A.S Chem Unit 2 Module 2

aimee1234's version from 2015-04-24 07:04

Section 1

Question Answer
What two ways can ethanol be made?Ethanol can be made by the hydration of ethene or by the fermentation of sugars
How is ethanol made by hydration?Ethanol is manufactured industrially by the CATALYTIC hydration of ethene, using steam in the prescence of a PHOSPHORIC ACID catalyst. The reaction is carried out at HIGH TEMPERATURE and MODERATE PRESSURE and can be operated CONTINUOUSLY
Is the hydration of ethene reaction reversible and what does this mean? What happens to any unreacted gases?The reaction is REVERSIBLE and so the conversion of ethene is INCOMPLETE - only 5% of the ethene is converted into ethanol. Any unreacted gases are RECYCLED and are passed through the reactor again. Overall, 95% conversion achieved.
How is ethanol produced by fermentation?Carbohydrates are converted into ethanol and carbon dioxide - sugar or starch is usually used as the carbohydrate source. Fermentation is carried out in solution at relatively low temperatures, in the prescence of yeast. The reaction is CATALYSED by an ENZYME in the yeast.
Is the fermentation of carbohydrates to ethanol anaerobic or aerobic?The fermentation of carbohydrates to ethanol is ANAEROBIC - it does not require oxygen, therefore it is important that fermentation is carried out in the ABSENCE OF AIR.
Is fermentation slow or fast at 25 degrees? What about 37 degrees?Reaction is slow at temperatures below 25 degrees, while at temperatures above 37 degrees, the enzyme starts to denature and lose its efficiency

Section 2

Question Answer
What is ethanol used in?Ethanol is used in fuel to increase the octane rating of the fuel - the resulting fuel burns more cleanly
What is methanol used for?Methanol is an important feedstock for the chemical industry and can be easily converted into METHANAL and ETHANOIC ACID. Methanol can be used as a clean burning fuel.
By what method is the ethanol used in alcoholic drinks made by?Ethanol used in alcoholic drinks is made via fermentation
What is ethanol an important solvent in?Ethanol is an important solvent in METHYLATED SPIRITS and is being developed as an ALTERNATIVE for petrol to fuel cars

Section 3

Question Answer
What melting and boiling points do alcohols have and what is this down to?Hydrogen bonds are the strongest intermolecular forces. The relatively high melting and boiling points of alcohols result from the prescence of hydrogen bonds between the alcohol molecules.
What do the high melting and boiling points and the hydrogen bonds mean about volatility for alcohols and what is volatility?Volatility is the ease that a liquid turns into a gas, and it increases as boiling point increases. Alcohols have a relatively low volatility
Do alcohols dissolve in water? Why do they/don't they?Alcohols DISSOLVE IN WATER because hydrogen bonds form between the polar -OH groups of the alcohol and water molecules.
Does solubility increase or decrease as chain length increases?Solubility decreases as the chain length increases, because a larger part of the alcohol is made up of a non-polar hydrocarbon chain, and the hydrocarbon chain does not form hydrogen bonds with water molecules.

Section 4

Question Answer
What happens to alcohols in a plentiful supply of oxygen?In a plentiful supply of oxygen, alcohols burn completely to form carbon dioxide and water
What can primary and secondary alcohols be oxidised using? What is a suitable one?Primary and secondary alcohols can be oxidised using an oxidising agent. A suitable oxidising agent is a solution containing ACIDIFIED DICHROMATE IONS, H+/Cr2O7(2-)
What can the oxidisng agent be made from?This oxidising mixture can be made from potassium dichromate, K2Cr207, and sulphuric acid, H2SO4
What happens to the acidified potassium dichromate during the reactionDuring the reaction, the acidified potassium dichromate changes colour from orange to green
What happens when you gently heat a primary alcohol with potassium dichromate?Gentle heating with acidified potassium dichromate, a primary alcohol can be OXIDISED to form an ALDEHYDE.
What symbol represents an oxidising agent?[0]
What happens when you do stronger heating on a primary alcohol?On stronger heating with EXCESS acidified dichromate, the alcohol will be COMPLETELY OXIDISED, passing through the aldehyde stage, to form a CARBOXYLIC ACID.
What do you need to to when preparing aldehydes in the laboratory?When preparing aldehydes in the laboratory, you will need to distill off the aldehyde from the reaction mixture as it is formed. This prevents the aldehyde being OXIDISED FURTHER to a carboxylic acid.
What is done to the reaction mixture when making a carboxylic acid?When making the carboxylic acid, the reaction mixture is usually heated under reflux before distilling off the product
As well as the aldehydes/carboxylic acids, what is also formed during the oxidation of a primary alcohol?Water

Section 5

Question Answer
What are secondary alcohols oxidised by and what do they form?Secondary alcohols are oxidised by acidified dichromate ions to form KETONES. Ketones CANNOT BE OXIDISED FURTHER
What are tertiary alcohols oxidised to?Tertiary alcohols are RESISTANT to oxidation. The oxidising agent remains ORANGE in colour

Section 6

Question Answer
When is an ester formed and what is the reaction known as?An ester is formed when an alcohol is WARMED with a CARBOXYLIC ACID in the prescence of an ACID CATALYST. The reaction is known as ESTERIFICATION.
What happens to the -OH bond of an alcohol during esterification?The -OH bond in the alcohol is broken and WATER is formed. The water molecule comes from the OH of the CARBOXYLIC ACID group and the H of the ALCOHOL GROUP.

Section 7

Question Answer
What can an alcohol be dehydrated to form?An alcohol can be dehydrated to form an ALKENE in the prescence of an ACID CATALYST in an ELIMINATION REACTION
What happens during the dehydration of an alcohol?The alcohol is heated under reflux, in the prescence of PHOSPHORIC ACID for about 40MINUTES.
What is formed from the dehydration of an alcohol?An alkene and water is formed

Section 8

Question Answer
What general formuala do the halogenoalkanes have?Halogenoalkanes have the general formula CnH2n+1X, where X represents the halogen atom
Do halogenoalkanes contain single or double bonds?Halogenoalkanes contain only single bonds.
What do halogenoalkanes contain?Halogenoalkanes contain a polar carbon-halogen bond. The halogen atoms are more electronegative than the carbon atoms. The bonded electron pair is attracted more towards the halogen atom than towards the carbon atom. The result is a polar bond
Does the polarity of the halogens increase or decrease going down the group?The electronegativity of the halogens decreases down the group, resulting in a decrease in polarity of the carbon-halogen bond from fluorine to iodine
What do halogenoalkanes react with and what is this called?Halogenoalkanes react with nucleophiles in substitution reactions.
What happens during these reactions with the halogenoalkanes?The electron-deficient carbon atom in halogenakanes attracts nucleophiles such as water, OH- and NH3. The nucleophile replaces the halogen atom in the halogenoalkane, forming a compound containing a different functional group.

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