OCR 21st Century C7.2

Alcohols, carboxylic acids and esters
1. Alkenes
  1. Unsaturated molecules consisting of C=C double bonds. this increases its reactivity
  2. CnH(2n)
2. ESTERS
  1. Esters are formed when a carboxylic acid reacts with an alcohol in the presence of a strong catalyst (Sulphuric Acid). The general word equation is: carboxylic acid + alcohol → ester + water
  2. Chemical compiunds consisting of an alkyl group (CH2, CH3 etc.) adjacent to an ester linkage. Esters are derived when at least one -OH group (hydroxyl group) is replaced by an -O- alkyl group.
    1. Esters are ubiquitous and most naturally occur in fats and oils. Esters with low molecular atomic mass are commonly used in fragrances, essential oils and pheromones, flavourings and aromas. Esters are responsible for the smells and flavours of fruits. Esters are volatile so they can easily evaporate. Some esters are used as solvents, paint, ink, glue and in nail varnish remover as well as plasticisers
  3. Funtional Group -COO
  4. ethanol + ethanoic acid → ethyl ethanoate + water
    1. methanol + butanoic acid → methyl butanoate + water
  5. 1. Heating under reflux- The carboxylic acid, alcohol and catalyst are heated in a mantle (flame would cause ethanol to catch fire or evaporate). Cold water is pumped through the tube through a reflux condenser. This cools the gas produced which condenses and falls back again. the purpose is to try and react as many of the reactants together
    1. 2. Distillation- this separates you unreacted acid, catalyst and alcohol by heating the mixture in a fractioning column. Vapour rises when the temperature at the top reaches the boiling point of ethyl ethanoate, the liquid that flows out of the condenser is collected. However it is impure still
      1. 3.Purification- The distillate is shaken with an aqueous reagent to remove impurities. E.g sodium carbonate which neutralises acidic impurities. The ester doesn't mix with water in the sodium carbonate solution, so the lower layer (denser non-ester) can be tapped off.
      2. 4. Drying-The remaining upper layer is reacted with calcium chloride to remove ethanol. The organic layer is then transferred to a flask and solid anhydrous calcium chloride is added to remove any remaining water. The calcium chloride is removed by filtration.
        5.Distillation- The last stage to produce a pure ester. Again the slightly impure ester is boiled at the boiling point of ethyl ethanoate so that it will evaporate, and condense into pure dry ethyl ethanoate. Anti-bumping granules control the boiling and stop vigorous reactions from taking place.
  6. Fats and OIls
    1. Fats are esters of the alcohol glycerol (3 -OH hydroxyl goups)and fatty acids (carboxylic acids with long chains 16-20 carbon atoms)
      1. Fats have lots of energy so theyre good for storing energy. when an organism has more energy than it needs, it will store it as fat to use later.
      2. Saturated
        Saturated fats contain only single bonds and therefore has a linear shape. Molecules can therefore pack closer together resulting in higher intermolecular forces so more energy is required to overcome the forces resulting in a high MP+Bp and saturated fats being a solid at room temperature. They are bad for you because they can clog your arteries.
        Butter, cheese, margarine and lard are all saturated fats. Trans fatty acids are saturated molecules. Saturated molecules don't have double bonds resulting in a regular structure. ANIMAL FATS
      3. Unsaturated
        Unsaturated molecules have a C=C double bond in its molecule using an a change in the structure of the molecular arrangement. As the molecule can be less tightly packed, the intermolecular forces are weaker resulting ina low MP+BP and them being a liquid at room temperature therefoe they are considered oils. VEGETABLE OILS
Alkanes
1. Alkanes are a family of hydrocarbons. They are purified from crude oil and are important fuels.
  1. Methane- CH4
    1. Ethane-C2H6
      1. Propane- C3H8
        Butane-C4H10
  2. CnH(2n+2)
2. In the alkanes, the carbon atoms are bonded to each other by single covalent bonds (C–C), so we say that the compounds are saturated.
  1. Alkanes tend to burn well in plenty of air to produce carbon dioxide and water. For example: propane+oxygen→carbon dioxide+water C3H8+5O2→3CO2+4H2O
    1. CH4(g) + 2O2(g) → 2H2O(l) + CO2(g)
    2. Alkanes do not react with common aqueous reagents (substances dissolved in water i.e acids and alkalis) because the C-C and C-H bonds are difficult to break
      1. Alkanes are insoluble in water
Alcohol
1. Alcohols are a family of organic (carbon-based) compounds. The general formula is CnH(2n+1)OH
  1. Alcohols all contain the –OH group and this is generally responsible for their chemical properties and reactions.
    1. They are named after their parent alkanes
      1. Mol-CH4O
      2. Mol-C2H6O
      3. Methanol- CH3OH
        Ethanol- C2H5OH
        Used as a solvent that evaporates quickly and burns with a clean flame. Its also used in cosmetics, lotions and perfumes as it can mix with the oil (smell) and the water (bulk)
        BP- Ethanol:78.5oC, Water:100oC, Ethane:-103oC. This is because they have weaker intermolecular forces than water which are easily overcome but stronger intermolecular forces than alkanes. Longer chain alcohols have higher boiling points.
        The -OH functional group gives molecules a tendency to cling together, like water so they are a liquid at room temperature. The hydrocarbon parts of the molecules (like alkanes) have weak intermolecular forces. Without the functional group and its intermolecular forces, alcohols would be gases at room temperature.
        Oxygen is slightly negative and so attracts the slightly positive hydrogen of another ethanol molecules
        electrons spend more time around the oxygen molecule
        Volatile- liquid evaporates with fumes. Methane and Ethane are also volatile but a gas at room temperature
        Methanol is a chemical feedstock and the chemical industry uses converts methanol into a wide range of products e.g. adhesive, foams, solvents and windscreen washer fluid
2. Alcohols are good fuels because of the presence of the hydrocarbon chain. They burn in a good air supply to produce carbon dioxide and water. E.g. ethanol+oxygen → carbon dioxide+water C2H5OH+3O2 → 2CO2+3H2O
  1. Sodium
    1. ethanol + sodium → sodium ethoxide + hydrogen 2C2H5OH + Na → 2C2H5O-Na+ + H2
      1. Sodium sinks and reacts gently forming the solid ionic compound. Because alkanes do not react with sodium it is unlikely to be the carbon chain in the alcohol that is causing this reaction to take place.
        Water, on the other hand, reacts vigorously with sodium suggesting that it is the -OH group responsible for causing the reaction between alcohol and sodium because both alcohols and water include the -OH functional group.
      2. sodium + water → sodium hydroxide + hydrogen 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Ethanol Production
1. 1. Fermentation
  1. This where glucose is converted via anaerobic respiration into ethanol and carbon dioxide using enzymes (zymase) found in yeast as a catalyst
    1. Feedstocks include sugar beet, sugar cane, maize, corn and rice. Cellulose polymers are heated with acid to break them down into glucose
      1. the optimum temperature is around 37°C - any lower and the reaction is too slow, but any higher and the enzymes are denatured. An optimum pH is required because enzymes significantly high or low pHs will also change the active site. Zymase-pH of 4
        The concentration of ethanol produced by fermentation is 14-15%. If it rises higher than 15% it becomes toxic to the yeast, killing it and stopping the fermentation process
        If higher concentrations are required the mixture must be distilled. E.g spirits such as brandy and whiskey are 40-50% alcohol.
        The ethanol is heated in a fractional colum at a temperature between 78.5oC and 100oC. Doing this turns the ethanol into vapour which is condensed and collected leaving much of the water behind
2. 3. Biotechnology- Modified E-coli
  1. Many plants contain sugars that cannot be broken down by yeast. Modified E-coli. is able to convert all plant sugars into ethaol.
    1. The bacteria would normally produce ethanoic or lactic acid but the modification means that ethanol is produced instead
      1. Sugar→Ethanol+Carbon Dioxide
        Temp: 25-37oC
        pH:6-7
3. 2. Chemical Syntheis
  1. Fermentation is too slow to make ethanol on a large scale.
    1. Instead, it is made using ethane (hydrocarbon in crude oil) which allows high quality ethanol to be produced continuously and quickly. Ethene comes from the 'cracking' of ethane or naptha
      1. Ethene+Steam→Ethanol C2H4+H2O→C2H5OH
        300oC
        60-70x atmospheric temperature
        phosphoric catalyst
4. Sustainability
  1. 2. High temp= burning of non-renewable fossil fuels/crude oil
    1. 2. High Pressure= expensive equipment, energy and safety issues
      1. 2. Higher atom economy. Unreatyed reactants are recycled. Waste hydrogen=Haber Process
        1. Renewable feedstocks (grown). Sugar beet and yeast grow quickly
        1. Doesnt require as much fuel (temp and pressure low)
        1. Low atom economy
        1.Co2 is a greenhouse gas. However Carbon Neutral
        3. Bacteria so no ethical concerns
Carboxylic Acid
1. Carboxylic acids are weak acids which contain the –COOH group and this is generally responsible for their chemical properties and reactions.
  1. Carboxylic acid like all acids donates H+ ions when placed in water, this is known as disassociations. Some acids disassociate more in water than others- this gives us distinct strong and weak acids. MORE DISASSOCIATION=STRONGER ACID
    1. Carboxylic acids are weaker because they dissasociate less ions and because they are less reactive than strong acids such as hydrochloric acid, sulfuric acid and nitric acid
      1. Many carboxylic acids have unpleasant smells and tastes. They are responsible for the taste of vinegar and rancid butter as well as the smell of sweaty socks.
        Longer chain= weaker acid
        Methanoic acid has a lower pH (stronger) than Ethanoic acid. Why?
        In solution in water, a hydrogen ion is transferred from the -COOH group to a water molecule. For example, with ethanoic acid, you get an ethanoate ion formed together with a hydroxonium ion, H3O+.
        This reaction is reversible and, in the case of ethanoic acid, no more than about 1% of the acid has reacted to form ions at any one time.
        Methanoic acid is rather stronger than the other simple acids, and solutions have pH's about 0.5 pH units less than ethanoic acid of the same concentration.
        The structure of the two acids explains the difference in pH of methanoic acid. In methaoic acid, the HCOO- ions is more stable (remains as ion) than the CH3CO- ion in ethanoic acid. There is a greater amount of dissasociatiobn in methanoic acid (or the equilibrium lies further to the right). Alkyl groups push e- (electron) density towards the COO- group destabilising it. the longer the alkyl group, the less stable the COO- ions
    2. dilute solutions of weak acids have higher pH values than dilute solutions of strong acids
2. formed by oxidising major alchohols to form C=0

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OCR 21st Century C7.2

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	Criado por Pritesh Patel mais de 8 anos atrás