2 Reactivity series Flashcards
1
Q
What is the reactivity series?
A
Potassium
Sodium
Lithium
Calcium
Magnesium
Aluminium
Manganese
Zinc
Iron
Hydrogen
Copper
2
Q
How do you read the reactivity series?
A
From the bottom upwards. The elements at the bottom are less reactive than the ones at the top.
3
Q
What are some displacement reactions involving metal oxides?
A
- The reaction between magnesium and copper (II) oxide.
- The reaction between magnesium and zinc oxide.
- The reaction between carbon and copper(II) oxide.
4
Q
What is the apparatus needed for the reaction between magnesium and copper (II) oxide?
A
5
Q
What is step 1 of this reaction between magnesium and copper (II) oxide?
A
Magnesium powder and copper (II) oxide are mixed together and heated very strongly.
6
Q
What is step 2 of this reaction between magnesium and copper (II) oxide?
A
At the end, traces of white magnesium oxide are left on the ceramic paper.
7
Q
What is the word equation for the reaction between magnesium and copper (II) oxide?
A
Magnesium + copper(II) oxide –> magnesium oxide + copper
8
Q
What is the symbol equation for the reaction between magnesium and copper (II) oxide?
A
Mg + CuO —> MgO + Cu
9
Q
What kind of reaction is this one between magnesium and copper (II) oxide?
A
Displacement reaction.
10
Q
Why is this a displacement reaction?
A
The less reactive metal, copper, has
been displaced from its compound by the more reactive magnesium.
11
Q
How does displacement work?
A
Any metal higher in the reactivity series will displace one lower down from a compound.
12
Q
What would happen if you heated copper with magnesium oxide?
A
Nothing would happen because
copper is less reactive than magnesium.
13
Q
What does it mean in terms of displacement if copper is less reactive than magnesium?
A
Copper isn’t capable of displacing magnesium from magnesium oxide
14
Q
What happens during the reaction between magnesium and zinc oxide?
A
Heating magnesium with zinc oxide produces zinc metal.
15
Q
What is the word equation for the reaction between magnesium and zinc oxide?
A
Magnesium + Zinc oxide —> Magnesium oxide + zinc
16
Q
What is the symbol equation for the reaction between magnesium and zinc oxide?
A
Mg + ZnO —> MgO + Zn
17
Q
What is the reaction between carbon and copper (II) oxide?
A
A black mixture of carbon and copper (II) oxide is heated in a test-tube.
18
Q
What is observeable during the reaction between carbon and copper (II) oxide?
A
The mixture glows red hot.
19
Q
Why does the mixture glow red hot?
A
Because of the heat given out during the reaction.
20
Q
What happens to the copper?
A
It is left at the bottom of the tube.
21
Q
What colour is the copper in the tube?
A
Pink-brown.
22
Q
What is the symbol equation for the reaction between carbon and copper (II) oxide?
A
C + 2CuO —> CO2 + 2Cu
23
Q
What is an explanation of this equation for the reaction between carbon and copper (II) oxide?
A
Carbon is above copper in the reactivity series and displaces the copper from copper (II) oxide.
24
Q
What does it mean if a substance has been oxidised?
A
It has gained oxygen.
25
What is oxidation?
Gain of oxygen or loss of electrons.
26
What does it mean if a substance has been reduced?
It has lost oxygen.
27
What is reduction?
Loss of oxygen or gain of electrons.
28
What is an image that shows what happens in terms of oxidation and reduction using the reaction between magnesium and copper oxide?
29
What is a redox reaction?
Reduction and oxidation. A redox reaction involves both reduction and oxidation occurring together.
30
Why do oxidation and reduction always occur together?
Oxidation and reduction always occur together because if something loses
oxygen, something else must gain it.
31
What is a reducing agent?
Something that reduces something else by giving electrons to it. A reducing agent is oxidised in a chemical reaction.
32
What is the reducing agent in this equation using the reaction between magnesium and copper oxide?
Magnesium.
33
Why is magnesium the reducing agent?
The magnesium is the reducing agent because it takes the oxygen away
from the copper oxide, reducing it.
34
What is an oxidising agent?
Something that oxidises something else by taking electrons away from it. An oxidising agent is reduced in a chemical reaction.
35
What is the oxidising agent in this equation using the reaction between magnesium and copper oxide?
Copper oxide.
36
Why is copper oxide the oxidising agent?
The copper(II) oxide is the oxidising agent in this reaction because it gives
oxygen to the magnesium, oxidising it.
37
What always happens to the oxidising agent?
An oxidising agent always gets reduced in a chemical reaction because it
oxidises something else by giving away its oxygen.
38
What always happens to the reducing agent?
A reducing agent always gets oxidised in a chemical reaction because it takes
the oxygen away from something else and therefore gains oxygen itself.
39
What is the reducing agent in the reaction between magnesium and copper oxide?
Magnesium.
40
What is the oxidising agent in the reaction between magnesium and copper oxide?
Zinc oxide.
41
What happens in the reaction between magnesium and copper (II) oxide in terms of the various particles involved?
The magnesium and the copper are metals, are are made of metal atoms, but the copper{II) oxide and the magnesium oxide are both ionic compounds.
42
What ions does copper (II) oxide contain?
Cu2+ and O2-
43
What ions does magnesium oxide contain?
Mg2+ and O2-
44
How could we write these ions into the equation?
Mg + Cu2+ + O2- ---> Mg2+ + O2- + Cu
45
What happens to the oxide ion (O2-) in this reaction?
The oxide ion (O2-) does not change in this reaction. It ends up with a different
partner, but is totally unchanged itself.
46
What is happening in terms of the magnesium atoms in this reaction?
The magnesium atoms are turning into magnesium ions.
47
How does the transition between atoms to ions happen?
The magnesium atoms lose electrons to form magnesium ions.
48
What happens to these electrons?
These electrons are gained by the copper ions to form copper atoms
49
What kind of reaction is this?
We have described this as a redox reaction above in terms of loss/gain of oxygen, but now we can see that it was not the oxygen that was actually the important part, it has not changed.
50
How can we understand what is happening better on a molecular level?
We need the most fundamental definition of oxidation and reduction.
51
What is the most fundamental definition of oxidation?
Oxidation is loss of electrons.
52
What is the most fundamental definition of reduction?
Reduction is gain of electrons.
53
What is a mnemonic that can help us remember the fundamental definition of oxidation and reduction?
OILRIG
54
What do these letters stand for?
Oxidation
Is
Loss of electrons
Reduction
Is
Gain of electrons
55
What are some examples of salts?
Salts are compounds such as copper (II) sulfate, silver nitrate or sodium chloride.
56
What reactions will we look at?
We will explore some reactions between metals and solutions of salts in water.
57
What is an example of a reaction between metals and solutions of salts in water?
The reaction between zinc and copper (II) sulfate solution.
58
What type of reaction is the one between zinc and copper (II) sulfate solution?
A displacement reaction.
59
Which metal is displaced?
The copper is displaced by the more reactive zinc.
60
What is an observation that can be made during the reaction between zinc and copper (II) sulfate solution?
The blue colour of the copper (II) sulfate solution fades as colourless zinc sulfate is formed.
61
What is the symbol equation for the reaction between zinc and Copper (II) sulfate?
Zn(s) + CuSO4 (aq) -+ ZnS4,(aq) + Cu(s)
62
Which are the metals consisting simply of atoms?
The zinc and the copper.
63
Which are the metal compounds that are ionic?
Copper(II) sulfate and the zinc sulfate.
64
How can the equation showcasing the reaction between zinc and copper (II) sulfate be re-written to show the ions?
Zn + Cu2+ + SO42- ---> Zn2+ + SO42- + Cu
65
What is special about the sulfate ions in this reaction?
We can see that the sulfate ions are exactly the same on both sides of the
equation - they have not changed at all in the reaction.
66
What is the name given to these sulfate ions, as they haven't changed at all?
Spectator ions.
67
What do we do to these spectator ions?
We remove them from the ionic equation.
68
What does the proper ionic equation look like (without the spectator ions)?
Zn + Cu2+ ---> Zn2+ + Cu
69
What does an ionic equation show?
It shows the things that change in the reaction.
70
What is the name of this kind of reaction?
Redox reaction.
71
What is an image that shows how the equation between zinc and copper(II) sulfate is a redox reaction?
72
What happens to the Zn atoms?
They are oxidised to Zn2+ ions.
73
Why are they oxidised to Zn2+ ions?
Because they lose electrons.
74
What happens to the Cu2+ ions?
They are reduced to Cu atoms.
75
Why are they reduced to Cu atoms?
Because they gain electrons.
76
What can we do to the ionic equation?
We can split up the ionic equation to show the individual oxidation and reduction processes.
77
How can we split this ionic equation to show oxidation?
Zn ---> Zn2+ + 2e-
78
How can we split this ionic equation to show reduction?
Cu2+ + 2e- ---> Cu
79
What are these equations called?
Ionic half-equations.
80
What do ionic hal-equations focus on showing?
they show one of the processes (either oxidation or reduction) occuring in the reaction.
81
What is the correlation between oxidation and reduction?
In reality, these processes cannot occur one without the other: if something gains electrons, it has to get them from somewhere, so something else must lose electrons.
82
What is the definition of an oxidising agent in terms of electrons?
An oxidising agent is something that oxidises something else by taking
electrons away from it. Oxidising agents accept electrons and therefore are reduced in a reaction.
83
What is the definition of a reducing agent in terms of electrons?
A reducing agent is something that reduces something else by giving
electrons to it. Reducing agents give away electrons and therefore are
oxidised in a reaction.
84
What is the overall ionic equation for the displacement reaction between zinc and copper ions?
Zn + Cu2+ ---> Zn2+ + Cu
85
What is the reducing agent in this equation for the displacement reaction between zinc and copper ions?
The Zn reduces the Cu2+ by giving electrons to it and therefore the Zn is the reducing agent.
86
What is oxidised in this reaction between zinc and copper ions?
In the process of the reaction the Zn is oxidised because it has given electrons away (lost them).
87
What is the oxidising agent in this equation for the displacement reaction between zinc and copper ions?
The Cu2+ oxidises the Zn by taking electrons away from it, therefore Cu2+ is the oxidising agent.
88
What is reduced in this reaction between zinc and copper ions?
In the process the Cu2+ is reduced because it has taken electrons (gained them).
89
What happens in the reaction between copper and silver nitrate solution?
Silver is below copper in the reactivity series, so a coil of copper wire in silver nitrate solution will produce metallic silver.
90
What is a picture that shows the process of displacing silver from silver nitrate solution?
91
What is an explanation of this image that shows the process of displacing silver from silver nitrate solution?
It shows the silver being produced as a mixture of grey 'fur' and delicate crystals.
92
What happens to the solution?
It becomes blue.
93
Why does the solution become blue?
Due to the fact that copper (II) nitrate is produced.
94
What is the symbol equation to show the reaction between copper and silver nitrate?
Cu + 2AgNo3 ---> Cu(NO3)2 + 2Ag
95
Which ions are the spectator ions in this reaction?
The nitrate ions.
96
What is the final version of the ionic equation of the reaction between copper and silver nitrate?
Cu + 2Ag+ ---> Cu2+ + 2Ag
97
What kind of reaction is this one between copper and silver nitrate?
A redox reaction.
98
What is the reducing agent in this reaction between copper and silver nitrate?
The Cu is the reducing agent (it is oxidised).
99
Why is the Cu the reducing agent (it is oxidised)?
Because it gives electrons to the Ag+ ions to reduce them to Ag.
100
What is the oxidising agent in this reaction between copper and silver nitrate?
The Ag+ ions is the oxidising agent (it is reduced).
101
Why are the Ag+ ions the oxidising agent (they are reduced)?
Because it takes electrons away from the Cu atoms.
102
What are the ionic half-equation which shows oxidation in this reaction between copper and silver nitrate?
Cu ---> Cu2+ + 2e-
103
What are the ionic half-equation which shows reduction in this reaction between copper and silver nitrate?
Ag+ + e- ---> Ag
104
How do metals above hydrogen in the reactivity series react with water (or steam) to produce?
Hydrogen.
105
What happens if the metal reacts with cold water?
The metal hydroxide and hydrogen are formed.
106
What is the equation that shows what happens if a metal reacts with water?
Metal + cold water ---> Metal hydroxide + hydrogen
107
What happens if the metal reacts with steam?
The metal oxide and hydrogen are formed.
108
What is the equation that shows what happens if a metal reacts with steam?
Metal + steam ---> Metal oxide + hydrogen
109
What happens to how vigorous the reactions are as you move down the reactivity series?
The reactions become less and less vigorous.
110
How do metals below hydrogen in the reactivity series react with water or steam?
Metals below hydrogen in the reactivity series (such as copper) don't react
with water or steam. This is why copper can be used for both hot and cold
water pipes.
111
Which elements react very vigorously with water?
Potassium, sodium and lithium.
112
In what order do these elements become less vigorous and violent?
Potassium > sodium > lithium
113
What is the form of the equation that shows how potassium, sodium, and lithium all react with water?
2M + 2H2O ---> 2MOH + H2
114
What is M in this reaction?
You replace M by K, Na, or Li, depending on which metal is involved.
115
How does calcium react with cold water?
Calcium reacts gently with cold water.
116
What is an image of the apparatus used when calcium reacts with cold water?
117
What happens during the reaction between calcium and cold water?
The grey granules sink, but are carried back to the surface again as bubbles of hydrogen are formed around them.
118
What happens to the mixture?
The mixture becomes warm.
119
Why does the mixture become warm?
Because heat is produced.
120
What is formed when calcium and cold water react?
Calcium hydroxide is formed.
121
What are some characteristics of calcium hydroxide?
Isn't very soluble in water.
122
How does calcium hydroxide dissolve in water?
Some of it dissolves to give a colourless solution, but most of it is left as a white, insoluble solid.
123
What is the equation between calcium and cold water?
Ca + 2H2O ---> Ca(OH)2 + H2
124
How does magnesium react with cold water?
There is almost no reaction.
125
How does very clean magnesium react with cold water?
If the magnesium is very clean, a few bubbles of hydrogen form on it, but the reaction soon stops again.
126
Why is there almost no reaction between magnesium and cold water?
This is because magnesium becomes coated with insoluble magnesium hydroxide, which prevents any more water coming into contact with the magnesium.
127
What is the apparatus used to react magnesium with steam?
128
How is the mineral wool heated?
The mineral wool isn't heated directly.
129
How does heat then reach the mineral wool?
Enough heat moves back along the
test-tube to turn the water to steam.
130
What can be observed when the magnesium comes into contact with the steam?
The magnesium burns with a bright white flame in the steam, producing hydrogen, which can be ignited at the end of the delivery tube.
131
What is produced through the reaction of magnesium and steam?
White magnesium oxide is formed.
132
What is the symbol equation which represents the formation of this white magnesium oxide?
Mg + H2O ---> MgO + H2
133
What is the apparatus used to react zinc or iron with steam?
134
Why does this delivery tube need to be continuously heated?
If you stop heating while the delivery tube is still under the surface of the water, water is sucked back into the hot tube, which often results in it cracking.
135
What can be observed when zinc or iron reacts with steam?
With both zinc or iron, the hydrogen comes off slowly enough to be collected. Neither metal burns.
136
How does zinc and steam react?
Zinc oxide is formed.
137
What are the properties of zinc oxide?
It is yellow when it is hot, but white on cooling.
138
What is the symbol equation that shows the formation of zinc oxide?
Zn + H2O ---> ZnO + H2
139
How does iron and steam react?
A complicated oxide is formed, called tri-iron tetroxide Fe3O4 is formed.
140
What are the properties of tri-iron tetroxide?
The iron becomes slightly darker grey.
141
What is the first step to investigate the reactions between metals and dilute acids?
Set up four test-tubes and put about 2 cm3 of dilute hydrochloric acid
into each one.
142
What is the second step to investigate the reactions between metals and dilute oxides?
Put a small piece of magnesium, zinc, iron or copper into each
test-tube and observe any reaction that occurs.
143
What is the third step to investigate the reactions between metals and dilute oxides?
If there is fizzing, collect or trap the gas and test with a lighted splint -
a squeaky pop indicates the presence of hydrogen gas.
144
What is the fourth step to investigate the reactions between metals and dilute oxides?
Repeat the experiments with dilute sulfuric acid.
145
What is a diagram that shows the reactions between metals and hydrochloric acid?
146
What is magnesiums reaction with dilute hydrochloric acid?
Reacts vigorously with lots of fizzing. The gas produced gave a squeaky pop
with a lighted splint. A colourless solution is formed. The test-tube gets hot.
147
What is zincs reaction with dilute hydrochloric acid?
Steady reaction. Fizzing. Enough gas eventually collected to produce a
squeaky pop with a lighted splint. A colourless solution formed. The test-tube gets warmer.
148
What is irons reaction with dilute hydrochloric acid?
Slow fizzing. V ery little gas was collected in the time available. A very pale green solution formed. The test-tube got slightly warmer.
149
What is coppers reaction with dilute hydrochloric acid?
No change.
150
What are all these types of reactions?
Exothermic reactions.
151
What does exothermic mean?
They give out heat.
152
What can we do now that we have notice that there is a temperature change in the reaction?
We could measure this temperature change to compare the
reactivity of the metals.
153
What is something that we have to keep in mind when using the temperature change to compare the reactivity of the metals?
However, in order to do this we will have to think more carefully about the things that we have to keep the same in order to make this a valid (fair) test.
154
What things do we have to keep the same in reference to the hydrochloric acid?
- Volume.
- Concentration.
155
What things do we have to keep the same in this experiment in reference to the weight of the metal?
It is important that we use the same number of moles in each experiment rather than the same number of grams.
156
Why do we have to be careful about the moles and grams?
If we use 0.24g of metal in each
experiment, we can work out that this is 0.24/ 24 = 0.01 Omol magnesium but
0.24/ 56 = 0.0040mol iron.
157
What do chemical reactions depend on?
Now, chemical reactions depend on how many particles are present:
more moles and therefore more particles are present in the Mg
experiment and more heat would be given out because of this.
158
What is another variable that we should control in terms of the metal?
The surface area.
159
Why do we need to keep the surface area of the metal constant?
Although this does not affect the overall amount of heat given out in the
reaction, it will affect the speed at which the heat is given out, which can
affect the temperature change.
160
What is the first step of the method we use in order to see the reactions between metals and dilute acids but this time, involving numbers?
Measure out 50cm3 of 1 mol/dm3 hydrochloric acid using a 50cm3
measuring cylinder (this amount was chosen so that the hydrochloric
acid is in excess - there is more than enough to react with all the metal
in each case).
161
What is the second step of the method we use in order to see the reactions between metals and dilute acids but this time, involving numbers?
Pour the hydrochloric acid into a polystyrene cup (this is an insulator).
162
What is the third step of the method we use in order to see the reactions between metals and dilute acids but this time, involving numbers?
Measure the initial temperature of the hydrochloric acid.
163
What is the fourth step of the method we use in order to see the reactions between metals and dilute acids but this time, involving numbers?
Weigh out 0.010mol of magnesium (0.010 x 24 = 0.24g) powder.
164
What is the fifth step of the method we use in order to see the reactions between metals and dilute acids but this time, involving numbers?
Add the magnesium powder to the polystyrene cup, stirring rapidly,
and measure the maximum temperature reached.
165
What is the sixth step of the method we use in order to see the reactions between metals and dilute acids but this time, involving numbers?
Repeat with the other metals using 0.010 mol in each case.
166
What is the apparatus used when measuring the temperature change when a metal reacts with dilute hydrochloric acid?
167
What is a data table that we can get from the practical where we measure the temperature change when a metal reacts with dilute hydrochloric acid?
168
What do we do after we've worked out the temperature change for each experiment?
plot it as a bar chart.
169
Why do we use a bar chart?
We use a bar chart because the type of metal is not continuous data: the metal can be either magnesium or zinc, it cannot be anything in between.
170
What is an image of the results that we will likely get from the bar chart?
171
How can we explain this bar chart?
We can see from this data that magnesium caused the greatest temperature change and so is the most reactive metal of the four; copper caused no change and is the least reactive.
172
What is the pattern for the reaction of metals with acids?
It is the same as for the reaction between metals and water, but in each case the reaction is much more vigorous.
173
How do metals above hydrogen react with acids?
To form a salt and hydrogen.
174
What is the correlation between the metals position in the reactivity series and the violence of the reaction?
The higher the metal in the series, the more violent the reaction.
175
Metal + acid?
Metal + acid ---> Salt + hydrogen.
176
Metal + dilute sulfuric acid?
Metal + dilute sulfuric acid ---> Metal sulfate + hydrogen.
177
Metal + dilute hydrochloric acid?
Metal + dilute hydrochloric acid ---> metal chloride + hydrogen
178
How do metals under hydrogen in the reactivity series react with simple dilute acids?
Metals such as copper, silver and gold do not react with simple dilute acids such as sulfuric or hydrochloric acid.
179
How do potassium, sodium, lithium, and calcium react with acids?
These are too reactive to add safely to acids, the reaction is too violent.
180
When can calcium react with an acid?
Calcium can be used if the acid is very dilute.
181
How does magnesium react with cold dilute acids?
Magnesium reacts vigorously with cold dilute acids, and the mixture becomes hot.
182
What is formed when magnesium reacts with cold dilute acids?
A colourless solution of magnesium sulfate or chloride is formed.
183
What is an example of the symbol equation between magnesium and dilute sulfuric acid?
Mg+ H2SO4 → MgSO4 + H2
184
What are the properties concerning aluminiums reactivity?
Aluminium is slow to start reacting, but after warming it reacts very vigorously.
185
Why does aluminium react slowly?
There is a very thin, but very strong, layer of aluminium oxide on the surface of the aluminium, which stops the acid from getting to it.
186
Why can aluminium start reacting when its heated then?
On heating, the acid removes this layer, and the aluminium can show its true reactivity.
187
What is an example of the symbol equation between aluminium with dilute hydrochloric acid?
2Al + 6HCI → 2AICl3+ 3H2
188
How do zinc and iron react in the presence of different temperatures?
Zinc and iron react slowly in the cold, but more rapidly on heating.
189
Are the reactions of zinc and iron vigorous?
The vigour of the reactions is less than that of aluminium.
190
What does zinc form in reactions?
The zinc forms zinc sulfate or zine chloride and hydrogen
191
What does iron form in reactions?
The iron forms iron(II) sulfate or iron(II) chloride and hydrogen.
192
What is the symbol equation for the reaction between zinc and sulfuric acid?
Zn + H2SO4 ---> ZnSO4 + H2
193
What is the symbol equation for the reaction between iron and hydorhcloric acid?
Fe + 2HCI ---> FeCI2 + H2
194
What is step 1 of finding the approximate position of a metal in the reactivity series using water and dilute acids?
Add a very small piece of metal to some cold water. If there is any rapid reaction, then the metal must be above magnesium in the reactivity series.
195
What is step 2 of finding the approximate position of a metal in the reactivity series using water and dilute acids?
If there isn't any reaction, add a small amount of metal to some dilute hydrochloric acid (or dilute sulfuric acid). If there isn't any reaction in the cold acid, warm it carefully.
196
What is step 3 of finding the approximate position of a metal in the reactivity series using water and dilute acids?
If there is still no reaction, the metal is probably below hydrogen in the reactivity series. If there is a reaction, then it is somewhere between magnesium and hydrogen.
197
Why is this method a bit inaccurate?
It also depends on its surface area, and whether the surface is free from dirt or an oxide coating.
198
When does iron rust?
in the presence of oxygen and water.
199
What is rust?
The corrosion of iron in the presence of water and oxygen. The rust formed has the formula Fe2O3.xH2O, where x is a variable number, and can be called hydrated iron (III) oxide.
200
What does rusting occur with?
rusting occurs with iron and the most common alloy or iron, mild steel.
201
What kind of reaction is rusting?
it can be described as a redox reaction - the iron is oxidised.
202
What is something to bear in mind about corrosion and rusting?
Many metals corrode, but it is only the corrosion of iron that is referred to as rusting.
203
What are ways of preventing rusting?
- Using barriers.
- Galvanising.
- Sacrificial protection.
204
Why does using barriers prevent rusting?
The most obvious way of preventing rusting is to keep water and oxygen
away from the iron.
205
What are the methods of using barriers?
You can do this by painting it, coating it in oil or grease,or covering it in plastic. Coating the iron with a metal below it in the reactivity series (e.g. coating steel with tin for tin cans) is also a barrier method.
206
What is the barrier method?
A method of rust prevention by coating iron with paint, oil, grease, or plastic, so that oxygen/water cannot reach the iron/steel.
207
What is an advantage of using the barrier method?
Barrier methods are usually quite cheap ways of preventing rusting.
208
What is a disadvantage of using the barrier method?
A problem with barrier methods is that once the coating is broken, the iron underneath is exposed to oxygen and water and the iron will rust (even the bits that are not directly exposed to the air/water).
209
What is preventing rusting by galvanising?
Galvanised iron is iron that is coated with a layer of zinc.
210
What is galvanisation?
A method of preventing rusting by coating iron with a layer of zinc.
211
Under which conditions does the zinc layer work?
As long as the zinc layer is unsratched, it serves as a barrier to air and water.
212
What happens when the zinc on the surface is scratched away?
The iron still doesn't rust even when some of the zinc on the surface is scratched away to expose the iron.
213
Why doesn't the iron rust?
This is because the zinc is more reactive than iron, and so reacts with oxygen/water more readily than the iron does.
214
What happens to the zinc?
The zinc corrodes instead of the iron.
215
How do you prevent rusting by using sacrificial prevention?
Zinc, magnesium, or aluminium blocks are attached to metal hulls or keels of ships to prevent the iron/steel from rusting.
216
When does sacrificial prevention only work?
You have to use a metal that is more reactive than iron.
217
Why does the metal have to be more reactive than iron?
The more reactive metal reacts (is oxidised) more readily in the presence of oxygen/water than the iron.
218
What does the corrosion of the more reactive metal prevent?
It prevents the iron from rusting. Such blocks are called sacrificial anodes.
219
What needs to be done with these sacrificial anodes?
They need to be replaced occasionally when all the more reactive metal has been oxidised.
220
When is sacrificial protection used?
This type of protection is used on
large structures where it would be very difficult to use a barrier method
effectively.
221
What kind of method is galvanising?
It is a combination of a barrier method and sacrificial protection.
222
What is sacrificial protection?
A method of preventing rusting
by attaching a block of a more reactive metal to iron. The more reactive metals undergo oxidation in preference to
the iron.
223
What is a real-life use of sacrificial protection?
Underground pipelines are also protected using sacrificial anodes.
224
Why is this an effective use of sacrificial protection?
In this case,lumps of magnesium are attached at intervals along the pipe. The very reactive magnesium corrodes in preference to the iron. The electrons produced as the magnesium forms its ions prevent the ionisation of the iron.
