Unit 2.7

• There are 2 main processes to manufacture ethanol: fermentation and hydration.
• The hydration of ethene is when ethene and steam raect together at 300°C and 70atm in the presence of a phosphoric acid catalyst.
• Fermentation is the process of converting sugars into ethanol. Sugar (dissolved in water) and yeast are added together. This mixture is then left in a warm place. Ethanol is removed from the final mixture using fractional distillation as ethanol will boil before water (at 78°C).
• Short chain alcohols (3 carbons) are soluble in water but longer chains are insoluble. All alcohols can form hydrogen bonds with water but long hydrophobic chains in larger alcohols prevent the molecules from being hydrated (surrounded by water molecules).
• Biofuels are produced from living organisms. There are 2 types: bioethanol and biodiesel.
• Bioethanol is formed from the fermentation of sugars in plants (sugar cane)
• Biodiesel is made from oils contained in the seeds of some plants.
• Biofuels release energy when burned and are often blended with conventional fossil fuels.
• Advantages of biofuels:

  They are renewable. Carbon dioxide is taken in by growing plants and used in photosynthesis. This offsets some of the CO2 produced by burning biofuels. Reduces reliance on fossil fuels (which are running out)
• Disadvantages of biofuels:

  Factories need to be built. Deforestation takes place. Arable/pastoral land is used to grow crops for biofuels. Water and fertilisers are required to grow crops.
• Alcohols can be dehydrated (removal of water molecule) to form alkenes in an elimination reaction.
• Concentrated sulfuric acid, phosphoric acid or heated aluminium oxide can be used to dehydrate alcohols.
• Alcohols can be oxidised using oxidising agents such as acidification potassium manganese (VII) KMnO4 or acodified potassium dichromate (VI) K2Cr2O7
• To oxidises alcohols the alcohol is refluxed with the oxidising agent to give the product.
• Carboxylic acids of 4 or less carbons are soluble in water due to the polar OH group. Acids with 5 or more chains become increasingly insoluble, as the carbon chain is non-polar and can only form temporary dipoles.
• Volatility refers to how readily a substance vaporises
• Carboxylic acids can form dimers, strong hydrogen bonds between the different OH groups, forming a circle. This increased interaction between carboxylic acids means that more energy is needed to separate them, so the volatility of the acid decreases.
• miscibility refers to how easily a liquid with water.
• Smaller chain alcohols are miscible in water due to their ability to form hydrogen bonds between their polar OH groups and the water molecules.
• When alcohols are mixed with water, the hydrogen bonds between the water molecules and the hydrogen bonds between the alcohol molecules break, and new alcohol-water hydrogen bonds form. this is possible as there is no significant difference in energy when this happens.
• miscibility decreases as the carbon chain of alcohols increases in length. this is due to the
• 1st degree alcohols are oxidised into aldehydes before being oxides to carboxylic acids.
• 2nd degree alcohols are oxidised into ketones
• 3rd degree alcohols resist oxidation
• Carboxylic acids will turn litmus paper from blue to red.
• Carboxylic acids will react with carbonates to produce effervescence due to the CO2 produced
• Carboxylic acids are weak acids. They easily donate a proton (H+) from the COOH group, so that the negative charge can be delocalised between the COO- group. This stabilises the COO- group, and an equilibrium occurs. This means that the acid does not fully dissociate, meaning that it is weak.
• Biodiesel is produced from oil and fats found in some seeds
• The general formula of carboxylic acids is CnH2n+1COOH