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A-levels > Chemistry- Alcohols, Aldehydes, Ketones and carboxylic acids > Flashcards

Chemistry- Alcohols, Aldehydes, Ketones and carboxylic acids Flashcards

1
Q

What is the primary, secondary and tertiary structure of an alcohol?

A

Primary: R-OH
Secondary: RCH(OH)R’
Tertiary: RC(OH)R’R”

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2
Q

What are the alcohols (primary, secondary and tertiary) oxidised to?

A

Primary —[O]—>Aldehyde—[O]—> Carboxylic acid
Secondary —[O]—> Ketone
Tertiary (cannot be oxidised)

Oxidation reagents:
Acidified Potassium Dichromate

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3
Q

What is the test for an oxidation reaction of an alcohol & determining what alcohol structure there is?

A

Tollens- (silver Nitrate / NH3) = silver mirror or black precipitate

Benedicts/Fehlings = Brick Red precipitate

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4
Q

What are the tests for an Aldehyde?

A

Fehlings / Benedicts reagent
- Brick red / orange precipitate

Tollens reagent
- Forms a mirror (for positive result)

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5
Q

What is the test for tertiary alcohols?

A

Reaction with sodium carbonate solution.

Tertiary alcohols effervesce

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6
Q

What happens during oxidation of a primary alcohol?

A

Primary alcohol —[O]—> Aldehyde
Aldehydes can be distilled off after reflux reaction of a primary alcohol.
Aldehyde —[O]—> Carboxylic Acid,
If not distilled and alcohol is oxidised to completion then a carboxylic acid forms.

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7
Q

What is the functional group for an Aldehyde?

A

RCHO

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8
Q

What happens during the oxidation of a secondary alcohol?

A

Alcohol —[O]—> Ketone

Formed when secondary alcohols are heated under reflux.

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9
Q

What is the Functional group for a ketone?

A

R-C(-R)=O

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10
Q

What happens during the oxidation of a tertiary alcohol?

A

Tertiary alcohols do not oxidise (no change)

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11
Q

How can you test for a primary, secondary or tertiary alcohol or aldehydes and ketones?

A 
1) Heat with H2SO4/ K2Cr2O7
No colour change = 3' alcohol.
2) Green solution
2' or 1' alcohol
3) distil and test with tollens or Fehlings
No colour change = 2' Alcohol
Colour change = 1' Alcohol.
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12
Q

Why are only small ketones and aldehydes soluble in water?

A

The smaller ketones and aldehydes can form hydrogen bonds in water due to electronegative oxygen atoms in their structure bonding to water molecules.
Larger aldehydes and ketones with large R-groups (hydrocarbon chain) are less soluble as the longer chain is non-polar and cause solubility to decrease.

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13
Q

What intermolecular forces are present in an alkane, ketone and alcohol and their effect on their boiling points

A

Butane - Only van der waals forces so have a low boiling point
Ketone - Dipole dipole forces and van der waals so middle boiling point
Alcohol - Hydrogen bonds and van der waals so high boiling point.

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14
Q

Why are ketones and aldehydes susceptible to attack from nucleophiles?

A

C=O is a polar bond due to electronegativity between carbon and oxygen.
Nucleophiles attack the slightly positive carbon and the double bond means that an addition reaction is possible.

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15
Q

Why is the nucleophilic addition of cyanide useful?

A

Very useful due to the number increase in carbon number within the molecule.
Nitrile and hydroxy can react at a later date.

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16
Q

What isomers are produced from nucleophilic addition with cyanide?

A

Nucleophilic addition with cyanide to an aldehyde or asymetric ketone produces optical isomers.
Nucleophilic addition to a symetrical ketone does not produce an optical isomer.

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17
Q

What kind of mixture is produced when a nucleophile reacts with an asymetric isomer.

A

50% : 50%

Racemic mixture

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18
Q

What is the carbon with 4 different groups off it called?

A

Chiral carbon (chiral centre)

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19
Q

Why is HCN gas not used practically or in a lab?

A

Toxic gas and hard to prevent escaping into the laboratory.

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20
Q

What substances are used to introduce cyanide into a molecule.

A

Use NaCN or KCN followed by dilute HCl.
Na/KCN —> Source of CN ions
Dilute HCl —> Source of H+ ions

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21
Q

What is the reverse reaction to oxidation and what is the reducing agent?

A

Reduction reaction

Hydride ion H-

22
Q

What source of Hydride ions is used in reduction of carbonyl gorups? (C=O)

A

NaBH4

Sodium Tetrahydrioborate III

23
Q

Why would NaBH4 not reduce Alkenes (C=C) bonds?

A

Hydride ion (H-) is negative and therefore will not react/attack electron dense area on the pi bond of C=C.

24
Q

Define a chiral molecule

A

A molecule where a carbon has 4 different groups attached called a chiral centre or Asymetric carbon

25
Q

Define a Racemic mixture

A

Where a 50:50 mixture of two (optical isomers) is produced. A mixture of 50:50 enantiomes.

Optical Isomers often produced from nucleophilic addition.

26
Q

Explain why carboxylic acids are soluble in water

A

Due to the carboxyl group RCOOH being able to form hydrogen bonds with water molecules.
Carboxylic acids with < 4 carbon atoms are completely soluble in water. >4 carbon atoms cause the molecule to become less and less polar and therefore lose solubility.

27
Q

What is special about Carboxylic acids boiling points compared to Alkanes of a similar Mr?

A

Carboxylic acid boiling points are much higher than alkanes of a similar Mr.
Since carboxylic acids can form hydrogen bonds therefore increase their boiling point compared to easily overcome van der waals forces of attraction.

28
Q

What can be formed form carboxylic acid molecules in a pure carboxylic acid?

A

May form Dimers (2 monomers joined together by a hydrogen bond)

29
Q

What is the test for a Carboxylic acid?

A

Add sodium carbonate solution.

The carboxylic acid is present if effervescence occurs with sodium carbonate.

30
Q

Describe the reaction equation between magnesium and ethanoic acid.

A

Mg + 2CH3COOH —(H2O)—> (CH3COO-)Mg^2+ + H2

Until water is added, ethanoic acid is not dissociating easily. Adding H2O causes an equilibrium shift to the right and more product (magnesium ethanoate) is produced.

31
Q

How is an ester formed?

A

Alcohol + Carboxylic Acid Ester + Water

An acid catalyst is used in formation.

32
Q

Why is a base hydrolysis of an ester better than a metal and a carboxylic acid?

A

Base hydrolysises of esters are better as this will go further to completion since no equilibrium forms

33
Q

What is the structure of soap?

A

Sodium/Potassium salt of a fatty acid.
(Na+O-)-C(-R)=O
Hydrophilic ionic end (polar) and hydrophobic hydrocarbon end (non-polar)

34
Q

What is formed from the base hydrolysis of a triglyceride?

A

Heating with Sodium Hydroxide = A Hard Soap

Heating with Potassium Hydroxide = A soft soap

35
Q

What are the products of a base hydrolysis of triglyceride?

A

Soap

Glycerol (Propan-1,2,3-triol)

36
Q

What are the uses of Propan-1,2,3-triol?

A 
Solvent in food
Pharmaceutical applications
Attracts water
Prevents foods from drying out
Plasticiser in PVC and other plastics.
37
Q

How does Soap Work?

A
  • Soap interacts when in between oil and water.
  • Carboxylate ion end dissolves in water and hydrocarbon end dissolves in oil.
  • This stabilises the oil droplets as soap ions arrange themselves around each droplet of oil.
  • Each droplet is surrounded by a negative charge so droplets repel each other.
  • Hydrogen bonds form with water molecules so the oil droplets can be removed.
38
Q

How do you make biodiesel?

A

Methano l + vegetable oil —> Methyl Ester + Glycerol
Animal Fats (Biodiesel)
Waste oil

Similar to making soap -> makes methyl esters and not sodium salts.

39
Q

How does biodiesel form?

A

After the reaction between the triester/trigylceride
- 2 layers form.
Glycerol is denser than the methyl ester and therefore biodiesel forms a layer ontop of glycerol (propan-1,2,3-triol.

40
Q

Why do Methyl Esters not dissolve in gylcerol?

A

Methyl Esters could form hydrogen bonds with glycerol however the length of the R-gorups are too long (non-polar sections) so solubility is prevented.

41
Q

Define a nucleophile.

A

A species which is an electron pair donor (usually a negative ion and/or has a lone pair)

42
Q

Define an Electrophile

A

A species which is an electron pair acceptor (usually an electron deficient ion/molecule)
They attack areas of high electron density.

43
Q

What is an addition reaction?

A

Where you could chemically add one molecule into another molecule.
(1 molecule formed as a product of 2 molecule)

44
Q

What is an elimination Reaction?

A

Remove a molecule from another molecule to form 2 separate molecules.

45
Q

What is a substitution reaction?

A

Where one molecule is swapped/substituted for another molecule.

46
Q

What is an Acyl group?

A

R-C=0(-Z) where z can be anything.

47
Q

Give some examples of Acyl molecules.

A

Ester: RCOOR Ethyl Ethanoate
Acyl Chloride: RCOCl Ethanoyl Chloride
Acid Anhydride RCOOCOR Ethanoic Anhydride

They are all acid derivatives made from carboxylic acids.

48
Q

What is Acylation?

A

The process by which an acyl group is introduced into another molecule.

49
Q

What are the possible nucleophiles for an acylation reaction?

A

Water - Produce carboxylic acids
Alcohol - Produce esters
Ammonia - Produce amides
Amines - Produce N-substituted amides.

50
Q

What is the functional group of an Amide?

A

O=C-N-H

A-levels (23 decks)

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