Chemistry Igcse Flashcards
Ionic bonds
soluble, not volatileconduct electricityhigh melting and boiling points
Covalent bonds
insoluble (water), volatiledoesn't conduct electricity low melting and boiling points
Metallic bonding
positive metal ions and electrons
Diamond (macromolecule)
tetrahedralhard, stronghigh melting point, don't conduct, insoluble
Silicon dioxide (macromolecule)
tetrahedralhard, stronghigh melting point, don't conduct, insolubleeach oxygen - 2 siliconeach silicon - 4 oxygen
graphite (macromolecule)
strong bonds within layers, weak between layershigh melting point, insolubleconduct, slippery because of layers
diamond uses
cutting tools, jewellry
graphite uses
lubricant for engines and locks, electrodes for electrolysis
silicon dioxide uses
sandpaper, to line furnaces (cheap, natural)
moles equations
moles= mass / mrconc. = moles / volume1 mole = 24 dm3
electrolysis - copper electrodes
impure copper (anode) - Cu --> Cu2+ + 2e-pure copper (cathode) - Cu2+ + 2e- --> Cuelectrolyte - copper sulphate
electroplating
metal (anode) - Cu --> Cu2+ + 2e- object (cathode) - Cu2+ + 2e- --> Cuelectrolyte - has to include the metal ions
electrolysis - molten compound
metal (cathode)non-metal (anode)
electrolysis - solution at the cathode
metal or hydrogen (if the metal is more reactive)ion + e- --> metal / hydrogen
electrolysis - solution at the anode
halide or oxygen (if the solution is dilute or no halide)ion --> halide / oxygen + e-
Simple cell
more reactive metal (cathode) - loses massMg --> Mg2+ + 2e-electrons travel through wire - electric current and Mg ions released into solution.less reactive metal (anode) - unchanged 2H+ + 2e- --> H2 (from electrolyte)
Increase voltage of a simple cell
make metals reactivity further apartmake acid (electrolyte) stronger
Fuel cell
Hydrogen oxidised (cathode)2H2 + 4OH- --> 4H20 + 4e-Oxygen reduced (anode)O2 + 2H + 4e- --> 4OH-electrons go through wire (current) to anode and OH ions go through electrolyte to cathode. hydrogen, oxygen pumped in.
Hydrogen as a fuel + uses
2H2 + O2 --> 2H20 + energyexplodes when lit - rockets, in spacecraft (fuel cell)Safe, clean
Electrolysis of brine NaCl
chlorine (anode) - 2Cl- --> Cl2 + 2e-hydrogen (cathode) - 2H+ + 2e- --> H2Sodium hydroxide left as solution
Sodium hydroxide uses
soaps, detergent, dyes, medical drugs
Chlorine uses
PVC, bleach, paints, dyes, medical drugs
Hydrogen uses
making ammonia, margarine, fuel
Factors that change reaction rate
Surface areaConcentrationTemperatureCatalystPressure (for reversible reaction)
Redox identifying agents
Potassium manganate - oxidising agentpurple -> colourlessPotassium iodide - reducing agentcolourless -> red-brown (blue-black with starch)
acid + metal
salt + hydrogen
acid + oxide/hydroxide
salt + water
acid + carbonate
salt + water + carbon dioxide
base + ammonium salt
salt + water + ammonia (NH3)
basic oxides
alkaline, metals
acidic oxides
acidic, non-metals
amphoteric oxides examples
usually metalloids - Al, Zn, Pb
neutral oxides examples
CO, H2O, N2O
Extracting metals - charge
Coke, metal ore, limestone
Extracting metals - coke burnt
C + O2 --> CO2C + CO2 --> 2CO
extracting iron - haematite (main reaction)
Fe2O3 + 3CO --> 2Fe + 3CO2
Extracting zinc - zinc blende (main reactions)
(2ZnS + 3O2 --> 2ZnO + 2SO2)ZnO + CO --> Zn + CO2
Extracting metals - impurities
(CaCO3 --> CaO + CO2) - thermal decompositionCaO + SiO2 --> CaSiO3Slag (calcium silicate) - used for concrete on roads
Extracting metals - waste gases
CO2N (unreacted in air)SO2 - only zinc
Extracting aluminium - bauxite
Oxide mixed with molten cryolite for lower boiling pointAluminium (cathode) - Al3+ + 3e- --> AlOxygen (anode) - 2O2- --> O2 = 4e-
Stainless steel
iron, chromium, nickel - doesn't rustcar parts, sinks, cutlery
Mild steel
iron, carbon - hard, strongships, cars, machinery
Aluminium alloy
light, strongaircraft
Brass
copper, zinc - hard, doesn't corrodedoorknobs, instruments
bronze
copper, tin - harder than brass, doesn't corrode, sonorousbells, statues, ornaments
Don't break down in thermal decomposition
Potassium, Sodium
Thermal decomposition of carbonate
CO3 --> oxide + CO2
Thermal decomposition of hydroxide
OH --> oxide + H2O
Thermal decomposition of nitrate
NO3 --> oxide + NO2 + O2
Making steel
Burnt in oxygenCO2, SO2 - impurities released as gases Limestone addedSiO2 - slag producedOther elements added after
Test for water
Anhydrous copper sulphatewhite -> blueAnhydrous cobalt chlorideblue -> pink
Water uses
Home - drinking, cooking, washing, flushingIndustry - crops, as a solvent, steam, washing, lower temperatures
Treatment of water supplies
1. Filter - remove solid particles2. Coagulant - chemical makes particles stick together3. Flotation tanks - make coagulated particles float to top4. Sand/ charcoal filter - remove bad smell, taste5. Chlorine - sterilise and kill bacteria6. Fluoride compound - prevent tooth decay
Pollutants and sources
Carbon monoxide - incomplete combustionSulfur dioxide and acid rain - fossil fuelsNitrogen oxides - car exhaustLead compounds - leaded petrol
Catalytic removal of nitrogen oxide in cars
nitrogen oxide --> nitrogen + oxygen (catalyst transition metal)carbon monoxide + oxygen --> carbon dioxide
Rusting conditions
oxygen and water
Rusting prevention eg. for iron
paint, plastic, grease coatinggalvanising (zinc coating) - keeps oxygen out and sacrificialSacrificial protection - more reactive metal is oxidised
Haber process equation
N2 + 3H2 --> 2NH3
Haber process conditions
Pressure - high (200atm)Temperature - compromise (450 degrees) - low better but too slowCatalyst - ironRemove product, recycle unreacted gases
Hydrogen, Nitrogen sources
Nitrogen - fractional distillation of air / burn hydrogen in air (N2 + O2 + H2O --> N2 + 2H2O)Hydrogen - cracking orMethane + steam (heat, catalyst)
Contact process
S + O2 --> SO22SO2 + O2 --> 2SO3dissolve in conc. sulphuric acid --> oleum mix with waterSO3 + H2O --> H2SO4
Contact process conditions
Pressure - normal - high better but no needTemperature - compromise (450 degrees)Catalyst - vanadium oxide
Sulphur sources
fossil fuels, metal ores, element underground/on volcano rims
Sulphur dioxide uses
bleach when making paper, food preservativepollutant - acid rain, harm people
Sulphuric acid uses
paints, dyes, plastics, soaps, detergents, sulphate salts (fertilisers)
Limestone -> lime -> slaked lime
CaCO3 --> CaO + CO2 (thermal decomposition)CaO +H2O --> Ca(OH)2
Calcium carbonate uses
remove impurities (slag)make cement, plaster(heat with clay and add hydrated calcium sulfate - gypsum)
Lime, slaked lime uses
Neutralise soils and lakesFlue gas desulphurisation
Flue gas desulphurisation
SO2 + Ca(OH)2 --> CaSO3 + H2ORemove sulphur dioxide from power station waste gases2CaSO3 + O2 + H2O --> 2CaSO4.2H2O (gypsum)
Fractional distillation
Refinery gasGasolineNaphthaKerosene/ ParaffinDiesel/gas oilFuelLubrication fractionBitumen
Fractional distillation uses
Refinery gas - heating and cookingGasoline - fuel in carsNaphtha - making chemicalsKerosene/parrafin - jet fuelDiesel - diesel enginesFuel - for ships, home heating systemsLubricating - lubricant, wax, polishesBitumen - making roads
Alkanes
all single bonds - saturatedBurn in airSubstitution reactions with chlorine (with UV light)
Manufacture of alkenes
Cracking of alkanes - heat with a catalystAlkane --> smaller alkane and alkene
Alkene
Double bond - unsaturatedTest with bromide water - turns orange -> colourless
alkene -> alkane
alkene + hydrogen --> alkane
Addition polymerisation
monomers (identical alkene molecules) makes a polymer - long chain molecule and nothing elseMakes plasticsheat, pressure and a catalyst - add (poly) in front
Condensation polymerisation
monomers (2 different molecules) makes a polymer - long chain molecules and a small moleculeMakes fibres
Manufacture of alcohol - fermentation
glucose --> ethanol + carbon dioxide (enzymes in yeast) ethanol separated by fractional distillation
Manufacture of alcohol - hydration
ethene + steam --> alcohol (with a catalyst - phosphoric acid)
Advantages and disadvantages of alcohol production
Fermentation- Renewable- BUT slow (batch process), CO2 waste, yeast stops working when too much product/ liquid too warmHydration- 100% atom economy- Fast, continuous- BUT non-renewable, expensive (need heat for steam)
Alcohol
OH - functional groupCombustion - fuelAs a solvent - glue, cosmeticsAlcoholic drinks
Manufacture of carboxylic acid
Oxidation of alcohol 1. Fermentation - left in air2. With oxidising agent (potassium manganate)
Carboxylic acid
COOH - functional groupethanoic acid (vinegar) - weak acid - only partially ionised
Manufacture of esters
Condensation polymerisation of carboxylic acid and alcohol Alcohol - yl, Acid - anoateeg. ethyl propanoate - small molecule water, ester link
Esters and uses
COO - functional groupused for artificial flavours and fragrances
Ester link
Terylene, fats and oils, lipids
amide link
Nylon, protein
Carbohydrates
mono saccharides --> polysaccharides
Synthetic polymers uses
Nylon - thread, ropes, fishing netsTerylene - thread, fabric for shirts and bed linenPolychloroethene - tables, water pipes, waterproof clothing, insulation for wires, Polyethene - tables, water pipes, plastic bags, bottles, chairs, toys
Hydrolysis of natural polymers
eg. protein to amino acids, carbohydrates to mono-saccharidesHeat with hydrochloric acid - reverse of condensation