Organic Analysis
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Identification of alkene by test-tube reactions
Reagent: Bromine water Result: Orange colour decolourises
Identification of aldehyde by test-tube reactions
Reagent: Tollens’ reagent Result: Silver mirror formed OR Reagent: Fehling’s solution Result: Blue solution to red precipitate
Identification of carboxylic acid by test-tube reactions
Reagent: Sodium carbonate Result: Effervescence of CO2 evolved 2CH3COOH + Na2CO3 → 2CH3COONa+ + H2O + CO2
What reagent can be used to identify primary/secondary alcohols and aldehyde? Observation?
Reagent: acidified potassium dichromate (VI) and sulfuric acid Result: Orange to green colour change
Identification of chloroalkane by test-tube reactions
Reagent: Warm with silver nitrate Result: Slow formation of white precipitate of AgCl
Conditions, reaction and observations when using Tollens’ Reagent
Conditions: heat gently Reaction: -aldehydes are oxidised by Tollens’ reagent into a carboxylic acid Ag+ ions are reduced to Ag Observation: Aldehydes: silver mirror coats the inside of the test tube Ketones: no visible change
Conditions, reaction and observations when using Fehling’s solution
Conditions: heat gently Reaction: aldehydes are oxidised by Fehling’s Solution into a carboxylic acid -blue Cu2+ ions are reduced to CuO Observation: Aldehydes: Blue Cu2+ ions in solution change to a red precipitate of Cu2O Ketones: no visible change
Conditions: heat gently Reaction: aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.
How is Tollen’s reagent made What is the active substance.
Mix aqueous ammonia and silver nitrate Complex ion [Ag(NH3)2]+
purpose of mass spectroscopy
to find the Mr of of a compound
what is m/z ratio
the mass of the fragment divided by charge
what is the last peak on a mass spec graph
molecular ion peak or M+1 peak this is the same as the relative molecular mass of the molecule
advantage of high resolution mass spec
allows identification of different molecules with the same molecular mass rounded to the nearest whole number measures the Mr to several decimal places, unlike low resolution mass spec (only measures to nearest whole number)
What factors affect the frequency of IR absorbed by a covalent bond
the atoms that are either side of the bond position of the bond in the molecule (e.g. O-H in alcohol vs carboxylic acid)
values of the fingerprint region? use?
500-1500cm-1 side and position of the peaks are unique to a particular molecules, allows specific molecules to be identified
to identify the molecule, what can the finger print region be compared to?
know library of spectra
what does extra peaks in the fingerprint region show?
impurities in the sample
what do greenhouse gases absorb and how?
infrared radiation -electromagnetic radiation from the sun is absorbed by Earth -GHG some is re-emitted as IR -
steps for structural determination
-find empirical formula using percentages of element find molecular ion peak/Mr/ m/z ratio find molecular formula
State why the precise relative atomic mass quoted in the table for the 12C isotope is exactly 12.00000
by definition / as a standard
Test for haloalkanes
• Add aqueous silver nitrate. • Ppt forms (slowly - slow step is dependant on C-Hal bond being broken). • • Cl = white ppt. - Br = cream ppt. - I = yellow ppt.