500cm⁻¹
- Unique to each compound
- Spectrum can be compared to a database to identify compound
Why do greenhouse gasses absorb infrared radiation?
They contain bonds that are very efficient at absorbing IR radiation
Feature of the carbon dioxide IR spectroscopy graph
C=O peak appears outside the usual range
Molecular ion
The line with the largest m/z ratio - this peak gives the Mr of the compound
The atomic mass of carbon-12 is exactly 12.00000 by……
Definition
What can high resolution mass spectrometry be used for?
Differentiating between two compounds that have the same Mr to 1dp (provided they have different molecular formulae)
What is combustion analysis used for?
Finding the empirical formula of organic substances
Combustion analysis
Mass of C =
(mass of CO₂ / 44) x 12
Combustion analysis
Mass of H =
(mass of H₂O / 18) x 2
Combustion analysis
Mass of X =
mass of CⱼHₖOₗ - (mass of C + mass of H)
