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Chemistry > S4 Organic Chemistry > Flashcards

S4 Organic Chemistry Flashcards

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1
Q

What is petroleum?

A

It is a mixture of hydrocarbons of different boiling points. It is separated into useful fractions by fractional distillation.

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2
Q

How does fractional distillation of petroleum take place? (4)

A

1) heat to vaporise crude oil. Hot vapour rises up the fractionating column
2) crude oil is heated into vapor and separated into different fractions due to their boiling points. They condense at different temperatures
3) hydrocarbons with short carbon chains and lower boiling points condense and escape from the top of the fractionating column
4) hydrocarbons with long carbon chains and higher boiling points condense and are collected at the bottom of the fractionating column.

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3
Q

What are the products of separation of petroleum and what are their functions?(6)

A

1) petrol (gasoline) as fuel for cars
2) naphtha as feedstock (raw material) for chemical industry
3) paraffin(kerosene) as fuel for heating and cooking and aircraft engines
4) diesel as furl for diesel engines
5) lubricating oils as lubricants and making polishes and waxes
6) bitumen for making road surfacesp

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4
Q

What is a homologous series?

A

It is a group of compounds with the same general formula,(specify formula). Its successive members differ by a -CH2- unit. They have similar chemical properties and shows a graduation in physical properties: a result of increase in size and mass of molecules

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5
Q

How are organic compounds named by prefix? (1-6)?

A 
1 Carbon atom: Meth-
2 Carbon atoms: Eth-
3 Carbon atoms: Prop-
4 Carbon atoms: But-
5 Carbon atoms: Pent-
6 Carbon atoms: Hex-
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6
Q

What is the function group of alkanes?

A

It does not have a function group.

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7
Q

What are alkanes?

A

They are a homologous series of saturated hydrocarbons, with the general formula of CnH2n+2, where n=no. of carbon atoms in 1 molecule. They are saturated as they contain only carbon-carbon single covalent bonds.

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8
Q

What are isomers?

A

Isomers are molecules with the same molecular formula but different structural formula (画出来的). Isomers of the same compound have similar chemical properties (if from same homologous series) but different physical properties. They need not be from the same homologous series.

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9
Q

What are 4 physical properties of alkanes?

A

1) melting and boiling point increases with increasing number of carbon atoms due to stronger intermolecular van der Waals’ forces of attraction, more energy is needed to overcome the attraction
2) viscosity (resistance to flow) increases as molecular size increases(move down homologous series)
3) flammability decreases with increasing carbon chain
4) insoluble in water, soluble in organic solvent

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10
Q

What happens when we move down the homologous series? (3)

A

1) increasing number carbon atom
2) increasing molecular size
3) increasing carbon chain

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11
Q

What are chemical properties of alkanes?(3)

A

1) generally unreactive as they are saturated with Single C-C and C-H bonds
2) combustion of alkanes
3) substitution reactions with halogen

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12
Q

What are 2 possible outcomes of combustion of alkanes/alkenes?

A

1) complete combustion with sufficient oxygen produces carbon dioxide and water
2) incomplete combustion when there is insufficient oxygen produces carbon monoxide and water/soot (unborn carbon) and water

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13
Q

What is substitution reaction with halogens?

A

In the presence of ultraviolet light, hydrogen atoms in the alkane are replaced by halogen atoms one at a time, forming hydrogen chloride as a by-product.

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14
Q

What are 2 examples of substitution reaction with halogens?

A

1) substitution of methane in excess chlorine gives rise to monochloromethane (CH3Cl), dichloromethane (CH2Cl2), trichloromethane (CHCl3) and tetrachloromethane (CCl4), and byproduct hydrogen chloride
2) substitution in limited chlorine gives rise to monochloromethane (CH3Cl) and hydrogen chloride only

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15
Q

Define alkenes.

A

Alkenes are a homologous series of unsaturated hydrocarbons with the general formula, CnH2n, when n=number of carbon atoms in one molecule

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16
Q

What is the function group of alkene?

A

Carbon-carbon double bond

C=C

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17
Q

How can alkenes be manufactured?

A

Catalytic cracking of crude oil/hydrocarbons. It is a process large long-chain alkane molecule is broken up into small molecules, with the conditions of 600 degrees celsius, pressure and catalysts Al2O3 or SiO2. Sometimes a porous pot is used as it contains both catalysts. Alkenes and hydrogen gas is produced.

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18
Q

Why is cracking essential?(3)

A

1) it is used to produce petrol, which is in great demand
2) it produces short-chain alkenes which are used as starting materials to form ethanol and plastic
3) it produces hydrogen as a byproduct

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19
Q

What are saturated hydrocarbons?

A

They are hydrocarbons with carbon-carbon single bonds

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20
Q

What are unsaturated hydrocarbons?

A

they are hydrocarbons with carbon-carbon (double/triple bond).

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21
Q

How can saturated be tested?

A

Reddish brown aqueous bromine turns colourless when added to unsaturated compounds.

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22
Q

What are 2 chemical properties of alkenes?

A

1) combustion of alkenes

2) addition reaction of alkene (hydrogenation, hydration, bromination, addition polymerisation)

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23
Q

What is hydrogenation? List 1 example.

A

It is reacting an alkene with hydrogen gas to form an alkane. It requires Nickel or platinum as catalyst, and 200C of temperature. One example product is margarine(alkane), which is made by reacting vegetable oils with hydrogen.

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24
Q

What is hydration? List 1 example.

A

It is reacting alkene with steam to form an alcohol. It requires phosphoric (V) acid (H3PO4) as catalyst, 300C temperature, and 60 atm pressure. One example is to manufacture ethanol from ethene.

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25
Q

What is bromination? List 1 example use.

A

It is to react alkenes with aqueous bromine (Br2) or any halogen to form alkyl halide, an alkane with halogen atoms. One example is to test for presence of unsaturated hydrocarbon

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26
Q

What is addition polymerisation? List 1 example use.

A

Large number of identical or similar monomers (with unsaturated double or triple bonds) join together to form a long chain molecule without losing any atoms or molecules. Catalyst is required at 200C temperature and 1000atm pressure. Its product is poly(name of alkene). One example use is to make plastic.

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27
Q

How do alkenes react?

A

They react by breaking the C=C bond or add atoms across the double bond.

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28
Q

What is polyunsaturated?

A

It means the presence of more than 1 carbon-carbon double bond/triple bond.

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29
Q

What are the uses of petroleum?(2)

A

1) main sources of energy

2) used as chemical feedstock (from naphtha)

30
Q

What are 3 problems relating to using petroleum?

A

1) it is non renewable and finite
2) it can cause pollution and global warming
3) it needs conservation as the supply of petroleum is decreasing rapidly

31
Q

How can we conserve petroleum?(3)

A

1) reduce number of motor vehicles the road; drive cars that consume less petrol and take public transport
2) using alternative energy sources like solar and nuclear energy
3) power stations can be better designed to use petroleum more efficiently

32
Q

What is the general equation for combustion of any hydrocarbon?

A

Hydrocarbon + oxygen -> carbon dioxide, water, heat energy

33
Q

define alcohols.

A

Alcohols are an homologous series containing the hydroxyl (-OH) functional group. Their general formula is CnH2n+1OH.

34
Q

What are 2 physical properties of alcohols.

A

1) boiling point of alcohol are higher alkanes of similar size&mass. Boiling point increases as molecular size increases as more energy is needed to overcome strong van der Waals’ forces of attraction between molecules.
2) they are soluble in both water and organic solvents. Solubility of water decreases as length of hydrocarbon chain increases

35
Q

What are 4 chemical properties of alcohols?

A

1) neutral although it contains -OH Group
2) combustion
3) oxidation
4) dehydration

36
Q

How does combustion of alcohol take place?

A

An alcohol burns in air to produced carbon dioxide, water vapour, and a clean flame.

37
Q

How is combustion of alcohols useful? (3)

A

1) it is a clean fuel with little pollutant
2) less likely than conventional fuels to explode in an accident as its first 4 members of the series are liquid, which has lesser surface area than gas
3) when alcoholic beverage is burnt with food, it gives a distinct flavour.

38
Q

What is oxidation in alcohol?

A

Alcohols are oxidised to form water and corresponding carboxylic acids, where the number of carbon atoms remain the same

39
Q

How does oxidation in alcohol take place? What are the 2 results?

A

Warm with acidified KMnO4 (aq)/ acidified K2Cr2O7/oxygen with bacteria (2[O]).

1) purple acidified KMnO4 turns colorless
2) orange acidified K2Cr2O7 turns green

40
Q

How is oxidation of alcohol useful?(1)

A

The police uses a breathalyser to test the amount of alcohol consumed by drivers. It contains K2Cr2O7 that changes from orange to green if a certain amount of alcohol is present in the breath.

41
Q

What is dehydration of alcohol?

A

Alcohols lose water to give alkenes with the dehydrating agent H2SO4.

42
Q

How can alcohols be manufactured? (2)

A

1) catalytic addition/hydration of alkene

2) fermentation

43
Q

Define fermentation.

A

It is a chemical process in which microorganisms such as yeast act on carbohydrates to produce ethanol and carbon dioxide. Yeast contains enzymes which breakdown glucose to form ethanol and carbon dioxide.

44
Q

What are 2 conditions of fermentation of alcohol?

A

1) 37C as enzymes will denature and stop fermentation if beyond it
2) absence of oxygen for yeast’s anaerobic respiration

45
Q

Describe the lab apparatus for fermentation of ethanol. (2)

A

1) A glucose (any carbohydrate) solution is mixed with yeast and kept at 37C in a conical flask.
2) it is connect to a testube of limewater. The limewater prevents air from entering the apparatus, while the rubber bung connected is secured tightly to the flask, ensuring an air-tight environment for anaerobic respiration.

46
Q

Since fermentation can only yield a maximum of 18-20% ethanol, what happens to the set up?

A

The yeast cells will die beyond the concentration and stop fermentation. Dilute ethanol solution has to be separated from the mixture to obtain alcohol and allow fermentation to continue.

47
Q

What happens if ethanol is exposed to air? Include an equation.

A

It turns sour after a few days as bacteria in the air oxidizes ethanol to form ethanoic acid.

C2H5OH + 2[O] -> CH3COOH + H2O

48
Q

What are 3 uses of ethanol/alcohol?

A

1) in alcoholic drinks
2) as a solvent. It is a good solvent that dissolves many substances that are not soluble in water, and is often used in plants.
3) as a fuel. It is a main constituent of methylated spirit, which is used in spirit lamps and burners for cooking.

49
Q

Define carboxylic acids.

A

They are a saturated homologous series containing the functional group carboxyl (-COOH). They have a general formula of CnH2n+1COOH, where n begins with 0.

50
Q

What are 2 acidic properties of carboxylic acids?

A

1) weak acids that dissociate partially in water to give low concentration of hydrogen ions
2) behave like acids in chemical reactions and can react with reactive metals, metal carbonates, bases (metal replaces H in COOH)

51
Q

What are 2 physical properties of carboxylic acids?

A

1) soluble in water because of carboxyl group

2) relatively high melting and boiling points - liquid at room temperature

52
Q

What are carboxylic acid formed salt compounds named?

A

Prefix-noate

Eg ethanoate

53
Q

What is a use of carboxylic acid?

A

It can used to test for identity as alcohol. Alcohol are oxidised to form respective carboxylic acids when heated with oxidising agent, acidified KMnO4 (aq).

54
Q

What are esters?

A

Esters are compounds formed when a carboxylic acid reacts with an alcohol. this reaction is known as esterification.

55
Q

What is the functional group of esters?

A

Ester linkage

56
Q

How are esters prepared?

A

Conditions: heating under reflux with concentrated sulfuric acid as catalyst
Reagents: carboxylic acid and alcohol
Condensation reaction of carboxylic acid and alcohol to form ester and water. Bond breaks at -/-O-H of acid and at O-/-H of ethanol

57
Q

How are esters named?

A

first part: the alcohol used to prepare ester, eg ethyl

second part: carboxylic acid used to prepare ester, eg ethanoate

58
Q

State two uses of esters.

A

1) Solvents for cosmetics and glues.

2) it has a sweet fruity smell, which is used in preparation of perfumes and artificial food flavourings.

59
Q

Define macromolecules/polymers.

A

It is any long chain molecule that contains a large number of monomers joined together by covalent bonds through polymerisation.

60
Q

What are 2 types of reactions to form polymers?

A

1) addition polymerisation

2) condensation polymerisation

61
Q

What is additional polymerisation?

A

It is when unsaturated monomer units join together without losing any molecules or atoms. The empirical formula of the monomer and the polymer is the same. (Can be different monomers)

62
Q

What are 3 conditions required for additional polymerisation?

A

1) high pressure (1000atm)
2) high temperature (200C)
3) catalyst

63
Q

How is poly(ethene) formed?

A

At high temperature and pressure, and the presence of a catalyst, the Carbon-carbon double bond of the alkene monomers break. Each monomer forms single bonds with 2 other monomers. Eventually, they join to form poly(ethene).

64
Q

Give 3 examples of addition polymers.

A

1) Poly(ethene). It is used to make plastic bags and clingfilm. It is flexible but difficult to break.
2) polystyrene. Hard, light and brittle, it is used to make disposable containers
3) perspex is used to make car windowscreens. It is transparent and less easy to break than glass.

65
Q

What are 2 properties/uses of addition polymers?

A

1) good insulators of heat and electricity

2) resistant to chemical attack

66
Q

What is condensation polymerisation?

A

Monomers with 2 reactive functional groups (same or different) join together to form a polymer with the loss of small molecules such as water or hydrogen chloride.

67
Q

What are 2 types of condensation polymers? What are their linkage structures?

A

1) polyamide - amide linkage(O=C-O)

2) polyesters - ester linkage (H-N-C=O)

68
Q

Give an example of a polyamide.

A

Made from condensing dicarboxylic acid and diamine, it produces water as a byproduct.

69
Q

Give an example of a polyester.

A

Made from condensation polymerisation, it is made from benzene-1, 4-dicarboxylic acid, etahne-1,2-diol. It produces water as a byproduct.

70
Q

What are synthetic or man-made fibres?

A

They are plastics spun into threads, such ad curtains, parachutes and fishing lines. Clothes made from these fibres are shrink-proof and crease-proof.

71
Q

What are the advantages of using plastic?(4)

A

1) relatively cheap
2) easily moulded into various shapes
3) light, tough, waterproof
4) durable (non-biodegradable)

72
Q

What are 3 disadvantages of using plastic?

A

1) flammable
2) since modern buildings are insulated and furnished with plastic materials, when plastic burn, fire can spread quickly and produce poisonous gas
3) plastics are non-biodegradable. It cannot be decomposed by micro-organisms. It hence requires landfill sites which takes up land space, and also causes land pollution.

Chemistry (19 decks)

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