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properties of alkenes
• have the same general formula • differ by CH2 in molecular formulae from neighbouring compounds • show a gradual variation in physical properties, such as their boiling points
what is the general formula for alkenes
CnH2n
first 3 alkenes
ethene propene butene
alkenes are unsaturated, what does this mean
they have a double carbon bond
what is a functional group
an atom, or a group of atoms, which determine the main chemical properties of an organic compound
what happens when we combust alkenes
the products are water, carbon dioxide and unburnt carbon particles, because of incomplete combustion - alkenes burn in air with a smoky flame
what is hydrogenation
reacting an alkene with hydrogen
what happens during hydrogenation
• two hydrogen molecules add across the double bond • double carbon to carbon bond converted into single • an alkane is produced
how would we increase the yield of ethanol in a reversible reaction
pass back unreacted ethene and steam back through the catalyst
properties of hydration reactions
• water must be in the form of steam • phosphoric acid used as a catalyst • temperature at 300 degrees, pressure at 70 atmospheres • forms alcohols • reversible reaction
properties of alkenes reactions with halogens
• halogen molecules are added across the double bond • double carbon bond turns into single
uses of alcohols
• fuels • solvents • alcoholic drinks
how to test for alkanes or alkenes
• bromine water test • there is no change when an alkane is mixed with bromine water • bromine water goes colourless when mixed with an alkene
how can we make ethanol
by reacting ethene with water - using fermentation
what is an advantage of hydrating ethene
the reaction produces a high yield of ethanol
disadvantages of hydrating ethene
• high temperature meaning lots of energy • ethene from the reaction comes from crude oil which is not renewable
how does fermentation work
• Start with a sugar solution such as glucose • Mix it with yeast • The yeast converts the sugar solution to a solution of ethanol, carbin dioxide gas is also produced
what are the conditions needed for fermentation
30 degrees - reaction must take place in anaerobic settings (without oxygen)
advantages of fermentation
• low temperature means the reaction does not require a lot of energy • sugar from the reaction comes from plants and is therefore renewable
.disadvantage of fermentation
the product is an aqueous solution of ethanol, meaning we need to purify the ethanol by distillation, which requires energy
describe alcohols solubility in water
they are soluble in water and form neutral solutions
as the number of carbon molecules in an alcohol increases…
the solubility decreases
what are the products when sodium reacts with an alcohol
an oxide and hydrogen gas - eg sodium ethoideplus hydrogen
what is an oxidising agent
a substance that can oxidise other substances in a chemical reaction