Topic 7 - Organic chemistry Flashcards
What is a homologous series
A homologous series is a group of organic compounds that have similar chemical properties, due to them having the same functional group/general formula
as the chain length of a hydrocarbon increases …
The hydrocarbons become more viscous -(thick) and less volatile - (harder to evaporate), and they become less flammable
in fractional distillation which hydrocarbons are at the top of the fractionating column
Shorter chain hydrocarbons are at the top because they have lower boiling points
Longer chain hydrocarbons are at the bottom of the fractionating column because they have higher boiling points,
note- the bottom is hotter than the top since it is closer to the source of heat
How does fractional distillation work
Crude oil is a mixture of hydrocarbons with different boiling points.
1. heat the crude oil to a very high temperature so that all of the compounds are evaporated from liquid to gas.
2.The hot gaseous hydrocarbons then rise up the fractionating column (since hot gas rises).
3.As they rise, they cool down, because the top of the column is cooler than the bottom.
The hydrocarbons will condense when they become cooler than their boiling point, and the liquid hydrocarbons then collect in trays and drain out.
4 The longer chain hydrocarbons condense at the bottom of the fractionating column since they have high boiling points.
5 Meanwhile the shorter chain hydrocarbons condense at the top of the column because they have much lower boiling points.
Describe steam and catalyctic cracking
Catalyctic - first the hydrocarbon vapourised and added to a heated iron oxide powder at approx 500C
Steam - First hydrocarbon vapourised and then mixed with steam and then heated at very high temperatures to split the hydrocarbon into a shorter more useful alkane and an alkene
why is cracking useful
it breaks down larger alkanes into shorter alkane+ an alkene and this is needed since shorter length hydrocarbons are needed for fuels - high demand
what are the 3 addition reactions with alkenes and the conditions for it
alkene and hydrogen with catalyst forms an alkane 150ºC using a nickel catalyst
alkene and water in high temperatures (about 300 ºC
Pressure 60 – 70 atm +Concentrated phosphoric acid catalyst)
forms an alcohol eg : ethanol and ethene gas and water have to be separated , ethene gas= low BP so cooling it keeps it as a gas but the ethanol and water condense into liquid forms but then these undergo fractional distillation
alkene and Halogen - normal room temp , mix ethene and bromine water forms DIBROMOethane or DICHLOROethane ect , bromine water goes colourless since all bromine used up to react with ethene
addition Polymers
many monomers(alkenes) reacted at high pressure with catalyst
in addition polymerisation reaction :
reactant side n on the left side of brackets towards middle and a double bond present
Product side n on lower right side of brackets with no double bond but the single bonds on the left and right side of the 2 carbons , going through and out the brackets
equations for making ethanol
Fermentation - C6 H12 O6 ➔ 2 CH3 CH2 OH + 2 C02
from a hydration reaction - C2 H4 + H2O ➔ C2 H5 OH
Conditions for ethanol production from fermentation
in fermentation tanks. Requires yeast cells which have naturally occurring enzymes to catalyse the reaction. Temperatures of 30-40 °C ( optimum temp for enzymes). Must be anaerobic conditions , so that the ethanol isn’t oxidised to ethanoic acid.
advantages - Glucose and yeast are renewable resources
disadvantages - slow , + ethanol produced isn’t pure so f.d has to happen
how condensation polymerisation works
A diol (a double functional group alcohol eg ethane diol) and a dicarboxylic acid are linked together , 2 different monomers linked together ,when they react they usually lose small molecules such as water, and so reaction is called condensation reaction.
Both monomers have to have 2 functional groups
how to draw a condensation polymer
remove 2 OH ‘s from the dicarboxylic acid
remove 2 H’s from the Diol from the OH
connect them both with an ester link - C , double oxygen bond above , with a single oxygen to its left
what monomers are DNA , proteins and carbohydrates made of
DNA - 2 polymer chains made of nucleotides
Proteins - Amino acids together form a polypeptide and then polypeptides combined together or folded up
in amino acids theres 2 different functional groups - H-N-H (amino group) and carboxyl group - C , double bond O and single bond OH and an ‘ R : group - changes depending on which group it is
polypeptides are formed by condensation polymerisation
Carbohydrate - Glucose and fructose are the monomers
properties of alcohols
flammable - undergo complete combustion - used as fuels
Soluble , have neutral PH to dissolve in water - used as a solvent in industry - can dissolve hydrocarbons and lipid compounds
can be oxidised to from a carboxylic acid
