C19 metals and their reactivity

Chapter 19
Metals and Their Reactivity
LEARNING OUTCOMES

 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

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.

Chapter 19
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.

Chapter 19
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)

Chapter 19
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.

Chapter 19
Alloys of metals
 A mixture of a metal with
another metal (or non-metal) is
called an alloy.
Brass
 Brass is an alloy of copper and
zinc; bronze is an alloy of copper
and tin.
Bronze

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

Chapter 19
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.

Chapter 19
Quick Check 1
1. 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.
Solution

Chapter 19
Solution to Quick check 1

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

Chapter 19
The Reactivity Series
 The Reactivity Series Potassium (K) Most reactive
shows the order of Sodium (Na)
reactivity of metals in Calcium (Ca)
their reactions with Magnesium (Mg)
water, steam, and Aluminium (Al)
dilute acids. Zinc (Zn)
Iron (Fe)
Lead (Pb)
Copper (Cu)
Silver (Ag) Least reactive

Chapter 19
How to remember the Reactivity Series
Potassium (K) Katty’s Most reactive
Sodium (Na) Naughty
Calcium (Ca) Cat
Magnesium (Mg) Mingled with
Aluminium (Al) Alice and
Zinc (Zn) Zarina;
Iron (Fe) Fearlessly
Lead (Pb) Plundering her
Copper (Cu) Cupboard of
Silver (Ag) Silver Least reactive

Chapter 19
The Reactivity Series
Most Reactive Potassium
React with cold Explode with
Sodium
water steam and
Calcium
dilute acids
……………......
Magnesium React with
Aluminium React
dilute acids
Zinc with
with
Iron steam
decreasing
Lead vigour
……………….. Do not react
Copper with water,
Silver steam or dilute
Least Reactive
acids

Chapter 19
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)

Chapter 19
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)

Chapter 19
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 the
formation of calcium hydroxide, which is not
very soluble in water.
pop
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.

Chapter 19
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)

Chapter 19
Reaction of magnesium with steam
 An experiment is set up as
shown in the diagram.
 When the test tube is heated,
steam is produced which reacts
with the hot magnesium ribbon.
 The magnesium reacts with the steam,
producing hydrogen gas which burns at the
jet of the glass tube.
 Mg + H2O  MgO + H2

Chapter 19
Reactions with dilute acids Potassium (K)
Sodium (Na)
 All metals from lead and above
Calcium (Ca)
react with dilute acids to form a
……………………
salt and hydrogen.
Magnesium (Mg)
React with
 The higher the metal is in the
dilute acids
Aluminium (Al)
reactivity series, the more Zinc ( Zn)
vigorous the reaction. Iron (Fe)
 Potassium, sodium and
Lead (Pb)
……………………
calcium will explode with
No reaction Copper (Cu)
acids, while lead will only react with dilute Silver (Ag)
very slowly when heated. acids

Chapter 19
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.

Chapter 19
Non-reactivity of Aluminium Potassium (K)
 Aluminium which is Sodium (Na)
relatively high in the Calcium (Ca)
Reactivity Series seems to ……………………
have no reaction with water, Magnesium (Mg)
steam and dilute acids. Aluminium (Al)
Zinc ( Zn)
This is because aluminium is
Iron (Fe)
coated with a thin layer of aluminium …………………
oxide that is invisible to the naked Lead (Pb)
eye. This layer protects the metal Copper (Cu)
from contact with the reagents. Silver (Ag)

Chapter 19
Quick Check 2
1. 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

Chapter 19
1. (a) Potassium, (b) copper
2. Sodium, calcium, magnesium, aluminium, zinc, copper
3. Hydrogen gas
4. (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

Chapter 19
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 oxides
Potassium
Sodium
Calcium Not reduced by
carbon
Magnesium
Not reduced Aluminium
by hydrogen (Carbon)
Zinc
Iron
Lead Reduced by
(Hydrogen) carbon

Reduced by Copper
hydrogen Silver

Chapter 19
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)

Chapter 19
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)

Chapter 19
Displacement Reactions Zinc metal
 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.

Zn + CuSO4  ZnSO4 + Cu
Copper
The zinc has displaced the copper from the coating
copper(II) sulphate solution because zinc is
more reactive than copper.
Copper(II)
 In general, a more reactive metal will displace a less sulphate
reactive metal from their salts in solution. solution

Chapter 19
Displacement Reactions
Zinc metal
 If a piece of zinc is placed in
magnesium sulphate solution,
no reaction will take place.
 This is because zinc is less
reactive than magnesium No reaction
(lower in the reactivity
series than magnesium) and
hence cannot displace
magnesium ions from its magnesium
sulphate
solution. solution

Chapter 19
Displacement of metal from their oxides
 A more reactive metal can
displace a less reactive metal Potassium (K)
Most reactive
from its oxide when they are
heated together. Sodium (Na)
Calcium (Ca)
E.g. 2Al + Fe2O3  Al2O3 + 2Fe Magnesium (Mg)
 This reaction is used in
Aluminium (Al)
the production of Zinc ( Zn)
“thermite”, which uses Iron (Fe)
the molten iron formed Lead (Pb)
to repair cracks on Copper (Cu)
railway lines. Silver (Ag) Least reactive

Chapter 19
Action of heat on metal carbonates
 Carbonates decompose
when heated to produce Potassium (K) Carbonates not
decomposed by
the metal oxides and heat
carbon dioxide. Sodium (Na)
E.g. CaCO3  CaO + CO2 More difficult
Calcium (Ca)
 However, the more Magnesium (Mg) Carbonates
reactive the metals Aluminium (Al) decomposed
by heat
are, the more Zinc ( Zn)
difficult it is for their Iron (Fe)
carbonates to Lead (Pb)
decompose. Copper (Cu) Easier

Silver (Ag)

Chapter 19
Thermal stability of metallic compounds

Chapter 19
Reactions of metallic compounds
with acids and alkalis

Chapter 19
Quick Check 3
1. 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) 
heat
(e) ZnCO3(s) 
Solution
(f) Mg(s) + Al2O3(s) 

Chapter 19
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
heat

(e) ZnCO3(s)  ZnO(s) + CO2(g)
(f) 3Mg(s) + Al2O3(s)  3MgO(s) + 2Al(s) Return

Chapter 19

To Learn more about Metals, click on the
links below!
1. http://www.chemicalelements.com/groups/alkali.html
2. http://www.ndt-
ed.org/EducationResources/CommunityCollege/Materials/Introduction
/metals.htm

C19 metals and their reactivity

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