ORGANIC ANALYSIS
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what does the mass spectrometer detect when organic molecules are passed through it?
it detects both the whole molecule and fragments of the molecule
what is the highest mass/charge ratio due to?
the original molecule that hasn’t fragmented (called the molecular ion) .
why is the mass/charge ratio equal to the Mr?
As the charge of the ion is +1 the mass/ charge ratio is equal to Mr e.g. Mr =16 charge=+1 16:1 so it's just 16 mass:charge=Mr
what is the general formula for how the molecular ion is formed?
M → [M]+. + e–
define molecular ion?
molecular ion is the molecule with one electron knocked off (It is both an ion and a free radical)`
what is high resolution mass spectrometry used for?
High resolution mass spectrometry can be used to determine the molecular formula of a compound from the accurate mass of the molecular ion
up to how many decimals can high resolution mass spectroscopy measure up to? + benefit of this?
High resolution mass spectroscopy can measure the mass to 5 d.p. This can help differentiate between compounds that appear to have similar Mr (to the nearest whole number)
why will there be 2 molecular peaks if a compound contains a chlorine or a bromine?
If a compound contains a chlorine or a bromine atom then two molecular ion peaks will occur : a M and a M+2 peak will occur due to the two naturally occurring isotopes of chlorine or bromine.
what information can complicated spectra tell us?
Complicated spectra can be obtained than provide information about the types of bonds present in amolecule
what is the region above 1500 cm-1 called?
functional group identification
what is the region below 1500 cm-1 called?
fingerprinting
how do we use infrared spectroscopy to identify compounds?
Complicated spectra can be obtained than provide information about the types of bonds present in a molecule
what does ‘rogue’ absorption mean?
“rogue” absorptions can also occur and are indicators of impurities
what is a disadvantage of infrared spectroscopy?
The absorption of infra-red radiation by bonds in this type of spectroscopy is the same absorption that bonds in CO2 , methane and water vapour in the atmosphere do - that causes the green house effect.
describe the mechanism of the greenhouse effect
1- UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface. 2- The Earth radiates out infrared long wavelength radiation. 3-The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere. 4-This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.
what is the test for alkenes and the positive result?
bromine water orange colour decolourises
what are the 2 test for aldehydes and their positive result?
Fehling’s solution Blue solution to red precipitate Tollens’ reagent silver mirror formed
what is the test for carboxylic acids and the positive result?
sodium carbonate effervescence of CO2 evolved
what is the test for primary, secondary alcohols and aldehydes and their positive result?
sodium dichromate and sulfuric acid orange to green colour change
what is the test for chloroalkanes and the positive result?
warm with silver nitrate slow formation of white precipitate of AgCl
how is tollens reagent formed?
Tollens’ Reagent formed by mixing aqueous ammonia and silver nitrate.
what is the active substance in tollens reagent ?
The active substance is the complex ion of [Ag(NH3)2]+
what are the conditions of Tollens’ reagent?
heat gently
what is the reaction that occurs when tollens reagent is used?
aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms