Chemistry Unit 7 Revision Notes PDF
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This document provides revision notes on chemistry, covering the topics of metal reactions with water and acids, metal displacement reactions, and rusting of iron. It includes various equations and descriptions of the processes involved.
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Chemistry Unit 7 Revision Notes Metals Reacting with Water and Acids The chemistry of the metals is studied by analysing their reactions with water and cids a Based on these reactions a reactivity series of metals can be produced The series can be...
Chemistry Unit 7 Revision Notes Metals Reacting with Water and Acids The chemistry of the metals is studied by analysing their reactions with water and cids a Based on these reactions a reactivity series of metals can be produced The series can be used to place a group of metals in order of reactivity based on the observations of their reactions with water and acids Reaction with Water The reactions of potassium and sodium have already been seen previously in the alkali metals, but the reaction with calcium and water is given here for reference: Ca (s) + 2H2O (l) ⟶ Ca(OH)2 (aq) + H2(g) Calcium + Water ⟶ Calcium Hydroxide + Hydrogen The reactions with magnesium, iron and zinc and cold water arevery slow Reaction with Dilute Sulphuric or Hydrochloric Acid O nly metalsabove hydrogenin the reactivity series willreactwith dilute acids The more reactive the metal then the more vigorous the reaction will be Metals that are placed high on the reactivity series such as potassium and sodium re very dangerous and react explosively with acids a The general equation is: Metal + Acid ⟶ Salt + Hydrogen Metal Displacement Reactions T he reactivity of metals decreases going down the reactivity series This means that a more reactive metal will displace a less reactive metal from its ompounds c Two examples are: ○ Reacting a metal with a Metal Oxide (by heating) ○ Reacting a metal with an aqueous solution of a metal compound E.g It is possible to reduce Copper(II) Oxide by heating it with Zinc The reducing agent in the reaction is zinc: Zn + CuO → ZnO + Cu Displacement Reactions between Metals & Aqueous Solutions of Metal Salts The reactivity between two metals can be compared using displacement r eactions in salt solutions of one of the metals This is easily seen as the more reactive metal slowly disappears from the solution, displacing the less reactive metal ○ E.g Magnesium is a reactive metal and can displace copper from copper(II)sulfate solution: Mg + CuSO4→ MgSO4 + Cu The blue colour of the CuSO4 solution fades as colourless magnesium sulfate s olution is formed Copper coats the surface of the magnesium and also forms solid metal which falls to the bottom of the beaker Order of Metal Reactivity Rusting of Iron Rusting is the name given specifically to the corrosion of iron in the presence of water and oxygen from the air: Iron + Water + Oxygen ⟶ Hydrated Iron(III) Oxide Rust is a soft solid substance that flakes off t he surface of iron easily, exposing fresh iron below which then undergoes rusting ○ Over time all of the iron rusts and its structure becomes weakened Oxygen and watermustbe present for rust to occur Boiled water removes any dissolved oxygen and calcium chloride is a drying agent Rust Prevention Barrier Methods C an be prevented by coating iron with barriers If the coatings are washed away or scratched, the iron is will be exposed to water nd oxygen and will rust a Once iron begins to rust, it will continue to corrode internally ○ Rust is porous and allows both air and water to come into contact with fresh metal underneath any barrier surfaces Common barrier methods include: paint, oil, grease, and electroplating Sacrificial Protection C an be prevented from rusting using the reactivity series Amorereactive metal can be attached to alessreactive metal The more reactive metal will oxidise and therefore corrode first, protecting the less reactive metal from corrosion Zinc is more reactive than iron therefore will lose its electrons more easily than iron and is oxidised more easily For continued protection, the zinc bars have to be replaced before they completely corrode Galvanising rocess where the iron to be protected is coated with a layer of zinc P Can be done by electroplating or dipping it into molten zinc ZnCO3 is formed when zinc reacts with O2 and CO2 in air and protects the iron If the coating is damaged or scratched, the iron is still protected from rusting by sacrificial protection Oxidation and Reduction Oxidation & Reduction (in terms of oxygen) The reactions of metals with oxygen, such as in iron rusting can be classified as xidation o Oxidation is any reaction in which a substance gains oxygen Theoppositeof oxidation isreduction Reduction is a reaction in which a substance loses oxygen ○ E.g Zn + CuO → ZnO + Cu is a redox reaction Oxidationcannot occurwithout reduction happening simultaneously, hence these are called redox reactions The Copper (II) Oxide supplies the oxygen, so it is the oxidising agent The zinc is the reducing agent because it removes the oxygen Oxidation & Reduction in terms of electrons Displacement reactions can be analysed in terms redox reactions by studying the transfer of electrons ○ E.g Mg and CuSO4 Mg (s) + Cu2+ (aq) + SO42- (aq) → Mg2+ (aq) + SO42- (aq) + Cu (s) Mg (s) + Cu2+ (aq) → Mg2+ (aq) + Cu (s) This equation is an example of a balanced ionic equation which can be further split into two half equations illustrating oxidation and reduction individually: Oxidising Agents in terms of electrons O xidising agents will oxidise other species in a reaction ○ They are themselves reduced therefore will ○ gain electrons E.g Fe has been oxidised and Cu2+ has been reduced Therefore Cu2+ is the oxidising agent he Fe atom is oxidised (loses electrons) and the Cu2+ ion is reduced (gains electrons). T Cu2+ is the oxidising agent
