chemistry notes

atoms. moleculesl elements, compounds and mixtures

ELEMENT =a pure substance made of only 1 type of atom.- hydrogen. COMPOUND- 2 or more different types of atoms chemically bonded together- water MIXTURE: 2 or more different types of atoms mixed together by not chemically bonded- sweater, air. ATOM- smallest part of an element, made of electrons, protons and neutrons. MOLECULES: a substance made of units of the same type of atom chemically bonded.

enthalpy experiments- calorimetry

EXPERIMENTS: do a chemical reaction. measure the temperature change of the reactants-products in the reaction. use the enthalpy calculation method to find the heat energy change, then calculate the enthalpy change from this. issues with experiments- heat loss to the surroundings reduces accuracy- results always lower than actual energy. to improve accuracy: use polystyrene cup. put lid on cup. place cup in beaker of cotton wool. stir to ensure even heat energy distribution. keep checking temperature to make sure final temperature was the highest/lowest temperature recorded. or could do a combustion experiment by burning a fuel, heating water sing the heat energy produced and measuring the temperature change of the water.

electrolysis of dilute sulphuric acid

3 ions involved- SO42-, H+ AND OH-. only the ions from water are involved in there half equations. at positive anode: 4OH- ---> 2H2O + O2 + 4e hydroxide goes to anode instead of sulphate as hydroxide always moves unless a valid is present. this is oxidation negative cathode: 2H+ + 2e --- -> H2 H+ goes the the electrode as its the only positive ion it gets reduced. key points: twice as much hydrogen forms as oxygen as, looking at the half equations, for every four moles of electrons flowing through the circuit, only 1 mole of oxygen is produced for eery two moles of hydrogen. this means the hydrogen tan has more space in it. purpose of sulphuric acid: increase conductivity so more ions are released to speed up electriiysys.

METALLIC BONDINGA

= BONDING BETWEEN 2 METAL ATOMS deifntion- the force of attraction between positive metal ions and negative localised electrons. each metal atom loses its outer shell electrons so it has a full outside electron hell, these means the metal atoms become positive metal ions as they have los electron. the lost electrons from a sea of delocalised electron. the bond is held together by the electrostatic attraction between the positive metal ions and the negative sea of delocalised electrons. form giant metallic structures. PROPERTIES of giant metallic structures: conductive- delocalised electrons are free, can move to carry charge high m/b points- all bonsai re metallic, strong electrostatic attraction between pos metal ions and neg decollated electrons requires much energy to break. malleable- layers of metal ions able to slide over each other as ion displacement can occur withut electrostatic repulsion occurring.

CRUDE OIL

= a mixture of hydrocarbons that is a fossil fuel that can be separate d into different fuels depending on hydrocarbon chain length, done by fraction distillation. Refinery gases- fuel for heating appliances. gasoline- petrol/car fuel naptha- pharmaceuticals kerosine- airplane fuel diesel oil- bus and lorry fuel lubricating oil- oiling joints fuel oil- heating homes Bitumen0 making tarmac FRACTION DISTILLATION: fractionating column that is hotter at bottom than top- (temperature gradient- 400 vs 40 degrees). crude oil placed at bottom of the column, heated to 400c. each fraction evaporates and rises each fraction cools and condenses at the point when the temperature of the column is equal to its boiling point. depending on hydrocarbon chain length, as this affects boiling point, each fraction condenses at a different point and is tapped off sportily. shorter hydrocarbons condense furthe rup tube as they have lower boiling points, longer hydrocarbons condense lower down tube as the have higher boiling points and temperatures are high at the bottom and low at the top SHORT HYDROCARBONS: volaitle not viscous ignite easily low boiling points good fuels condense higher up fractionating column. lONGER HYDROCARBONS: not very volatile high viscosity d'ont ignite easily high boiling points poor fuels- don't burn well condense lower down fractionating column.

COVALENT BONDING

= a shard pair of electrons between 2 non metal atoms. held together by the electrostatic attraction between the positively charged nucleus of each atom and the opposite atom's negatively charged electron. occurs so both atoms can gain a full outside electron shell, become stable. eg- hydrogen chloride, hydrogen in g1, one electron, needs to gain an electron to become stable, chlorine in group 7 so also needs to gain an electron to become stable, therefore each am gives an electron to form a shared pair so both now have full outside heels, forming a compound. SIMPLE COVALENT STRUCTUFES: low m/B points as intermolecular forces of attraction are very weak, require little energy to break. mostly liquids or gases- weak intermolecular forces can't withstand room energy at room temperature. not conductive- no free electrons to move to carry charge. some of them sullen de to weak intermolecular forces that break down completely. GIANT COVALENT STRUCTURES: giant strtcure made of many atoms in which all bond are covalent. DIAMOND: carbon allatrope. each carbon atom nodded to 4 others, all 4 unpaired other shell electrons used in bonding. very hard + high m/b point- all bonds covalent, require much energy to break. insulators- each c bonds to 4 others, all electrons in shared pairs, none are free to move to carry charge. insoluble- covalent bonds very strong- atoms can't be pulled apart in liquids to dissolve. GRAPHITE carbon allatrope each carbon atom bonded to 3 others, leaving a 4th electron in each outer shell that's free to move between layers- free electrons can move to carry charge- graphic is conductive. soft/slippery- atoms fromm layers that are able to slide over each other, causing layers to seperate- used in pencils and as a lubricant. high m/b point- all bonds are covalent, require much energy to be broken. insoluble in all liquids- covalent bonds throughout are stonrg, atoms can't be pulled apart in a liquid to dissolve. less dense than diamond- layers have space between them .

rate of reaction

= amount of retaken used or product formed / time the collision theory: chemical reactions can only occur when particles collide with enough energy (activation energy) and correct orientation. activation energy = the minimum amount of energy required for colliding particles to react. collision theory states reaction rate depends on:; the frequency of collisions per second between reactant particles. the energy with which particles collide (as this increases the success rate of collisions) thereore, to increase rate of reaction, increase the number of successful collision between reactant particles per second.

electrolysis basics

= the breakdown of an ionic compound into its original elements by passing an electric current through it. positive electrode = anode negatie eletrode = cathode PANIC positive ions = cations negative ions = anions electolyte = the liquid / solutions that conducts the electricity.

acids vs bases

ACIDS: substances that release H+ ions when they are dissolved in wtaer- are H+ / proton donors. pH lower than 7 BASES: substances that react with /n neutralise acids by taking H+ ions (H+/prton acceptors). pH above 7 eg- metal oxides, hydroxides and metal carbonates. alkalis = soluble bases which have OH- ions. ACID STRENGTHA STRONG acid- all molecules in the lattice split up into ions when acid dissolves, more H+ ions. weak acids- fewer molecules split up into ions when acid disclosed, less h+ ions. ACID CONCENTRATION: concentrated acids- low ratio of water molecules to ions. dilute acids- high ratio of water molecules to ions.

testing for anions

ANIONS = negative ions HALOGENS- add nitric acid to remove impurities that may give a positive test. add silver nitrate observe the colour of the precipitate formed. CL- = white (and dissolves in dilute ammonia) Br- cream (only dissolves in conc ammonia) I- = yellow (doesn't dissolve in ammonia) always remember I- is the last one and is yellow and then work backwards. TESTING FOR SULPHATE- SO4 2- add hydrochloric acid to remove impurities that may give a positive test add barium chloride if a sulphate ion was present, a white barium sulphate precipitate all form CARBONATE - CO3 2- DILUTE HYDROCHLORIC acid this will form carbon dioxide + water + salt test for carbon dioxide using limewater if the carbon dioxide test is positive, the original cation was carbonate.

the dehydration of ethanol

An H2O is removed from ethanol to form ethene + water. this is done using a HOT ALUMINIUM OXIDE CATALYST. C2H5OH -----> H2O + C2H4 ethene can be tested for by adding bromine water, observing a orange to colourless colour change.

tests for cation ions

CATIONS = POSITIVEA- no preliminary acids to remove soluble impurities. GROUP 1 AND TWO METALS- flame test. clean platinum nichrome wire in HCL then burn till colourless flame then dip in solid sample and burn, observe the flame colour. Li+ = crimsons red Na+ = yellow orange K+ = lilac Ca 2+- brick red Mg2+ = white TRANSITION METALS- CU 2+, FE2+, FE3+ add sodium hydrocide solution observe the colour of the precipitate formed CU2+- blue Fe2+- swampy green Fe3+- foxy brown Cu2+ + 2OH---> Cu(OH)2 Fe3+ + 3OH ---> Fe(OH)3 Testing FOR AMMONIUM- NH4 + ; SODIUM HYDROXIDE THEN TEST FOR AMMONia add sodium hydroxide solution, this will produce ammonia gas from the ammonium ions. test for ammonia by adding damp b blue litmus paper, seeing if it goes red. NB- YOU MUST HEAT THE AMMONIA FIRST. if the test for ammonia is positive, ammonium ins were present.

Ion formulas

CO3 2- = carbonate NO3 - = nitrate OH - = hydroxide SO4 2- = sulfate NH4 + = ammonium HCO3 - = bicarbonate

dissosiation of hydrogen chloride.

HC gas dissociates in water as its ions are electrostatic ally pulled apart by water's polar molecules charges. this forms H+ ions and Cl- ions. therefore the solution becomes an acid as it contains H+ ions- H+ ions. however HCL gas does;t dissociate in organic solvents as they don't have polar molecules with charges to electrostatic ally pull apart HCL molecules into H+ ad CL- ions.

organic chemistry definitions

HOMOLOGOUS SERIES- group of compounds with trends in physical properties, similar chemical properties. HYDROCARBON- compounds made up of only hydrogen and carbon atoms saturated- when a compound contains the maximum number of bonds possible- only single bonds unsaturated- when a compound doesn't have the max number of bonds- has a doubled bond general formula = the most si plied ration of molecules in a compound. structural isomers- compounds with the same molecular formula but a different structural formula - to make, just move a ch3.

oxygen reactions

MAGNESIUM: brush with a bright white flame. magneisum oxide formed- white powder. alkaline 2Mg + O2 -----> 2MgO Carbon reacting with oxygen carbon urns in air if strongly heated. orange/yellow flame produced co2- acidic. C + O2 ---> CO2 sulfur burns with pale blue flame produced suffer dioxide- acidic S + O2 makes SO2

metals vs no metals

METALS: solid at room temp shiny if polished conduct electricity and heat (conductors). malleable (bend without breaking. ductile (can stretch into wires). react to form alkaline metal oxides. NON METALS: solids, liquids or gases at room temperature. not shiny don't conduct electritiy or heat except graphite. brittle (break easily when solid). cannot stretch easily.

Carbon dioxide formation and proerties/uses

METHOD 1- CALCIUM CARBONAE + HYDROCHLORIC ACID: calcium carbonate (marble chips) + hydrochloric acid -----> calcium chloride + water + CO2 2HCL + CaCO3 ----> CaCL + CO2 + H2O METHOD 2: THERMA DECOMPOSITION OF COPPER (II) CARBONATE copper (ii) carbonaye heated so it breaks down into carbon dioxide + copper oxide copper (ii) carbonate -->(heat) copper oxide + carbon dioxide CuCO3 --->(heat) CuO + CO2 PROPERTIES OF CARBON DIOXIDE: soluble in water but only under pressure- used to make drinks fizz- as, when cap is screwed, the gas is dissolved as pressure is high, when the cap is unscrewed, pressure decreases, the carbon acid turns back into gas forming bubbles. fire extuingishers- denser than air so sinks over fire, prevents o2 getting to the fire, flames die out. but- co2 is a greenhouse has, causes climate change/global warming

pollutant gases

NITROGEN OXIDES: nitrogen dioxide and nitrogen trioxide. formed in car engines where temperatures are high enough to allow nitrogen and oxygen to react to form nitrogen oxide. N2 + 2O2 --> 2NO2 or N2 + 3O2 --> 2NO3 SULPHUR DIOXIDE: formed in heavy industry and power plants when fossil fuels with sulphur impurities are burnt, allowing sulphur to react with oxygen in the air at high temperatures to form sulphur dioxide. S + O2 --> SO2 ACID RAIN; nitrogen dioxides ands sulphur dioxide in the atmosphere dissolve into water in clouds to form nitric acid or sulphuric acid so rain released is acidic- acid rain. negative impacts: kills aquatic life by changing ph of water bodies. kills vegetation and trees leaches away nutrients in soil. damages features on limestone buildings/structures.

gas tests

OYXGEN- relights a glowing splint. CARBON DIOXIDE- bubble through limewater, limewats goes cloudy, white precipitate forms. HYDROGEN-place a lit plint in test tube of gas, squeaky pop sound made if it is hydrogen. CHLORINE- TURNS DAMP BLUE LITpaper red then bleach it white. AMMONIA- turns damp red lit paper blue.

mole formulas

RFM = the mass number of all elements in a compound added together. 1 mole = 6.023 x10^23 atoms of a substance- this is the avogadro number. moles = mass / rfm volume of gas (dmcubed) = moles x 24 volume of gas (cmcubed) = moles x 24,000 moles = cv/1000 concentration: moldm3 to gdm3 = x by RFM. empirical formula =the simplest positive integer ratio of elements in a compound. moleculer formula = the exact number of atoms in a single molecule. reacting masses or empirical formula- use table method. percentage yield = actual mass/theoretical mass x 100

seperation techniques

SIMPLE DISTILLATION- solvent from solution. salt solution heated in flask, water evaporates but salt doesn't, water condensed using cool water jacket and is collected. FILTRATION- insoluble solid from liquid mixture poured into filter paper in a filter funnel, solid residue left behind and filtrate passes through. FRACTIONAL DISTILLATION: several miscible liquids mixture is heated in flask. ethanol evaporates at 78C and is cooled and condensed, water remains in flask, can then be heated and evaporated, cooled and condensed. PAPPER CHROMATOPGRAPHY: a mixture of coloured substances soluble in the same solvent. eg-- seperating an ink into its dyes. pencil line drawn near bottom of filter paper and spots of ink drawn onto the line. paper is dipped in solvent. solvent trabels ip the paper and carries the dyes with it. due to the dyes having different solubility's, they are carried at different and stop running up the page at different distances. the larger molecules are, the less soluble. from this you can tell- the solubility of the dye (distance ) + if two dyes travel the same distance and are the same colour, they are the same. RF value = compound distance / solvent distance CRYSTALLISATION- soluble solid (solute) from solution. solution slowly heated in an evaporating dish. some of the solvent evaporates and the solution slowly gets more concentrated. when crystals begin to form, the solution stops being heated and is left in a warm place till the rest of the solvent evaporates, leaving solid crystals. crystals are dried in a desiccator.

solids liquids and gases

SOLIDS: very strong forces of attraction particles held close together in fixed regular arrangement, densely packed. particles can't move due to high forces of attraction but can vibrate on the spot. can't be compressed- particles are already close together so have no space to move into. don't flow or take shape of container. can't change volume. LIQUIDS: strong forces of attraction. particles can move freely as forces of attraction are weak enough to allow this. particles held fairly densely but in random arrangement. flow and take the shape of containers as particles can move. can't be compressed as particles packed too densely. can't change volume. Gases: very weak forces of attraction. very low particle density- particles are far apart due to weak forces of attraction. particles can move freely due to weak forces of attraction.- move at higher speeds than liquid particles- more kinetic energy. flow and take the volume of a container- weak f of a particles can mov3 freely in all directions. can be compressed as density is low- spaces for particles to move into.

factors that affect rate of reaction

TEMPERATURE: rate of reaction increases with temperature as: movement- particles have more kinetic energy, move around more at higher speeds, higher frequency of collisions therefore (the number of successful collisions per second increase.) = the link phrase. energy- particles have gained heat energy, have more energy, more particles will have activation energy, means there more of the collisions are successful so link. CATALYST~: catalysts - substances that increase the rate of reaction without being used up in the process- chemically unchanged at end.. rate increases with catalysts as: they provide an alternative route with lower activation energy. this means more of the collisions between particles are successful ash more colliding reactant particles have the energy to react. this link. CONCENTRATION: rate increases with concentration and with pressure as: if a solution is more concentrated/at higher pressure, there are more reactant particles in the same volume, this increases the number of collisions between reactant particles so link. however, rate tends to decrease towards the end of a reaction because concentration does. SURFACE AREA: rate increases with surface area as more reactant particles are exposed to each other, free to collide without having to wait for other particles to react- increases the number of collisions per second, there link.

alkenes

Unsaturated hydrocarbons- have a double C=C bond, made of only H and C atoms Homologous series- trends in physical properties, similar chemical properties. general formula = CnH2n start from ethene as have to have two carbons at least. REACTIONS: react eith halogens like bromine in normal conditions. ADDITION REACTION- both bromine atoms get added to ethene. alkenes double bond gets broken. NB- orange to colourless colour change from bromine solution + ethene to dibromoethane. for chemical equation, just add up products. NB- halogens are diatomic on their own.

water and hydrogen

WATER FORMATION- HYDROGEN COMBUSTION: when hydrogen combusts, it reacts with oxygen in the air to form water + much energy. hydrogen burns with an almost colourless flame. hydrogen + oxygen ----> water 2H2 + O2 ----> 2 H2O TESTing for water: use anhydrous copper sulphate when anhydrous it is a white powder, when water is added, it becomes hydrated, turns blue. water purity testL pure ater boils at exactly 100 and metals at exactly 0. if water isn't pure, boundaries/range gets wider- melting point decreases, boiling point increases. the more dissolved substances are in water, the more these temperatures change.

the reactivity series

a list of metals and carbon and hydrogen, in auwpards ascending order of reactivity. potassium metla sabove carbon- electrolysis sodium calcium magnesium auminium CARBON zinc metals in middle- from ores by reduction using carbon iron lead HYDROGEN copper metals at bottom- occur native silver gold platinum carbon

ACID REACTIONS

acid + metal ----> salt + hydrogen ACID + BASE --> SALT + WATER the base can be a metal oxide, hydroxide or carbonate.] if a carbonate: ACID + METAL CARBONATE ----> SALT + WATER + CARBON DIOXIDE. a salt = an ionic compound produced when the hydrogen in an acid is replaced by a metal. to name a salt, just combine the names of the two reactants.

energy level diagrams

activation energy = the initial rise in the line from the reactants to the peak of the curve. NB- even if reaction is negative, the curve first rises to a peak then falls. diffierence in height between reactants and products = enthalpy change = ∆H as is the energy given out or taken in during reaction. exothermic- products lower than reactants. endothermic- products higher than reactants. to show the effect of a catalyst- draw a second curve that starts and finished at the same heights but has a lower peak and reaches the height of the products earlier.

the excess method

add an excess of an insoluble solid base to an acid. the solid will dissolve in the acid as it reacts. when the excess solid stops reacting and sinks to the bottom, all the acid has reacted. filter out the excess insolble solid base. evaporate off the water to the point of water of crystallisation allow the solution to cool. filter the solution again to collect the crystals. dry the crystals using filter paper. make sure- the solid base is in excess to all the acid reacts to make neutral products. filter the solution of the excess insoluble base to ge a pure/neutral salt solution.

the titration method.

adding a soluble base to an acid. or vice versa. neutrlaisation reaction to make salt + water. pipette and pipette filler to fill a knoewn volume of alkali and pour this into the conical flask with some indictor. fill a bette as far as the measurements go with acid so you have a non volume of acid.- below eye level and using a funnel. titrate the acid into the alkali gradually while swirling the flask. when the indicator colour change is permanent, stop triturating (titrate gradually as you approach the endpoint_. record the volume of acid needed to neutralise alkali, repeat twice and find average then repeat without indictor using the average volume to get a pure salt solution. evporate and salt slutions to water of crystallisation then cool, filter again and dry to get alt crystals.

SALT SOLUBILITY RULES

all nitrates are soluble. most chlorides are soluble except silver chloride. most sulphates are soluble except barium and calcium sulphate. all sodium potassium and ammonium salts are soluble. all carbonates except sodium potassium and ammonium ones are soluble. most sluble salts- excess method. sodium potassium and ammonium salts- titration method. insoluble salts- precipitation method.

aluminium and iron properties and uses

aluminium = low density- aeroplane bodies. iron = strong- car bodies, iron nails, ships and bridges.

electrolysis of aluminium oxide

aluminium oxide ore = bauxite = Al2O3 stage 1- reduce the operating temperature of bauxite by dissolving it in MOLTEN CRYOLITE. therefore thebcryolite- reduces the operating temp, acts as a solvent and increases conductivity. stage 2- the ions present are just al3+ and O2- the half equations are simple positive anode: 2o2- ----> O2 + 4e oyxgen ions get oxidised. negative cathode: Al3+ + 3e ---> Al al gets reduced as it gains electrons. NB- the electrodes are made from carbon allotrope graphite- wears away as reacts with oxygen produce dot form carbon dioixide- electrodes need to be regularly replaced. the negative cathode is at the bottom and sides, the positive anodes hang from the top main reason process isxpensice = high electricity cost as melting point of bauxite is high, much energy needs to be supplied to create high temperatures, as the operating temp is still 1000c even after molten cryolite.

atomic structure, isotopes and relative atomic mass

aotma = a central nucleus, made of protons and neutrons, surrounded by electrons that orbit in shells. proton- located in nuceus, mass = 1, +1 charge. neutron- located in nucleus, mass = 1, charge = 0. electron- located in atomic shells, mass = 1/2000, charge = negative. elements always have the same number of protons as electrons. ISOTOPES: 2 elements with the same number of protons but a different number of neutrons (same atomic number but different mass number. look and react identically to each other. are the same element as have the same proton number. MASS NUMBER = TOP = protons + neutrons ATOMIC NUMBER = bottom = protons (therefore also the number of electrons) RELATIVE ATOMIC MASS: the average mass number of all isotopes of an element. (percent x mass number)x(other percent x other mass number) all divided by 100.

periodic table

arranged so elements ascend in atomic number from left to right. groups = columns indicating valency / the number of outer shell electrons. periods = the rows, elements in the same period have the same number of electron shells. diagonal line under boron = metal non-metal divide. elements in the same group have similar reactors as they have the same valency, same number of electrons in their outer shel, so gain or lose the same number f electrons when reacting. electron configuration = 2, 8, 8

electrolysis of brine

brine = salty water = sodium chloride dissolved in water. comleted in diaphragm cell with membrane to keep chlorine and hydrogen products apart as they react explosively, 3 products- two from electrodes and one when leftover ions react ions = NA+, H+ and OH-, CL-. AT positive anode: 2Cl- -----> CL2 + 2E cl ions move instead hydroxide as they are halide ions, they get oxidised. at the negative cathode: 2H+ + 2e ----> H2 hydroge ions move to cathode as sodium is more reactive than hydrogen hydrogen gets reduced NB- NaOH (sodium hydroxide) is formed when NA+ ions and OH- ions leftover bond. PRODUCTS: sodium hydroxide- yelow flame test colour, used to make soap and bleach to sterilise stuff by killing bacteria. chorine- turns damp blue litmus paper red then bleaches it white used to kill bacteria / for sterilisation of swimming pools. hydrogen- sqeuaky pop after litnsplint, manufacture of ammonia in hater process + making margarine.

alkane combustion

complete combustion- enough oxygen present. alkane + oxygen ---> carbon dioxide + water carbon dioxidde- global warming. Incomplete combustion- not enough oxygen present. alkane + oxygen ----> carbon monoxide _ water. carbon monoxide-toxic gas, asphyxiation.

cataytic cracking

crude oil produces a surplus of long chain hydrocarbons which have little demand as they make poor fuels that don't burn well. crackng = a thermal decomposition reaction with breaks down long chain hydrocarbons into a short chain alkane + alkenes. s short chain alkanes- burn well, make good fuels. alkenes- used to make addition polymers and ethene is used to make ethanol. CONDITINS- 600-700C CATALYST = ALUMINIUM OXIDE HIGH PRESSURE. eg- cracking of decade C10H22 -> C5H12 + C2H4 + C3H6 short alkane + alkenes

Halogen displacement

displacement reaction = a reaction where a more reactive substance swaps place with a less reactive substance. when a free halogen is added to a solution that contains a halogen compound with a less reactive halogen, the halogen reacts with the spectator ion to form a new compound. nB- halogens are diatomic. organic solvents (like cyclohexane and lotxane) can be added to the products of of displacement reactions to identify the free halogen produced chlorine- turns pale yellow bromine- turns orange iodine- turns pink halogen displacement reactions are redox reactions as both oxidation and reduction takes place: the more reactive halogen gains an electron so is reduced.]the less reactive halogen loses an electron so is oxidsed. NB- reducing agent- reduces something else, is oxidised. oxidising agent- oxidises something else, is reduced. ionic equations can be writeen- remove spectator non/halogen ions and give charges, then label where oxidation and reduction has occurred. NB- halogen forms diatomic molecules, it never has single atoms.

the electrolysis of molten salts

e.g. lead (ii) bromide PbBr2- the simplest electrolysis. ions- = Pb2+ and Br- at the negative cathode- Pb2+ + 2e --> Pb this is reduction- gain of electrons at the positive anode 2Br ---> Br2 + 2e this is oxidation- loss of electrons NB- lead bromide must be molten so ions are free to move to carry charge so the electrolyte conducts electricity.

ethanol production

ethanol = C2H5OH used in drinks and as biofuel. is an alcohol as contains an OH group bonded to a carbon chain. method 1- FERMENTATION OF SUGARS. yeast added to a sugar solution made using sugar cane. yeast is deprived of oxygen, anaerobically respires to convert glucose to ethanol + carbon dioxide. C6H12O6 ------> 2C2H5OH + CO2 done at 30c, normal pressure. uses batch process, slow reaction rate produces impure ethanol that needs further refining through fractional distillation. method 2- HYDRATION OF ETHENE: uses raw material crude oi to create reaction conditions. ethene reacted with steam using a PHOSPHORIC ACID CATALYST to produce ethanol. conditions = intense- 300c, 60-70 atmospheres. efficient continuous process. ethanol produced is pure C2H4 + H2O ---- C2H5OH PROS AND CONS OF EACH METHOD: Fermantion`;: reneqable, low energy costs and cheap in tropics where lots of sugar cane but inefficient as slow reaction rate impure ethanol and expensive in cold climates. Hydration of ethene: produces pure ethanol heap in cold countries and efficient as high rate and continuous process but non renewable, high energy costs and expensive in countries with low oi reserves.

ADDITION PLYMERS

formed when many small molecules called monomers (usually alkenes) join to form a long chain addition polymer. monomer - normal molecule with no brackets and an N before the first carbon. polymer- square brackets, double bond breaks open, squiggles by the end carbons and an n next to the bottom right hydrogen. FORMATION: the double C=C bond in the monomers breaks open and single bonds form. the molecules join together to form a long chain polymer. the reaction occurs with a catalyst at high pressure. the polymer product has only single ebonds- is saturated whereas the monomers had a double bone- were unsaturated. Uses: Poly(ethten) flexible- plastic bags `+ electrical insulator. polypropene- storng- buckest and cranes. polychloroethene- non stick pans. polymers hard to dispose of as are inert so non-biodegradable and release toxic gases like co2 when burnt. polychloroethene- ethene but swap an h with a CL polypropene- swap an H with a CH3.

acid formulas

hydrochloric acid = HCL sulphuric acid = H2SO4 nitric acid = HNO3

Bond energy

in a chemical reaction, reactant bonds are broken and product bonds are formed. to break a reactant bond you must supply energy- endothermic. to form a product bond this releases energy- exothermic EXOETHERMIC REACTIONS: the energy released in bond formation is greater than the energy take in from the surroundings in bond breaking- the reaction gives out heat energy to the surroundings, temperature rises. ENDOTHERMIC REACTION: the energy used in breaking reactant bonds is greater than the energy released hen product bonds are formed- the reaction takes in energy from the surroundings in the form of heat energy, temperatures falls. ENTHALPY CHANGES: an enthalpy change = the overall change in energy in a reaction (of the chemicals themselves, not of the surroundings). symbol = ∆H. unit = KJ/mol- the amount of energy in kilojoules per mole of reactant. exothermic reactions- negative enthalpy change as chemicals lose energy when giving it to to the surroundings. endotehrmic- positive enthalpy change as reactants gain energy when taking it in from the surroundings.

Oyxgen in the air

in dry (no water vapour) and unpolluted air: 78.1% = nitrogen21.0% = oxygen 0.9% = argon 0.04% = carbon dioxide to show that 21% of air is oxygen: copper and syringe method: syringes contain 100cm3 of air at the start. an excess of copper is heated by the bunsen while air is pushed back and forth over the copper by the syringes. the oxygen in the air is used up reacting with the copper to form black copper (ii) oxide. the bunsen position is varied to make sure all the copper is heated. once all the oxygen in the tubes is used up, the excess copper stops reacting (turning black). the volume of the air will now be 79, proves 21% of air is oxygen. copper + oxygen ---> copper (ii) oxide. 2cu + o2 ----> C CuO USING THE RUSTING OF IRON: damp ron wool placed in a test tube containing air. test tube is inverted in a beaker of water and the level of water in the tube is recorded using a rub er band. tube left for a week / until all iron ha rusted so all the oxygen in the tube is used pup. % of water level increase should be 21% as oxygen is used to oxide the iron in damp air, causing it to rust. NB- can 8se the smouldering of phosphorus to produce phosphorous oxide instead.

IONIC BONDING

ionic bonding = between a metal atom and a non- metal atom. bond is held together by the electrostatic attraction between oppositely charged ions. definition = EABOCI- electrostatic attraction between oppositely charged ions. the higher the charges of the ions, the stronger the bond as the stronger the electrostatic attraction. structure- ionically bonded molecules form a GIANT IONIC LATTICE, properties: 1. high melting point- all bonds are strong ionic bonds that require much energy to break. 2. crystalline- ions are regularly packed in the lattice. Brittle- any small ion displacement mens like ions come into contact and repeal each other.r soluble in water- water is polar, so the charges of the atoms in its molecules pull ions apart from the lattice. insoluble in organic solvents- molecules of solvents not polar, can;t elecrtostatically pul ions apart from the lattice. conductive when a liquid or dissolved- ions pulled apart from the lattice, free to move to carry charge. not conductive when solid- ions in fixed positions in the giant ionic lattice, can't move to carry charge.

THE BLAST FURNACE

ior is found as an ore in the earth- hematite- Fe2O3 coke is used to reduce the hematite to pure iron by reacting with the oxygen in the ore to make carbon dioxide. then, limestone (CaCO3) calcium carbonate is used to remove impurities by reacting with them to form molten slag. METHOD: 1.- Iron ore is reduced to iron. coke iron and limestone added to hot blast furnace. the coke burns with oxygen in the air to make CO2 C + O2 -> CO2 carbon + oxygen --> carbon dioxide. 2. the carbon dioxide reacts with unburnt coke to form carbon monoxide: CO2 -> C --> 2CO carbon dioxide + carbon --> carbon monoxide then the carbon monoxide reduces the iron or to iron by reacting with the oxygen to form co2 + iron 3CO + Fe2O3 --> 3CO2 + 2Fe the iron produced is molten, runs to the bottom of the furnace and is tapped off then purified. stage 2- removing impurities. main impurity is sand (silicon dioxide), this is removed by the limestone. 1. the imetstone is thermally decomposed by heat to make calcium oxide + carbon dioxide. CaCO3 --------> CaO + CO2 calcium carbonate -> calcium ocide + carbon dioxide. 2. the calcium oxide then reacts with the sand to form slag (calcium silicate) which is molten and gets tapped off seperately. CaO + SiO2 ---------> CaSiO3 calcium oxide ---> calcium silicate (slag)

NOBLE GASES

located in group 0 (/grou 8). al form colourless gases at room temperature. very unreactive- have a full outside electron shell, don;t need to trade electrons in reactions. monatomic atoms- full outside shell, atoms don;t need to bond with anything to gain or lose electrons. AS YOU GO DOWN THE GTORUP: density increases. boiling points increase. REACTIVITY DOESN'T CHANGE- all element equally unreactive as they all have full outside electron shells. USES: helium- filling baloons, less dense than air so rises. neon- red lighting, ldoesn;t react with the hot filament. radon- emits radiatin, cancer treatment. argon- forms a motionless gas shield for welding and cutting.

ALKALI METALDS:

located in group 1 on far left. the most reactive metals in periodic table as all have 1 electron in their outside shell, can lose it quickly in reaction to gain a full outside electron shell and become stable. low densities for metals. AS YOU GO DOWN THE GROUP REACTIVITY INCREASES AS: outside electron further away from nucleus, n's forces of attraction are less strong, it can be lost easier. outside electron shielded y inner electron shells that have pulls to offset the attracting forces of the nucleus. densities increase. NB- as you go down the group atomic number increases. Properties: soft shiny malleable ductile low boring and melting points conduct heat and electricity. low density. shiny and silver when cut but tarnish within seconds as react with oxygen in the air. REACTIONS OF ALKALIO METALS: alkali metal + oxygen ---> alkaline metal oxide. alkali metal + water -----> metal hydroxide + hydrogen. metal hydroxide = alkaline strong- 11-14pH. REACTIONS WITH WATERa: Sodium: floats on the water as its less dense. disappears effervessence due to H2 produced. pushed around surface of water by H2. lithium: reacts slower than sodium. dissappears heat produced less quick- less vigourous. still some effervescence. moves around surface but slower POTASSIUM - most reactive. reacts faster than sodium- morevigouroly burns with a lilac flame sometimes explodes. rubidium/caesium- react even more vigorously , often explode.

HALOGEns

located in group 7 very reactive- have 7 electrons in outer shel, so can easily/quickly gain a full outside electron shell by gaining only 1 electron- this can be done quickly. form 1- ions as they gain an electron in reaction. PHYSICAL PROPERTIES: non metals not conductive (no free electrons to move to carry charge), brittle crumby solids, toxic due to reactivity, smell strongly. fluorine- pale yellow gas chlorine- green/yellow gas. bromine- red/brown liquid iodine- silver solid REACTIVITY: INCREASES GOING UP THE GROUP: particles have less electrons so less shell so the outer electron shell is closer to the nucleus- the outside electron can be gained quicker as the attraction between the positive nucleus and the negative electron gained is stronger as the distance is lower. less electron sheilding- outer shell is closer to nucleus, attraction between nucleus and negative electron gained is strong were as less negative electrons to offset the pos charge of the nucleus.

precipitation methiod

mixing two solutions (soluble aqueous salts) that contain the ions needed. pick 2 solutions with ions needed, if given solids in exam state that ou have to dissolve them in water to get an aqueous solution. mix the solutions together to get a suspended solid salt price + solution. filtelr, wash and dry in them oven to get salt. can be written as ionic equation with ions that make up the salt as reactants, then the salt as the product while giving charges.

Bond energy calculations

molar enthalpy change also = ∆H = total energy absorbed to break bonds - total energy released in making bonds = left - right then add units KJ/mol and include the pos or neg sign at the beginning.

electrolsysis ion rules

negative anions: OH always goes to electrode unless a valid is present, then the halide goes. positive cations- the more reactive ion stays in the solution and the less reactive one moves to the electrode. to work out the products of electrolysis: work out the ions present then use the above rules to see which ones move to the electrodes and form elements.

enthalpy calculations

once you have the temperature change, which you have calculated experimentally. u can calculate heat energy change and then enthalpy change. HEAT ENERGY TRANSFERRED: Q = M x C x ∆T = mass of water x 4.2(heat capacity) x temp change of water. this = the heat energy transferred in joules. (if you use grams). THEN- convert the heat energy transferred to KILOJOULES by dividing by 1000. MolAR ENTHALPY CHANGE this is basically the total energy transferred divided by the number of moles to get the energy transfer per mole of reactant. make sure the heat energy transferred has been converted from joules to kilojoules. use the mole equations to calculate the moles of reactant used to produce the energy energy transfer. divide the energy transfer in KJ by the number of moles to get the energy transferred per mole (molar enthalpy change). add a positive or negative depending on if the reaction was end or exo (see temperature change). then add delta H and units. eg- ∆H = -325.98KJ/mol

faraday calculations

one faraday = 1 mole of electrons Q = IT charge = current x time 1 faraday = 96,000 coulombs of charge = 1 mole of electrons. use these equations to find the current for one mole of electrons in a certain time, then use ratios to find the current for the moles of electrons you actually have.

pH scale and indicators

pH scale: 1-14 7 = neutral = green less than 7 = acid = yellow to orange to red more than 7 = alkaline = dark green to purple to dark purple Indicators: litmus paper: blue turns red for acired turns blue for alkaline doesn't tell you strength phenolphthalein: colourless in acid pink in alkaline methyl orange red in acid yellow in alkaline universal indicator gives colours on pH scale scale- shows strength but gradual change means hard to know when endpoint of reaction reached.

THE HABER PROCESS

produces ammonia from nitrogen and hydrogen. SOURCES- nitrogen obtained from air, hydrogen from cracking hydrocarbons or natural gas. AMMONIA USESL ostwald process- nitric acid. making fertiliser- ammonium nitrate made by reacting with nitric acid. the reaction: N2 + 3h2 ----><- 2NH3 nitrogen + hydrogen -><- ammonia. forwards reaction is exothermic (JH = neg) notes on method: nitrogen and hydrogen added in 1:3 ratio as reaction states 3x moles of nitrogen to hydrogen. ammonia gas produced is cooled and condensed back into liquid in condenser then tapped off separately. unused hydrogen and nitrogen (unreacted gases) are recycled back into reaction chamber to react to form more ammonia. ACTUAL CONDITIONS- IRON CATALYST 200 ATMOSPHERES 450C tmperature OPT CONDITIONS AND WHY NOT USED: temperature- LOW as forwards reaction is exo means temp decrease causes pos of equilibrium to shift right, increase ammonia yield. BUT- not used as rate of reaction is too low at low temperature- compromise temperature of 450C used. Pressure- HIGH as less moles on right hand side so increase in pressure causes pofE to shift right, increasing ammonia yield. BUT- high pressure is expensive to create and dangerous (explosions)- COMPROMISE PRESSURE OF 200 ATMOSPHERES is used.

DYNAMIC EQUILIBRIUM

reversibe reactions in a closed system always reach a state of dynamic equilibrium. a closed system = no reactants or products can escape and no new substances can be introduced. dynamic = the reaction takes place in both directions (forwards and reverse). equilibrium = there are constant concentrations of both reactants and products. SHIFTING THE POSITION OF EQUILIBRIUM the pofE can shift left or right ] if the pofE moves to one side of the reaction, the product yield of the produces on that side increases. the movement of the pofE is determined by le chateliers principle which states that, if the reaction conditions are changed, the position of equilibrium moves to counteract that change. CONDITIONS THAT CAN CHANGE: TEMPERATURE: look at the ∆H enthalpy value to see if the forwards reaction is ex or end (ex is neg, end is pos). increase temperature- pofE moves to/favours the endothermic side to absorb the additional heat energy- endothermic product yield increases. decrease temperature- pofE moves to/favours the exothermic side to release heat energy to make up for loss- exothermic product yield increases. PRESSURE: count the number of moles on each side of the reaction. increase pressure= pofE moves to/favours the side with the least number number of moles to minimise the pressure increase- products yield of sidewith les moles increases. decrease pressure- position of equilibrium moves to/favours side with most number o moles to minimise pressure dectrease- product yield of side with more moles increases.

reversible reactions basic info and easy examples

reversible reaction = where the products can themselves react with each other to produce the original reactants. EG1- thermal decomposition of ammonium chloride. NH4CL --->/<----NH3 + HCL ammonium chloride --->/<---- ammonia + hydrogen chloride. white solid to colourless gases. gases rise up test tube but, when they cool, they react together and reform the salt- rings of solid white powder. DEHYDRATION OF COPPER (II) SULPHATE blue solid when hydrated, white powder when anhydrous but, if done i closed system, the water will eventually condense back into a liquid and react with the anhydrous to form hydrated again. chem test for water but not for purity.

alkanes

saturated hydrocarbons in a homologous series- trends in physical similar chemical, only carbon and hydrogen, only single bonds. general formula = CnH2n methane, ethane, propane, butane, pentane, hexane. REACTIONS: generally unreactive. without UV light- do not react with halogens used to tell the difference between alkanes and alkenes. with UV light- SUBSTIUTION REACTION one halogen atom swaps place with a hydrogen e.g. to form bromoethane + hydrogen bromide. Bromine + methane ------> bromoethane + hydrogen bromide. NB- CATALYST = UV LIGHT

prapering oxygen in the lab

the catalytic decomposition of a hydrogen peroxide solution with a catalyst of solid manganese oxide to form oxygen and water. Hydroge peroxide -----. water + oxygen 2h2o2 ------> 2H2O + O2 NB- at tje begiing, some air may rise through the delivery tube + some oxygen produced may dissolve in the water. + the bung needs to be replaced quickly after the catalyst is placed in otherwise some o2 will escape the system.

Diffusion

the movement of particles from areas of high concentration to areas of low concentration. only occurs in liquids and gases where particles can move freely. slower in liquids than gases as more particles to collide with, slowing down diffusing particles. NB- lighter, smaller particles diffuse faster. EXPERIMENT: hydrochloric acid and ammonium are soaked into cotton, which is put at either end of a closed tube. the particles evaporate and move down tube. when the two particles meet, they react to form a white ring of ammonium chloride. ammonium particles = light so faster, travel further in same time, ring is formed closer to hydrochloric acid.

THE CONTACT PROCESSO

used to make sulphuric acid. USES OF SULPHURIC ACID: phosphate fertilisers detergents- cleaning and sterilisation as kills bacteria. paints- titanium dioxide in white paint. raw materials- sulphur from rocks and natural gases, oxygen from air and water. METHOD: 1. first the sulphur is burnt in air to make sulphur dioxide S + O2 -> SO2 sulphur + oxygen -> sulphur dioxide. 2.- the key REVESIBLE REACTION: the sulphur dioxide is oxidised further using a V2O5 VANADIUM OXIDE catalyst to form sulphur trioxide 2SO2 + O2 -><- 2SO3 sulphurn + oxygen -><- sulphur trioxide. 3. the sulphur trioxide is dissolved in concentrated sulphuric acid to form liquid oleum (H2S2O7 SO3 + H2SO4 --> H2S2O7 sulphur trioxide + sulphuric acid -> liquid oleum 4- the oleum is diluted with water to form sulphuric acid H2S2O7 + H2O ---> 2H2SO4 ACTUAL REACTION CONDITIONS: 450C (same as haber) LOW PRESSURE- 2 ATMOS VANADIUM (5) OXIDE CATALYST - V2O5 OPT CONDITIONS AND WHY NOT USED TEMPERATURE- LOW as forwards reaction is exothermic so low them causes product yield to shift right exo, increase sulphur trioxide yield. COMP TEMP 450 USED as low temp decreases rate of reaction. PRESSURE- HIGH AS INCREASE IN PRESSURE cause pofE to shift right to side with least moles, increasing yield of sulphur trioxide. but- high pressure necessary (not worth expense and danger of explosion) as compromise temperature already gives a high yield f 99%.

compound formulas

water = H2O carbon dioxide = CO2 carbon monoxide = CO methane = CH4 ammonia = NH3

Dilution of coloured substances

when a coloured substance is diluted it is placed in a solvent to weaken its colour this occurs as the particles of the substance are very small so spread out among the solvent particles. therefore smaller particles dilute quicker as they move quicker to spread out. adding more solvent to a diluted substance dilutes it more/makes the colour fade further as the substance particles are now spread further apart.

rusting of iron

when iron is exposed to oxygen in air with water present, it rects with oxygen to form iron (ii) oxide- rust. this corrodes the iron. to prevent rusting- coat it with a more reactive metal like zinc- galvanising (sometimes sacrificial protection but galvanising is better) or paint it / add an oil layer so no oxygen can get to it

rate of reaction experimental things to note

when repeatingl always add one reactant in excess or add known volumes of both kept the same to ensure a fair gets. keep amount/mass/volume of reactants the same always. ensure all variables apart from the independent are control variables kept constant. bets way f measuring rate = measuring mass lost . the cross method- only works when solutions are translucent _ is subjective. could measure volume of gas produced.