ORGANIC ANALYSIS Flashcards
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
what is the observation with Tollens’ reagent?
with aldehydes, a silver mirror forms coating
the inside of the test tube. Ketones result in no change
what is the formula for Tollens’ reagent reacting with ethanal?
CH3CHO + 2Ag+ + H2O –> CH3COOH + 2Ag + 2H+
what is the reagent for Fehling’s solution?
Fehling’s Solution containing blue Cu 2+ ions
what are the conditions for Fehling’s solution?
heat gently
what is the reaction that occurs with Fehling’s solution ?
aldehydes only are oxidised by Fehling’s Solution into a carboxylic acid. The copper (II) ions are reduced to copper(I) oxide
what is the observation with Fehling’s solution?
Aldehydes :Blue Cu 2+ ions in solution change to
a red precipitate of Cu2O.
Ketones do not react
what is the formula ethanal reacting with Fehling’s solution?
CH3CHO + 2Cu2+ + 2H2O –> CH3COOH + Cu2O + 4H+
how do we test for the presence of carboxylic acids?
The presence of a carboxylic acid can be tested by addition
of sodium carbonate. It will fizz and produce carbon dioxide
what is the formula for ethanoic acid reacting with sodium carbonate?
2CH3COOH + Na2CO3 –> 2CH3CO2-Na+ + H2O + CO2
how do we test for carbon dioxide?
This gas can be collected and tested using limewater.
This solution will turn cloudy if the gas is CO2
what does IR spectroscopy test for?
functional groups present in organic compunds
how does IR radiation work?
The IR radiation is passed through a sample where the different types of bonds absorb the radiation in different amounts.
These varying amounts of absorbance are measured and recorded allowing certain bonds and therefore functional groups to be identified.
A spectrum is produced from the measurements which has characteristic curves fro the different functional groups
