9.4 - Reactivity Series.pdf

Reactivity series What is the reactivity series of metals? The chemistry of the metals is studied by analyzing 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...

Reactivity series What is the reactivity series of metals? The chemistry of the metals is studied by analyzing 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 Reaction with Metal Reaction with acid water oxygen 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 Copper No reaction Reacts steam or water No reaction with Silver No reaction Reacts steam or water No reaction with Gold No reaction No reaction steam or water Least reactive How to remember the reactivity series Observations from the table above allow the following reactivity series to be deduced The order of this reactivity series can be memorized using the following mnemonic ○ “Please send cats, monkeys and cute zebras into hot countries signed Gordon" Reactivity Series Mnemonic  Metal Abbreviation Most reactive Potassium P - Please Sodium S - send Calcium C - cats, Magnesium M - monkeys, Aluminium A - and Carbon C - cute Zinc Z - zebras Iron I - into Hydrogen H - hot Copper C - countries Silver S - signed Gold G - Gordan  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 Magnesiu Mg + H2SO4 → MgSO4 Mg + 2HCl → MgCl2 + H2 m + H2 Zn + H2SO4 → ZnSO4 + Zinc Zn + 2HCl → ZnCl2 + H2 H2 Fe + H2SO4 → FeSO4 + Iron Zn + 2HCl → ZnCl2 + H2 H2 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 Explaining reactivity Extended tier only Metal atoms form positive ions by loss of electrons when they react with other substances The tendency of a metal to lose electrons is a measure of how reactive the metal is A metal that is high up on the series loses electrons easily and is thus more reactive than one which is lower down on the series 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 ○ 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 color of the CuSO4 solution fades as colorless 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 The reaction between magnesium and copper sulfate Diagram showing the color 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 Magnesium and iron(II) Mg + FeSO4 → MgSO4 Magnesium sulfate and iron sulfate + Fe Zn + FeCl2 → ZnCl2 + Zinc and iron chloride Zinc chloride and iron Fe Fe + AgNO3 → Iron and silver nitrate Iron(II) nitrate and silver Fe(NO3)2 + 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: ○ Magnesium and zinc are both more reactive than iron but magnesium is more reactive than zinc ○ 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: ○ Mg > Zn > Fe > Cu > Ag Reactivity of aluminum Aluminum 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 aluminum oxide which is very thin This layer prevents reaction with water and dilute acids, so aluminum can behave as if it is unreactive