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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).
Alkenes are highly flammable and burn readily in air. With sufficient amount of oxygen gas, combustion of alkenes forms carbon dioxide and water. In our experiment, the combustion of cyclohexene burns in an orange flame and produces relatively high amount of black soot. The black soot produced is actually carbon monoxide. Cyclohexene undergoes incomplete combustion to form carbon, carbon monoxide and water. The combustion of cyclohexene produces a sootier flame than the cyclohexane. This is because the carbon to hydrogen ratio is higher in cyclohexene. When the percentage of carbon is higher, more oxygen is needed to oxidize the compound.
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Using good laboratory techniques, potassium hydrogen phthalate was weighed by difference into a conical flask. 25cm3 distilled water was added and was then mixed until the potassium hydrogen phthalate had dissolved. Phenolphtalein indicator was added and the solution was carefully titrated with an unknown concentration of NaOH solution until a pale-pink end point was reached. The titration was repeated for accuracy. Results Potassium hydrogen phthalate: 1. Weight by difference = 0.5525g 2. Weight by difference = 0.5089g 3. Weight by difference = 0.5193 g Titration Data for NaOH Initial Burette Reading (cm3)
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The reason we used a glass pipette, was because this is much more equipment then the regular pipette. We then emptied this into a 250ml conical flask on a white tile, and added 3 of drops of litmus indicator. We carefully poured, sulphuric acid into a Burette, using a funnel and pipette, till it was exactly at 0, to make sure this was at 0; we checked that the meniscus just touched the top of the line, at eye level.
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Similarly, the latter have higher boiling points than their tertiary isomerides. Among isomeric alcohols, the boiling point decreases with increase in branching in the alkyl group. Boiling points of alcohols are much higher than those of alkenes, halo alkenes or ethers of comparable molecular masses. This is because in alcohols intermolecular hydrogen bonding exists due to which a large amount of energy is required to break these bonds. Smaller molecules of alcohols are soluble in water. However, when the number of carbon reaches to four and beyond, its solubility in water reduced and will form two obvious layers.
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When denaturing occurs the original structure of the protein is lost and cannot reform. The enzyme becomes ineffective as a catalyst and reduces the rate of reaction as the concentration of enzyme is lowered. Each type on enzyme has its own range of pH in which it functions to its optimum. For example intercellular enzymes have an optimum pH of 7 that is neutral conditions. Strongly acidic or alkaline conditions denature enzymes. Intracellular enzymes such as digestive enzymes work best in acidic or alkaline conditions.
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The methanol catalyses the reaction, and splits the vegetable oil into 3 methyl esters. The glycerol which joined the 3 fatty acids is left over as a by-product. Candidate Vegetable Oils One of the main forms of energy is chemical potential that refers to the energy held within the bonds of chemical compounds present as both ionic and covalent bonds. Vegetable oils have a large amount of stored chemical potential energy. This is because the long acid chains have a large molecular weight, resulting in reserves of chemical energy within the bonds.
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Experiment Hypothesis: The energy released by an alcohol increases as the number of carbon atoms increases.
Van der Waals forces between shorter chain molecules are weak. Between molecules with a longer chain of atoms, giving many points of contact multiple van der Waals forces operate. Branched-chain hydrocarbons are more volatile (have lower boiling temperatures) than unbranched-chain hydrocarbons. Hydrocarbon polymers have molecules which are continuous chains, containing thousands of repeating units. The long, strand-like molecules of poly (ethane) can align themselves to give thousands of contacts between atoms and set up very strong attractions through the operation of multiple van der Waals forces.
- Word count: 2201