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Science C4 - Chemical Changes - Coggle Diagram
Science C4 - Chemical Changes
Reactivity Series, Metal Oxides and Extraction of Metals
Reactivity of metals
The reactivity series
Metals above carbon are extracted by electrolysis
Metals below carbon are extracted by reduction using carbon (metal oxide + carbon -> metal + carbon dioxide)
Gold and sliver cannot be extracted
metal oxides
Most metals in ores are chemically bonded to other elements in compounds. Many of these metals have been oxidised (have oxygen added) by oxygen in the air to form their oxides. If you want to extract metals from their oxides then you need to remove oxygen
extraction of metals by reduction
OILRIG
Oxidation Is Loss of electrons, Reduction Is Gain of electrons
When reactions involve reduction and oxidation, they are known as redox reactions
Metals and Acids, Weak Acids and Strong Acids
Reactions of Acids
Metals and Acids
Acids react with some metals to produce salts and hydrogen
Metal + acid --> salt + hydrogen
Reactions between metals and acid only occur if the metal is more reactive than the hydrogen in the acid. If the metal is too reactive, the reaction with acid is violent
The salt that is made depends on the metal and acid used
Strong and weak acids
A strong acid is completely ionised in aqueous solution (hydrochloric, nitric and sulphuric acid)
A weak acid is only partially ionised in aqueous solution (ethanoic, citric and carbonic
pH, Neutralisation and Salts
pH and Neutralisation
Indicators are substances that change colour when you add them to acids and alkali
for example, Litmus goes red in acid and blue in alkali
Universal indicator, is made from many dyes and used to tell you the pH. The pH scale goes from 0 (most acidic) to 14 (most alkali) Aqueous (in water) solutions of acids have a pH of less than 7 and alkalis, greater than 7 and anything in the middle is neutral.
In neutralisation, reactions between an acid and alkali, hydrogen ions react with hydroxide ions to produce water
Salts
acids are neutralised by alkalis (e.g. soluble metal hydroxides) and bases (e.g. insoluble metal hydroxides and metal oxides) in order to produce salts and water and by the metal carbonates to produce salts, water and carbon dioxide.
acid+ alkali --> salt + water
acid + bases --> salt + water
acid + metal carbonate --> salt + water + carbon dioxide
Electrolysis
when an ionic compound is melted or dissolved in water, the ions are free to move about the liquid/solution. These liquids/solutions are able to conduct electricity and are called electrolytes
passing an electric current through electrolytes causes the ions to move to the electrodes
Positive ions go to the negative cathode and are reduced (gain of electrons)
Negative ions go to the positive cathode and are oxidised (loss of electrons)
Ions are discharged at the cathodes producing elements and this is called electrolysis.
At the negative electrode: metal will produced on the electrode if it is less reactive than hydrogen. Hydrogen will be produced if the metal is more reactive than hydrogen
At the positive electrode, oxygen is formed. If you have a halide ion (Cl-, I-, Br-), then you will get chlorine, bromine or iodine formed at that electrode.
This happens because in the aqueous solution, water molecules break down producing hydrogen ions and hydroxide ions that are discharged
Electrolysis of metal ores
Metals can be extracted from molten compounds using electrolysis. Large amounts of energy are used in the extraction process in order to melt the compounds and to produce the electrical current
Aluminium is manufactured by electrolysis of molten aluminium oxide. Aluminium oxide has a very high melting point so is mixed with molten cryolite, lowering the temp in order to carry out electrolysis.
Aluminium goes to the negative cathode and sinks to the bottom.
Oxygen forms at positive electrodes. The oxygen reacts with the carbon electrode making carbon dioxide causing damage. The electrode needs replacing due to this reaction.
