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Chemistry > TOPIC 7 - HYDROCARBONS > Flashcards

TOPIC 7 - HYDROCARBONS Flashcards

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1
Q

What is a hydrocarbon?

A

A hydrogen is a compound that is formed from carbon and hydrogen atoms only.

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2
Q

What are alkanes?

A

Alkanes all have C-C single bonds. They are the simplest type of hydrocarbons you can get.

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3
Q

What is the general formula for alkanes?

A

Cn H2n+2

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4
Q

Why are alkanes saturated?

A

Alkanes are saturated because each carbon atom forms four single covalent bonds.

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5
Q

What are the first four alkanes?

A

Methane
Ethene
Propane
Butane

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6
Q

What properties do hydrocarbons with short chains have?

A 
Less viscous (more runny)
More volatile (lower boiling points)
The more flammable
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7
Q

What is the equation for the complete combustion of hydrocarbons?

A

hydrocarbon + oxygen = carbon dioxide + water (+energy).

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8
Q

Why are hydrocarbons used as fuels?

A

They release a high amount of energy when they combust completely.
Both the carbon and the hydrogen are oxidised.

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9
Q

What is crude oil?

A

A fossil fuel. It is formed from the remains of plants and animals, mainly plankton, that died millions of years ago and were buried in mud. Over millions of years, with high temperature and pressure, the remains turned to crude oil, which can be drilled up from rocks where it is found.

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10
Q

What technique is used to separate hydrocarbon fractions?

A

Fractional Distillation.

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11
Q

How does fractional distillation work?

A

The oil is heated until most of it has turned into gas. The gases enter a fractionating column (and the liquid bit is drained off).
In the column there is a temperature gradient (hot at the bottom and gets cooler as you go up).
The longer hydrocarbons have high boiling points. They condense back into liquids and drain out of the column early on, when they are near the bottom. The shorter hydrocarbons have lower boiling points. They condense and drain out much later on, near the top of the column where it is cooler.
You end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points.

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12
Q

What are organic compounds?

A

Compounds containing carbon atoms.

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13
Q

What is cracking?

A

Splitting up long chain hydrocarbons. Cracking produces alkenes.
Some of the products of cracking are used as fuels eg petrol for cars.

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14
Q

What are alkenes used for?

A

Alkenes are used as a starting material when making lots of other compounds and can be used to make polymers.

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15
Q

What type of reaction is cracking?

A

A thermal decomposition reaction - breaking molecules down by heating them.

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16
Q

How does thermal decomposition break molecules down?

A

The long-chain hydrocarbons are heated to vaporise them.
Then the vapour is passed over a hot powered aluminium oxide catalyst.
The long chain molecules split apart on the surface of the specks of catalyst - this is catalytic cracking.

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17
Q

What is catalytic cracking?

A

The long-chain hydrocarbons split apart on the surface of the specks of catalyst - this is called catalytic cracking.

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18
Q

What is steam cracking?

A

You can crack hydrocarbons if you vaporise them, mix them with steam and then heat them to a very high temperature. This is known as steam cracking.

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19
Q

Give an example of a chemical equation for cracking?

A

decane —> octane + ethene

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20
Q

What does cracking produce?

A

Alkenes.

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21
Q

What are alkenes?

A

Hydrocarbons which have a double bond between two of the carbon atoms in their chain. The double nond means they have two fewer hydrogens compared to alkanes containing the same number of carbon atoms. This makes them unsaturated.

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22
Q

Why are alkenes more reactive than alkanes?

A

Their double bond can open up to make a single bond, allowing the two carbon atoms to bond with other atoms - this makes the alkenes reactive.

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23
Q

What is the general formula for alkenes?

A

CnH2n

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24
Q

What are the first four alkenes?

A

Ethene
Propene
Butene
Pentene.

25
Q

How do alkenes burn?

A

With a smoky yellow flame. This is because they tend to undergo incomplete combustion. This means you can get carbon and carbon monoxide, which is a poisonous gas.

26
Q

What is the equation for the incomplete combustion of alkenes?

A

alkene + oxygen —> carbon + carbon monoxide + carbon dioxide + water (+energy).

27
Q

What is a functional group?

A

A functional group is a group of atoms in a molecule that determine how that molecule typically reacts.

28
Q

How do alkenes most commonly react?

A

Most of the time, alkenes react via addition reactions. The carbon=carbon bond will open up to leave a single bond and a new atom is added to each carbon.

29
Q

What is hydrogenation?

A

Addition of hydrogen is known as hydrogenation.
Hydrogen can react with the double-bonded carbons to open up the double bond and form the equivilent, saturated, alkane.

The alkene is reacted with hydrogen in the presence of a catalyst.

30
Q

How does steam react with alkenes to form alcohols?

A

When alkenes react with steam, water is added across the double bond and an alcohol is formed.
Eg ethanol can be made by mixing ethene with steam and then passing it over a catalyst.

31
Q

How can ethanol be made industrially?

A

After the reaction with steam has taken place, the reaction mixture is passed from the reactor into a condenser. Ethanol and water have a higher boiling point than ethene, so both condense whilst any unreacted ethene gas is recycled back into the reactor. The alcohol then can be purified from the mixture by fractional distillation.

32
Q

How do halogens react with alkenes?

A

Alkenes also react in addition reaction with halogens such as bromine, chlorine and iodine. The molecules formed are saturated, with the C=C carbons each becoming bonded to a halogen atom. Eg bromine and ethene react together to form bibromoethane.

33
Q

How can the addition of bromine to a double bond be used to test for alkenes?

A

When orange bromine water is added to a saturated compound, like an alkane, no reaction will happen and it will stay bright orange.
If it is added to an alkene the bromine will add across the double bond, making a colourless dibromo-compound - so the bromine water is decolourised.

34
Q

What are polymers?

A

Polymers are long molecules formed when lots of small molecules called monomers join together. This reaction is called polymerisation.

35
Q

What conditions are needed for polymerisation to happen?

A

High pressure and a catalyst.

36
Q

How are addition polymers made?

A

Made from unsaturated monomers. They have a double covalent bond. Lots of unsaturated monomer molecules (alkenes) can open up their double bonds and join together to form polymer chains. This is called addition polymerisation.

37
Q

How do you draw the displayed formula of an addition polymer?

A

Start by drawing the two alkene carbons, replace the double bond with a single bond and add an extra single bond to the end of the carbons.
Then fill in the rest of the groups in the same way that they surround the double bond in the monomer. Then put a pair of brackets around the repeating bit, and put an n after it. This shows that there are lots of monomers.

38
Q

How do you name a polymer?

A

The type of monomer that formed it, with the word poly in front. Eg propene becomes polypropene.

39
Q

What is the general formula for alcohols?

A

CnH2n+1 OH

40
Q

What are the first four alcohols in the homogolous series?

A

Methanol
Ethanol
Propanol
Butanol

41
Q

What are the properties of alcohols?

A

Alcohols are flammable. They undergo complete combustion in air to produce carbon dioxide in the air.
The first four are soluble in water. Their solutions have a neutral pH.
React with sodium, one of the products of this reaction is hydrogen.
Can be oxidised by reacting with oxygen to produce carboxylic acid.

42
Q

What are alcohols used for?

A

Solvents and fuels.
Used as solvents because they can dissolve most things water can dissolve, but they can also dissolve substances that water cannot dissolve. eg oils

The first four alcohols are also used as fuels. Eg ethanol is used in spirit burners. It burns fairly cleanly and does not smell.

43
Q

How can ethanol be made through fermentation?

A

Fermentation uses an enzyme in yeast to convert sugars into ethanol. Carbon dioxide is also produced. The reaction occurs in solution so the ethanol produced is aqueous.

sugar —> ethanol + carbon dioxide.

Fermentation happens fastest at a temperature of around 37 degrees celcius, in a slightly acidic solution and under anaerobic conditions. This provides optimum conditions for the enzyme.

44
Q

What is the functional group of carboxylic acids?

A

-COOH

45
Q

What are the first four carboxylic acids in the homogolous series?

A

Methanoic acid
Ethanoic acid
Propanoic acid
Butanoic acid.

46
Q

How do carboxylic acids react?

A

They react with carbonates to produce a salt, water and carbon dioxide. The salts formed in these reactions end in -anoate. Eg mathanoic acid will form methanoate.

47
Q

What is the equation when ethanoic acid reacts with sodium carbonate?

A

Ethanoic acid + sodium carbonate —> sodium ethanoate + water + carbon dioxide.

48
Q

Why do carboxylic acids form weak acidic solutions?

A

They do not ionise completely.

49
Q

What is the functional group of esters?

A

-COO-

50
Q

When are esters formed?

A

Esters are formed from an alcohol and a carboxylic acid. An acidic catalyst is usually used (e.g. concentrated sulfuric acid).

alcohol + carboxylic acid —> ester + water.

51
Q

What reaction takes place to form ethyl ethanoate?

A

Ethyl ethanoate can be made from ethanoic acid and ethanol with an acidic catalyst.

52
Q

How can polymers be made?

A

Condensation polymerisation.

53
Q

What are condensation polymers?

A

Condensation polymerisation involves monomers which contain different functional groups. The monomers react together and bonds form between them, making polymer chains. For each new bond that forms, a small molecule (for example, water) is lost. This is why it is called condensation polymerisation.

Two monomer types each containing two of the same functional groups OR one monomer type with two different functional groups.

Two types of product - the polymer and a small molecule (e.g. water).

Two reactive groups on each monomer.

54
Q

What is addition polymerisation?

A

Only one monomer type containing a C=C bond.
Only one product formed.
Carbon-carbon double bond in monomer.

55
Q

What is an amino acid?

A

Amino acids have an amino group and a carboxyl group. An amino acid contains two different functional groups - a basic amino group (NH2) and an acidic carboxyl group (COOH). E.g. glycine.

56
Q

What are proteins?

A

Proteins are polymers of amino acids.
Amino acids can form polymers known as polypeptides via condensation polymerisation.
The amino group of an amino acid can react with the acid group of another, and so on, to form a polymer chain. For every new bond that is formed a molecule of water is lost.
One or more long-chains of polypeptides are known as proteins.
Polypeptides and proteins can contain different amino acids in their polymer chains. The order of the amino acids is what gives proteins their different properties and shapes.

57
Q

How are DNA molecules made?

A

Made from nucleotide polymers.
DNA is made of two polymer chains of monomers called nucleotides. The nucleotides each contain a small molecule known as a ‘base’ (4 bases - A, C, G and T). The bases on the different polymer chains pair up with each other and form cross links keeping the two strands of nucleotides together and giving the double helix structures.
The order of the bases acts as a code for an organism’s genes.

58
Q

How do simple sugars form polymers?

A

Sugars are small molecules that contain carbon, oxygen and hydrogen. Sugars can react together through polymerisation reactions to form larger carbohydrate polymers, e.g. starch, which living things use to store energy, and cellulose, which is found in plant cell walls.

Chemistry (38 decks)

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