Ri Y4 Chem 2022 FE Revision Metals and Electrolysis Ans.pdf

1 Reactivity Series of Metals Metals can be ranked in a series based on their reactivity with water, steam and dilute acid. This series also indicates whether a metal can be extracted by reduction of its ore using carbon or hydrogen, and whether the compound (carbonate) of a metal is stable to heat. The table below ranks 12 (out of about 100) metals, from most reactive to least reactive. The more reactive metal can reduce. the ion or compound of a less reactive metal to form that less reactive metal. Alternatively, we say, the more reactive metal can displace the less reactive metal from its salt solution or oxide. Examples: 1 Zn (s) + CuSO4 (aq)  Cu (s) + ZnSO4 (aq) or Zn (s) + Cu2+ (aq)  Cu (s) + Zn2+ (aq) Observations: the blue solution fades in colour and a pink or brown solid is formed Explanation: the blue of the solution is due to Cu 2+ (aq) and as its concentration falls the blue colour fades off. The solid copper metal is formed which appears as pink or brown or red-brown in colour. 2 2Al (s) + Fe2O3 (s)  Al2O3 (s) + 2Fe (s) Extraction of Metals Many metals are extracted from their oxides (ores) by reduction with carbon or carbon monoxide. Those that cannot be extracted by such a method (e.g. aluminium) would usually be extracted by electrolysis. Iron is extracted in a blast furnace at above 1000 oC. The inputs into the furnace are haematite (Fe 2O3), coke (C), limestone (CaCO3) and hot air. The outputs are molten iron, molten slag (CaSiO3) and waste gases such as CO2. The main reaction is Fe2O3 (s) + 3CO (g)  2Fe (l) + 3CO2 (g) The side reactions are 1. Generate CO (the reducing agent): C + O2  CO2, then CO2 + C  2CO 2. Remove sand (acidic impurity): CaCO3  CaO + CO2, then CaO + SiO2  CaSiO3 (slag) Alloying Metals are soft and malleable due to the regular layers of atoms that can slide over each other easily. So they are usually mixed with other metals or with carbon to form alloys which are harder and stronger – since the atoms are of different sizes they no longer form regular layers and thus cannot slide over each other. Iron is alloyed with carbon to make steel. Mild steel ( or low-carbon steel, with ~0.25% carbon) is the most common steel, used to make car bodies, bridges and railway lines. Hard steel (or high-carbon steel, with ~1% carbon) is harder and less malleable or more brittle than mild steel, and is used to make tools. Stainless steel has additives other than carbon; it is used to make cutlery and surgical instruments. Corrosion of Metal The corrosion (or rusting) of iron requires air(oxygen) and water Rusting can be prevented by 1. Surface protection: cover the iron with a barrier (paint or oil or plastic or metal such as tin or chromium) to block air and water from reaching the iron underneath. 2. Sacrificial protection: coat the iron with zinc (or have the iron in contact with magnesi um or zinc). The more reactive metal re