Organic chemistry Flashcards

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1
Q

What is crude oil?

A

Crude oil is:
* formed over millions of years from the fossilised remains of plankton
* found is porous rock in the Earth’s crust.
* a finite (non renewable) resource that is used to produce fuels and other chemicals

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2
Q

What are hydrocarbons?

A
  • Most of the compounds in curde oil are hydrocarbons (molecules made of only hydrogen and carbon atoms).
  • Hydrocarbon molecules vary in size, which affects their properties and how they can be used as fuels.
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3
Q

What is the trend in increasing hydrocarbon length?

A

The larger the hydrocarbon:
* the more viscous it is (i.e. the less easily it flows)
* the higher its boiling point
* the less volatile it is
* the less easily it ignites

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4
Q

How is crude oil separated?

A
  • Crude oil can be separated into different fractions (parts) by fractional distillation.
  • Each fraction contains hydrocarbon molecules with similar number of carbon atoms.
  • Most of the hydrocarbons obtained are alkanes.
  • First, the crude oil is heated until it evaporates.
  • The vapour moves up the fractionating column.
  • The top of the column is much colder than the bottom.
  • Shorter hydrocarbon molecules can reach the top of the fractionating column befpre they condense and are collected.
  • Longer hydrocarbon molecules condense at higher temperatures and are colllected lower down the column.
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5
Q

What are alkanes?

A
  • Carbon atoms are linked to four other atoms by single bonds.
  • Alkanes only contain single bonds and are described as saturated hydrocarbons (because they contain the maximum number of bonds possible).
  • Alkanes are fairly unreactive, but they burn well.
  • The general formula for alkanes is double the carbon atoms and add two to get the number of hydrogen atoms.
  • The shorter chain alkanes release energy more quickly by burning, so there is greater demand for them as fuels.
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6
Q

What occurs during the combustion (burning) of hydrocarbon fuels?

A

During the combustion (burning) of hydrocarbon fuels:
* both carbon and hyrdogen are oxidised
* energy is released
* waste products are produced, which are released into the atmosphere.

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7
Q

What occurs during the incomplete combustion of hydrocarbon fuels?

A
  • If combustion is not complete, then carbon monoxide, unburnt fuels and solids particles containg soot (carbon) may be released.
  • Carbon monoxide is a colourless, odourless and toxic gas.
  • Solid particles in the air, called particulates, can cause global dimming by reducing the amonut of sinlight reaching the Earth’s surface and cause damage to people’s lungs.
  • Due to high temperatures reached when fueldd burn, nitrogen in the air can react with oxygen and form nitrogen oxides.
  • These gases can cause respiratory problems in people and react with rain water (in the same way as sulfur dioxide) to form acid rain, which can damage plants and buildings.
  • Sulfur can be removed from fuels before burning (in motor vehicles) and removed from the wastee gases after combustion (in power stations).
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8
Q

What is cracking?

A
  • Longer chain hydrocarbons can be broken down into shorter, more useful hydrocarbons. This process is called cracking.
  • Cracking is an inddustrial process.
  • The two main methods of cracking are steam cracking and catalytic cracking.
  • The products of cracking incluse alkanes and another type of hydrocarbon called alkenes.

During steam cracking:
* the hydrocarbons are mixed with steam
* they are heated to 850 degrees celsius

During catalytic cracking:
* the hydrocarbons are heated until they vapourise
* the vapour is passed over a hot aluminium oxide catalyst
* a thermal decomposition reaction then takes place

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9
Q

How are the products of cracking used?

A
  • No atoms are made or destroyed during the cracking reaction, so the chemical equation must always balanced.
  • The alkanes produced are valuable as fuels.
  • There is a high demand for fuels with small chains of carbon atoms because they are easy to ignite and have low boiling points.
  • The alkenes produced can be used to make a range of new compounds, including polymers and industrial alcohol.
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10
Q

How can bromine water be used to test for alkenes?

A
  • Alkenes are more reactive than alkanes.
  • They react when shaken with bromine water, turning it from orange to colourless.
  • This can be used to differentiate between alkanes and alkenes.
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