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Chemistry > A2 Chemistry Unit 4 Answers > Flashcards

A2 Chemistry Unit 4 Answers Flashcards

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0
Q

What are Ketones?

A

Ketones are carbonyl compounds where two different carbons are attached to the carbonyl group itself: CH3COCH3

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1
Q

What are Aldehydes?

A

Aldehydes are carbonyl compounds with at least one H attached to the carbonyl group itself: CH3CHO

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2
Q

What are carbonyl compounds?

A

Carbonyl groups consist of a carbon-oxygen double bond

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3
Q

Making Aldehydes from alcohols

A

Aldehydes can be formed from PRIMARY alcohols, but they must be distilled to avoid further oxidation into a carboxylic acid.

Aldehyde: CH3CH2OH + [O] -> CH3CHO + H2O

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4
Q

Making ketones from alcohols

A

Ketones can be formed from SECONDARY alcohols, and cannot go any further.

Ketone: CH3CHOHCH3 + [O] -> CH3COCH3 + H2O

The colour will go from orange to green when doing this reaction

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5
Q

[O]

A

K2Cr2O7

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6
Q

What alcohol would you use to make Hexanal?

A

Hexanol

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7
Q

What alcohol would you use to make C2H5CHO?

A

Propanol

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8
Q

What alcohol would you use to make

3-methylhexan-2-one

A

3-methylhexan-2-ol

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9
Q

What alcohol would you use to make C2H5COCH3?

A

Butan-2-ol

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10
Q

What alcohol would you use to make 3-methylpentanal?

A

3-methylpentanol

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11
Q

How to identify a carbonyl compound?

A

Strong peak at 1400-1600 on IR Spectrum
OR
Forms bright orange crystalline precipitate when reacted with 2,4-dinitrophenylhydrazine

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12
Q

How to find out whether your carbonyl is an aldehyde or a ketone?

A

Add Tollen’s Reagent - [Ag(NH3)2]+
Acts as an oxidising agent that will oxidise aldehydes but not ketones.
The Ag ion is reduced and forms silver precipitate in the test tube.
This is known as the silver mirror test.

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14
Q

How to work out which aldehyde or Ketone you have

A

React unknown with 2,4-dinitrophenylhydrazine.
Once purified the orange substance has a clear defined boiling point.
Compare to a database to find out which substance you have.

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15
Q

Delocalised electron

A

– Electrons that are shared between more than two atoms

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16
Q

Addition reaction

A

A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule

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17
Q

Substitution reaction –

A

A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms

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18
Q

Electrophile

A

An atom (or group of atoms) which is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond

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19
Q

Electrophilic substitution

A

A type of substitution reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond

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20
Q

Reaction mechanism

A

A series of steps that, together, make up the overall reaction

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21
Q

Curly arrow

A

A symbol used in reaction mechanisms to show the movement of an electron pair during the breaking or formation of a covalent bond

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22
Q

Functional group

A

The part of the organic molecule responsible for its chemical reactions

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23
Q

Electronegativity

A

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

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24
Q

Stem

A

The longest carbon chain present in an organic molecule

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25
Q

Suffix

A

The part of the name added after the stem

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26
Q

Redox reaction

A

A reaction in which both reduction and oxidation take place

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27
Q

Reflux

A

The continuous boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry

28
Q

Nucleophile

A
  • An atom (or group of atoms) which is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond
29
Q

Esterification

A

– The reaction of an alcohol with a carboxylic acid to produce an ester and water

30
Q

Hydrolysis

A

– A reaction with water or hydroxide ions that breaks a chemical compound into two compounds

31
Q

Zwitterion

A

– A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. As both charges are present there is no overall charge

32
Q

Peptide

A

– A compound containing amino acids linked by peptide bonds. Often the number of amino acids is indicated by the prefix, di-, tri-, tetra-:
dipeptide = 2 amino acids
tripeptide = 3 amino acids
tetrapeptide = 4 amino acids

33
Q

Condensation reaction

A

– A reaction in which two small molecules react together to form a larger molecule with the elimination of a small molecule such as water

34
Q

Hydrolysis

A
  • A reaction with water or hydroxide ions that breaks a chemical compound into two compounds
35
Q

Stereoisomers

A

– Species with the same structural formula but with a different arrangement of the atoms in space

36
Q

Chiral carbon

A

– A carbon atom attached to four different atoms or groups of atoms

37
Q

Optical isomers

A

– Stereoisomers that are non-superimposable mirror images of each other; also called ‘enantiomers’

38
Q

Repeat unit

A

– A specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside which is the symbol n

39
Q

Biodegragable polymer

A

– A polymer that breaks down completely into carbon dioxide and water

40
Q

Degradable polymer

A

– A polymer that breaks down into smaller fragments when exposed to light, heat or moisture

41
Q

Pharmacological activity

A

– The beneficial or adverse effects of a drug on living matter

42
Q

Phase

A

– A physically distinctive form of a substance, such as the solid, liquid and gaseous states of ordinary matter

43
Q

Mobile phase

A

– The phase that moves in chromatography

44
Q

Stationary phase

A

– The phase that does not move in chromatography

45
Q

Adsorption

A

– The process by which a solid holds molecules of a gas or liquid or solute as a thin film on the surface of a solid or, more rarely, a liquid

46
Q

Chromatogram

A

– A visible record showing the result of separation of the components of a mixture by chromatography

Rf = distance moved by component
distance moved by solvent front

47
Q

Retention time

A

– In gas chromatography, it is the time for a component to pass from the column inlet to the detector

48
Q

Chemical shift

A

A scale that compares the frequency of an NMR absorption with the frequency of the reference peak of TMS at δ = 0 ppm

49
Q

Describe how the delocalised electron system in benzene occurs

A

Each of the 6 carbons in benzene has an unpaired electron in a p-orbital.
The 6 p-orbitals overlap sideways (π bonding) to form the delocalised system.

50
Q

Why is the Kekule structure of benzene not the most accurate way of describing it?

A

A.
In benzene the C-C bonds are all the same length unlike normal double and single bonds.
Benzene is resistant to electrophilic attack unlike alkenes.
The enthalpy of hydrogenation of benzene is less exothermic than expected.

51
Q

Q.

Why is benzene more resistant to electrophilic attack than alkenes or phenol?

A

A.
Benzene has delocalised electrons.
Benzene has a low electron density.
Benzene cannot induce a dipole in structures.

Phenol has a lone pair of electrons in a p-orbital of the O in the OH group, that is delocalised into the ring.
Phenol has a higher electron density.
Phenol can induce a dipole in structures.

Alkenes have localised electrons (at C=C bond).
Alkenes have a high electron density.
Alkenes can induce a dipole in structures.

52
Q

Q.

How do you test for a carbonyl compound and to find out what type of carbonyl compound it is?

A

A.
Use 2,4-DNPH.
Carbonyl compounds form an orange precipitate.

Use Tollens reagent.
Aldehydes are oxidised to carboxylic acids and Ag+ ions are reduced to Ag, giving a silver mirror.
Ketones have no reaction with Tollens.

53
Q

Why do carboxylic acids have high boiling points and why are they soluble in water?

A

They contain -OH groups and can form hydrogen bonds between themselves and with water molecules. The more hydrogen bonds that can be formed, the more soluble things are.

54
Q

What is the systematic name of glycerol?

A

Propane-1,2,3-triol

55
Q

Why are trans fatty acids worse for our health?

A

There is a link between trans fatty acids, an increase in bad cholesterol and increased risk of coronary heart disease.

56
Q

Why could biodiesel be a good alternative fuel?

A

Both the alcohol (methanol/ethanol) and the triglycerides come from renewable resources.

57
Q

Describe what is meant by an α-amino acid?

A

A structure where an amine group and a carboxylic acid group are attached to the same carbon atom as a H atom and an R group.

58
Q

What is meant by isoelectric point?

A

It is the point at which a zwitterion exists.

59
Q

Why do scientists believe that condensation polymers are better for the environment than addition polymers?

A

Condensation polymers can hydrolyse or are degradable/biodegradable/photodegradable.
Polyesters hydrolyse at the C-O bond.
Polyamides hydrolyse at the C-N bond.
Photodegradable polymers break up as the C=O bond absorbs radiation.

60
Q

What are the disadvantages of pharmaceuticals containing a mixture of optical isomers?

A

They can have harmful side effects.
They have a reduced effectiveness (a larger dose is needed).
The isomers are expensive/difficult to separate.

61
Q

How can pharmaceuticals be made containing just one optical isomer?

A

Using :
Chiral synthesis/chiral catalysts
Enzymes or bacteria
Natural chiral starting reagents/molecules

62
Q

How are components of a mixture separated in TLC (or other examples where solid stationary phases are used)?

A

By relative adsorption. The stronger they adsorb, the smaller the Rf value.

63
Q

How are components of a mixture separated in GC (or other examples where liquid stationary phases are used)?

A

By relative solubility. The more soluble they are, the longer the retention time.

64
Q

Q.

What are the limitations of chromatography techniques?

A

Similar compounds have similar retention times/Rf values.

Unknown compounds have no reference retention time/Rf value for comparison.

65
Q

How can GC-MS analyse a mixture?

A

GC separates the mixture into components.

MS analyses components and compares mass spectra to known examples in a database.

Chemistry (4 decks)

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