C19 metals and their reactivity

Describe the physical and chemical properties of metals;

Explain why metal alloys are often used in place of metals;

Discuss the reactivity of metals, and deduce the order of reactivity of metals based on experimental results of data supplied

Describe the reactions of metallic hydroxides, nitrates and carbonates

LEARNING OUTCOMES

Metals and Their Reactivity Chapter 19

Physical Properties of metals Metals are usually hard and shiny. They are malleable (can be bent or hammered

into sheets) and ductile (can be stretched or drawn into wires).

Pure metals are weak because their atoms can slide over each other easily when a force is applied.


Physical Properties of metals Metals are good conductors of heat and electricity. Metals have high density.

They have high melting points and boiling points.

E.g. iron has a melting point of 1538 oC and tungsten has a melting point of 3422 oC.


Chemical Properties of metals Metals lose electrons to form positively charged ions

(electropositive).Cu Cu2+ + 2e−

Most metals react with acids to produce hydrogen gas.Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g)

Metals form basic oxides when they react with oxygen.2Ca(s) + O2(g) 2CaO(s)

Most metals react with water to produce metallic hydroxides and hydrogen gas.

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)


Structure of metals The atoms of metals are packed

very closely together in neat layers.

Pure metals are weak because the layers of atoms can slide over one another when a force is applied.


Alloys of metals A mixture of a metal with another metal (or non-metal) is called an alloy.

Brass

BronzeBronze

Stainless steel

Brass is an alloy of copper and zinc; bronze is an alloy of copper and tin.

Stainless steel is an alloy of iron and small amounts of carbon, chromium and nickel.


Structure of alloys In alloys, the atoms of different

metals or elements are of different sizes.

This disrupts the orderly layers of atoms and makes it harder for the layers of atoms to slide over one another when a force is applied. This explains why alloys are harder and stronger than the pure metals.


Quick Check 11. State 2 physical properties of metals which make them useful

as constructing materials.2. What is meant by the terms: “ malleable” and

“ ductile ” ?3. What is an “ alloy” ? Give two examples of alloys.4. Explain why alloys are harder and stronger than the pure

metals.5. Explain why brass is used for making the pins of the power

plug, instead of pure copper.SolutionSolution


1. (a) Metals are strong and malleable.(b) They can withstand high temperatures.

2. Malleable means it can be hammered into sheets without breaking; Ductile means it can be stretched into wires without breaking.

3. An alloy is a mixture of a metal with another element. Brass and steel are examples of alloys.

4. Unlike pure metals, the atoms in an alloy are of different sizes. This makes it more difficult for the atoms to slide over each other when a force is applied.

5. Brass is harder and stronger than pure copper.

Return

Solution to Quick check 1


The Reactivity Series The Reactivity Series

shows the order of reactivity of metals in their reactions with water, steam, and dilute acids.

Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Silver (Ag)

Most reactiveMost reactive

Least reactiveLeast reactive


How to remember the Reactivity Series

Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc (Zn) Iron (Fe) Lead (Pb) Copper (Cu) Silver (Ag)

Katty’sNaughtyCatMingled withAlice andZarina;FearlesslyPlundering herCupboard ofSilver

Most reactive

Least reactiveLeast reactive


The Reactivity SeriesPotassium Sodium Calcium ……………...... Magnesium Aluminium Zinc Iron Lead ……………….. Copper Silver

Most Reactive

Least Reactive

React with cold React with cold waterwater

React React withwithsteamsteam

Do not react Do not react with water, with water, steam or dilute steam or dilute acidsacids

Explode with Explode with steam and steam and dilute acidsdilute acids

React with React with dilute acidsdilute acidswith with decreasing decreasing vigourvigour


Reaction of potassium with water The first three metals: potassium, sodium and calcium react very vigorously with cold water to produce hydrogen gas and an alkali. When a small piece of potassium is placed into a trough of water, it immediately bursts into flames, and moves rapidly on the water surface. The hydrogen gas given off makes it burn explosively. An alkali, potassium hydroxide, is also formed.

2K(s) + 2H2O(l) 2KOH(aq) + H2(g)


Reaction of sodium with water Sodium reacts less vigorously than potassium with cold water.

When a small piece of sodium is placed into a trough of water, it melts into a silvery ball and darts about on the water surface. It may occasionally burst into flame. An alkali, sodium hydroxide, is left in the solution.

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)


Reaction of calcium with water When a small piece of calcium is placed in a beaker of water, it sinks to the bottom of the water. It reacts vigorously with the water, producing bubbles of hydrogen. The water turns slightly milky due to theformation of calcium hydroxide, which is not very soluble in water.

Ca(s) + 2H2O(l) Ca(OH)2 (aq) + H2 (g)

The hydrogen can be collected in a test tube and tested with a lighted splint.


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Reactions with steam Magnesium, zinc and iron do not react with cold water but react with steam when heated to produce hydrogen and a metal oxide:

Equations:

Mg(s) + H2O(g) MgO(s) + H2(g)

Zn(s) + H2O(g) ZnO(s) + H2(g)

3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)


Reaction of magnesium with steam

When the test tube is heated, steam is produced which reacts with the hot magnesium ribbon.

An experiment is set up as shown in the diagram.

The magnesium reacts with the steam, producing hydrogen gas which burns at the jet of the glass tube. Mg + H2O MgO + H2


Reactions with dilute acids Potassium (K) Sodium (Na) Calcium (Ca) ……………………Magnesium (Mg) Aluminium (Al) Zinc ( Zn) Iron (Fe) Lead (Pb)……………………Copper (Cu)Silver (Ag)

All metals from lead and above react with dilute acids to form a salt and hydrogen.

The higher the metal is in the reactivity series, the more vigorous the reaction.

Potassium, sodium and calcium will explode with acids, while lead will only react very slowly when heated.

React withdilute acids

No reaction with dilute acids


Reactions of metals with dilute hydrochloric acid

The picture shows that magnesium reacts very vigorously with dilute hydrochloric acid, followed by zinc.

Lead has almost no reaction with dilute hydrochloric acid.

Copper does not react with dilute hydrochloric acid.


Non-reactivity of Aluminium Potassium (K) Sodium (Na) Calcium (Ca) ……………………Magnesium (Mg)

Zinc ( Zn) Iron (Fe) …………………Lead (Pb)Copper (Cu)Silver (Ag)

Aluminium which is relatively high in the Reactivity Series seems to have no reaction with water, steam and dilute acids.

This is because aluminium is coated with a thin layer of aluminium oxide that is invisible to the naked eye. This layer protects the metal from contact with the reagents.

Aluminium (Al)


Quick Check 21. Which metal is (a) the most reactive, (b) the least reactive, in the

reactivity series? (Exclude silver)2. Arrange the following metals from the most reactive to the least reactive:

calcium, zinc, magnesium, sodium, copper and aluminium.3. What gas is given out when metals react with water and dilute acids ?4. Write a balanced chemical equation for the following reactions:

(i) sodium and water, (ii) magnesium with steam, (iii) zinc with dilute hydrochloric acid.

5. When a piece of aluminium was placed in a test tube containing dilute hydrochloric acid, there was no reaction. When the aluminium was rubbed with some sodium hydroxide solution and then re-immersed in the hydrochloric acid, the aluminium reacted vigorously with the acid.Explain why this happens.

Solution


1. (a) Potassium, (b) copper2. Sodium, calcium, magnesium, aluminium, zinc, copper3. Hydrogen gas4. (i) 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

(ii) Mg(s) + H2O(l) MgO(s) + H2(g)(iii) Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

5. The piece of aluminium was coated with a layer of aluminium oxide which protects it from the hydrochloric acid. Rubbing it with sodium hydroxide removed the layer of aluminium oxide, and hence the aluminium was able to react with the hydrochloric acid. Return



The Reactivity series and ease of forming ions The reactivity series is related to the ease of the metals in

forming positive ions by losing electrons. The more easily a metal loses its outermost electron(s), the

more reactive it will be. A more reactive metal will form a more stable compound with a

non-metal. Hence It is more difficult for oxides and carbonates of the more reactive metals to be reduced or decomposed by heat.


Reduction of metal oxidesPotassium Sodium Calcium Magnesium Aluminium

Zinc Iron Lead

Copper Silver

Not reducedby hydrogen

Reduced by hydrogen

Not reduced by carbon

Reduced by carbon

(Carbon)

(Hydrogen)

Reduction of metal oxides by carbon Oxides of metals which are below carbon in the reactivity series are reduced to the metal when heated with carbon.

This process is used in the industry to obtain the metals from their ores.

Examples:

ZnO(s) + C(s) Zn(s) + CO(g)

CuO(s) + C(s) Cu(s) + CO(g)


Reduction of metal oxides by hydrogen

Oxides of metals which are below hydrogen in the reactivity series are reduced to the metal when heated with hydrogen.

Examples:

CuO(s) + H2(g) Cu(s) + H2O (g)

AgO(s) + H2(g) Ag(s) + H2O(g)


Displacement Reactions When a piece of zinc is placed in copper(II)

sulphate solution, a brown layer of copper is formed on the surface of the zinc.

Zinc metal

Coppercoating

Copper(II)sulphate solution

The zinc has displaced the copper from the copper(II) sulphate solution because zinc is more reactive than copper.

Zn + CuSO4 ZnSO4 + Cu

In general, a more reactive metal will displace a less reactive metal from their salts in solution.


Displacement Reactions If a piece of zinc is placed in

magnesium sulphate solution, no reaction will take place.

Zinc metal

No reaction

magnesiumsulphate solution

This is because zinc is less reactive than magnesium (lower in the reactivity series than magnesium) and hence cannot displace magnesium ions from its solution.


Displacement of metal from their oxides A more reactive metal can

displace a less reactive metal from its oxide when they are heated together.

E.g. 2Al + Fe2O3 Al2O3 + 2Fe

Potassium (K) Sodium (Na) Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc ( Zn) Iron (Fe) Lead (Pb)Copper (Cu)Silver (Ag)

Most reactive

This reaction is used in the production of “thermite”, which uses the molten iron formed to repair cracks on railway lines. Least reactive


Action of heat on metal carbonates Carbonates decompose

when heated to produce the metal oxides and carbon dioxide.

E.g. CaCO3 CaO + CO2

Potassium (K)

Sodium (Na)

Calcium (Ca) Magnesium (Mg) Aluminium (Al) Zinc ( Zn) Iron (Fe) Lead (Pb)Copper (Cu)Silver (Ag)

Carbonates not decomposed by heat

Carbonatesdecomposedby heat

More difficult

Easier

However, the more reactive the metals are, the more difficult it is for their carbonates to decompose.


Thermal stability of metallic compounds


Reactions of metallic compounds with acids and alkalis


Quick Check 31. Arrange the following metals in order of their ease of forming positive ions,

starting from the most difficult:lead, magnesium, sodium, iron, calcium, copper, potassium, zinc.

2. State what will happen when a piece of iron is placed in a beaker of copper(II) sulphate solution. Write a chemical equation for the reaction.

3. Complete the following reactions. (a) Mg(s) + ZnSO4(aq) (b) Zn(s) + Pb(NO3)2(aq) (c) Al(s)+ Zn(NO3)2(aq (d) Cu(s) + ZnSO4(aq)

(e) ZnCO3(s) (f) Mg(s) + Al2O3(s)

Solution


heat

1. Copper, lead, iron, zinc, magnesium, calcium, sodium and potassium.2. The iron will turn reddish-brown as it has displaced copper from the copper(II)

sulphate solution. The blue copper(II) sulphate will become pale green in colour.Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

3. (a) Mg(s) + ZnSO4(aq) MgSO4(aq) + Zn(s)(b) Zn(s) + Pb(NO3)2(aq) Zn(NO3)2(aq) + Pb(s) (c) 2Al(s)+ 3Zn(NO3)2(aq) 2Al(NO3)3(aq) + 3Zn(s)(d) Cu(s) + ZnSO4(aq) No reaction

(e) ZnCO3(s) ZnO(s) + CO2(g)

(f) 3Mg(s) + Al2O3(s) 3MgO(s) + 2Al(s)

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heat

1. http://www.chemicalelements.com/groups/alkali.html

2. http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Introduction/metals.htm

To Learn more about Metals, click on the links below!


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