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Chemistry OCR A Level > Module 4.2 > Flashcards

Module 4.2 Flashcards

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1
Q

Give an overview of alcohols

A
  • Aliphatic

- General formula = CnH2n+1OH

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2
Q

Describe the polarity of alcohols

A

The electronegative oxygen from the OH (of the alcohol) draws electron density from hydrogen making it slightly positive (delta-positive). This slightly positive hydrogen can attract the lone pair of an oxygen from a neighbouring molecule (such as water) forming hydrogen bonds with it.

Therefore, alcohols are polar.

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3
Q

What bonds to alcohols form with water? (and between what atoms)

A

Alcohols can form hydrogen bonds with water.

Between H( (H must have a delta positive charge on it) and O (O must have a delta negative charge on it and a lone pair)

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4
Q

Explain in terms of hydrogen bonding, the solubility of alcohols compared with alkenes

A
  • When you mix an alcohol, with water, hydrogen bonds are formed.

If it’s a small alcohol, hydrogen bonding lets it mix freely with water. Therefore, small alcohols are soluble in water.

However, in larger alcohols, most of the molecule is NON-POLAR. So there is less attraction for the polar water molecules. This means that as alcohols increase in size, their solubility decreases.

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5
Q

Explain in terms of hydrogen bonding, the relatively low volatility of alcohols compared with alkenes

A

Alcohols have a relatively low volatility because the hydrogen bonds require so much energy to break.

Another saying for this is : Alcohols don’t evaporate easily to gas because the H bonds require so much energy to overcome.

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6
Q

What are the 3 types of alcohol?

A

Primary
Secondary
Tertiary

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7
Q

Define a primary alcohol

A

An organic compound, with an OH group, in which the OH group is at the end of a carbon chain.

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8
Q

Define a secondary alcohol

A

An organic compound, with an OH group, in which the OH group is attached to a carbon atom that is attached to 1 hydrogen

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9
Q

Define a tertiary alcohol

A

An organic compound, with an OH group, in which the OH group is attached to a carbon atom which is attached to no hydrogen groups

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10
Q

Give examples of a primary alcohols

A 
Ethanol
Butanol
Hexanol
Propan-1-ol
Pentan-1-ol
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11
Q

Give examples of secondary alcohols

A

Propan-2-ol
Butan-2-ol
Hexan-2-ol
Pentan-2-ol

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12
Q

Give examples of tertiary alcohols

A

2-methylpropan-2-ol
2-methylbutan-2-ol
3-methylpentan-3-ol

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13
Q

What are the products in the complete combustion of an alcohol?

A

Carbon Dioxide and Water

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14
Q

How do you balance the reaction between an alcohol and oxygen?

A
  • First balance the hydrogen
  • Then balance the carbon
  • Lastly balance the oxygens
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15
Q

What does the sign [O] represent?

A

An oxidising agent

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16
Q

Describe the oxidation of primary alcohols to form aldehydes (Give the reagents, conditions, the observation, a generic equation and an example equation)

A 
Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4
Conditions = Distillation
Generic = R-CH2-OH + [O] → R-CHO + H2O
Example = CH3CH2OH + [O] → CH3CHO + H2O 
Colour change - Orange to Green
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17
Q

Describe the oxidation of primary alcohols to form carboxylic acids(Give the reagents, conditions, the observation, a generic equation and an example equation)

A

Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4
Conditions = Reflux
Generic = R-CH2-OH + 2[O] → R-COOH + H2O
Example = CH3CH2OH + 2[O] → CH3COOH + H2O
Colour change - Orange to Green

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18
Q

State the functional group and location of aldehydes

A

CHO Functional Group

Location = End of the chain

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19
Q

What do aldehydes end in?

A

-al

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20
Q

State the functional group and location of carboxylic acids

A

COOH Functional Group

Location = At the end of the chain

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21
Q

What do carboxylic acids end?

A
  • oic acid
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22
Q

Describe the oxidation of secondary alcohols to form ketones

Give the reagents, conditions, the observation, a generic equation and an example equation

A

Regeants - Oxidising agent (Acidified Potassium Dichromate) = K2Cr2O7/H2SO4
Conditions = Reflux
Generic = R-CH(OH)-CH3 + [O] →R-C(O)-CH3 + H2O
Example = CH3CH2CH3 + [O] → CH3COCH3 + H2O
Colour change - Orange to Green

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23
Q

Describe the resistance of oxidation of tertiary alcohols

A

Tertiary alcohols cannot be oxidised using an oxidation agent such as acidified potassium dichromate because in order for oxidation to occur, the -OH must be attached to a carbon that has at least ONE hydrogen attached to it. For tertiary alcohols, this is not the case

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24
Q

Describe the dehydration of water from alcohols to form alkenes
(Give the reagents and conditions)

A

Reaction name = Dehydration
Regeants = CONC sulphuric acid OR CONC phosphoric acid
Conditions = Reflux, 180 degrees celsius
Products = Alkene + Water

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25
Q

Describe the substitution of nucleophiles to go from a haloalkane to a alcohol

A

Reaction name = Nucleophilic Substitution of haloalkanes
Regeants = Halide ions (from HX)
Conditions = CONC sulphuric acid OR CONC phosphoric acid and ROOM Temperature

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26
Q

Describe the hydrolysis of haloalkanes in a substitution reaction by aqueous alkali

A 
Reaction name - Nucleophilic sub
Conditions = Reflux (heat) in aq solution
Regeant = NaOH 
Nucleophile used = OH- ion (from NaOH)
Product = Alcohol + X-
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27
Q

How can we experimentally compare the rates of hydrolysis of different C-X bonds in terms of precipitation formation?

A

React the different C-X bonds (C-F,C-Cl,C-Br and C-I) with silver nitrate and ethanol to see how fast each precipitate forms.

The faster the precipitate forms, the faster the rate of hydrolysis

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28
Q

What C-X bond forms a precipitate the quickest? What does this us about the rate of reaction

A

The C-I (Iodine bond) bond takes the least amount of time to for a ppt. This means that it has the fastest rate of reaction.

Iodine the fastest rate of reaction

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29
Q

What colour is the precipitate formed by Chlorine?

A

White

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30
Q

What colour is the precipitate formed by Bromine?

A

Cream

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31
Q

What colour is the precipitate formed by Iodine?

A

Yellow

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32
Q

How can we experimentally compare the rates of hydrolysis of different C-X bonds in terms of bond enthalpy?

A

How quickly different haloalkanes are hydrolysed depends on bond enthalpy.
Weaker C-X bonds break more easily so they react faster, (Weakest C-X bond is C-I) meaning that Iodine is the most reactive element of group 7
Stronger C-X bonds break less easily so they react slower, (strongest C-X bond is C-F) meaning that Fluorine, is the less reactive element of group 7

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33
Q

In terms of bond enthalpy, which C-X bond gives the slowest rate of hydrolysis?

A

C-F (Fluorine bond) this is because it has the highest bond enthalpy. it will break last meaning that it has the slowest rate of hydrolysis

34
Q

In terms of bond enthalpy, which C-X bond gives the fastest rate of hydrolysis?

A

C-I (Iodine bond) this is because it has the smallest bond enthalpy, it will break first meaning that it has the fastest rate of hydrolysis

35
Q

Define the term nucleophile

A

An electron pair DONOR

36
Q

Give 4 examples of a nucleophile

A

Hydroxide ion, Cyanide ion, Ammonia and Water

37
Q

Describe the mechanism of nucleophilic substitution of primary haloalkanes

A

The nucleophile uses it lone pair to provide the electrons for a new bond. Simultaneously, the most electronegative element in that bond, takes the electrons from the C-X bond. The halogen becomes displaced and results in a direct attack by a nucleophile.

38
Q

What is a CFC?

A

A Chloroflurocarbon (type of hydrocarbon where, a carbon atom is bonded to both a Cl atom and an F atom)

39
Q

Why are CFCs still in use today?

A

They are:

  • Very stable
  • Volatile (low boiling point)
  • Non - flammable
  • Non - toxic
  • Inert (unreactive)
40
Q

Why is the ozone layer good?

A

It absorbs a lot of harmful radiation (UV radiation).

UV radiation can lead to sunburn and skin cancer. Ozone reduces the levels of these events occurring

41
Q

Why is the ozone layer depleting?

A

The ozone layer is depleting because CFCs in the upper atmosphere absorb UV radiation and split to form CHLORINE FREE RADICALS. These free radicals catalyse the destruction of ozone. This is because they destroy ozone molecules and then are regenerated destroying even more ozone.

42
Q

Give the mechanism for the free radical substitution using CF2Cl2 (Show Initiation and Propagation)

A

Initiation:
CF2Cl2→ CF2Cl• + Cl•

Propagation
Cl• + O3 → ClO• + O2
ClO• + O → Cl• + O2

Overall

O3 + O → 2O2

43
Q

What other compounds can deplete ozone?

A

Nitrogen Dioxide (NO2)

44
Q

Give the mechanism for the free radical substitution using NO2

A

NO• + O3 →•NO2 + O2
•NO2 + O → •NO + O2

Overall
O3 + O → 2O2

45
Q

What is reflux?

A

A technique that makes sure you don’t lose any volatile organic substances

46
Q

What does reflux do, and how does it do it?

A

It ensures that the reaction does not boil away as it prevents the evaporation of regeants.

The mixture is heated in a flask filled with a vertical condenser. This continously boils, evapourates and condenses the vapours and recycles the back into the flask, giving them time to react

47
Q

What is distillation?

A

A technique that separate substances with different boiling points

48
Q

What does distillation do, and how does it do it?

A

Distillation separates substances in terms of increasing boiling point.

We gently heat a mixture of substances. These substance will evaporate out in order or increasing boiling point.

49
Q

What is redistllation?

A

A technique used to purify volatile liquids.

Redistillation is just distillation again but instead of using a reaction mixture, this time we are using an impure product

50
Q

What is separation?

A

A technique used to remove any water soluble impurities

51
Q

How does separation work?

A

Pour the mixture into a separation funnel and wadd water

  • Shake and allow to settle
  • Open the stopper on the separating funnel
  • Run off the aq layer and collect products
  • Dry with a drying agent such as CaCl2 or MgSO4
52
Q

What is the functional group of alcohols?

A

-OH

53
Q

What is the functional group of alkanes?

A

-C-C

54
Q

What is the functional group of alkenes?

A

-C=C

55
Q

What is the functional group of haloalkanes?

A

-C-X

56
Q

What is the functional group of amines?

A

-C-NH2

57
Q

What is the functional group of nitriles?

A

-C-C≡N

58
Q

What is the functional group of carbonyls?

A

-C=O

59
Q

What is the functional group of carboxylic acid?

A

-COOH

60
Q

What is the functional group of esters?

A

-COO

61
Q

What is the functional group of acyl chlorides?

A

-COCl

62
Q

What is the functional group of acid anhydrides?

A

-ROOCOR’

63
Q

What does Infrared radiation cause covalent bonds to do?

A

Vibrate and absorb energy

64
Q

Describe the link between absorption of IR by atmospheric gases containing C=O, O-H and C-H bonds and global warming

A

Gases in the atmosphere that contain C=O, C-H or O-H bonds are able to absorb IR and re-emit it in all directions including back to Earth, keeping the Earth warm.

65
Q

What had the government done to address greenhouse gases and the issue of climate change?

A
  • Kyoto Protocol

- Subsidise renewable energy suppliers such as wind and solar farms

66
Q

To make interpretation of an IR spectra, what 3 things must you do?

A
  • Look at the location wavelength and range of the wavelength
  • Look at the type of peak (Broad, Sharp etc)
  • Allocate certain bonds to certain peaks using the data sheet provided in exams
67
Q

Describe the use of Infrared Spectroscopy to monitor gases causing air pollution and in modern day breathalysers to measure ethanol in breath

A

Infrared spectroscopy is used breathalysers to work out if a driver is over the drink-drive limit.

Infrared spectroscopy is also used to monitor the concentration of polluting gases in the atmosphere. These include CO and NO, which are both present in our emissions.

68
Q

What can Infrared spectroscopy be used for?

A

To measure the level of ethanol in breath (breathalysers)

To monitor the level of gases causing air pollution

69
Q

To find the relative molecular mass of a compound, you look at the?

A

Molecular ion peak

70
Q

Molecular ion peak value = ?

A

The relative molecular mass of a compound

71
Q

What type of molecules show up on mass spectrums?

A

ONLY IONS

72
Q

What can use to find specific parts of a compound, when given the Mz value?

A

Fragmentation patterns

73
Q

What common fragment has a Mr of 15?

A

CH3+

74
Q

What common fragment has a Mr of 29?

A

C2H5+

75
Q

What common fragment has a Mr of 17?

A

OH+

76
Q

What common fragment(s) has a Mr of 43?

A

CH3CH2CH2+ or CH3CHCH3+

77
Q

When breaking down a compound to find its fragment what do we produce?

A

A radical and a positive ion (the fragment)

We only care about the positive ion

78
Q

Finish of the fragmentation reaction in which CH3+ is produced

A

CH3CH2CH3 → CH3CH2• + CH3+

79
Q

How can you master mass spectroscopy?

A
  • Identify potential fragments (must be positive ions)
  • Piece them together to form a molecule with the correct Mr
  • If given, find the empirical and molecular formula
  • Find the Mr of the graph
  • If given use IR spectra to help you
  • Triple check
80
Q

In an exam, when asked to give the structure of a compound given IR spectra, Mass spectra and the empirical/molecular formula, what do you do?

A

1) Use the composition to work out the molecular formula of the compound
2) Work out what functional groups are in the compound from its infrared spectrum
3) Use the mass spectrum to work out the structure of the molecule

Chemistry OCR A Level (15 decks)

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