3.6 Organic Analysis

Shake with bromine water, result is bromine water is decolourised (orange to colourless)

Add NaOH(aq) and warm, acidity with HNO3, add AgNO3 (aq) Result: precipitate of AgX (for Cl = white Br = cream I = yellow)

Add acidified K2Cr2O7 (potassium dichromate(VI)) and heat Result: colour change from orange to green for primary and secondary alcohols ( no change for tertiary alcohols)

• Warm with Fehlings’s solution, result: brick red ppt forms (from blue solution) • Warms with tollens reagent result: “silver mirror” (Ag(s) ppt) forms

Add Na2CO3 (aq) Result CO2(g) given off - effervescence

Used to find the relative molecular masses of organic compounds Compounds is dissolved in solution, ionised by high voltage supply (to mostly 1+ ions) accelerated by a negatively charged plate, becomes a beam of ionised molecules, reach detector and cause a current to flow. Time of flight used to work out m/z value and plot graph

Shows m/z value (mass divided by ionic charge) since most ions are 1+, this effectively shows Mr

The molecular ion is shown as a peak, but it will also fragment into smaller molecules, so these peaks are shown aswell Also due to isotopes of atoms, different peaks may be seen

A stream of gas carries a mixture of vapours through a column packed with solids, different compounds move through at different speeds, so they are separated. The amount of each compound can then be measured

Gas chromatography linked to mass spectrometry

Powerful chemical analysis - forensic work, measuring water pollution, drug testing on athletes, racehorses

Mass spectrometry which gives Mr to 3d.p. Or 4d.p. are called high resolution (low resolution is to nearest whole number)

Distinguish between compounds that have the same Mr to the nearest whole number, but are made up of different atoms and therefore have different values of Mr to 3d.p.

They are constantly vibrating - they can absorb infrared radiation that is the same frequency as their frequency of vibration

Vibrate faster (with higher frequency)

Vibrate slower (with lower frequency)

Every bond has a unique vibration frequency in the infrared region of the EM spectrum Bonds absorb radiation that has the same frequency as their frequency of vibration Infrared radiation emerged from a sample is missing the frequencies that have been absorbed—> this information can be use to identify the compounds functional group

Beam of infrared radiation with a range of frequencies is passed through the sample Radiation that emerges is missing frequencies that have been absorbed by the bonds in the sample Graph is plotted of intensity against frequency of radiation

The frequencies where radiation has been absorbed - match to table to find out which bonds they represent

Area of the infrared spectrum below wavenumber of 1500cm^-1 Many peaks, caused by complex vibrations of the whole molecule. Unique to every compound, so can be used to identify compounds

The fingerprint region’s pattern is matched to a database on a computer to identify the compound accurately