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CHEMISTRY AS > * Whats in a medicine > Flashcards

* Whats in a medicine Flashcards

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1
Q

What oxidising agent is used to oxidise alcohols

A
  • acidified potassium dichromate (VI)
  • to oxidise alcohols to carbonyl compounds (aldehydes and ketones) and carboxylic acids
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2
Q

How is an alcohol oxidised to just the aldehyde?

A
  • gently heating ethanol with potassium dichromate(VI) solution and sulfuric acid in a flask produces ethanal (an aldehyde)
  • but once the ethanal is formed, there will be lots of oxidising agent around left to turn it into a carboxylic acid
  • to get just the aldehyde - you need to get it out of the oxidising solution as soon as it is formed
  • done with distillation apparatus
  • the aldehyde which boils at a lower temperature than the alcohol evaporates and is distilled off immediately
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3
Q

How is an alcohol oxidised to a carboxylic acid?

A
  • alcohol has to be vigorously oxidised
  • the alcohol is mixed with excess oxidising agent and heated under reflux
  • heating under reflux means you can increase the temperature of an organic reaction to boiling point, without losing volatile solvents, reactants, or products
  • any vaporised compounds are cooled so that they condense and drip back into the reaction mixture
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4
Q

Draw the reaction for a primary alcohol being oxidised to an aldehyde and then to a carboxylic acid

A
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5
Q

How is an alcohol oxidised to a ketone

A
  • refluxing a secondary alcohol with acidified potassium dichromate(VI) will produce a ketone
  • ketones can’t be oxidised easily, so even prolonged refluxing wont produce anything more
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6
Q

Draw a phenol

A
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7
Q

Draw 2 methylphenol

A

number the carbons starting from the one with the -OH group

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8
Q

Draw 3-chlorophenol

A
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9
Q

Draw salicylic acid

A
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10
Q

How are esters made using a phenol

A
  • just like other alcohols, phenols reaxct with acid anhydrides to form ester and carboxylic acid
  • unlike other alcohols, phenols will not react with carboxylic acids to form an ester
  • good way to test whether a substance is a phenol or a different alcohol
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11
Q

Are phenols acidic, alkaline or neutral? Explain

A
  • Phenols are weak acids
  • phenols dissolve a little bit in water to form a phenoxide ion and an H+ ion. So solution formed is weakly acidic
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12
Q

Do phenols react with alkalis?

A
  • phenols react with alkalis to produce salt and water
  • for example phenols react with sodium hydroxide solution at room temperature to form sodium phenoxide and water. the hydrogen ion on the phenol is removed by the OH- ion
  • carboxylic acids also react with alkalis
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13
Q

do phenols react with carbonate solutions

A
  • phenols dont react with carbonate solutions
    • because carbonates (e.g. sodium carbonate Na2CO3) are not strong enough bases to remove the hydrogen ion from the phenol (alkalis are strong enough bases)
  • good way to tell phenols apart from carboxylic acids
    • because carboxylic acids react with alkalis and carboantes (giving of CO2 gas)
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14
Q

Why do we use reflux instead of using a bunsen burner

A
  • organic reactions can be slow and the substances are usually flammable and volatile (theyve got low boiling points)
  • if you use put the organic solutions in a beaker and use a bunsen burner to heat them theyll evaporate or catch fire before they have time to react
  • to get round this problem we reflux
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15
Q

Describe refluxing

A
  • to reflux, heat the solution in a flask fitted with a vertical Liebig condenser - this causes the solution to continuously boil/evaporate and then condense back into the flask, giving it time to react
  • heat the solution electronically - hot plates, heating mantles, or electrically controlled water baths are normally used. This avioids naked flames that might ignite the compounds
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16
Q

Describe a method for reflux

A
  • heating under reflux is used for reactions involving volatile liquids, it ensures that reactants and/or products do not escape whilst the reaction is in progress
  • 1) Put the reactants into a pear-shaped or rounded-bottomed flask and add a few anti-bumping granules - these granules burst the bubbles in the boiling mixture and reduce the chance of boiling over
  • 2) Do not stopper the flask - doing this would cause pressure to build up and the glassware could crack or the stopper could fly out (serious accident could result)
  • 3) Attach a condenser vertically to the flask so that water flows into the condenser at the bottom and out of the condenser at the top. This ensures that the condenser is always full of cold water
  • 4) Heat so that the reaction mixture boils gently using heating mantle. When refluxing correctly, any vapours should reach no more than half way up the condenser before condensing back into a liquid. The liquid should drip back into the reaction flask steadily
17
Q

Why do we use distillation

A
  • distillation can be used to separate a mixture of miscible liquids with unique boiling points. By heating the mixture, each pure component is vaporised, condensed and collected. The components will evaporate in the order of their boiling points - the one with the lowest boiling point will evaporate first
  • Quickfit glassware commonly used for distillation
    • has ground glass joints that can be sealed using grease to prevent loss of reagents
18
Q

Describe infrared spectroscopy

A
  • in infrared spectroscopy - a beam of IR radiation is passed through a sample of a chemical
  • the IR radiation is absorbed by covalent bonds in the molecules, increasig their vibrational energy
  • bonds between different atoms absorb different frequencies of IR radiation. Bonds in different places in a molecule absorb different frequencies too
    • so O-H in an alcohol and O-H in a carboxylic acid absorb different frequencies
  • an infrared spectrometer produces a spectrum that shows you what frequencies of radiation the molecules absorbing
  • you can use it to identify the functional groups in a molecule
  • also means you can tell if a functional group has changed during a reaction
    • e.g. if you oxidise an alcohol to an aldehyde, O-H absorption would disappear from spectrum and C=O would appear
19
Q

What is the wavenumber

A
  • measure used for frequency (its just 1/wavelength in cm)
20
Q

What are mass spectra used for?

A
  • working out relative atomic mass
  • mass spectra for molecular samples
21
Q

Describe the use of mass spectrometry to identify a compound

A
  • mass spectrum produced by a mass spectrometer. The molecules in the sample are bombarded with electrons, which remove an electron from the molecule to form a molecular ion, M+(g)
  • to find the relative molecular mass of a compound you look at the molecular ion peak (the M peak)
  • the mass/charge value of the molecular ion peak is the molecular mass
22
Q

Describe how the molecular ion can be broken down into smaller fragments

A
  • the bombarding of electrons make some of the molecular ions break up into fragments
  • the fragments that are ions show up on the mass spectrum, making a fragmentation pattern. (can be used to identify molecules and even their structure)
  • to work out the structural formula you have to work out what ion could have made each peak from its m/z value. (assume m/z value of a peak matches the mass of the fragment ion)
23
Q

how do you identify a compound by combining techniques of mass spectrometry and IR spectrometry

A
  • work out what functional groups are in the compound from its IR spectrum
  • use the mass spectrum to work out the structure of the molecule
24
Q

What is the m/z value of a CH3+ ion on a mass spectrum

A

15

25
Q

What is the m/z value of the fragement ion, C2H5+ on a mass spectrum

A

29

26
Q

What is the m/z value of the fragement ion, CH3CH2CH2+ on a mass spectrum

A

43

27
Q

What is the m/z value of the fragement ion, CH3CH2CH2+ on a mass spectrum

A

43

28
Q

What is the m/z value of the fragement ion, OH+ on a mass spectrum

A

17

CHEMISTRY AS (24 decks)

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