Chemistry iGCSE Notes

1a) States of matter

Boiling - All of the particles have enough energy to break away. Only happens at the boiling point.Evapouration - Only the surface particles have enough energy to break away. Happens at any temperature.

b) Atoms

Particles are small - Keep diluting potassium (VII) manganate and the colour still remains ∴ there are still a lot particles coloured purple yet we started with a tiny crystal of potassium manganate ∴ the particles are microscopicParticles diffuseGas - 2 flasks - 1 air,1 bromine. After 5 mins brown colour is equalLiquid - potassium (VII) manganate colours the whole water purple after 6 hours

The only way to determine if a chemical reaction occurred is if a new substance has been made

d) Moles

Remember: Period (across) = No. of shells Column (downwards) = No. of outer shell electronsRelative Atomic Mass (Ar) - Weighted average mass of the isotopes of an element Relative Formula Mass (Mr) - Average mass of a compoundMole - 6.02 x 10^23 particles (atoms/molecules/ions/electrons/formulae (eg.NaCl)) in a substanceRemember when calculating empirical formula the Mr is only monatomic not diatomic (eg. Mr of O is 16 not 32)

f-h) Ionic, Covalent, Metallic Substances

Ions formed by the gain or loss of electronsIonic bond- A strong electrostatic attraction between oppositely charged ionsIonic Crystal - A giant 3 dimensional lattice structure held together by the attraction between oppositely charged ions! Remember transfers electrons not gives !↑ Melting point : Giant ionic lattice with strong electrostatic forces of attraction between oppositely charged ions which extend throughout the lattice and require a lot of energy to overcomeHard - Electrostatic forces of attraction between oppositely charged ions is very strong so the ions are held firmly in placeBrittle - When a sharp force is applied the layers of ions are dislodged so like charges are next to each other and thus repel. Shatter!↑ charge = ↑ melting point - ↑ charge means stronger electrostatic forces of attraction (so the ions are held together more firmly.) This requires more energy to overcome these forces and separate the ions ∴ ↑ melting pointTalk abut IONS

Covalent bond formed by the sharing of a pair of electrons between 2 atomsCovalent bond - A shared pair of electrons. / A strong electrostatic attraction between the bonding pair of electrons and the nuclei of the atoms involved in the bond↓ Melting point : Simple molecular structure. Only weak inter-molecular force of attraction which require little energy to be overcome. (Strong covalent bonds are not broken, only the weak intermolecular forces between the molecules)Talk about MOLECULESDiamond/Graphite ↑ Melting point - A giant covalent structure. Each atom forms 4 (or 3) covalent bonds. ∴Many strong covalent bonds which extend throughout the whole structure have to be broken so a lot of energy is requiredDiamond strong - Atoms held very tightly by the many strong covalent bonds throughout the whole structure, so are hard to remove.Graphite lubricant - Weak forces of attraction between the graphite layers so they can easily slide off.Graphite conducts - Each carbon atom only forms 3 bonds so only 3 out of the 4 outer electrons are used in bonding. ∴ 1 electron from each atom is delocalised and free to move around. Since some of the electrons can move freely electricity is conducted

Metal - Giant 3 dimensional lattice of positive metal ions surrounded by a sea of delocalised elections.Metallic bond - The electrostatic forces of attraction between the +ve ions and -ve electrons (This is what holds the metal together)Conduct - Delocalised electrons from the atoms are charged and free to move around.Malleable - The layers of metal ions can slide over each other without disrupting the bonding as the electrons are free to move around.Talk abut metal IONS

i) Electrolysis

Electrolyte - The substance that is being electrolysedElectrodes - The electrical connectors between the electrolyte and the external circuit. (Normally carbon or platinum)Covalent - Not charged and no free electronsIonic - No free ions. Molten/Solution - Ions are charged and free to move around. PANCAnode (+ve) attracts Anion (-ve)Cathode (-ve) attracts Cation (+ve)! Remember the diatomic gases !Aqueous rules:Cathode (-ve)If the metal is less reactive than hydrogen, then that metal is dischargedIf the metal is more reactive than hydrogen, then hydrogen (H2) is releasedAnode(+ve)If a halide is present, then the halogen is producedIf a halide is not present, then oxygen (O2) is discharged : 4OH- → 2H2O + O2 + 4e-CalculationsQ=It (Q in Coulombs and t in seconds)1 Faraday/1 mole of electrons = 96,000 C! Remember the same amount/no. of moles of electrons is flowing in both equations. They are in the same circuit. !

2) Chemistry of the elements

Periodic TablePeriod - across. Same number of shellsGroup - downwards. Same number of outer shell electronsMetals - Form basic oxide. Conduct electricity (+ heat) Non metals - Form acidic oxides and do not conduct electricity

Group 1React with oxygen to form metal oxides which are whiteReact with water to form hydroxides. These hydroxides are soluble in water so make it an alkaline solutionSolutions of the metals are colourless (only transition metals form coloured compounds + solutions)

Group 7Chlorine - Gas - pale greenBromine - Liquid - dark red (poisonous red/brown vapour)Iodine - Solid - dark grey (poisonous purple vapour)Chlorine water - Pale yellow/greenBromine water - Pale orangeAqueous Iodine (doesn't dissolve in water) - Dark red/brownMost reactive halogen displaces all the other halides from their salts (eg. Potassium halide)X2 + 2Y- → 2X- + Y2It is a Redox reaction (OILRIG)

Transition MetalsOnly transition metals form coloured compoundsHave variable valenciesGood conductors of heat + electricityForm coloured compounds + solutionsHigh density + strongHave high melting points (except mercury)Much less reactive than Group 1/2 metals. i.e. Takes time to react with water + oxygen

2d) Oxygen and Oxides

N2 - 78.1%O2 - 21.0%Ar - 0.9%CO2 - 0.04%Testing O2Copper turnings and gas syringe. Turns black.Iron in a test tube + beaker with water. Rusts.Reaction with phosphorus4P(s) + 5O2(g) → 2P2O5Making O2Hydrogen Peroxide (aq) decomposes. Add black Manganese (IV) Oxide as a catalyst through thistle funnel. Collect via side arm boiling tube over water2H2O2 → 2H2O + O2 Reactions with O2Oxygen + Magnesium : Bright white light and a white powder of MgO formed. Basic.Oxygen + Carbon : Yellow/orange flame. Forms CO2. Acidic.Oxygen + Sulfur : Blue flame. Forms SO2. Acidic.Making CO2Calcium Carbonate CaCO3 + HCl → CaCl2 + H2O + CO2Thermal decompositon of copper(II) carbonate. Turns green to black.Acid rainSO2 and NOx from power stations and factories react with water to make it acidicLeaches minerals out of the soil so trees dieLower pH of lakes. Aquatic life diesWeathers buildings made of limestone and ironSolutions : Remove sulphur from fuels, 'Scrub' power stations + factories to remove SO2 and NOx, use catalytic converters in cars (NOx → N2).

e) Hydrogen and Water

Water testWhite Anhydrous copper(II) Sulphate turns blueORBlue cobalt chloride paper turns pinkPurity testCheck if it boils at exactly 100C and freezes at exactly 0C

f) Reactivity Series

Redox reaction - A reaction where both oxidation and reduction are occurringOxidation - The addition of oxygenReduction - The removal of oxygen OR/ANDOIL RIG (of electrons)metal + cold water → metal hydroxide + hydrogenmetal + steam → metal oxide + hydrogen

3) Organic Chemistry

Fraction distillation (base temperature of 350°C)Bitumen - Road surfacesFuel oil - Lubricant. Industrial heating and ships' boilersDiesel - Fuel for heavy engines. Buses, Trains, LorriesKerosine - Aviation fuel. "Paraffin" lamps Gasoline - PetrolRefinery gases - Domestic heating and cookingCarbon monoxide is poisonous because it reduces the capacity of the blood to carry oxygen

Monomer - A molecule that can bind to other monomers to form a polymerPolymer - A long chain of monomers joined togetherAddition Polymerisation - A polymer which is formed when many monomers bond together without the loss of any atom or moleculeCondensation Polymerisation - A polymer formed when monomers combine and produce another small molecule such as waterAddition Polymerspoly(ethene) - Low Density poly(ethene) used for plastic bags. High Density poly(ethene) used for plastic bottlespoly(propene) - Used to make ropes and crates. Stronger than poly(propene)poly(chloroethene) / PVC - Used for garden drain pipes or replacement windows. Electrical insulationAddition Polymers are not biodegradable due to - Their strong carbon-carbon bond making them inertBiodegradable - The ability for a molecule to be broken down by micro-organismsNylon is formed by condensation polymerisation and this produces small molecules, such as water.

4b) Energetics

Neutralisation, Dissolving, Displacement Reactions - In a polystyrene cup add 1 reactant, record temperature, add other reactant, record final temperatureCombustion - Weigh fuel and starting temp of water in copper calorimeter, heat water until temp rises by 20-30°C, Weigh fuel and final tempEndothermic (+ΔH) e.g - Thermal decomposition, electrolysis, ethanoic acid + sodium carbonateExothermic (-ΔH) e.g - Combustion, neutralisation, water + calcium oxideQ=mcΔtmolar enthalpy change = Q/nBond energies = Σ bonds broken - Σ bonds made

c) Rates of reaction

SA - Gas syringe, conical flask with HCl and CaCO3. Record vol. of gas every 20 seconds upto 5 mins. Repeat with new SAConc. - Conical flask with cotton wool 'bung' on weighing scale. Different HCL conc. and same sized CaCO3. Measure mass every 30 secondsTemperature - Heat conical flask with Sodium Thiosulphate to a determined temperature. Place it over a cross on white paper. Add HCl and cotton wool 'bung'. Record start temp. Time how long before the cross can't be seen from above. Record final temp. Calculate average temp. for the graph. Repeat using different temps. (15-55°C)Catalyst - Hydrogen Peroxide decomposing in conical flask with gas syringe. Measure volume of oxygen every 20 seconds. Repeat with different catalyst (eg. Manganese (IV) Oxide)

d) Equilibria

Copper(II) Sulphate crystals - When heated turn blue to white (dehydration). Then when you add water it turns white to blue (hydration)Heat NH4Cl - White crystals disappear from the bottom and reappear at the top. NH4Cl(s) ⇌ NH3(g) + HCl(g)Reversible reaction - A reaction that can go forwards or backwardsDynamic Equilibrium - When the forward and backward reactions are still taking place at the same rate so there is no visible changeLe Chatelier's Principal - A reaction at equilibrium will react to oppose any changes to its conditions

5) Chemistry in Industry

Aluminium - ElectrolysisOre = BauxitePurified to give Aluminium Oxide. Al obtained using electrolysis. (molten cryolite solvent + carbon electrodes)Iron - Blast furnaceOre = Haemotite (mainly Iron(III) Oxide)Fe obtained using a blast furnace (coke (displacement), limestone (removes SiO2), air)Ammonia - Haber ProcessHydrogen - From natural gas or cracking hydrocarbonsNitrogen - From the airTemperature about 450°C~200 atmIron catalyst Ammonia used for the manufacture of fertilisers, nitric acid, nylonSulphuric Acid - Contact ProcessMainly Sulphur (element) burnt in air or sulphide ores heated stronglySulphuric acid (twice as much is produced later on)Temperature about 450°C~2 atmVanadium(V) Oxide catalystSulphuric acid used for the manufacture of detergents, fertilisers, paints (eg. extracting white pigment TiO2)Sodium Hydroxide & Chlorine - Electrolysis in diaphragm cellConcentrated solution of sodium chloride (brine)Titanium anode on the left (chlorine extracted), Steel cathode on the right (hydrogen extracted), Contaminated Sodium Hydroxide drained on the bottom right. Permeable diaphragm ensures no NaOH reacts with chlorine forming bleach, or hydrogen with chlorine forming an explosive mixtureSodium Hydroxide used for manufacture of bleach, paper (breaks wood into pulp) and soap (Reacts with animal and vegetable fats/oils)Chlorine used for sterilising water supplies, manufacture of bleach and HCl(Hydrogen used as a fuel)