Electrolysis of NaOH and H2SO4
Hydrogen forms at the cathode, oxygen forms at the anode.
At the anode; 4OH- - 4e- ----> O2 + 2H2O
At the cathode; 2H+ + 2e- ---> O2 + 2H2O
Electrolysis of CuSO4
The electrodes used are made of carbon. At the cathode copper forms. At the anode oxygen forms.
At the anode; 4OH- - 4e- -----> O2 + 2H2O
At the cathode; Cu-2 + 2e- ----> Cu
(the minus 2 on copper means it has an extra 2 electrons)
Solids can't be electrolysed because it has ions which are fixed in position. This means it must be molten or melted.
Fuel cells work because the reaction between hydrogen and oxygen is exothermic.
At the cathode oxygen gains electrons and reacts with water from the electrolyte to make OH- ions. These OH- ions then move to the anode, where hydrogen combines with the OH- to produce water and electrons. The electrons then flow through an external circuit from the anode to the cathode.
In a space craft fuel cells are useful because it provides water and energy, is lightweight, compact and has no moving parts. The car industry is producing fuel cells because there would be no CO2 emissions and there is a large source of hydrogen available by decomposing water. But fuel cells will still produce pollution because they often contain poisonous catalysts and the production of the hydrogen and oxygen will require energy which may come from fossil fuels.
Redox Reactions and the Rusting of Iron
Oxidation is loss of electrons, reduction is the gain. OIL RIG.
The rusting of iron is a redox reaction because iron looses electrons but oxygen gains electrons.
iron + oxygen + water ----> hydrated iron (III) oxide
Galvanised iron is covered with a layer of zinc. This stops water and oxygen reaching the surface of the iron. The zinc can also act as a sacrificial metal. Like magnesium, zinc is more reactive than iron. This means that the zinc/magnesium will loose electrons instead of iron.
In a displacement reaction metal ions are reduced by gaining electrons, but metal atom is oxidised by losing electrons.
Fermentation and Ethene
Word equation for fermentation; glucose ---> carbon dioxide + ethanol
Symbol; C6H12O6 ----> 2CO2 + 2CO2 + 2C2H5OH
Ethanol is made from a glucose solution. Enzymes in yeast are used to catalyse the reaction and there has to be no oxyegn available so the yeast will perform anaerobic respiration. Fractional distillation is then used to get the ethanol. In fermentation a suitable temperature is needed. Too low and the yeast will be inactive, but too high and the enzymes will be denatured.
Fermentation is better than hydration of ethene because it uses a renewable source. Fermentation also uses low temps and the material used has a low value. But the hydration of ethene produces pure ethanol and uses a continuous process.
For industrial use ethanol is made by passing ethene and steam over a heated phosphoric catalyst. Ethene (C2H4) + water (H2O) ----> ethanol (C2H5OH). This is the hydration of ethene method.
CFCs are banned because they deplete the ozone layer. They do this because the CFCs are broken down in the stratosphere by UV light to release very reactive chlorine atoms. These chlorine atomsthen react with many, many ozone molecules.
These very reactive chlorine atoms are formed when carbon-chlorine bonds break. This is because the covalent bond can break evenly, so each atom gets one of the shard electrons. The unpaired electron (represented by a dot) will make the chlorine a free radical and very recative.
CFCs are only removed slowly in the stratosphere because it requires strong UV light to break them up. The depletion of the ozone layer allows more UV radiation to reach earth because less is being absorbed.
We get temporary hardness in water because calcium carbonate in rocks will react will dissolved CO2 and water to form soluble calcium hydrogen carbonate.
Permenant hardness is caused by dissolved calcium sulphate.
Boiling can remove temporary hardness. This is because the decomposition of calcium hydrogen carbonate gives us insoluble calcium carbonate (limescale), water and CO2. This means that the soluble calcium ions are changed into insoluble compounds.
Decomposition of calcium hydrogen carbonate;
Ca(HCO3)2 ---> CaCO3 + H2O +CO2
If things are unsaturated they will have double covalent bonds. We can find out whether the oil or fat is saturated by using bromine water; if it is saturated the bromine will stay orange. But if it's unsaturated the bromine will become clear.
This works because an addition reaction takes place at the carbon-carbon double bond and a colourless dibromo compound is then formed. Saturated compounds can't react with bromine because they don't have carbon-carbon double bonds.
Oil, Animal Fats and Vegetable Fats
They are all esters. Margarine can be made from vegetable oil by passing hydrogen through the oil in the presence of a nickel catalyst. The addition of hydrogen to the unsaturated bonds results in saturated C-C bonds, increasing the melting point of the oil so hardening it.
Immiscible liquids (e.g. water and oil) can form an emulsion if an emulsifier is added to them. The emulsifier will make one liquid split into tiny droplets and spread throughout the liquid.
Soap and glycerol are produced when natural fats and oils are split up by hot sodium hydroxide soluton. This process is called saponification and is a hydrolysis reaction.
Word equation for saponification;
fat + sodium hydroxide ---> soap + glycerol
Detergents and Dry Cleaning
Detergents are molecules with a hydrophyllic head and a hydrophobic tail.
A dry cleaning solvent removes stains because there are weak intermolecular forces between molecules of grease and weak intermolecular forces between molecules of the sovent. The solvent molecules will form intermolecular bonds with molecules of grease and surround the grease.