Chemistry - Chem 6: Carbon chemistry

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What is a covalent bond?
It is a bond involving two atoms with a shared pair of electrons.
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What the group number represent?
the number of outer (valence) electrons in an atom.
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What are molecules?
The groups of atoms formed by covalent bonds.
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When does covalent bonding usually take place?
Between non-metal atoms.
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Desribe the strength fo covalent bonds
Very stronger. they get stronger as the number of covalent bonds eincrease (double-bonds are stonger that sing)
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What are compounds of simple molecules like?
Poor electrical conductivity and low melting points
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Describe the attraction between the molecules
weak intermolecular forces - Van der Waals forces
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What do Van der Waals forces depend on?
the number of electrons per molecule (size) and the distance between the molecules. more electrons - stonger; closer together - stonger
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What is crude oil?
A mixture of hydrocarbons (fossil fuel)
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What is a hydrocarbon?
A molecule containing only carbon atoms and hydrogen atoms. (organic because they contain carbon)
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How do you make useful substances from crude oil?
e.g. petrol - undergo fractional distillation. the oil is vaporised and put into a fractionating column as a gas.
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What happens in the fractionating column?
The column is hot at the bottom and cooler at the top so the different fractions condense at different heights in the column according to their boiling points.
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the more carbon atoms in the molecule...
... the higher the boiling point
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Which hydrocarbons condense at the bottom and the top of the column?
Long-chain hydrocarbons condense at the bottom and short chain ones condense at the top.
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What else can fractionally distilled to provide the gases?
liquid air for nitrogen, oxygen and argon
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What are alkanes?
hydrocarbons with the general formula CnH2n+2. an example of a homologou sseres
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What are the first four alkanes?
methane, ethane, propane and butane
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As the number of carbon atoms in the molecules increase...
... so does the boiling point, viscosity, darkness. The volatility and flammability decrease
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What does complete and incomplete combustion of hydrocarbons produce?
carbon dioxide (greenhouse gas and global warming) and water. incomplete - carbon monoxide and particles of carbon (global dimming)
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What else may hydrocarbons produce?
they release sulphur dioxide (acid rain)
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What do car engines produce?
nitrogen oxides (acid rain and asthma in children)
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What is cracking?
the process in which large alkanes are broken down into smaller alkanes and alkene. It involves heating the alkane to high temperatures strongly at low pressure and in the resence of a catalyst.
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What happens during cracking?
the C-C bonds are broken which requires a lot of energy. Oxygen needs to be excluded. There is more demand fro the smaller alkanes and alkenes than for bitumen
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What are alkenes?
Hydrocarbons in which there is a double bond: C=C. General formula is CnH2n. They are unsaturated, which means that their double bonds can react with hydrogen to make alkanes
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What happens when alkenes are reacted with bromine water or iodine solution?
They go from brown to colourless
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How can ethene be converted to ethanol?
By reacting it with steam in the presence of a phosphoric acid catalyst at 300degresscelsius and high pressure.
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What can ethene be used for?
ripen fruit such as bananas
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How are polymers made?
From monomers (alkenes) link together to form a long chain of repeating units called a polymer
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What are polymers at room temperature?
solids. they are saturated molecules with no double bonds an dwill not react with bromine water. they become soft when heated and can be shaped easily. they do not have one melting point as they contain different-sized molecules.
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Can polymers degrade easily?
No but they can be disposed of by incineration but this makes carbon dioxide and toxic fumes
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Give an example and use of a smart polymer
designed to have specific properties. light-sensitive polymers - less stick with ligh for plasters, hydrogels swell in water, shapememory polymers
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How are vegetable oils extracted, made and what are they used for?
from seeds and flowers which contain some unsaturated molecules. They are hardened by heating to 60 degress with a hydrogen and nickel catalysts converting them to alkanes with a higher melting point - margarine
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Why do we need fats?
fats - make cell membranes to provide fat layer beneath the skin for insulation, to make energy and to protect organs.
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Which fats are bad for us?
saturated as they are likely to caus blocking of the arteries - heart attacks and strokes
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What are emulsions?
stable mixtures of oil and water held by emulsifiers.
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What do emuslifiers have?
hydrophilic heads and hydrophobic tails.
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What are emulsifiers used for?
make icecreamsn xreanier and margarines easier to spread
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Give some alternative fuels
hydrogen - only produces water and lots of energy but is explosive and requires electrolysis, bioethanol - carbon neutral, renewable, increases food prices
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How can ethanol be obtained?
by reacting alkenes with steam. ethanol - cheaper, non-renewable, net release of carbon dioxide is greater
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Other cards in this set

Card 2


What the group number represent?


the number of outer (valence) electrons in an atom.

Card 3


What are molecules?


Preview of the front of card 3

Card 4


When does covalent bonding usually take place?


Preview of the front of card 4

Card 5


Desribe the strength fo covalent bonds


Preview of the front of card 5
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