C7- Chemistry for a sustainable world

A summary of the C7- Chemistry for a sustainable world module from the OCR 21st century chemistry textbook

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  • Created by: R_Hall
  • Created on: 17-05-11 14:15

Alkanes

  • Alkanes are a family of hydrocarbons
  • There are many alkanes- methane, ethane, propane, butane
  • Alkanes burn in plenty of air to produce carbon dioxide and water
  • Alkanes are oily; they don't dissolve in water or mix with it.
  • 1-4 carbon= gas, 4-17 carbon= liquid, 17+ carbon= solid
  • Alkanes are unreactive towards aqueous reagents because the C-C and C-H bonds are unreactive
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Alcohols

  •  Methanol- needed to manufacture adhesives, foams, solvents, solvents and windscreen washer fluid. Ethanol- used in wine, beer and spirits. Also used in cosmetic lotions and perfumes
  • The characteristic properties of alcohols are due to the presence of the -OH functional group
  • Methanol and ethanol are liquid at room temp.- alkanes with comparable molecular masses are gases. The attractive force between molecules of alcohols are stronger that alkanes
  • The presence of an -OH group of atoms gives the molecules the tendency to cling together (like water)
  • Alcohols burn in air because of the presence of a hydrocarbon chain
  • Alcohols react with sodium in a similar way to water- both water and alcohol molecules have -OH group.
  • Only the H atom attached to the O atom reacts. (H-C, H atoms are inert)
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Carboxylic acids

  • The functional group is -COOH, gives characteristic properties of carboxylic acids
  • Many carboxylic acids have unpleasant smells and tastes; butonic acid= rancid butter
  • Vinegar is a dilute solution of ethanoic acid (beer- OXIDISATION- vinegar)
  • Carboxylic acids ionize to produce hydrogen ions when dissolved in water. Only ionize slightly- weak acids
  • Carboxylic acids show normal reactions of acids with metals, carbonates and alkali's
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Esters

  • Esters have distinctive smells and are responsible for the smells and flavours of fruits. They are used to flavour and scent foods, perfumes
  • They are also used as plasticisers and solvents
  • Fats are tri-esters of glycerol and fatty acids (carboxylic acids in fats and oils)
  • Living organisms make fats and oils as an energy store
  • Animals fats are mostly saturated molecules (molecule contains as much hydrogen as it can take) and vegetable oils are mostly unsaturated molecules
  • Saturated compounds most are C-C bonds , unsaturated compounds some are C=C bonds
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Energy changes

  • Exothermic-An exothermic reaction gives out heat to its surroundings (combustion, magnesium and hydrochloric acid)
  • Endothermic-An endothermic reaction takes in energy from its surroundings (melting, boiling, photosynthesis and citric acid and sodium hydro carbonate)
  • Energy is needed to break chemical bonds and energy is given out when chemical bonds form
  • Activation energy- The minimum energy needed in a collision between molecules if they are needed to react. The height of the energy barrier between reactants and products in a chemical change
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Reversible reactions and equilibria

  • Some chemical reactions are reversible; eg. water freezes to ice, ice melts to water, water heats to steam, steam condenses to water
  • Reversible reactions reach a state of equilibrium- a state of balance in a reversible reaction where neither the forward nor backward reaction is complete
  • Dynamic equilibrium- At equilibrium, the forward and back reactions are still continuing, but at equal rates so there is no overall change (chemical equilibria are dynamic)
  • Understanding chemical equilibrium can allow scientists to control the pH of a solution
  • Hydrochloric acid is a strong acid- all the molecules of hydrogen chloride ionize when the gas dissolves in water
  • Carboxylic acids are weak acids. In a dilute solution of ethanoic acid 1 out of 100 molecules ionize. In the solution there is dynamic equilibrium
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Analytical procedures

  • Qualitative analysis- Any method for identifying the chemicals in a sample (TLC)
  • Quantitative analysis- Any method for determining the amount of chemical in a sample (acid- base titration)
  • An analysis must be carried out on a sample that represents the bulk of the material under test (a representative sample)
  • Many analytical methods are based on samples in a solution
  • Standard procedures are needed for the collection (athlete urinates in front of testing officer), storage (coded) and preparation of a sample
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Chromatography

  • In chromatography substances are separated by movement of a mobile phase (The solvent that carries chemicals from samples) through a stationary phase (The medium mobile phase passes through).
  • Aqueous solvent- water is the solvent
  • Non- aqueous solvent- a solution other than water is the solvent
  • IN each component in a sample, there is dynamic equilibrium between the stationary and mobile phases
  • Separation by chromatography depends on the distribution of the compounds in a sample between the mobile and stationary phases
  • Reference materials-Known chemicals used in an analysis for comparison with unknown chemicals
  • Rf (retardation factor) = distance travelled by solute/ distance travelled by solvent
  • Locating agent- a chemical used to show up colourless spots on a chromatogram
  • Retention time- The time it takes for a component in a mixture to pass through a stationary phase
  • On chromatograms, the peak signifies a compound and the height of the peak is the volume of a compound in a mixture
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Quantitative analysis by titration

  • Main stages of a quantitative analysis
  • 1. Accuratly measuring a mass or volume of sample
  • 2. Using replicate samples
  • 3. Dissolving samples quantitatively
  • 4. Measuring the solution
  • 5. Calculating a value from the measurements
  • 6. Estimating a degree of uncertainty
  • Concentrations of solutions are measured in g/dm cubed
  • Measurement uncertainty- variations in analytical results owing to factors that the analyst can not control. Can be systematic (gives consistently higher) or random (range of wrong results)

 

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The chemical industry

  • Bulk chemicals are made on a large scale (eg. chlorine, sulfuric acid, ethene), fine chemicals are made on a smaller scale (eg. drugs, pesticides, food additives)
  • New chemical products or processes are the result of an extensive programme of research and developments
  • Governments have strict regulations to control chemical processes as well as the storage and transport of chemicals to protect people and the environment
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What are the characteristics of green chemistry?

  • The production of useful chemicals involves several stages (preparation of feed stocks, synthesis, separation of products, handling of by-products and wastes and monitoring of purity)
  • The sustainability of any chemical process depends on-
  • 1. If the feedstock is renewable
  • 2. The atom economy (mass of atoms in product/ mass of atoms in reactants x100)
  • 3. The nature and amount of by-products or wastes
  • 4. Energy inputs and outputs
  • 5. Environmental impact
  • 6. Health and safety risks
  • 7. Social and economic benefits
  • A catalyst provides an alternative route for a reaction with lower activation energy
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Making ethanol by three methods

  • Ethanol is made on an industrial scale as a fuel, solvent and as a feedstock for other processes
  • There is a limit to the concentration of ethanol solution that can be made by fermentatition
  • Ethanol solution can be concentrated by distillation to make products such as whisky and brandy
  • To make ethanol by fermentation of sugar and yeast, optimum conditions are needed (35c and pH 7)
  • Genetically modified E.coli bacteria can be used to convert waste biomass from a range of sources into ethanol (reaction at 37c)
  • Ethane (from oil refining) can be converted to ethanol if it is reacted with steam at a high temperature and with high pressure
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Comments

alex colton

Really helpful thanx

alex:)

oyindamola

thanks

Tommi

thanks this helps

Super Voltage

Thank You Very Much. This is very Helpful. 

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