Chapter 5 Reactivity PDF

Chapter-5- Reactivity What is the reactivity series of metals? The chemistry of the metals is studied by analysing their reactions with water and acids Based on these reactions a reactivity series of metals can be produced The series can be used to place a group of metals in...

Chapter-5- Reactivity What is the reactivity series of metals? The chemistry of the metals is studied by analysing their reactions with water and acids 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 The non-metals hydrogen and carbon are also included in the reactivity series as they are used to extract metals from their oxides Reactivity Series of Metals Reaction with cold Metal Reaction with acid Reaction with oxygen water Most reactive Potassium Reacts violently Reacts violently Reacts quickly in air Sodium Reacts quickly Reacts quickly Reacts quickly in air Calcium Reacts less strongly Reacts vigorously Reacts readily Slow reaction (reacts Magnesium Reacts vigorously Reacts readily with steam) Slow reaction (reacts Aluminium Reacts readily Reacts readily with steam) Carbon Very slow reaction Zinc (reacts slowly with Reacts less strongly Reacts steam) Very slow reaction Iron (reacts slowly with Reacts less strongly Reacts steam) Hydrogen No reaction with steam Copper No reaction Reacts or water No reaction with steam Silver No reaction Reacts or water  No reaction with steam Gold No reaction No reaction or water Least reactive Reaction of metals with cold water The more reactive metals will react with cold water to form a metal hydroxide and hydrogen gas Potassium, sodium and calcium all undergo reactions with cold water as they are the most reactive metals: metal + water → metal hydroxide + hydrogen For example, calcium and potassium: Ca (s) + 2H2O (l) → Ca(OH)2 (aq) + H2 (g) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g) Reactions of metals with steam Metals just below calcium in the reactivity series do not react with cold water but will react with steam to form a metal oxide and hydrogen gas, for example, magnesium: Mg (s) + H2O (g) → MgO (s) + H2 (g) Reaction with dilute acids Only metals above hydrogen in the reactivity series will react with dilute acids Unreactive metals below hydrogen, such as gold, silver and copper, do not react with 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 are very dangerous and react explosively with acids When acids react with metals they form a salt and hydrogen gas: The general equation is: metal + acid ⟶ salt + hydrogen Some examples of metal-acid reactions and their equations are given below: Acid-Metal Reactions Table  Metal Sulfuric acid Hydrochloric acid Magnesium Mg + H2SO4 → MgSO4 + H2 Mg + 2HCl → MgCl2 + H Zinc Zn + H2SO4 → ZnSO4 + H2 Zn + 2HCl → ZnCl2 + H Iron Fe + H2SO4 → FeSO4 + H2 Zn + 2HCl → ZnCl2 + H Reaction with oxygen Some reactive metals, such as the alkali metals, react easily with oxygen Silver, copper and iron can also react with oxygen although much more slowly When metals react with oxygen a metal oxide is formed, for example, copper: metal + oxygen → metal oxide 2Cu (s) + O2 (g) → 2CuO (s) Gold does not react with oxygen Deducing the order of reactivity The order of reactivity of metals can be deduced by making experimental observations of reactions between metals and water, acids and oxygen The more vigorous the reaction of the metal, the higher up the reactivity series the metal is A combination of reactions may be needed, for example, the order of reactivity of the more reactive metals can be determined by their reactions with water The less reactive metals react slowly or not at all with water, so the order of reactivity would need to be determined by observing their reactions with dilute acid Temperature change in a reaction can also be used to determine the order of reactivity The greater the temperature change in a reaction involving a metal, the more reactive the metal is Displacement reactions between metals and aqueous solutions of metal salts Any metal will displace another metal that is below it in the reactivity series from a solution of one of its salts This is because more reactive metals lose electrons and form ions more readily than less reactive metals, making them better reducing agents The less reactive metal is a better electron acceptor than the more reactive metal, thus the less reactive metal is reduced  o OILRIG: reduction is gain of electrons Magnesium + copper sulfate Magnesium is a reactive metal and can displace copper from a copper sulfate solution Magnesium loses its electrons more easily and the ion of the less reactive metal, copper, will gain these electrons to form elemental copper This is easily seen as the more reactive metal slowly disappears from the solution, displacing the less reactive metal magnesium + copper sulfate → magnesium sulfate + copper Mg (s) + CuSO4 (aq) → MgSO4 (aq) + Cu (s) The blue colour of the CuSO4 solution fades as colourless magnesium sulfate solution is formed Copper coats the surface of the magnesium and also forms solid metal which falls to the bottom of the beaker Diagram showing the colour change when magnesium displaces copper from copper sulfate By combining different metals and metal salts solutions it is possible to come up with a relative reactivity order Metal Solutions Displacement Table Mixture Products Equation for Reaction Mg + FeSO4 → MgSO4 + Magnesium and iron(II) sulfate Magnesium sulfate and iron Fe  Zinc and iron chloride Zinc chloride and iron Zn + FeCl2 → ZnCl2 + Fe Fe + AgNO3 → Fe(NO3)2 + Iron and silver nitrate Iron(II) nitrate and silver 2Ag Copper and iron(II) chloride No reaction ------ Silver and copper(II) sulfate No reaction ------ Zinc and magnesium chloride No reaction ------ From this table we can deduce the order of reactivity: o Magnesium and zinc are both more reactive than iron but magnesium is more reactive than zinc o Copper and silver are both less reactive than iron but silver is less reactive than copper The order of reactivity of the metals tested can be therefore be deduced as: o Mg > Zn > Fe > Cu > Ag Reactivity of aluminium Aluminium is high in the reactivity series, but in reality, it does not react with water and the reaction with dilute acids can be quite slow This is because it reacts readily with oxygen, forming a protective layer of aluminium oxide which is very thin This layer prevents reaction with water and dilute acids, so aluminium can behave as if it is unreactive