The Reactivity Series of Metals.docx

7/29/2019 The Reactivity Series of Metals.docx

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Metals

The Reactivity Series of Metals:

The reactivity series is metal is an arrangement of the metals (and carbon andhydrogen) in order of their reactivity starting with the most reactive metal at

the top and ending with the least reactive metal at the bottom.

The reactivity of a metal is determined by its ability to form a positive ion.For example, potassium is extremely reactive because it has only one valence

electron, so it is very easy to lose it forming a positive ion.

One the other hand, copper is a weakly reactive metal because it has morevalence electrons so it is harder for it to become a positive ion.

Reactions of Metals:

The reactivity series of metals was deduced by performing severalexperiments in the lab which enabled scientists to arrange metals according

to their reactivity with dilute acid, oxygen (air), and water.


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Reactions with Dilute Hydrochloric Acid:

In the previous chapter, you studied those reactions involving a metal and an acid are used to prepare solublesalts and that this method is only suitable for preparing salts of moderately reactive metals (MAZIT). This isbecause any metal more reactive that magnesium will react very violently with acids which is dangerous.

Metal + HClMetal Chloride + Hydrogen

Metals Reactivity with Dilute HClPotassium, Sodium &Calcium

React extremely violently with rapid effervescenceand splashing

Magnesium & Aluminum React violently with rapid effervescenceZinc, Iron & Lead React slowly with bubblesCopper, Silver, Gold &Platinum

Do not react


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Hydrogen

Reactions with Oxygen in Air:

Most metals react with oxygen from air forming a metal oxide. You have previouslystudied that metal oxides are basic oxides and that some of them are insoluble in waterand some of them are soluble in water forming an alkaline solution. The most reactivemetals like potassium, sodium, calcium and magnesium react with oxygen with a very

bright flame and producing white ashes and their oxides are soluble. Moderatelyreactive metals like aluminum and zinc react with oxygen forming white powderedashes but their oxides are insoluble. Iron and copper react very slowly with oxygen. Theresult of iron oxygen reactions is rust which is reddish brown iron oxide. When acopper lump reacts with oxygen, a white layer of black copper oxide forms on it. Whenthe lump gets covered by this layer; the reaction stops. Oxides of iron and copper are

insoluble. Metals that are less reactive than copper like silver, gold and platinum do notreact with oxygen.

Note: When aluminum reacts with oxygen, a layer of aluminum oxide adheres andcovers the aluminum. At this point no further reaction can take place.


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Reactions of Metals with Water and Steam:

Some metals are so reactive that they will just react with water immediately if they

come in contact. Other metals will react slowly will cold water, but with steam theyreact much faster. And other metals can only react slowly with steam. Unreactive metalssuch as silver and gold do not react with water.

Potassium, sodium and calcium react vigorously with cold water and may catch on fire.The products of these reactions are metal hydroxide and hydrogen gas. If hydrogen gasbeing produced accumulates it may ignite and cause an explosion.

Metal + WaterMetal hydroxide + Hydrogen

E.g.: 2Na + 2H2O 2NaOH + H2

Magnesium, aluminum, zinc and iron are less reactive. They react with steam forming

metal oxide and hydrogen. Magnesium and aluminum will react vigorously with steamwhile zinc and iron react slowly.

Metal + SteamMetal Oxide + Hydrogen

E.g.: Magnesium + SteamMagnesium oxide + Hydrogen


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Competition Reactions in Solid State:

Previously youve studied displacement reactions which are pre-formed in aqueous

states. A very similar reaction takes place in the solid state, it is calledthermitereaction. This reaction is used to repair damaged railway lines. In this reaction,aluminum and iron (III) oxide are the reactants. In the reaction, aluminum removes theoxygen ion from iron and bonds with it. This happens because aluminum is morereactive than iron. The products are aluminum oxide and iron in molten form. In thefixing procedure, the reactants are put in the cut in the railway line and the reaction is

triggered by heating using a magnesium fuse. The reaction leaves aluminum oxide andmolten iron with then condenses in the cut welding it. Like displacement reactions, thisreaction is exothermic.

2Al + Fe2O3Al2O3 +2Fe

Competition Reactions in Aqueous State:

These are ordinary displacement reactions in which the two positive ions compete forthe negative ion. The ion of the more reactive metal wins. Zinc is higher than copper inthe reactivity series. If zinc is added to a solution of copper nitrate, a displacementreaction will take place in which the zinc will displace the copper ion from the solutionin its salt. The products of this reaction are zinc nitrate and copper. Copper salt


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solutions have a blue color which fades away as the reaction proceeds because theconcentration of the coppersalt decreases. This type of reaction also helped inconfirming reactivity of metals since the more reactive metal displaces the less reactive

one.

Zn + Cu(NO3)2 Zn(NO3)2 + Cu


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Action of Heat on Metal Compounds:

Applying heat to a metal compound such as potassium nitrate will cause it to

decompose into potassium nitrite and oxygen. This is a thermal decomposition reaction.Metal: Anion:

Nitrate (NO3) Carbonate (CO3) Hydroxide (OH)Potassium

SodiumMetal NitrateMetal nitrite +

OxygenNO DECOMPOSITION

CalciumMagnesiumAluminum

ZincIronLead

Copper

Metal NitrateMetal oxide +Nitrogen dioxide + Oxygen

Metal CarbonateMetal oxide + Carbon

dioxide

Metal hydroxideMetal oxide +

Hydrogen

SilverGold

Metal NitrateMetal +Nitrogen dioxide + Oxygen

Metal CarbonateMetal + Carbondioxide + Oxygen

-


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Silver and gold hydroxides do not exist.

Ions of more reactive metals tend to hold on tightly to their anions and do not

decompose easily this is why lots of heat is needed.


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Extracting Metals From Their Ores:

Most metals do not exist in nature as pure elements. Instead, they are found as naturally

occurring compounds calledores. Ores are naturally occurring minerals from which ametal can be extracted. Most ores are metals oxide, carbonate or sulfide mixed withother impurities. The extraction of metal from ores begun long ago when people startedpurifying iron from its iron oxide ore by reducing it using charcoal. This was possiblebecause carbon is more reactive than iron so it can reduce it take the oxygen ion from it.But then other metals were discovered which were higher than carbon in the reactivity

series. Those metals were not possibly extracted from their ores until in the 19th centurywhen a method of extracting them by electrolysis was invented. The method extractinga metal depends on its reactivity.


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Metals - in decreasing order of

reactivityReactivity

potassium Extract by electrolysis

Extract by reaction with carbon or carbonmonoxide

Extracted by various chemical reactions


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Extraction of Aluminum:

Aluminum exists naturally as aluminum oxide (alumina) in its ore, which is called

bauxite. Because aluminum is a very reactive metal, it holds on very tightly to the anionit bonds with, which is oxide in this case. This is why the best way to extract and purifyaluminum is by electrolysis in a cell like the one below.

In this cell, the electrodes are made of graphite (Carbon). The cathode is a layer at thebottom of the cell and the anodes are bars dipped in the electrolyte. The electrolyte inthis process is a molten mixture of aluminum oxide and cryolite. Aluminum oxide by itsself has a very high melting point of 2050oC which is higher than the melting point ofthe steel container in which this process is done. That means the steel container will


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melt before the aluminum oxide. This is why aluminum oxide is mixed with cryolitewhich decreases the melting point of it to under 1000oC, thus saving a lot of moneybecause heating is expensive and preventing the steel container from melting. Heat must

be continuously supplied to the mixture to keep it molten. Aluminum oxide does notconduct electricity when solid because it does not have free mobile ions to carry thecharge.

Aluminum oxide is purified from impurities of oxide by adding sodium hydroxide Aluminum oxide is mixed with cryolite and put in the electrolysis cell

Heat is given in until the mixture becomes molten Electrolysis start Oxide ions get attracted to the anode and discharged (oxidation); 2O2-, 4eO2 Aluminum ions get attracted to the cathode and discharged and settle at the bottom

of the container (reduction); Al3+ + 3e Al Oxygen gas evolves and is collected with waste gases Aluminum is sucked out of the container at regular intervals

Oxygen gas which evolves reacts with carbon from the cathode forming CO2. Thecathode gets worn away. To solve this, the cathode is replaced at regular intervals. Heatsupply is very expensive; this is why cryolite is used to decrease the melting point ofaluminum oxide and this process is done in plants which use hydroelectric energybecause it is cheap.


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Uses of aluminum:

Construction of air-craft bodies because aluminum is very strong and very light andit is resistant to corrosion

Food containers because it is resistant to corrosion Overhead power cables because it conducts electricity, is very light, malleable and

ductile. Although it is strengthened with steel core


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Extraction of Iron:

The ore of iron is called hematite. It consists of 60% iron in form of Iron oxide (Fe2O3)

with other impurities such as siliconoxide (SiO2). This process takes place in a tower called a Blast furnace.

Substances Products andWasteMaterials

(Hematite)

coal)

(Calciumcarbonate)

dioxide

(Calciumsilicate)


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Substances are put in the blast furnace The process starts by blowing in hot air at the bottom of the furnace Coke burns in oxygen from the hot air producing carbon dioxide; C + O2 CO2 Heat makes lime stone decompose into calcium oxide and carbon

dioxide; CaCO3 CaO + CO2 Carbon dioxide produced goes up the furnace and reacts with more coke up there

producing

carbon monoxide; CO2 + C 2CO Carbon monoxide is a reducing agent. It rises further up the furnace where it meets

iron oxide and starts reducing it producing iron and carbon dioxide; Fe2O3 + 3CO 2Fe + 3CO2

Calcium oxide which was produced from the thermal decomposition of lime stoneis a base. It reacts with impurities of hematite such as silicon oxide which is acidic

forming calcium silicate which is called slag; CaO + SiO2 CaSiO3

Molten Iron and slag produced trickles down and settles at the bottom of thefurnace. Iron is denser than slag so it settles beneath it.Iron and slag are tapped off separately at regular intervals and pure iron is collectedalone

Waste gases such as carbon dioxide formed in the process and nitrogen and othergases from air blown in escape at the top of the furnace.


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The Blast Furnace

How to extract iron from its ore

The method

Three substances are needed to enable to extraction of iron from its

ore. The combined mixture is called the charge:-Iron ore, haematite - often contains sand with iron oxide, Fe2O3.-Limestone (calcium carbonate).-Coke - mainly carbon.

The charge is placed a giant chimney called a blast furnace. The blastfurnace is around 30 metres high and lined with fireproof bricks. Hotair is blasted through the bottom.


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- Both the slag and iron are drained from the bottom of the furnace.- The slag is mainly used to build roads.-The iron whilst molten is poured into moulds and left to solidify - this is called cast iron

and is used to make railings and storage tanks.The rest of the iron is used to make steel.


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Conversion of Iron into Steel:

Iron produced in the blast furnace is calledpig iron. It contains 4% carbon as well as

other impurities such as sulfur, silicon and phosphorus which make it hard and brittle.It got that name from the fact that it has to be poured into mould called pigs before it isconverted into steel. Most of produced iron is converted into steel because steel hasbetter properties.

Making steel out of pig iron is a process done in a basic oxygen furnace:

Molten pig iron is poured into the oxygen furnace A water cooled lance is introduced which blows oxygen onto the surface of the

molten iron Impurities start to react Carbon is oxidized into carbon monoxide and carbon dioxide and escape Sulfur is oxidized into sulfur dioxide and escapes Silicon and phosphorus are oxidized into silicon oxide and phosphorus pentoxide

which are solids. Calcium oxide (lime) is added to remove the solid impurities as slag which is

skimmed off the surface Throughout the process, sample of the iron are being taken and analyzed for the

percentage of carbon present in it. When the percentage of carbon desired is

reached, the furnace is switched off and the steel is collected.


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There are many different forms of steel. Each has different components and propertiesand is used for different purposes.

Steel Composition Properties UsesMild Steel 99.5% Iron

0.5% CarbonEasily worked lostbrittleness

Car bodieslarge structuresMachinery

Hard Steel 99% Iron

1% Carbon

Tough and brittle Cutting tools and chisels

StainlessSteel

87% Iron13%Manganese

Tough and springy Drill bits and springs andchemical plants


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Extraction of Zinc:

The ore of zinc is called zinc blende and it is made of zinc sulfide. Zinc is obtained from

zinc sulfide by converting it into zinc oxide then reducing it using coke, but first zincsulfide must be concentrated.

Zinc sulfide from zinc blende is concentrated by a process called froth floatation. In thisprocess, the ore is crushed and put into tanks of water containing a frothing agentwhich makes the mixture froth up. Hot air is blown in and froth starts to form. Rockimpurities in the ore get soaked and sink to the bottom of the tank. Zinc sulfideparticles cannot be soaked by water; they are lifted by the bubbles of air up with thefroth and are then skimmed off. This is now concentrated zinc sulfide.

Then, zinc sulfide gets heated very strongly with hot air in a furnace. Zinc sulfide reactswith oxygen from the air to produce zinc oxide and sulfur dioxide gas which escapes aswaste gas.

2ZnS + 3O2 2ZnO + 2SO2

Sulfur dioxide is used in the manufacture of sulfuric acid.

Zinc oxide produced is put into a furnace with powdered coke. The mixture is heatedtill 1400oC. Carbon from the coke reduces the zinc oxide into zinc producing carbon

monoxide which escapes as waste gas.


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ZnO + C Zn + CO

Carbon monoxide produced is hot and is used to heat the furnace to reduce heating

costs. The pure zinc produced is collected and left to cool down. Zinc is used in manyways like the production of the alloy brass, galvanization and making car batteries.

Extraction of Copper:

Copper is one of the most popular metals. Native copper occurs in some regions in theworld. Otherwise, copper exists in its ore, copper pyrites (2CuFeS2). You have studiedbefore that copper can be purified by electrolysis. It can also be extracted from it ore byconverting pyrites into copper sulfide by reacting it with oxygen:

2CuFeS2 + 4O2 Cu2S + 3SO2 + 2FeO

Sulfur oxide produced escapes as waste gas and iron oxide impurities are removed byheating the mixture with silicon converting it in to iron silicate which is run off. Theremaining copper sulfide is then heated strongly with air. Copper sulfide reacts withoxygen from air producing sulfur oxide which escapes as waste gas and pure copper.

Cu2S + O2 2Cu + SO2


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Thus copper is extracted.

Uses of Copper:

In electrical wires because it is a perfect electrical conductor and very ductile,malleable and cheap

Making alloys such as bronze and brass Cooking utensils because it conducts heat and it is has high melting and boiling

points and also resists corrosion Electrodes because it is a good conductor of electricity Water pipes because it is resistant to corrosion


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Sulphur

Sulphur is a non metal element in group 6 of the periodic table. Sulphur has many useful

properties which make it widely used in the industry.

Sources of Sulphur:

Sulphur is found in many places in the world in different forms. It usually exists in

volcanic regions in USA, Mexico and Sicily. Sulphur could also be obtained from somemetal ores like Copper pyrites (CuFeS2) and Blende (ZnS).

Properties of Sulphur:

In room temperature, sulphur is a yellow, brittle solid which doesnt conduct electricityas it is a non-metal. Sulphur is insoluble in water. It is able to react with both metals andnon-metals.


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Sulphur Dioxide:

Sulphur dioxide is the product of combustion of sulphur or sulphur-containing fuels. As

you have studied in the previous chapter, it is an air pollutant as it causes acid rain.However, SO2 has important uses too:

Bleaching wood pulp for the manufacturing of paper It is used as a food preservative as it kills bacteria Manufacturing of Sulphuric acid

Contact Process (Manufacturing of Sulphuric Acid):

Sulphuric acid is one of the most important chemicals in the industry since it has a rolein the manufacturing of almost every product. Sulphuric acid is manufactured by aprocess called Contact Process and it involves several steps:

1.Making the sulphur dioxide2.Converting the sulphur dioxide into sulphur trioxide3.Converting the sulphur trioxide into sulphuric acid

1. Making the sulphur dioxide

Sulphur is first burned in air producing sulphur dioxide:


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S(s)+ O2(g) SO2(g)

2. Converting the sulphur dioxide into sulphur trioxide:

This is a reversible reaction, and the formation of the sulphur trioxide is exothermic.

2SO2(g)+ O2(g) 2SO3(g)3. Converting the sulphur trioxide into sulphuric acid

This can't be done by simply adding water to the sulphur trioxide - the reaction is souncontrollable that it creates a fog of sulphuric acid. Instead, the sulphur trioxide is firstdissolved in concentrated sulphuric acid:

H2SO4(l)+ SO3(g)H2S2O7(l)

The product is known as fuming sulphuric acid or oleum.

This can then be reacted safely with water to produce concentrated sulphuric acid -twice as much as you originally used to make the fuming sulphuric acid.

H2S2O7(l)+ H2O(l) 2 H2SO4(l)

The average percentage yield of this reaction is around 30%.


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Properties & Uses of Sulphuric Acid:

Sulphuric acid is a very strong acid. It is a dibasic acid which means it every molecule ofit produces two hydrogen ions when it is dissolved in water. Sulphuric acid has someother unique properties. For example, it is a dehydrating agent. This means it eliminateswater from compounds.

E.g.: CuSO4.5H2O CuSO4 + 5H2O

E.g.: C6H12O6 6C + 6H2O

It is also a drying agent. This means it removes water from mixtures. Dont confuse that

dehydrating agent.

The Reactivity Series of Metals.docx

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