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Flashcards in C1- useful substances from crude oil Deck (23)
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1
Q

Why are fuels from oil mixtures containing large hydrocarbon molecules inefficient?

A

they do not flow easily and are difficult to ignite. Crude oil often contains too many large hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand.

2
Q

What does cracking do?

A

Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules.

3
Q

How does cracking work?

A

Fractions containing large hydrocarbon molecules are heated to vaporise them. They are then either:
passed over a hot catalyst, or
mixed with steam and heated to a very high temperature.
These processes break chemical bonds in the molecules, causing thermal decomposition reactions. Cracking produces smaller alkanes and alkenes (another type of hydrocarbon).

4
Q

What are alkenes?

A

The alkenes are a family of hydrocarbons that share the same general formula:

CnH2n

The general formula means that the number of hydrogen atoms in an alkene is double the number of carbon atoms.

5
Q

Alkenes are unsaturated hyrdocarbons. What does this mean?

A

They contain a double covalent bond, which is shown as two lines between two of the carbon atoms. The presence of this double bond allows alkenes to react in ways that alkanes cannot. They can react with oxygen in the air, so they could be used as fuels. But they are more useful than that: they can be used to make ethanol and polymers (plastics) - two crucial products in today’s world.

6
Q

How do you test for unsaturation?

A

Bromine water is a dilute solution of bromine, normally orange-brown in colour. It becomes colourless when shaken with an alkene (unsaturated), but its colour remains the same when it is shaken with alkanes (saturated).

7
Q

what are polymers?

A

Polymers are very large molecules made when many smaller molecules join together, end-to-end. The smaller molecules are called monomers.

8
Q

Why can alkenes act as monomers?

A

Alkenes can act as monomers because they are unsaturated (they have a double bond):

ethene can polymerise to form poly(ethene), also called polythene
propene can polymerise to form poly(propene), also called polypropylene.
9
Q

Drawing displayed formulas of polymers (keep revising this)?

A

Polymer molecules are very large compared with most other molecules, so the idea of a repeating unit is used when drawing a displayed formula. When drawing one, starting with the monomer:

change the double bond in the monomer to a single bond in the repeating unit
add a bond to each end of the repeating unit.
10
Q

What is polythene used for?

A

plastic bags and bottles

11
Q

What is polypropene used for?

A

crates and ropes

12
Q

What is polychloroethene used for?

A

water pipes and insulation on electricity cables

13
Q

What do the properties of polymers depend on?

A

the chemicals they are made from, and the conditions in which they are made.

14
Q

What is the difference between high density poly(ethene) and low density poly(ethene)

A

: LDPE, low-density poly(ethene), is weaker than HDPE, high-density poly(ethene), and becomes softer at lower temperatures.

15
Q

What are some of the uses of modern polymers?

A

new packaging materials
waterproof coatings for fabrics (such as for outdoor clothing)
fillings for teeth
dressings for cuts
hydrogels (for example for soft contact lenses and disposable nappy liners)
smart materials (for example shape memory polymers for shrink-wrap packaging).

16
Q

What are the advantages and disadvantages of polymers being unreactive?

A

they are suitable for storing food and chemicals safely. Unfortunately, this property makes it difficult to dispose of polymers. They can cause litter and are usually sent to landfill sites.

17
Q

How can we produce biodegradable plastics?

A

it’s possible to include substances such as cornstarch that cause the polymer to break down more quickly. Carrier bags and refuse bags made from such degradable polymers are available now.

18
Q

What are the advantages and disadvantages of recycling polymers?

A

Many polymers can be recycled. This reduces the disposal problems and the amount of crude oil used. But the different polymers must be separated from each other first, and this can be difficult and expensive to do.

19
Q

What is the chemical formula of glucose?

A

C6H12O6 (little numbers)

20
Q

How can you make ethanol from steam and ethene?

A

Ethanol can be made by reacting ethene (from cracking crude oil fractions) with steam. A catalyst of phosphoric acid is used to ensure a fast reaction.
ethene + steam → ethanol

21
Q

What is the disadvantage and advantage of using steam and ethene to make ethanol?

A

he process is continuous – as long as ethene and steam are fed into one end of the reaction vessel, ethanol will be produced. These features make it an efficient process, but there is a problem. Ethene is made from crude oil, which is a non-renewable resource.

22
Q

How is ethanol produced from fermentation?

A

Sugar from plant material is converted into ethanol and carbon dioxide by fermentation. The enzymes found in single-celled fungi (yeast) are the natural catalysts that can make this process happen.

C66H12O6 → 2C2H5OH + 2CO2

23
Q

What is the advantage and disadvantage of fermentation?

A

Produces carbon dioxide, but Unlike ethene, sugar from plant material is a renewable resource.

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