THE PRODUCTION OF MATERIALS
Physical properties of hydrocarbons:
· Hydrocarbons made up of hydrogen and carbon atoms only.
· Homologous series members have the same functional group and general molecular formula, but differ by a –CH2 group.
· Alkenes are unsaturated and non-polar molecules.
· Melting and boiling points in a series increases with length of the carbon chain.
Chemical properties of hydrocarbons:
· Alkanes are relatively unreactive.
· Alkenes are reactive, by addition reactions across their double bond.
· Alkenes decolourise bromine water by addition reactions.
· Alkenes can form polymers.
· Combustion of hydrocarbons in oxygen forms CO2 and H20.
Industrial ethylene:
· Ethylene is produced by thermal cracking, or fractional distillation.
· Cracking of alkanes uses hot, porous zeolite catalysts.
· Ethylene is used to manufacture many petroleum products, due to its reactive double bond.
· Addition polymerisation is when alkene monomers combine by addition reactions to form polymer chains.
Condensation polymers:
· Condensation polymers form when monomers bond, and a molecule (usually water) is eliminated.
· Polyesters are condensation polymers whose monomers have a –COOH or –OH group
· Polyamides are condensation products when dialkanoic acid and diamine monomers condense and a water molecule is eliminated.
· Biopolymers of glucose are starch and cellulose.
Ethanol:
· Ethanol is a colourless liquid with 78˚ boiling point and o.79g/cm³ density.
· Ethanol has C-O and O-H bonds, so bond polarity and hydrogen bonding makes it a good solvent.
· Ethanol is water miscible.
· Ethanol burns readily in air in an exothermic reaction.
· Ethanol is used as a petrol extender.
Production of ethanol:
· Ethanol is produced by catalytic hydration of ethylene using phosphoric acid.
· Ethanol can be produced by yeast fermentation brewing, followed by distillation.
Reactions involving metals:
· Electrochemical series lists metals in decreasing order of their ability to lose electrons.
· Metals lower in the series are harder to oxidise.
· Metals higher in the series are more powerful reductants.
· Any metal in the series will displace any metal below it from a solution of its salt.
Galvanic cells:
· Galvanic cells produce electrical energy from chemical energy by the transfer of electrons between reductants and oxidants.
· Voltage of a galvanic cell must be positive for a reaction to occur.
· Electrons flow from the negative electrode.
· Two half-cells are often used with separate electrolytes.
· Voltmeters measure the potential difference between the half-cells.
· A salt bridge links the half-cells, completing the internal circuit.
Electrode potentials:
· A table of standard reduction potentials is used to predict the voltage of a galvanic cell.
· Voltage of cell = voltage of cathode – voltage of anode.
· The farther apart the half-equations are on the reduction potential table, the larger the potential difference of the cell.
Batteries:
· Batteries are sources of electrical energy and consist of one or more galvanic cells attached in a series.
· Lead acid batteries are rechargeable.
· Dry cells and button cells are unable to be recharged.
Commonly used batteries:
· Dry cells are inexpensive, strong, have a low charge-storing capacity, have a short life, have low toxicity when discarded and are used for low drain appliances.
· Lead-acid batteries are used in motor vehicles, are reliable, are heavy, must be recycled due to toxic lead and paste and must be carefully recharged due to release of H2.
· Button cells are expensive, are small and light, provide constant stable long period voltage and recycled to extract silver.
Nuclear reaction equations:
· Unstable nuclei release particles and/or energy to become stable, and are called radioactive.
· The stabilisation process is called radioactive decay.
· Nuclei may be unstable because the neutron to proton ration is too high, the proton to neutron ratio is too high, or there are too many protons and neutrons (the nuclease is too heavy).
· Nucleuses lose mass by emitting alpha particles.
Production of radioisotopes:
· Transuranic elements are produced by neutron bombardment.
· Americium was formed by bombarding plutonium.
· Linear accelerators and cyclotrons may be used in neutron bombardment.
· Many radioisotopes are made by neutron irradiation of stable isotopes in a nuclear reactor.
· The half-life of a radioisotope is the time it takes for half the atoms originally present to decay.
Detection of radiation:
· Photographic film is darkened by radiation.
· Radiographers wear film badges to measure the extent of their radiation exposure.
· The Geiger-Muller tube and counter is based on radiation that ionises argon gas, resulting in a detectable electric pulse.
· The scintillation counter measures the fluorescence when substances are struck by ionising radiation, and hence measures the radiation.
· The gamma camera builds up an image from radiation emitted when radioactive tracers are used in the body.
Uses of radioisotopes in industry:
· Cobalt-60 is used to sterilise surgical instruments and detect flaws in metal.
· Strontium-90 is used gauge the thickness of extruded steel and for paper and plastic sheeting.
· Americium-241 is used in smoke detectors.
· Various isotopes are used to measure the age of water in artesian basins.
· Carbon-14 is used to follow the path of carbon during photosynthesis.
Uses of radioisotopes in nuclear medicine:
· Radioisotopes are administered to patients for diagnostic or therapeutic reasons.
· For diagnosis the radioisotope must have a short half-life and emit only gamma radiation.
· For treatment, the radioisotope must have a half-life that will not cause radiation damage, and must admit alpha and beta radiation to penetrate the lesion being treated. It must also emit gamma radiation to assess that the targeted body part has been reached.
THE ACIDIC ENVIRONMENT SUMMARY
PH of substances:
· Acids are water-soluble substances whose pH is less than 7.
· The strength of acids depends on the extent to which they ionise in water.
· Strong acids such ionise completely.
· Weak acids do not ionise completely and contain the acid and its ions in equilibrium.
· Bases are water-soluble substances whose pH is greater than 7.
· Strong bases dissociate completely.
· Weak bases do not dissociate or ionise completely.
· Neutral substances the [H+] present in pure water.
Neutralisation and Acid-Base Indicators:
· Reactions between acids and bases are called neutralisation.
· An acid-base indicator is an equilibrium mix of a weak acid and its anion, which have different colours.
· Indicators change colour with pH change.
· Dyes may be natural colouring materials or synthetic chemicals.
· Commonly used indicators are Methyl orange, Litmus, and Phenolphthalein.
Use of indicators:
· Soil testing, as plants will only grow in a narrow pH range.
· Acidic soils are made more basic by adding calcium carbonate.
· Basic soils are made more acidic by adding aluminium sulfate.
· PH can bet determined by the use of universal indicator or pH meters with enclosed probe type electrodes.
Oxide Classification:
· Most oxides of metals are basic.
· Some metal oxides are amphoteric and can react with both acids and bases.
· Most oxides of non-metals are acidic and covalent molecular.
· Across the periods, the acidity of oxides increases.
· Down the groups, basicity increases.
Acid Rain:
· Industrial pollution has resulted in an increase in acidity due to the formation of sulfurous and nitric acids.
· Toxic gases and oxides of nitrogen are released from motor vehicles and industrial smoke stacks.
· Acid rain has a pH of less than 5.6.
· Acid rain can result in the loss of aquatic life, the upsetting of the photosynthesis process, damage to forests, the leaching of aluminium from the soil into ground water, damage to buildings and marble statues and an increase in bronchitis.
Equilibrium and Le Chateliers Principle:
· In dynamic equilibrium the amounts of substances are constant, since the rate of forward reaction = the rate of reverse reaction.
· Le Chateliers principle states that if any chemical system is subjected to a change in concentration or temperature, the system will react in a direction to minimise the effect of the change.
Acidity and pH:
· Acids in aqueous solutions are called proton (H+) donors.
· As the [H+] increases, the pH will decrease.
· In a concentrated acid there is a large amount of acid per unit volume.
· The strength of acids is not the same as concentration.
· Equal concentrations of acids do not have equal pH values.
Acid – Base theory:
· Arrhenius in 1887 defined an acid as a substance that dissolves in water to produce hydrogen ions as its only positive ion in solution, and an alkali as a substance producing only hydroxide ions as its only negative ion in solution.
· Bronsted and Lowry in 1923 proposed that in all solvents an acid is a proton donor, and a base is a proton acceptor.
· An acid – base reaction is therefore the transfer of a proton from an acid to a base.
Amphiprotics and pH of salts:
· Amphiprotic acids can act as a base or an acid.
· Salts formed from a strong base/weak acid are alkaline.
· Salts formed from a strong acid/weak base are acidic.
Volumetric Analysis and Titration:
· In titration, the volumetric and conical flasks are receiving vessels and are rinsed with distilled water.
· Accurate acid/base titration curves can be obtained using a pH meter.
Buffers:
· Buffers are solutions that can resist changes in pH on addition of small amounts of an acid or base.
· A buffer is a mixture of a weak acid and its conjugate bas.
· Human blood is buffered at 7.4, and death occurs if 7.0>pH>8.4
· Oxygen in the blood is carried by large haemoglobin molecules and our oxygen system depends the chemical equilibrium haemoglobin + oxygen > oxyhaemoglobin.
Esters:
· Esters are molecules formed from a condensation reaction between an alkanol and an alkanoic acid.
· To favour the formation of the ester, the reaction mixture is refluxed using boiling chips to stop ‘bumping’. The ester is extracted.
· Esters are used in foods, food flavourings, solvents and soaps.
· Esters are good solvents as the dissolve both polar and non-polar organic compounds.
· Soaps are produced by the hydrolysis of long chain esters founds in vegetable oils and fats.
FORENSIC CHEMISTRY SUMMARY
Precautions at a crime scene:
· Is the collection and interpretation of clues from a crime scene, for later presentation at a court of law.
· The scientific methods objectives are to explain, to quantify and to predict.
· The work of forensic chemists is based on the ‘theory of exchange’.
· Crime scenes should be protected from contamination by wearing appropriate clothing.
· Forensic chemists must examine evidence objectively, and alls scientific analyses must be accurate and reproducible.
Classification of aliphatic carbon compounds:
· Alkanols have a have a hydroxyl (OH) group replacing a hydrogen atom.
· Alkanones have a C3O group.
· Alkanoic acids have a COOH group.
Organic analysis:
· Alkenes react with bromine water to decolourise it by addition reactions across the alkenes double bond.
· Alkanols react with sodium metal, but not sodium hydrogen carbonate.
· Primary and secondary alkanols are oxidised by potassium permanganate.
· Alkanoic acids turn red litmus blue, and form esters with alkanols.
Forensic evidence from soils:
· A preliminary separation is carried out using a stereoscopic microscope. Extraneous materials are mechanically separated.
· A mineral examination uses polarised light microscopy.
· Particle size distribution may be carried out.
· Colour comparison of soils depends on the chemical substances present in them.
· The pH of soils can easily be determined using a soil pH meter kit or universal indicator in paper or liquid form.
Carbohydrates:
· Carbohydrates are classified by the number of monomer units they contain.
· Monosaccharides are simple sugars with 5 or 6 carbon atoms.
· Disaccharides contain two monomer units and are formed as a result of acetal linkage, which is a condensation reaction involving the elimination of water.
· If an aldehyde group (CHO) is present, the sugar is an aldose.
· If a ketone (CO) group is present, the sugar is a ketose.
Reducing and non-reducing sugars:
· On warming the oxidising agent Benedict’s solution with a monosaccharide, a brick red precipitate will form.
Condensation reactions for polysaccharides:
· Many monosaccharides join to form polysaccharides, such as starch and cellulose.
Major polysaccharides:
· Cellulose is what makes up plant material, and is the most abundant naturally occurring compound.
· Glycogen is the form in which animal carbohydrate is stored.
· Starch is the form in which plant carbohydrate is stored.
Proteins:
· Proteins contain the atoms of carbon, hydrogen, oxygen and nitrogen.
· Structural proteins are ‘fibrous’ proteins and may be elastic or coiled.
· Physiologically active proteins include enzymes, some hormones, nucleo – proteins and blood proteins.
· Proteins consist of various combinations of a relatively small number of amino acids.
· Chain structure (the sequence of amino acid residues along the peptide chains) is the basis of amino acids.
· Side chains are important in link formation between polypeptide strands.
· Proteins can be broken into different lengths by enzymes.
· Enzymes are physiologically active proteins that have specific functions.
Principles of chromatography:
· Chromatography is a technique used to separate substances with similar physical and chemical properties.
· In paper chromatography, a piece of absorbent paper represents the stationary phase.
· The mobile phase is a solvent that rises up the paper causing the components of a mixture to separate.
· The Rf value = distance moved from origin by component/distance moved from origin by solvent.
· Each component has a characteristic Rf value, and by using known standards the compounds in a mixture can be analysed.
· Rf values will change with the solvent system.
Gas chromatography:
· Gas chromatography permits the separation of complex mixtures into individual compounds, and allows quantitative determination of each compound.
Principles of electrophoresis:
· Electrophoresis is the separation of molecules in an electric field.
· Molecules to be separated are applied to a supporting medium, such as gel or agar.
· The isoelectric point is the pH where there is no electric charge on the molecule.
· Electrophoresis assists the forensic chemist to identify the origins of proteins.
· DNA replicas can be placed in line on the gel.
· Electrically charged DNA molecules move through the gel with larger molecules moving shorter distances.
· DNA is stained and compared to known standards.
DNA testing:
· To identify a DNA pattern, skin, hair follicles, blood, semen or saliva can be used.
· DNA is durable to heat and moisture and slowly degrades in decomposing body tissue.
· DNA is organised into chromosomes containing genes.
· Nucleotides are units of nucleic acids.
· The non-coding sections between genes is used to identify intervals.
· The number of repeats is unique for each individual.
· Forensic scientists target one of these repeated sequences, and this is called single locus probing.
Identifying relationships using DNA testing:
· Chromosomes contain nucleotides identical to those of each parent as well as those that distinguish individually.
· DNA testing is used to identify individuals and for tracing the identity of parents.
The use of the mass spectrometer:
· Mass spectrometers depend on the difference in mass-to-charge ratio of ionised atoms or molecules to sperate them.
· The operating sequence is that gas-phase ions are created, then separated based on their mass/charge ration then to finally measure the quantity of ions.
· Mass spectrometers are used to determine the mass of naturally occurring isotopes and for calculating the average relative masses for the elements from mass spectrum results.
Emission spectra of elements:
· Each element has its own electron configuration.
· The emissions spectrum of elements is a result of electrons moving between the different electronic levels.
· Light is emitted when electrons fall from high energy levels to low ones.
· Each line in the emission spectrum corresponds to a possible transits ion between electron orbitals in the atom.
· Flame testing is used in for group 1 and 2 elements where one particular electron transition occurs more readily than any other.
Use of emission spectra:
· All elements have identifiable emission spectra that can be used to identify elements.
· Electrical discharge tubes atomise and excite gaseous elements.
· Gas in a glass tube will glow if a high voltage is passed through it.
· When light from the discharge tube is passed through a prism, discrete sharp lines at specific wavelengths replace the continuos colour band.
· These intense lines are called the bright light emission spectrum.
· No two elements have the same emission spectrum.
