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AS and A Level: Organic Chemistry
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Five equations you must know for organic chemistry
- 1 Alcohol + carboxylic acid = ester + water (eg CH3OH + CH3CH2COOH becomes CH3OOCH2CH3 + H2O)
- 2 Alkene + hydrogen = alkane (eg CH2=CH2 + H2 becomes CH3CH3)
- 3 Alkene + water = alcohol (eg CH2=CH2 + H2O becomes CH3CH2OH)
- 4 Halogenoalkane + hydroxide ion = alcohol + halide ion (eg CH3Br + OH- becomes CH3OH + Br-)
- 5 Alkene + hydrogen bromide = halogenoalkane (eg CH2=CH2 + HBr becomes CH3CH2Br)
Five facts about alcohols
- 1 Primary alcohols are oxidised into aldehydes and water, which are then oxidised into carboxylic acids. Secondary alcohols are oxidised into ketones and water. Tertiary alcohols cannot be oxidised.
- 2 Alcohols are oxidised by acidified potassium dichromate (H+/K2Cr2O7). This starts off orange and will turn green if it oxidises something (so with tertiary alcohols it will stay orange).
- 3 There are two ways of making alcohols: fermentation and hydration of alkenes. Fermentation is good because it uses renewable resources and does not take much energy, however it can only produce alcohol up to 14% before the yeast die.
- 4 Alcohols are soluble in water as they can make hydrogen bonds with the water. However, the “carbon chain” attached to the OH cannot interact with water and is insoluble. This means that alcohols become more insoluble the longer the carbon chain.
- 5 Alcohols have a very high melting and boiling point compared to alkanes of the same chain length. This is because they can form strong hydrogen bonds with each other that require a lot of energy to break.
Five facts about hydrocarbons
- 1 The longer the carbon chain the higher the higher the boiling point, as there will be more points of contact and stronger van der Waals forces.
- 2 The more branched the carbon chain the lower the boiling point, as the molecules will not be able to pack as close together and will have weaker van der Waals forces.
- 3 Hydrocarbons are insoluble in water as they cannot make intermolecular forces with them.
- 4 Hydrocarbons have low boiling and melting points as the only intermolecular forces that can hold them together are weak van der Waals forces which require little energy to break.
- 5 When processing crude oil (a hydrocarbon), the aim of the game is to get short, highly branched hydrocarbons. This will increase their volatility and make them a better fuel. We do this through: fractional distillation (sorts them into different sizes), cracking (splits long chains into short chains), isomerisation and reforming (makes the chains branched and cyclic).
From this, a graph of percentage ethanol solution against density was made. This graphs later compared to the density of the wine, so the percentage ethanol of the wine can be read off the graph. The samples of wine are then distilled, in order to extract the ethanol from the sample. Before distillation, the wine is made alkaline using Sodium Hydroxide. This is because the solutions of ethanol used in order to make the ethanol concentration against density calibration graph contained ethanol and water only, and it the sample of wine was not made alkaline then many of the volatile acids contained in the wine would distil off and affect results.
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Experiment to Determine Acidities of Wine. The purpose of this experiment is to determine the total and volatile acidities of each of the wines and compare them.5 star(s)
Tartaric acid requires two moles of NaOH for it to be neutralised. In order to calculate the volatile acidity of the wine, a sample of wine is evaporated using a steam evaporator, then made up to the original volume with deionised water and this process was repeated. The volatile acids evaporate away, while the remaining acids constitute what is known as the fixed acidity of the wine. This is made up to the original volume with deionised water and titrated with NaOH as before to give the acidity of this solution, which is known as the fixed acidity of the wine.The representative acid used here will again be Tartaric acid.
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Reactions of aldehydes and ketones. The purpose of this experiment is to compare some reactions of ethanal and propanone.5 star(s)
About 2 cm3 of 2,4-dinitrophenylhydrazine was added into the test tube. 4. The experiment was repeated using propanone instead of ethanal. Part 3: Oxidation reaction (a) With acidified potassium dichromate 1. 5 drops of ethanal, 2 drops of potassium dichromate solution and 10 drops of dilute sulphuric acid were added into a test tube. 2. The test tube was shook gently and was put into a warm water bath. 3. The experiment was repeated using propanone instead of ethanal.
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Chromic acid features chromium in an oxidation state of +6. It is a strong and corrosive oxidising agent. Apparatus and chemicals: Apparatus: Quick-fit distillation setup, anti-bumping granules, thermometer, conical flasks, beakers, filter funnel, filter paper, iced water bath, 10cm3 measuring cylinder, triple beam balance, dropper, suction flask Chemicals: About 3 cm3 propan-2-ol, 3 cm3 concentrated sulphuric acid, deionized water, 4g potassium dichromate (VI), 2-4-dinitrophenylhydrazine (2,4-DNP), anhydrous calcium chloride Procedure: Part 1: Oxidation of propan-2-ol and distillation 1. About 4g of potassium dichrome solid and 10 cm3 deionized water were added to a conical flask and the flask was well shaken to allow the solid to dissolve.
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mixed reactants will be placed on a paper marked with an "X" * Time taken for the precipitate to form and hide the "X" will be measured and recorded. * The experiment will be repeated for accuracy Apparatus: * 2M Hydrochloric Acid * 0.4 M Sodium Thiosulphate * Distilled Water * Thermometer * Stopwatch * Measuring Cylinders ( 10ml+ 50ml) * Measuring pipette * Conical Flask (100ml) * Marker * (Access to a fume cupboard) Method: Dilution of solutions to lower their concentrations: When diluting a solution, it is important to know that we are not losing any fraction of the solvent by mixing it with distilled water.
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Some nations (Australia, USA (Obama)) are reluctant to join because of the impact on their economies.(See Geog notes) The ozone layer The Ozone Layer absorbs much of the harmful ultraviolet radiation emitted by the sun, which, if it were to reach the Earth's surface unimpeded, would cause burning and skin cancer (also vitamin D :)) Ozone, O3 is constantly formed and broken down. An equilibrium with O2 and O* is present. Overall Equation: O3 ? O2 + O O3 + (UV Rad) --> O2 + O* O2 + O* --> O3 These two reactions would maintain a steady rate if undisturbed.
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An example of exothermic reaction is: photosynthesis in plants where the energy comes from the sunlight. Energy cannot be destroyed but it can transfer from one form to another. The total energy of a system of reacting chemicals and surroundings remains constant. The value for exothermic enthalpy change is always a negative value as the energy is lost to the surroundings ?H = -890.3 KJmol-1 The standard conditions to compare the enthalpy changes of various reactions are temperatures, pressures, amounts and concentrations of reactants or products. The standard conditions are: * A pressure of 100kilopascals (102kPa)
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Then we weight the dried product and recorded its melting point. Chemical reaction: Equation 1: Synthesis of Aspirin Preparation of silver chloride: Now I am going to explain the preparation of silver chloride; Materials : (a) silver nitrate (b) sodium chloride (c) cylinders (d) beaker (e) glass rod (f) filter paper (g) Buchner funnel (h) oven etc. Procedure 1. Firstly we had to measure 10 cm3 of silver nitrate and sodium chloride solutions in two separate measuring cylinders. 2.
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Design two experiments, one using titration and one using gas collection to show that H2SO4 is a dibasic acid.5 star(s)
- 1 Gas(dm3) - 2 Gas(dm�) - 3 Gas Average(dm�) To keep the results accurate we will keep all equipment and solutions used the same every time, we will do this experiment 3 times and take the average of the readings, and use this to see if H2SO4 is dibasic, theoretically we should measure 0.6dm3, although we may not get this exact reading for many reasons: * Inaccuracy when measuring solutions/weight of Mg. * Impurities in the solutions used e.g: Concentrated H2SO4:"Purity: 95%-98% Pure"  * If all the reactants weren't used up in the reaction.
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Beta particle is emitted when a heavy element decays with atomic number of above 82 decays. Alpha radiation reduces the ratio of protons to neutrons in the parent nucleus. A beta particle is emitted when there is too many neutrons, a neutron decays into a proton, an electron and an antineutrino. Difference between nuclear fission reaction and natural radioactive decay: The fission of a nucleus involves splitting it into two more or less equal fragments. For example uranium, in which it yields two or more lighter nuclei and a large amount of energy. If an atom of U- 235 is given sufficient energy through the absorption of one neutron, it enters an excited state and begins to oscillate.
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Once the solution had cooled 3.8g of p-acetamidophenol was added. Through the top of the condenser ethyl iodide (3.0cm3) was introduced to the pale green mixture and the mixture boiled at reflux temperature (20-25�). Ethyl iodide was obtained from a burette in the fume hood few minutes before its use, due to its flammable nature and harmful vapour. A darkening green colouration occurred while p-acetanilide dissolved changing through to brown and then yellow. Once the reflux was completed 40cm3 of water was added and the flask was left in ice for a few minutes to cool.
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is a constant known as the extinction coefficient. The absorbance A and extinction ? are sometimes defined in terms of the natural logarithm instead of the base-10 logarithm. Methodology: Colorimetric Analysis: At the beginning, 4cm3 decarbonated cola was transferred into a 100cm3 volumetric flask and diluted with distilled water. After, 25.0cm3 of the sample, 0mM (blank), 0.1mM, 0.2mM, 0.4mM and 0.6mM of phosphate standards (KH2PO4) were put into six 50ml volumetric flask separately. Then, 5ml of vanadate-molybdate reagent was added to each flask and all of the flasks were diluted with distilled water. Finally, the absorbance of each solution was measured at 400nm and recorded.
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and knowing all the bonds and structures of the two reactants in alcoholic combustion, it is relatively easy to calculate the total energy that will be given off by the alcohols when burnt; Alcohols No. of carbons C-H O-H O=O C-C C-O C=O O-H Enthalpy in kJ/mole Methanol 1 3 1 1.5 0 1 2 4 -658 Ethanol 2 5 1 3 1 1 4 6 -1276 Propanol 3 7 1 4.5 2 1 6 8 -1894 Butanol 4 9 1 6 3 1 8 10 -2512 Pentanol 5 11 1 7.5 4 1 10 12 -3130 These calculated values were made into a graph.
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As this is a low critical temperature it makes critical carbon dioxide very easy to work with. Another useful feature of critical carbon dioxide is that when it is in its solvent form it is able to be altered by making slight adjustments to temperature and pressure. The phase diagram below of carbon dioxide shows us that its triple point ( where all states of carbon dioxide exist together)
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Adding water to it gives a solution pale grey with green tinge. After dissolving the solutions turns clear with a green-grey colour and no precipitate. Prepare a solution of 6.0g of sodium ethanoate in 25cm3 of water in a conical flask. Sodium ethanoate is a white powder. It dissolves completely in water to give a colourless solution. Carefully add 2cm3 of ethanoic anhydride to the solution of phenylammonium chloride,and stir vigorously until all the ethanoic anhydride is dissolved. Ethanoic Anhydride smells of vinegar. Adding it to the phenylammonium chloride gives a solution with oily blobs with a sweet fruity smell.
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The I2 not yet reacted would then be titrated against thiosulphate solution, like the first equation, to determine its amount. This method is a kind of back titration. It is the excess amount of substance which is being titrated, but not the object being studied. This method is used when the direct titration of the object being studied is not suitable, which is why back titration is used in this method. Procedure 1. 0.682g of potassium iodate solid was weighed out.
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Sodium hydroxide is a caustic soda and so is not very dangerous however regular safety precautions (goggles, labcoats and gloves) and care is still carried out to prevent spillages. Ethanol is highly flammable and dangerous substance as it contains methanol. Therefore, it should not come into direct contact with any flame. It is harmful it swallowed, inhaled or comes into contact with skin. Observations: Methyl benzoate is originally a transparent liquid however the addition of the sodium hydroxide, ethanol and anti bumping granules turns the liquid cloudy.
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