Forum Thread

:) To record things

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Title: Chemistry IGCSE

Only key points I can't remember:

Electrolysis-
Molten lead bromide: PbBr2
Pb2+ + 2e- -> Pb (Cathode)
2Br- -> Br2 + 2e- (Anode)

Concentrated aqueous sodium chloride: NaCl
2H2O + 2e- -> H2 + 2OH-
2Cl- -> Cl2 + 2e- (Anode)
The brine (salt water) will turn into sodium hydroxide which is alkaline since Na+ and OH- ions are left in the solution

Molten sodium chloride: NaCl
Instead of hydrogen and hydroxide ions, Na metal and Cl gas will be produced

When using copper electrodes during the electrolysis of copper (II) sulfate (CuSO4), the solution will turn from blue to colourless as the copper is removed and pure copper will gather at the cathode (the anode contains a impure sample of copper).

Fuel cells:
Only consider hydrogen+oxygen fuel cells in ig!

Enthalpy-
Breaking bonds takes in energy
Creating bonds releases energy

CHEMICAL REACTIONS-
Copper(II) sulfate: white to blue after addition of water
Cobalt(II) chloride: blue to pink after addition of water

Haber process
N2+3H2->2NH3
The hydrogen comes from methane:
CH4+H2O->3H2+CO
CO+H2O->CO2+H2
The nitrogen comes from the air
Conditions:
-450 degrees celsius
-200 atm
-Iron catalyst

Contact process
2SO2 + O2 ->2SO3
The sulfur comes from burning sulfur or roasting sulfur ores
The oxygen comes from the air
Conditions:
-450 degrees celsius
-2 atm
-Vanadium(V) oxide

Oxidation number
-Oxidation number of elements in their uncombined state is zero
-The oxidation number of a monoatomic ion is the same as the charge on the ion
-The sum of the oxidation numbers in a compound is zero
-The sum of the oxidation numbers in an ion is equal to the charge on the ion

-Group 1 elements are always +1
-Group 2 elements are always +2
-Fluorine is always -1
-Hydrogen in always +1 except in metal hydrides where it is -1
-Oxygen is always -2 except in peroxides where it is -1 and F2O where it is +2

Metals-
Reactions with...
Dilute acids: Mg+2HCl->MgCl2+H2
Metal+acid->Salt+hydrogen
Cold water: 2Na+2H2O->2NaOH+H2
Metal+water->Base+hydrogen
Oxygen: 2Mg+O2->2MgO
Metal+oxygen->Metal oxide
Steam: Mg+H2O->MgO+H2
Metal+steam->Metal oxide+hydrogen

Brass is a mixture of zinc and copper, stainless steel is a mixture of iron, carbon, chromium, nickel and some other metals.

Reactivity series of metals:
Potassium->Sodium->Calcium->Magnesium->Aluminium->Carbon->Zinc->Iron->Hydrogen->Copper->Silver->Gold

Extraction of metals from their ores:
Iron from hematite
1. Burning coke to produce heat and carbon dioxide C+O2->CO2
2. Reduction of carbon dioxide to carbon monoxide C+CO2->2CO
3. Reduction of iron(III) oxide by carbon monoxide Fe2O3+3CO->2Fe+3CO2

Slag from limestone
1. Thermal decomposition of calcium carbonate to produce calcium oxide CaCO3->CaO+CO2
2. Reaction of calcium oxide with silicon oxide CaO+SiO2->CaSiO3

Aluminium from bauxite
1. Aluminium ore is treated to form aluminium oxide (Al2O3)
2. Extraction is only possible through electrolysis because aluminium's reactivity is higher than carbon. However, electrolysis requires aluminium oxide to be molten. Cryolite will reduce the melting point of Al2O3, achieving the electrolysis of the compound.
Cathode: 2Al3+ + 6e- -> Al2
Anode: 2O2- -> O2 + 4e-

Environment-
-Sedimentation and filtration to remove solids
-Carbon to remove tastes and odours
-Chlorine to remove microbes

Greenhouse gases cause global warming by trapping the thermal energy. After the sun's rays reach the Earth's surface, a lot of it is reflected back into the atmosphere. The gases will trap the reflected rays and reduce the thermal energy loss into space.

Nitrogen oxide:
They can cause photochemical smog, acid rain, and respiratory problems.

Organic chemistry-
A homologous series is a family of similar compounds with similar chemical properties due to the presence of the same functional group.

In a fractional distillation column for petroleum, the fractions obtained from bottom to top have:
-Decreasing chain length
-Higher volatility (evaporation)
-Lower boiling points (this is why they can be separated)
-Lower viscosity

Hydrogenation: Alkene+hydrogen(with a nickel catalyst)->Alkane
Hydration: Alkene+steam(with an acid catalyst)->Alcohol

How to manufacture ethanol?
1. Fermentation
C6H12O6->2C2H5OH+2CO2
Conditions: 25-35 degrees celsius+no oxygen present
2. Catalytic addition of steam to ethene
C2H4+H2O->C2H5OH
Conditions: 300 degrees celsius+60 atm+acid catalyst (e.g. acidified potassium manganate)

Ethanol can be converted into ethanoic acid by oxidising it using acidified potassium manganate.
C2H5OH+2O(from potassium manganate)->CH3COOH+H2O

Reactions of ethanoic acid with...
Metal: 2CH3COOH+Mg->(CH3COO)2Mg+H2
Ethanoic acid+metal->Salt+hydrogen
Base: CH3COOH+NaOH->CH3COONa+H2O
Ethanoic acid+base->Salt+water
Carbonates: 2CH3COOH+Na2CO3->2CH3COONa+CO2+H2O
Ethanoic acid+carbonate->Salt+water+carbon dioxide

Condensation polymerisation:
Polyesters are formed from dicarboxylic acids (H-O-C=O) and diols (H-O)
Polyamides are formed from dicarboxylic acids (H-O-C=O) and diamines (H-N-H)
-Proteins are natural polyamides formed from amino acid monomers with an amine functional group on one side and a carboxyl group on the other side. The carbon in the middle also connects to a hydrogen and a long carbon chain.