C7: Further Chemistry

C7: Further Chemistry

1. Organic Compounds

   • Organic Molecules and Functional Groups
     • Alkanes
       • ALKANES: a family of hydrocarbons
         • methane
         • ethane
         • propane
         • butane
       • made up of chains of carbon atoms surrounded by hydrogen atoms
       • all have the formula CₓH₂ₓ+₂, where x is the number of carbon atoms in the chain
       • only contain single covalent bonds between carbon atoms - they're SATURATED compounds
         • in UNSTAURATED compounds, there are carbon to carbon (C=C) bonds
       • burn to give carbon dioxide and water
         • alkane + oxygen → carbon dioxide + water
       • don't react with most chemicals
         • don't react with aqueous reagents
           • AQUEOUS REAGENTS: substances dissolved in water
         • don't react because the C—C and C—H bonds in them are difficult to break
     • alcohols have an -OH functional group and end in '-ol'
       • all alcohols have similar properties because they all have the -OH functional group
   • Alcohols
     • Alcohols
     • the general formula for an alcohol is CₓH₂ₓ₊₁OH
       • x again represents the number of carbon atoms in the chain
     • I need to know the first two alcohols...
       • methanol
         • CH₃OH
         • used in the chemical industry as a starting point for the manufacture of other chemicals
       • ethanol
         • C₂H₅OH
         • can be made by fermentation
         • used in perfumes and aftershave lotions, as it can mix with both the oils, which gives it the smell, and the water, which makes up the bulk
         • can be made from biomass
     • react with sodium
       • sodium + water → sodium ethoxide + hydrogen
       • although much less vigorously than with water
       • unlike alkanes
     • burn in air to produce carbon dioxide and water
       • ∵ ils contient hydrocarbon chains
   • Carboxylic Acids
     • all have the functional group -COOH
       • this gives them all similar properties
     • their names start with start with the usual meth/eth/prop/but and end in -anioc acid
     • • Жишээ нь:
         • methanoic acid
           • HCOOH
           • aka formic acid
         • ethanoic acid
           • CH₃COOH
           • aka acetic acid
     • react with stuff like other acids
       • carboxylic acid + metal → salt + hydrogen
         • ethanoic acid + magnesium → magnesium ethanoate
       • carboxylic acid + carbonate → salt + water + carbon dioxide
       • carboxylic acid + alkali → salt + water
     • are weak acids - less reactive than strong acids like HCl, H₂SO₄
     • have strong smells and tastes
       • vinegar, dilute ethanoic acid, is an example of this
   • Esters
     • esters have the functional group -COO-
     • formed when carboxylic acids react with alcohols in the presence of a strong acid catalyst
     • production of esters
     • uses
       • often used in flavourings and perfumes
         • many have sweet and fruity tastes and smells
         • volatile, so they're good for perfumes, as the molecules evaporate easily, so can drift into the smell receptors of your nose
       • also used as solvents for paint, glue, ink and in nail varnish remover
     • fats and oils are esters of glycerol and fatty acids
       • fatty acids = carboxylic acids with long chains (≈ 16 to 20 carbons)
         • fatty acids can be saturated (only C—C bonds) or unsaturated (C=C bonds)
       • glycerol = an alcohol
       • plants and animals make fats and oils to store excess energy
         • animal fats are mainly saturated, vegetable fats mainly unsaturated

2. Analysis

   • Analytical Procedures
     • QUALITATIVE analysis tells you what a sample contans
     • QUANTITATIVE analysis tells you how much of a substance a sample contains
     • chemical analysis is carried out on SAMPLES, ∵...
       • it might be hard to test all of a material if you've got lotsa it
       • if something goes wrong, you'll still be able to go back, take another sample and try again
     • samples are analysed in solution
       • if the solvent is water, it's aqueous, if not, it's non-aqueous
     • STANDARD PROCEDURE: everyone does everything the same way
       • scientists within companies, nations, or international groups agree to all use the same methods of working
         • the methods chosen are deemed the safest, most effective and most accurate
       • there are standard procedures for the collection, storage and analysis of samples
   • Chromatography
     • uses TWO PHASES
       • the MOBILE phase
       • the STATIONARY phase
     • CHROMATOGRAPHY: an analytical method used to separate then identify the substances in a mixture
   • Solution Concentrations
     • concentration = mass (of solute) ÷ volume (of solution)
       • concentration is measured in grams per dm³
         • 1 dm³ = 1 litre = 1000 cm³
     • a STANDARD SOLUTION = any solution that you know the concentration of
   • Titration
     • the main stages of a quantitative titration analysis are as follows...
       • measuring out accurately a specific mass or volume of the sample
         • working with replicate samples
           • dissolving the samples quantitatively
             • measuring a property of the solution quantitatively
               • calculating a value from the measurements
                 • estimating the degree of uncertainty in the results
     • titrations are used to check the purity of an acid or alkaline product

3. Green Chemistry

   • The Chemical Industry
     • lots and lots of chemicals are made for lots and lots of different things on different scales...
       • BULK
         • produced on a large scale, 例如...
           • ammonia
           • sulfuric acid
           • sodium hydroxide
           • phosphoric acid
       • fine
         • produced on a small scale, მაგალითად...
           • medicines
           • fragrances
           • food additives
     • new chemical products need lots of RESEARCH
       • before new chemical products are made, huge amounts of research has to be done
         • this can take years and years and be more expensive than a return train ticket to Scotland, but will all be worth it in the end
       • مثلا, to make a new production process run efficiently, a catalyst may need to be found, involving the following processes...
         • testing potential catalysts using trial and error
           • making computer models of the reaction to work out which substance might work as a catalyst
             • designing or refining the manufacture of the catalyst to ensure the safe, efficient and cost effective mass-production of the catalyst
               • investigating the risks to the environment posed by using the new catalyst and trying to minimise them
     • GOVERNMENT REGULATIONS protect people and the environment
       • this is done to protect workers, the general public and the environment
       • mar shampla, there are regulations about...
         • USING CHEMICALS
           • näiteks, sulfuric acid is sprayed on potato fields to destroy the leaves and stems of the plant, making it easier to harvest them
             • government regulations restrict how much acid can be used and require signs to be displayed to warn the public
         • STORAGE
           • many dangerous chemicals must be kept in locked storerooms
           • poisonous chemicals must be stored in either sealed containers or well ventilated store cupboards
         • TRANSPORT
           • lorries transporting chemicals that could be dangerous must display hazard symbols and identification numbers to help the emergency services to deal with any accidents or spills
   • Characteristics of Green Chemistry
     • there are several stages in the production of useful chemicals:
       • 1: the preparation of feedstocks
         • this requires raw materials, the naturally occurring substances which are needed, til dæmis...
           • crude oil
           • natural gas
         • FEEDSTOCKS: the actual reactants needed for the process, kwa mfano...
           • hydrogen
           • ethanol
         • the raw materials usually have to be purified in some way to make the feedstocks
         • 2: synthesis
           • the feedstocks (id est reactants) are converted in to products using way cool science stuff
           • the conditions must be carefully controlled to ensure that the reaction happens at a sensible rate
           • 3: separation of products
             • chemical reactions, as magic as they are, usually produce the substance that you want plus some other chemicals, known as by-products
             • sometimes there are also some reactants let over that didn't get used
             • everything has to be separated out so that the different chemicals can be dealt with in different ways
             • 4: monitoring the purity of the product
               • even after everyone has tried their best to separate everything out, there may still be some other bits and bobs mixed in with the 'final' product, ∴ it's not completely pure
                 • for this reason, the product has to be monitored to ensure that it stay between certain levels
                   • different industries need different levels of purity, depending on wat the product's going to be used for...
                     • if a product is going to end up inside people (id est medicines, nakadhalika), it should be pretty pure
                     • if a slightly impure product will be fine for the job, there's no point wasting time and money on purification, especially if you've never been to France. France is great.
             • 5: handling of by-products and wastes
               • où possible, waste products are sold or used in another reaction
               • if the reaction is exothermic, there may be waste heat
                 • heat exchangers can use excess heat to produce steam or hot water for other reactions, saving energy and money
               • waste products must be carefully disposed of so that they don't harm other people or the environment
                 • there are legal requirements about this
               • scientists, eg Carlos, must be very cautious when approaching wheat by-products
     • there are eight key questions about SUSTAINABILITY...
       • will the raw material run out?
       • how good is the atom economy?
       • what do I do with the waste products?
       • what are the energy costs?
       • will it damage the environment?
       • what are the health and safety risks?
       • any there any benefits or risks to society?
       • is it profitable?

4. Energy Changes

   • Energy Transfer
     • energy is always SUPPLIED to BREAK bonds
       • ergo bond breaking is an ENDOthermic process - energy must be supplied
       • and bond forming is an EXOthermic process - energy is released
       • so in EXOTHERMIC reactions, the energy released by forming bonds is greater than the energy used to break them
       • and in ENDOTHERMIC reactions, the energy supplied to break the bonds is greater than the energy released by bonds forming
   • Bond Energies
     • every chemical bond (isibonelo H — H) has a particular bond energy associated with it
       • the bond energy varies slightly depending on the compound the bond occurs in
       • one can use these known bond energies to calculate the overall energy change of a reaction
         • one uses the following formula:
           • overall energy = energy required to - energy released change break bonds by forming bonds
   • Catalysts
     • activation energy is needed to start a reaction
       • this can be lowered by using a catayst
     • some industrial reactions use enzyme catalysts

5. Reversible Reactions and Equilibria

   • Reversible Reactions
     • a REVERSIBLE REACTION: a reaction where the products of the reaction can themselves react to produce the original reactants
       • A + B ⇌ C + D
     • the Haber Process is a reversible reaction used to produce ammonia
       • N₂(g) + 3H₂(g) ⇌ 2NH₃(g) (+ heat)
       • the feedstocks for the process are nitrogen and hydrogen
         • the nitrogen is obtained from the air, which is 78% nitrogen
         • the hydrogen comes from the cracking of chemicals in natural gas using steam
       • ammonia is used in the manufacture of fertilisers, explosives, dyes, medicines and a variety of other chemicals
       • the reaction is carried out under certain conditions to make it as efficient as possible...
         • pressure: 200 atmospheres
         • temperature: 450°C
         • catalyst: iron
       • nitrogen fixation is a process that turns the N₂ in the air into ammonia
         • the Haber Process is a non-biological way of fixing nitrogen
   • Equilibria
     • if a reversible reaction takes place in a closed system, so that none of the reactants can escape, a state of dynamic equilibrium will always be reached
     • EQUILIBRIUM: when the relative (%) quantities of reactants and products will reach a certain balance and stay there
       • when this happens, there may still be reactions going on, but the forward and backwards reactions will be happening at the same rate - this is called DYNAMIC EQIULIBRIUM

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