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AQA A level Chemistry HJ > ORGANIC ANALYSIS > Flashcards

ORGANIC ANALYSIS Flashcards

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1
Q

what does the mass spectrometer detect when organic molecules are passed through it?

A

it detects both the whole molecule and fragments of the molecule

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2
Q

what is the highest mass/charge ratio due to?

A

the original molecule that hasn’t fragmented (called the molecular ion) .

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3
Q

why is the mass/charge ratio equal to the Mr?

A

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
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4
Q

what is the general formula for how the molecular ion is formed?

A

M → [M]+. + e–

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5
Q

define molecular ion?

A 
molecular ion is the molecule with one electron
knocked off (It is both an ion and a free radical)`
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6
Q

what is high resolution mass spectrometry used for?

A

High resolution mass spectrometry can be used to determine the molecular
formula of a compound from the accurate mass of the molecular ion

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7
Q

up to how many decimals can high resolution mass spectroscopy measure up to?

+

benefit of this?

A

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)

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8
Q

why will there be 2 molecular peaks if a compound contains a chlorine or a bromine?

A

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.

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9
Q

what information can complicated spectra tell us?

A

Complicated spectra can be obtained than provide

information about the types of bonds present in amolecule

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10
Q

what is the region above 1500 cm-1 called?

A

functional group identification

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11
Q

what is the region below 1500 cm-1 called?

A

fingerprinting

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12
Q

how do we use infrared spectroscopy to identify compounds?

A

Complicated spectra can be obtained than provide
information about the types of bonds present in a
molecule

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13
Q

what does ‘rogue’ absorption mean?

A

“rogue” absorptions can also occur and are indicators of impurities

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14
Q

what is a disadvantage of infrared spectroscopy?

A

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.

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15
Q

describe the mechanism of the greenhouse effect

A

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.

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16
Q

what is the test for alkenes and the positive result?

A

bromine water

orange colour decolourises

17
Q

what are the 2 test for aldehydes and their positive result?

A

Fehling’s solution
Blue solution to red precipitate

Tollens’ reagent
silver mirror formed

18
Q

what is the test for carboxylic acids and the positive result?

A

sodium carbonate

effervescence of CO2 evolved

19
Q

what is the test for primary, secondary alcohols and aldehydes and their positive result?

A

sodium dichromate and sulfuric acid

orange to green colour change

20
Q

what is the test for chloroalkanes and the positive result?

A

warm with silver nitrate

slow formation of white precipitate of AgCl

21
Q

how is tollens reagent formed?

A

Tollens’ Reagent formed by mixing aqueous

ammonia and silver nitrate.

22
Q

what is the active substance in tollens reagent ?

A

The active substance is

the complex ion of [Ag(NH3)2]+

23
Q

what are the conditions of Tollens’ reagent?

A

heat gently

24
Q

what is the reaction that occurs when tollens reagent is used?

A

aldehydes only are oxidised by Tollens’ reagent
into a carboxylic acid.
The silver(I) ions are reduced
to silver atoms

25
Q

what is the observation with Tollens’ reagent?

A

with aldehydes, a silver mirror forms coating

the inside of the test tube. Ketones result in no change

26
Q

what is the formula for Tollens’ reagent reacting with ethanal?

A

CH3CHO + 2Ag+ + H2O –> CH3COOH + 2Ag + 2H+

27
Q

what is the reagent for Fehling’s solution?

A

Fehling’s Solution containing blue Cu 2+ ions

28
Q

what are the conditions for Fehling’s solution?

A

heat gently

29
Q

what is the reaction that occurs with Fehling’s solution ?

A 
aldehydes only are oxidised by Fehling’s Solution into a carboxylic acid. The copper (II) ions are reduced
to copper(I) oxide
30
Q

what is the observation with Fehling’s solution?

A

Aldehydes :Blue Cu 2+ ions in solution change to
a red precipitate of Cu2O.

Ketones do not react

31
Q

what is the formula ethanal reacting with Fehling’s solution?

A

CH3CHO + 2Cu2+ + 2H2O –> CH3COOH + Cu2O + 4H+

32
Q

how do we test for the presence of carboxylic acids?

A

The presence of a carboxylic acid can be tested by addition

of sodium carbonate. It will fizz and produce carbon dioxide

33
Q

what is the formula for ethanoic acid reacting with sodium carbonate?

A

2CH3COOH + Na2CO3 –> 2CH3CO2-Na+ + H2O + CO2

34
Q

how do we test for carbon dioxide?

A

This gas can be collected and tested using limewater.

This solution will turn cloudy if the gas is CO2

35
Q

what does IR spectroscopy test for?

A

functional groups present in organic compunds

36
Q

how does IR radiation work?

A

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

AQA A level Chemistry HJ (28 decks)

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