AS chemistry ocr a unit 2
Chemistry discussion, revision, exam and homework help.
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Re: AS chemistry ocr a unit 2I suggest you go through the syllabus for unit 2 and make a list yourself and this will help your revision more.(Original post by hicky@picky)
what reactions are you supposed to know for AS unit 2 ocr a chemistry?
thaaank you
Here it is: http://www.ocr.org.uk/download/kd/oc...d_gce_spec.pdf -
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Re: AS chemistry ocr a unit 2There are a few reactions that we need to know. Firstly, here are the reaction mechanisms :
1.) Radical substitution e.g. C4H10 (alkane) with Br2. An alkane will reaction with a halogen in the presence of U.V light/ radiation or at a temperature of about 300 degrees celsius.
2.) Electrophilic addition e.g. addition of hydrogen gas to ethene/ hydrogenation
3.) Nucleophilic substitution e.g. Reaction of Aqueous hydroxide ions/water with 1-bromopropane (hydrolysis)
And here are the reactions
1.) Addition of hydrogen gas, H2 (g), to an alkene. A Ni, Nickel, catalyst is used at a temperature of 150 degrees celsius. The product formed is an alkane with the general formula CnH2n+2.
2.) Addition of Steam, H20 (g), to an alkene/ Hydration of an alkene. A phosphoric acid catalyst, H3PO4, is used at high temperatures and pressures. The product formed is an alcohol with the general formula CnH2n+1OH. E.g. Reaction of ethene, C2H4, with steam using a phosphoric acid catalyst, H3PO4, at a temperature of 300 degrees celsius and a pressure of 60 atm. Equation:
H2C=CH2 + H20 (g) -----------> CH3CH2OH......................Ad dition reaction- 2 reactants --> 1 product...= atom economy of 100%!
3.) Removal of water from an alkene/Dehydration. This is done using a concentrated Acid catalyst (usually a phosphoric acid catalyst or a sulfuric acid catalyst) at a high temperature and the product formed is an alkene with the general formula CnH2N. (this is an elimination reaction).
4.) Fermantation of glucose to produce bioethanol (basically, ethanol!) and carbon dioxide. Equation (essential to learn) :
C6H12O6 ------------> 2CH3CH2OH + 2CO2
This is carried out using yeast as an enzyme (specifically the zymase enzyme) at a temperature of 37 degrees celsius in the absence of air to prevent the oxidation of ethanol into ethanal or ethanoic acid, which would affect the flavour of the product. In addition it is worth knowing that this is a batch process and the toxicity of the alcohol means that alcohol with a maximum ethanol concentration of 15% can only be produced by this method. This is because, above and ethanol concentration of 15%, the zymase enzyme becomes denatured and fermentation ceases.
5.) Oxidation of primary, secondary alcohols. Primary alcohol- An alcohol in which the OH group is attached to a carbon with no alkyl groups or bonded to one alkyl group. Secondary Alcohol- An alcohol in which the OH group is attached to a carbon bonded to two alkyl groups.
- On gentle heating with acidified potassium dichromate (the oxidising agent- K2CR2O7/H2SO4) a primary alcohol is oxidised into an aldehyde. It is important that, as the aldehyde is formed, it is distilled off immiediately to prevent further oxidation to a carboxylic acid. The symbol [O] is used to represent the oxidising agent within the equation.
- On stronger heating with excess acidified dichromate can be further oxidised, passing through the aldehyde stage to form a carboxylic acid. This is carried out under reflux. Reflux is the continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry. An orange to green colour change is observed when the primary alcohol becomes oxidised into both an aldehyde and a carboxylic acid, the same colour change is also observed when a secondary alcohol is oxidised into a ketone. In this equation, the symbol 2[O] is used to represent the oxidising agent (2 as it is in 'excess')
-Secondary alcohols are oxidised into ketones. Ketones cannot be further oxidised. This is also carried out under reflux and [O] is used to represent oxidising agent. Ketones cannot be further oxidised.
- tertiary alcohols are resistant to oxidation and the oxidising agent remains orange in colour.
6.) Last one! Esterification. Esterification is the reaction of an alcohol with a carboxylic acid to produce an ester and water. This is done using an acid catalyst and heating.
