Chemistry
- Created by: AOconnor
- Created on: 14-05-18 19:42
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- Chemistry
- Electrolysis
- Decomposition of aqueous/molten ionic compounds using electricity
- Molten compounds (lead bromide)
- Process
- Melt lead bromide
- Positively charged lead ions go to cathode and form pure lead
- Negatively charged bromide ions go to anode and form bromine
- Melt lead bromide
- Half equations
- Anode
- 2Br(-) ---> Br2 + 2e(-)
- Cathode
- Pb(2+) + 2e(-) ---> Pb
- Anode
- Process
- Aqueous solutions
- Aqueous means dissolved in water
- Water molecules break down to form OH- and H+
- Anode
- If halide ions are present, the halogen is produced
- Halide ions = fluoride, chloride, bromide and iodide
- If no halide ions present, oxygen is produced
- Halide ions = fluoride, chloride, bromide and iodide
- If halide ions are present, the halogen is produced
- Cathode
- Least reactive element is formed out of hydrogen and metal
- Extracting metals (aluminium from aluminium oxide)
- Extracts metals more reactive than carbon
- Requires lots of energy and can be expensive
- Aluminium can be obtained via electrolysis of aluminium oxide
- Mixed with cryolite which lowers melting point so less energy needed (cheaper)
- Aluminium formed at cathode
- Al(3+) + 3e(-) ---> Al
- Oxygen gas forms at anode
- Anode is carbon, so reaction occurs and carbon dioxide is formed
- 2O(2-) ---> O2 + 4e-
- Extracts metals more reactive than carbon
- Molten compounds (lead bromide)
- Ionic compound must be in liquid form so ions can move freely and carry charge
- Electrodes are made from solids that can conduct electricity but are inert
- Substance being broken down is the electrolyte
- Anode is positive and cathode is negative
- Decomposition of aqueous/molten ionic compounds using electricity
- Reactivity of metals
- Oxidation is gaining oxygen
- Reduction is losing oxygen
- Metal oxides can be reduced by removing oxygen
- Lead oxide is reduced by heating with carbon to form lead and carbon dioxide
- Metal oxides can be reduced by removing oxygen
- Metals react with acids to produce salts and hydrogen
- Doing thee reaction can help place elements on reactivity series
- Method used to extract metals depends on its reactivity
- Most metals are found as metal oxides in earths crust
- Metals less reactive than carbon can be extracted by heating with carbon
- Alkalis
- Hydroxide ions make solutions alkaline
- 8-14
- Strong alkalis fully disassociate in water
- All OH- ions are released
- Alkalis are soluble bases
- Acids
- hydrogen ions make solutions acidic
- 1-6
- Strong acids fully ionise in water
- All hydrogen ions are released
- Strong acids have a higher concentration of H+ ions
- Neutralisation
- Acids are neutralised by soluble bases
- When they react the OH- ions and H+ ions react to form water
- Solution reaming is neutral (pH = 7)
- A salt is produced when the hydrogen ion in the metal is replaced by a metal ion
- When they react the OH- ions and H+ ions react to form water
- Acid + metal hydroxide ---> salt +water
- Acid + Metal oxide ---> salt + water
- Acid + metal carbonate ---> salt + water + carbon dioxide
- Acids are neutralised by soluble bases
- Salts
- Soluble salts are made by reacting acids with insoluble bases
- Practical
- Add metal oxide/carbonate to warm solution of acid until no more will react
- Filter excess metal oxide/carbonate to leave solution of salt
- Warm solution so water evaporates and crystals form
- Filter excess metal oxide/carbonate to leave solution of salt
- Add metal oxide/carbonate to warm solution of acid until no more will react
- Practical
- Soluble salts are made by reacting acids with insoluble bases
- Electrolysis
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