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Definitions
All definitions
| Term | Definition |
|---|---|
| The mole | of a substance is the amount of the substance that contains as many particles as 12g of carbon-12 |
| Molecular formula | of a compound is a formula showing the exact number of each type of atom present in the molecule |
| Empirical Formula | of a compound is a formula that gives the simples ratio between each atom in the compound or molecule |
| Isotope | is an atom of the same element that has the same atomic number but a different mass number e.g. C12, C13, C14 |
| Relative atomic mass | is the average mass of the atoms of the element relative to 1/12 of the mass of the C-12 isotope |
| Relative molecular mass | is the average mass of molecules of the compound relative to 1/12 of the mass of the C-12 isotope |
| Standard solution | a solution whose concentration is known |
| Primary standard | is a substance that can be obtained in a stable, 100% pure and soluble solid form so that it can be weighed out accurately to give a solution of accurate known concentration |
| Arrhenius's theory of acids | a substance that dissociated in water to form H+ ions |
| Arrhenius's theory of bases | a substance that dissociates in water to form OH- ions |
| Monobasic acis | can donate one H+ ion per molecule |
| Dibasic acid | can donate two H+ ions per molecule |
| Tribasic | can donate three H+ ions per molecule |
| Strong acid/ base | dissociates fully in water |
| Weak acid/ base | does not dissociate fully in water |
| Bronstad-Lowry theory of acids | acid is a proton donor |
| Bronsted-Lowry theory of bases | base is a proton acceptor |
| Amphoteric | a substance that can act as both an acid and a base |
| Conjugate pairs | conjugate acid/base pair is an acid and a base that differ by one proton |
| A salt | is formed when the hydrogen of an acid is replaced by a metal (or ammonium ion) |
| Neutralisation | the reaction between an acid and a base to produce a salt and water |
| Oxidation (in terms of oxygen) | occurs when a substance gains an oxygen |
| Reduction (in terms of oxygen) | occurs when a substance loses an oxygen |
| Oxidation (in terms of electron transfer) | the loss of electrons |
| Reduction (in terms of electron transfer) | the gain of electrons |
| Oxidation (in terms of oxidation number) | the increase of oxidation number |
| Reduction (in terms of oxidation number) | the decrease of oxidation number |
| Redox reaction | a reaction where substances undergo oxidation and reduction |
| Oxidising agent | is a substance that brings about oxidation in other substances but is reduced itself |
| Reducing agent | is a substance that brings about reduction in other substances but is oxidised itself |
| Efflorence | loss of water |
| Hard water | water that doesn't form a lather easily with soap |
| Hardness | is caused by the presence of Ca2+ or Mg2+ ions dissolved in the water. These ions react with the soap to form a scum rather than a lather |
| Temporary hardness | can be removed by boiling. Caused by Ca(HCO3)2 |
| Permanent hardness | cannot be removed by boiling. Caused by CaCl2, CaSO4, Ca(OH)2 |
| Suspended solids | solids that are floating on top or solids that are mixed (suspended) throughout the sample of water (dirt particles). Removed by filtration |
| Dissolved solids | solids that are soluble in the liquid. Removed by evaporation |
| Screening | water is passed through graded screens/ wire mesh to remove twigs and rubbish etc. |
| Settling/ Sedimentation | water is pumped into the bottom of sedimentation tanks so as not to disturb the clearer water at the top (maximise settling). The suspended particles settle to the bottom |
| Flocculation | a flocculating agent (Aluminium sulphate) is added. This causes dirt, suspended solids to coagulate together. This helps sedimentation. |
| Filtration | water is passed through beds of graded sand and gravel. Layers are cleaned regularly. Water that comes out is colourless but not fit for drinking. |
| Chlorination | chlorine of sodium fluoride is added to prevent tooth decay |
| pH adjustment | too acidic -> a base: Calcium Hydroxide can cause corrosion of pipes too basic -> an acid: dilute Sulfuric acid can cause hard water |
| Edta | ethylene diamine tetra acetic acid |
| Eutrophication | is the enrichment of water with nutrients (Nitrates and Phosphates) which leads to the excess growth of algal bloom and results in the dissolved oxygen levels being lowered |
| B.O.D (biological oxygen demand) | amount of dissolved oxygen consumed by a biological action when a sample of water is kept in the dark @ 20°C for 5 days |
| The Winkler Method | the method used to determine the amount of dissolved oxygen in a sample of river water |
| Cumulative poisons | build up in the body over time |
| Free Chlorine | chlorine that exists in water as Hypochlorous acid (HOCl) and the Hypochlorite ion OCl- |
| Activation energy | is the minimum energy colliding particles require for a reaction to occur |
| Effective collision | is a collision that will result in a reaction between colliding particles and results in a product being formed |
| Catalyst | a substance that alters the rate of a chemical reaction but is not consumed by the reaction |
| Inhibitors | a catalyst that slows down the rate of reaction |
| Homogeneous catalyst | the reactants and the catalyst are in the same phase |
| Heterogeneous catalyst | the reactants and the catalysts are in different phases |
| Autocatalysis | occurs when one of the products formed catalysis the reaction****** |
| Cathode rays | are streams of negatively charged particles called electrons |
| Atomic Radius | is half the distance between the nuclei of two atoms of the same element that are joined together by a single convalent bond |
| Ionisation energy | is the minimum energy required to remove the most loosely bound electron froma neutral gaseous atom in its ground state |
| Second ionisation energy | is the minimum energy required to remove the most loosely bound electron from a mono-positive ion |
| Energy level | a fixed energy value that an electron in an atom may have |
| Atomic Orbitals | is the region of space around the nucleus in which there is a high probability of finding an electron |
| Orbits | an orbit was used by Bohr to describe the papth of the electron travelling in a fixed path with a certain velocity at a precise distance from the nucleus |
| Quantisation | an electron can only have a specific energy value in a particular energy level |
| Continuous Spectrum | when white light is passes through a prism it is broken into an array of colours called a continuous spectrum |
| Lyman Series | n=1 ultra violet (high energy) |
| Balmer Series | n=2 visible spectrum |
| Pashen Series | n=3 Infrared |
| Electronegativity | is the force of attraction that an atom of an element has for a shared pair of electrons in a covalent bond |
| Electropositive elements | have a low electronegativity value |
| Pure covalent bond | if there is no difference between the electronegativity values of the two atoms |
| Polar covalent bond | if there is a difference of between 0 and 1.7 between the electronegativity values of the two atoms. Electrons not shared equally. |
| Ionic bond | if the difference between the electronegativity values of the two atoms is greater than 1.7 |
| Polar Molecules | the partial positive and partial negative poles in the molecule are separated by a distance |
| Non-polar molecules | are where the bond dipoles balance each other producing a molecular dipole (vector sum) of zero |
| Intra Molecular Bonding | these are attractive forces holding the atoms together within the molecules |
| Inter Molecular Bonding | these are attractive forces between the molecules |
| Van Der Waal forces | a type of intermolecular bonding with very weak attractive forces which occurs between non-polar molecules, and result in the formation of temporary dipoles |
| Dipole | is a pair of separated opposite charges |
| Permanent Dipole-Dipole forces | are forces of attraction between the partial negative charge of one molecule and the partial positive charge of the other molecule in polar molecules |
| Hydrogen bonding | is where Hydrogen is bonded to a small highly electronegative element like oxygen, nitrogen or fluorine |
| V.S.E.P.R (valence share electron pair repulsion theory) | Electron pairs repel each other to be as far apart as possible and give a shape |
| Bond pair | a pair of electrons that are involved in bonding |
| Lone pair | a pair of electrons not involved in bonding |
| Bond energy | average energy required to break one mole of bonds and to separate the atoms in the gaseous state |
| Linear shape | 2 bond pairs, 0 lone pairs, 180° angle |
| Triangular Planar shape | 3 bond pairs, 0 lone pairs, 120° angle |
| Tetrahedral shape | 4 bond pairs, 0 lone pairs 109.5° angle |
| Pyramidical shape | 3 bond pairs, 1 lone pair 107° angle |
| V-shaped shape | 2 bond pairs, 2 lone pairs 104.5° angle |
| D-block element | is where the electrons go into the d sublevel after an outer s sublevel |
| A transition metal | has an incomplete d sublevel and variable valencies |
| Valency | valency of an element is the number of atoms of hydrogen or any other mono-valent element with which the element combines |
| Covalent Bonding in terms of orbitals | is formed when two atomic orbitals overlap |
| A sigma bond | is a type of covalent bond when there is a head-on overlap of two orbitals |
| A Pi bond | is formed when there is a side-ways over-lap of two p-orbitals |
| Single bonds | contain one sigma bond only |
| Double bonds | contain one sigma and one pi bond |
| Triple bonds | contain one sigma bond followed by 2 pi bonds |
| Radioactivity | is the spontaneous breaking up of an unstable nuclei with the emission of alpha, beta and gamma particles |
| Alpha particles | have 2 protons and 2 neutrons stuck together, low penetrating power and can be stopped by a few cm of air or cardboard. positively charged- affected by magnetic/ electric fields e.g. Americium-241 used in smoke detectors |
| Beta particles | is simply an electron that is emitted from an unstable nucleus. Slight penetrating power, can be stopped by a sheet of Aluminium. Negatively charges- affected by magnetic/ electric fields e.g. used in carbon dating |
| Gamma particle | high energy electromagnetic radiation. Very penetrating, only stopped by a thick slab of lead. No charge, not affected by electric/ magnetic fields e.g. cobalt-60 used in cancer treatment |
| Half life | of an element is the time taken for half of the nuclei in any given sample to decay |
| Radioisotopes | are unstable, radioactive isotopes |
| Background radiation | more than half of background radiation is caused by radon gas which is formed by the decay of radioisotopes found in rocks |
| a gas | is a substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is contained |
| An ideal gas | is a gas which obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure |
| organic chemistry | is the study of the compounds of carbon |
| A Hydrocarbon | is a compound that contains Hydrogen and carbon only |
| A Homologous Series | is a group of compounds having the same general formula, same functional group, similar chemical properties, showing graduations in physical properties and each member differs from the previous member by a CH2 unit |
| Structural formula | of a compound shows the way the atoms are arranged in a molecule |
| Molecular Formula | tells us the actual number of atoms of each element in the molecule |
| Saturated Compounds | are compounds in which the C-C atoms are linked by single bonds only, contain no double/triple C-C bonds |
| Structural Isomers | are compounds with the same molecular formula |
| Alkanes | saturated hydrocarbons (all bonds are single) |
| Chloroalkanes | are compounds in which one or more of the hydrogen atoms in the alkane molecule have been replaced by a chlorine atom |
| Homolytic Fission | equal sharing of electrons- formation of radicals |
| Heterolytic fission | Unequal sharing of electrons- formation of ions |
| Unsaturated compounds | are compounds that contain at least one carbon to carbon double or triple bond |
| Alkenes | unsaturated hydrocarbons (containing at least one C-C double bond) |
| Alkynes | unsaturated hydrocarbons that contain a C-C triple bond |
| Aliphatic compounds | are organic compounds that consist of open chains of carbon atoms or closed chain compounds that resemble them in chemical properties. They do not contain a benzene ring |
| Aromatic compouns | are compounds that contain a Benzene ring structure in their molecules |
| Benzene | is not reactive is not an unsaturated compound, has bond lengths of between the length of a C-C single bond and a double bond. Highly toxic and carcinogenic. Non-polar, insoluble in (polar) water but soluble in cyclohexane |
| Delocalised electrons | do not belong to any particular atom |
| Crude oil | formed over hundreds of millions of years from the bodies of sea creatures that decayed under layers of sedimentary rock, as a result of pressure and heat |
| Fractional Distillation | involves the heating of crude oil and separating the various mixtures on the basis of their boiling points |
| Fractioning Column | is a tall cylindrical tower of steel, containing a series of trays to help collect the condensed liquid |
| LPG | Liquid Petroleum Gas |
| Mercaptons | are compounds containing sulphur that are added to gases to give them a distinct odour for safety purposes |
| Petrol and Naphta | fractions are used to make petrol. (winter: lower molecular mass components, more volatile. Summer: less volatile, not evaporate) |
| Kerosine | used for heating and aviation fuel and may be cracked to provide extra petrol |
| Gas oil | used to make diesel fuel for cars, trains etc. and can be cracked to produce extra petrol |
| Less Volatile tarry fractions | used to make candle wax, grease and bitimen for tarring roads |
| Smooth running of a car engine | depends on the petrol-air explosion occurring in the cylinder at just the right moment |
| Knocking/ Auto Ignition | is the tendency to premature ignition: petrol-air explosion too early-metallic noise from engine, caused by exploding when compressed as opposed to a spark for ignition, engine loses power and cylinders maybe damaged |
| Starting the egine | 1. petrol vaporises 2. petrol vapour mixes with air in the carburetor 3. this mixture comes into the cylinder (inlet valves) and is compressed 4. spark from spark plug ignites the compressed gases 5. gases expand -piston moves down |
| 6. piston comes back up, gases are pushed out process repeats 7. up/down motion of piston is converted rotational movement drives the vehicle | |
| Reduced knocking | straight chained alkanes ignite easily- causing knocking. Branched alkanes more efficient petrol |
| Octane number | of a fuel is a measure of the fuel to resist auto-ignition, measured by comparing performance to 2 reference hydrocarbons Heptane and 2,2,4trimethypentane. octane number 97 means 97% 2,2,4trimethylpentane and 3% heptane |
| Factors affecting octane number | short chain- high octane, more branched- high octane, cylic compounds (especially benzene) high octane |
| tetraethyl lead | used to reduce knocking in the past, but toxic to humans, and is a catalytic poison (inhibitor) in catalytic converter |
| new ways to increase octane number | 1.Oxygenates: methanol ethanol MTBE 2. Reforming: using catalysts to form ring compounds 3.Isomerisation: using heat and catalysts to branch isomers |
| 4.Catalytic cracking: using heat and a catalyst to break down long chains into short chained hydrocarbons. At least one product is unsaturated | |
| Bomb calorimeter | used in industry to accurately measure heats of combustion |
| Method of bomb calorimeter | 1.A known mass of substance placed in crucible 2.Pressurised with oxygen 3.Bomb placed in known quantity of water 4.Ignited electrically 5.Heat produced => E=mc∆θ |
| Steam burn worse than boiling water | 1.steam condenses on cold skin 2.excess energy of gaseous lost when turn to liquid |
| Heat of Combustion | heat given out when 1mole of a substance is burned in excess oxygen (kJ/mol) |
| Heat of Neutralisation | heat change that occurs when 1mole of H+ ions neutralise with 1mole of OH- ions (kJ/mol) |
| Heat of Formation | heat change that occurs when 1mole of a substance in its standard state is formed from its elements in their standard states (kJ/mol) |
| Heat of Reaction | heat change that occurs when the number of moles of reactants indicated in a balanced equation completely react (kJ/mol) |
| Kilogram Calorific Value | heat produced when 1kg of a fuel is burned in excess oxygen (kJ/mol) |
| Endothermic Reaction | heat is absorbed ∆H=+ |
| Exothermic Reaction | heat is produced ∆H=- |
| Alll heat of neutralisation values same for strong acids | all strong acids all completely dissociate in solution, all have the same fundamental change (H+ + OH- -> H2O) |
| Heat of neutralisation values smaller for weaker acids | only dissociate slightly for neutralisation full dissociation must occur. Heat needs to be supplied- endothermic reaction. Value of heat of neutralisation smaller. |
| Chemical Equilibrium | is a state of dynamic balance where the rate of the forward reaction is equal to the rate of the reverse reaction |
| Dynamic | the reaction hasn't stopped products are being formed and returning to reactants constantly |
| Equilibrium Constant Kc | [products]/[reactants] affected only by a change in temperature |
| Haber Process | manufacture of Ammonia: 1.Iron catalyst 2.Low temp (idea but too slow) 3.Higher temp is used with Fe catalyst 5.High Pressure (safety)(cost) |
| Contact Process | preparation of Sulphuric Acid (H2SO4) equation: 2SO2 + O2 -> 2SO3 catalyst: Vanadiumm Pentoxide V2O5 High pressure (tends to liquify SO3)(cost)(safety) |
| pH | -log10[H+] where [] is concentration measures in moles per litre |
| The range of indicator | is the spread of pH over which the which indicator changes colour |
| An indicator | is a weak acid or weak base that changes colour according to the pH of the solution that it is put into |
| Primary Alcohol | is one where the carbon atom joined to the -OH group is attached to only one other carbon atom |
| Secondary Alcohol | is one where the carbon atom joined to the -OH group is attached to two other carbon atoms |
| Tertiary Alcohol | is one where the carbon atom joined to the -OH group is attached to three other carbon atoms |
| Denaturing agent | toxic methanol added to industrial alcohol to prevent consumption |
| Fehling's solution | Fehling's A: Copper Sulphate in water Fehling's B: Potassium Sodium Tarterate & NaOH |
| Tollens reagent (Ammoniacal Silver Nitrate) Silver Mirror Test | silver nitrate, NaOH (brown precipitate formed), Ammonia (precipitate dissolves). If stored explosive products may form. |
| Glacial Acetic Acid | solid form of pure ethanoic acid |
| Dimer | when two hydrogen bonds occur between the carboxylic acids |
| Inductive effect | C in C=O is slightly positive, and attracts electrons from the oxygen in the O-H group. electrons pulling facilitates ionisation of H in O-H lost more easily |
| Resonance Hybrid | the negative charge that is delocalised and shared over the three atoms |
| Acid & Base (A Bee) | Salt & Water (Swam West) |
| Acid & Metal (A Mouse) | H2 (g) & Salt (Had Sex) |
| Acid & Carbonate (A Crazy) | CO2 & Salt & Water (Cat Went South) |
| Elimination reaction (condensation reaction) | results in the loss of water |
| Euganol | oil found in cloves |
| Steam Distillation | distillation carried out in a current of steam to avoid too high a temperature during distillation as a high temperature may destroy the plant material |
| Emulsion | a cloudy milky liquid in which the oil droplets are dispersed throughout the water |
| Esterification | is the reacting of a carboxylic acid and an alcohol to form an ester and water |
| Solvent Extraction | add emulsion to cyclohexane- dissolves non-polar oils. use separating funnel to separate water from cyclohexane & oils. Evaporate off cyclohexane to get pure oil |
| Base Hydrolysis/ saponification | a substitution reaction used in the making of soap |
| Vegetable fats &oils | unsaturated (double bond) |
| Animal fats & oils | are saturated (only single bonds) |
| Glycerol | by-product of soap preparation used to manufacture explosive nitroglycerine |
| Brine | a solution of NaCl in water- dissolves excess NaOH |
| Polymers | are long chain molecules made by joining together many small molecules (monomers) |
| Electrolysis | is the use of electricity to bring about a chemical reaction |
| Electrolyte | compound which when molten or dissolved in water conducts electricity due to presence of ions |
| Electrodes | two rods dip into electrolyte and make electrical contact |
| Inert | do not react with electrolyte merely carry the current |
| Active | react with the electrolyte |
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