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Chemistry A-Level > CD 9, 10, 11 > Flashcards

CD 9, 10, 11 Flashcards

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1
Q

what is reacted with aldehyde and ketones to extend their carbon chain

A

HCN

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2
Q

what is a nitrile group and what are the two ways to get rid of it

A

C=N
(TRIPLE BOND)
- nitrile group can be hydrolysed into a carboxylic acid or dehydrated into an amine

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3
Q

what is a carbonyl group and what compounds contain them

A
  • C=O
  • aldehydes and ketones
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4
Q

why do aldehydes and ketones differ in terms of oxidation

A
  • aldehydes contain a hydrogen atom attached to the carbonyl group, this means that aldehydes react with a range of oxidising agents whereas ketones will not
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5
Q

how do you distinguish an aldehyde from a ketone, what is the problem with this method

A
  • heat the sample under reflux with acidified potassium dichromate
  • aldehyde sample will turn from orange to green
  • problem is that this result would also be produced for a primary/ secondary alcohol
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6
Q

How is Fehling’s test conducted and what is it used to test for

A
  1. a mixture of Fehling’s A and B is warmed in a water bath with an aldehyde and the solution should change from blue to brick red precipitate
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7
Q

describe in detail what Fehling’s solution is comprised of

A
  • made from a mixture of Fehling’s A and Fehling’s B
  • Fehling’s A contains the weak oxidising agent Cu 2+
  • Fehling’s B which is an alkaline solution containing a bidentate ligand
  • Cu 2+ ions are reduced to copper (I) ions, precipitated as copper oxide Cu2O, forming the brick red precipitate
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8
Q

How is the test will Tollen’s reagent conducted

A
  • aldehydes are oxidised into carboxylate ions
  • Tollen’s reagent is warmed with aldehyde in a test tube using a water bath
  • a silver mirror forms on the inside of the tube
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9
Q

Explain what Tollen’s reagent is formed from

A
  • Formed by dissolving silver (I) oxide, Ag2O in ammonia to form the complex ion [Ag(NH3)2]+
  • when tollen’s reagent is added to an aldehyde, Ag+ ions are reduced to elemental silver, which appears as a silvery layer on the surface of the test tube
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10
Q

what are aldehydes and ketones reduced to and what is used in this process

A
  • aldehydes are reduced to primary alcohols
  • ketones are reduced to secondary alcohols
  • the powerful reducing agent NaBH4, sodium tetrahydridoborate (III)
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11
Q

what addition reactions do aldehydes and ketones take part in

A
  • undergo addition reactions with hydrogen cyanide in acidic conditions across the C=O bond to form cyanohydrins / 2-hydroxynitriles
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12
Q

define
- nitrile
- cyanohydrin

A

nitrile - a functional group in which a carbon is triple bonded to a nitrogen
cyanohydrin - a functional group where a cyanide group and an alcohol group is bonded to the same carbon atom

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13
Q

what is hydrogen cyanide replaced with in laboratories and why

A
  • cyanide is too hazardous to use the laboratory
  • acidified potassium cyanide is used to replace it, as it is a source of CN- and H+ ions
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14
Q

what occurs in the mechanism of the addition reaction of HCN and aldehyde/ ketone

A
  • two stages
    1. cyanide ion CN- is a nucleophile and attracted to carbon in the carbonyl group as it has a partial positive charge
    2. New carbon-carbon bond forms and electrons from C=O move to oxygen which then carries a negative charge, the it takes up a proton from the solvent (water) to become OH
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15
Q

how to choose a starting material for synthesis

A
  • available in suitable quantities
  • cost is low enough to make synthesis economic
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16
Q

benzene —> halogenated benzene
- electrophilic substitution

A
  • benzene reacts with liquid bromine or chlorine gas
  • presence of FeBr3 or AlCl3
  • both reactions occur at room temperature
  • bromine is decolourised and fumes of HBr are given off
17
Q

benzene —> nitrobenzene
- electrophilic substitution

A

benzene + HNO3 (nitric acid)
- in the presence of concentrated H2SO4 and at 55 degrees
- produces nitrobenzene
- nitrating mixture is a mix of concentrated nitric acid and concentrated sulphuric acid

18
Q

nitrobenzene —> phenylamine
- electrophilic substitution

A

nitrobenzene heated under reflux with HCl, in the presence of tin
forms benzene and NH2

19
Q

benzene —> acyl-substituted benzene
- electrophilic substitution

A

benzene + acyl chloride (or acid anhydride) + AlCl3
—> C6H5COR + HCl
- occurs under anhydrous conditions

20
Q

benzene —> sulfonated benzene
- electrophilic substitution

A
  • benzene + conc. H2SO4 —> benzene sulfonic acid + H+
  • heated under reflux
21
Q

benzene —> alkyl substituted benzene
- electrophilic substitution

A

benzene + chloroethane —> ethyl benzene + HCl
- heated under reflux in the presence of anhydrous aluminium chloride (AlCl3)

22
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- addition

A
  • two molecules that react together to form a single product
  • aldehydes ad ketones
23
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- elimination

A
  • a small molecule, such as water or HCl is removed from a larger molecule, leaving an unsaturated molecule
  • alcohols
  • haloalkanes
24
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- condensation

A
  • two molecules reacting together to form a larger molecule, and a smaller molecule
  • carboxylic acids and alcohols
  • acyl chlorides, alcohols and amines
25
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- substitution

A
  • one group of atoms takes the place of another
  • halo alkanes
  • alcohols + hydrogen halides
26
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- oxidation

A
  • oxygen atoms are gained of hydrogen atoms are lost
  • alcohols
  • aldehydes
27
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- reduction

A
  • oxygen atoms are lost or hydrogen atoms are gained
  • aldehydes and ketones
  • nitro groups
28
Q

define the type of reaction and give an example of a functional group that takes part in this reaction
- hydrolysis

A
  • bonds are broken by the action of water
  • esters
  • amides
  • nitriles
  • haloalkanes
29
Q

define hydrolysis

A
  • is a reaction in which bonds are broken by the action of water
30
Q

define the two types of synthetic reactions

A
  • functional group interconversion - one functional group into another
  • reactions that alter the carbon skeleton of the molecule (that form or break carbon-carbon bonds)

Chemistry A-Level (26 decks)

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