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Chemistry exam questions > Organic chem 2 > Flashcards

Organic chem 2 Flashcards

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1
Q

Propane and butane have boiling points of -42.1°C and -0.5°C, respectively. Explain why propane has a lower boiling point than butane. (L.C)

A

Propane smaller with fewer electrons, therefore weaker intermolecular forces.

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2
Q

Name the homologous series to which propane and butane belong. Draw the structural formula of propane. (L.C)

A

Alkanes

CH₃CH₂CH₃ - DRAW!

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3
Q

Propane and butane have boiling points of -42.1°C and -0.5°C, respectively. Explain why propane has a lower boiling point than butane. (L.C)

A

Propane smaller with fewer electrons, therefore weaker intermolecular forces.

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4
Q

What is meant by saying that compounds are structural isomers? Draw the structural formula of the isomer of butane (L.C)

A

Structural isomers are molecules with the same molecular formula but different structural formulas.
- (CH₃)₂CHCH₃

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5
Q

Give the name or chemical formula of the solid X used in the preparation of ethene. What is the colour of this solid? (L.C)

A

Aluminium oxide

White

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6
Q

Write a balanced equation for the reaction involved in the preparation of ethene. What term describes this type of reaction. (L.C)

A

C₂H₅OH → C₂H₄ + H₂O

- Elimination

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7
Q

State four precautions that should be observed when carrying out the preparation of ethene by this method. (L.C)

A
  • Keep gas from flame
  • Safety glasses
  • Tie hair back
  • Air-tight stopper
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8
Q

Explain the term unsaturated (L.C)

A

Contains a multiple bond between two carbon atoms.

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9
Q

Give the name or formula of the solid Y used in the preparation of ethyne in the school laboratory. Describe the appearance of this solid. (L.C)

A

Calcium dicarbide

Black / grey

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10
Q

Describe a test you could carry out on a sample of either gas to show that it is unsaturated. What would you observe during the test? (L.C)

A

Test - Add bromine water until decolorises

Observe - Double carbon-to-carbon bond present

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11
Q

Give a major use of ethene. (L.C)

A

Manufacture of polythene

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12
Q

Give a major use of ethyne (L.C)

A

Cutting metals / welding metals

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13
Q

Both ethene and ethyne can be burned in air. What is most noticeable difference seen when these combustions are carried out in a school laboratory? (L.C)

A

Ethene less luminous/smoky

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14
Q

Write a balanced equation for the complete combustion of ethene. (L.C)

A

C₂H₄ + 3O₂ → 2CO₂ + 2H₂O

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15
Q

Write a balanced equation for complete combustion of ethyne. (L.C)

A

2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O

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16
Q

Dehydrocyclisation is one of the processes used to increase the octane numbers of hydrocarbons. What two changes to the hydrocarbon molecules occur during this process? (L.C)

A
  • Removal of hydrogen

- Ring formation

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17
Q

Ethanol is an example of an oxygenate. Give another example of an oxygenate. Give two reasons why oxygenates are added to petrol. (L.C)

A
  • Methanol
  • Raise octane number
  • Decrease knocking
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18
Q

Crude oil is separated into a number of fractions in oil refining. Name the two fractions which contain molecules with the carbon chain lengths needed for petrol. (L.C)

A
  • Light gasoline

- Naptha

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19
Q

What is meant by the octane number of a fuel? (L.C)

A

The measure of the tendency of fuel to resist auto-ignition.

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20
Q

The two hydrocarbons used as references when establishing the octane number of a fuel are heptane and 2,2,4 - trimethylpentane. Draw the structure of each of these molecules. (L.C)

A

Check answer in notes!

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21
Q

Give the name and formula of the solid A which is heated using the Bunsen Burner. (ethene prep) (L.C)

A

Aluminium oxide / Al₂O₃

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22
Q

Identify the solid B which is used to keep the ethanol at the end of the test tube. (ethene prep) (L.C)

A

Glass wool

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23
Q

What precautions should be observed when heating is stopped? Why is this necessary? (ethene prep) (L.C)

A

Remove the delivery tube from the trough of water and

disconnect tube from test tube to prevent suck-back.

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24
Q

Give one major use of ethene gas. (L.C)

A

Manufacture of polythene

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25
Q

In which fraction of crude oil do pentane and its isomers occur? (L.C)

A

Light gasoline

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26
Q

Naptha and gas oil are two of the hydrocarbon fractions obtained from the fractional distillation of crude oil. How do the molecules of the naptha fraction differ from the molecules of the gas oil fraction. (L.C)

A

Naptha have shorter chains and gas oil have longer chains

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27
Q

Bitumen is a residue fraction obtained from crude oil. Give one use for bitumen. (L.C)

A

Road surfacing / roofing

28
Q

What is catalytic cracking? What is its economic importance in oil refining? (L.C)

A

Cracking involves changing long chained hydrocarbons for which there is low demand, into short chained hydrocarbons for which there is high demand.

29
Q

What is the function of the glass wool? (prep ethene)(L.C)

A

Keeps ethanol at the end of test tube to avoid wetting the aluminium oxide.

30
Q

Identify the solid X and describe its appearance. (prep ethene) (L.C)

A

Aluminium oxide

White powder

31
Q

State and explain two safety precautions which should be observed when carrying out the student experiment (prep of ethene) (L.C)

A

Keep away from gas as gas is flammable

Air-tight stopper as it stops ethene escaping

32
Q

Write a balanced equation for the reaction involved in this preparation. (ethene) (L.C)

A

C₂H₅OH → C₂H₄ + H₂O

33
Q

Define the term unsaturated. (L.C)

A

Contains only single bonds around carbon atoms.

34
Q

Describe how you would carry out another test to confirm that ethene is unsaturated. (other than potassium manganate) (L.C)

A

Add bromine water

Red / orange / yellow → colourless

35
Q

Describe the flame that would be observed when a combustion test is carried out on a sample of ethene gas. (L.C)

A

Yellow / luminous / smoky sooty flame

36
Q

Write a balanced equation for the combustion of ethene in excess oxygen. (L.C)

A

C₂H₄ + 3O₂ → 2CO₂ + 2H₂O

37
Q

Identify the liquid x and the solid y (prep of ethyne gas) (L.C)

A 
X = water
Y = calcium dicarbide
38
Q

Describe the appearance of calcium dicarbide. (L.C)

A

Black / dark

39
Q

Write a balanced equation for the reaction between water and calcium dicarbide. (L.C

A

2C₂H₂ + 5O₂ → 2CO₂ + 2H₂O

40
Q

Butane is a major component of LPG. What do the letters LPG stand for? (L.C)

A

Liquefied petroleum gas

41
Q

Draw the two structural isomers of butane. (L.C)

A

IN NOTES!!

42
Q

Why are mercaptans added to natural gas? (L.C)

A

To give an odour to detect leaks

43
Q

What environmental change or effect is associated with the release of methane to the atmosphere? (L.C)

A

Greenhouse effect / global warming / reducing ozone damage

44
Q

Apart from leaking pipes, name a major source from which methane is released to the atmosphere? (L.C)

A

Fossil fuels / oil / coal

45
Q

What structural feature of 2,2,4-trimethylpentane results in it having a high octane rating? (L.C)

A

Branching / methyl branches

46
Q

Give a structural feature which increase the octane number of a hydro carbon other than branching. (L.C)

A

Ring

47
Q

Classify C₃H₆ as having one, two or three tetrahedrally bonded carbon atoms. (L.C)

A

One

48
Q

What is meant by octane number? (L.C)

A

The measure of the tendency of a fuel to resist auto-ignition.

49
Q

What is meant by the term structural isomer? (L.C)

A

Molecules with the same molecular formulas but different structural formulas.

50
Q

Give two features of alkanes that make them less prone to ‘knocking’. (L.C)

A
  • Short chained

- Highly branched

51
Q

What are mercaptans used for? (L.C)

A

Are used to alert to leakage as they have a strong smell (from the sulfur).

52
Q

Oxygenates are often added to petrol. Give an example of an oxygenate and explain why it is added to petrol. (L.C)

A

Addition of alcohol, to increase the octane number of the petrol and they cause less pollution as they reduce the level of carbon monoxide in the exhaust fumes.

53
Q

What lead compound used to be added to petrol? Explain why it was added to the petrol and give a reason why it is no longer added to petrol. (L.C)

A

Tetraethyl lead

  • Allowed the petrol to burn smoothly
  • Toxic, harmful to environment and people’s health.
54
Q

Petrol is obtained from crude oil in an oil refinery. Name the process used to obtain the petrol from crude oil.

A

Fractional distillation

55
Q

Explain the term catalytic cracking and briefly say why it is used? (L.C)

A

Involves changing long chained hydrocarbons for which there is low demand, into short chained hydrocarbons for which there is high demand.
- It is used to prevent auto-ignition (knocking)

56
Q

Name two features of the structure of alkanes that would make them less prone to knocking. (L.C)

A
  • Short chained

- Highly branched

57
Q

Give the name and structural formula of the substance found in petrol that is given an octane number of 100. (L.C)

A

2,2,4 trimethylpentane

C₈H₁₈ / (CH₃)2CHCH₂C(CH₃)₃

58
Q

Give a wide scale use of ethyne. (L.C)

A

Cutting and welding metals

59
Q

Describe what you would see if ethyne is burned. Write a balanced equation for this reaction. (L.C)

A

A smoky luminous flame

2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O

60
Q

Name the reagent you would use to show that ethyne is unsaturated and describe what you would observe when this reagent is applied to a sample of ethyne gas and shaken. (L.C)

A

Water (check)

61
Q

Draw diagrams to represent the structure of (i) benzene and (ii) methylbenzene. (L.C)

A

In notes!!

62
Q

What does aromatic compound mean? (L.C)

A

Aromatic - contains a benzene ring in the structure

Compound - A substance that is made up of two or more elements combined together chemically.

63
Q

Describe what you would expect to see if a test tube of ethyne is burned in air. (L.C)

A

Smoky luminous flame

64
Q

Define octane number. (L.C)

A

The octane number of a fuel is the measure of its tendency to resist ‘knocking’.

65
Q

Give an everyday use of ethyne. (L.C)

A

Cutting and welding metals

66
Q

Classify C₃H₇OH as having one, two or three tetrahedrally bonded carbon atoms. (L.C)

A

Three

67
Q

Classify CH₃COCH₃ as having one, two or three tetrahedrally bonded carbon atoms. (L.C)

A

Two

Chemistry exam questions (29 decks)

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