THE REACTIVITY SERIES

 Keywords

• Alloy
• Blowpipe
• Metal
• reactivity series

 By the end of this chapter, you will be able to:

(a) appreciate that metals vary in their chemical reactivity and can be arranged in a reactivity series.

(b) understand that alloys are mixtures of a metal and other metals and / or non-metals and compare the properties of common metals with their alloys.

Competency

 You should be able to evaluate data on reactivity in order to arrange metallic elements according to their reactivity.

5.1 Introduction

In Chapter 3 , you learnt how to classify substances as metals and non – metals according to their physical properties and use. We are going to examine some

of the chemical properties of metals in this chapter. Metals react differently with different substances . It is of great importance to know the order in which metals react and, thus , the reactivity series. The reactivity series of metals is an important concept in Chemistry and has implications for corrosion of metals and its prevention, metal extraction, storage of reactive metals. The higher the metal in the series, the more reactive it is and you usually observe a – faster and more exothermic (heat releasing) more vigorous reaction with oxygen, water or an acid.

We shall be reacting selected metals with water and dilute acids. Thereafter, we shall attempt to establish an order showing how reactive metals are.

5.2 Chemical properties of metals

HOW FAST DO METALS REACT WITH WATER?

 In the previous class, we learnt that metals can react with water and steam.

For example, sodium reacted with cold water, violently bursting in a yellow flame. Do you remember the products? The products were hydrogen gas and metal hydroxide.

 The word equation is:

                Metal + Water → Metal hydroxide + Hydrogen

Molecular equation

e.g Na(s) + H2O(l) → NaOH(aq) + H2(g)

 In this section, we are going to find out how fast this reaction can be with different metals. We shall consider the rate at which hydrogen gas is evolved.

Activity 5.1 Investigating how fast metals react with cold water

In this activity, you will work in groups to investigate how fast metals react with cold water.

What you need

• Metal samples: calcium, copper, iron, magnesium and zinc.
• Cold water, phenolphthalein indicator.
• Beakers or test tubes, spatula.
• Stop clock or watch or timer.

What to do

1. Put about 100 cm ‘ of cold water in five separate beakers or test tubes.
2. Add a spatula end full of small pieces of each metal sample into the beakers.
3. Watch the beakers for some few minutes.
4. What do you observe? Which metal bursts into flames in water?
5. Which metal starts floating after some time?
6. Feel each of the beakers with your hands. How did the beakers feel?
7. Add 2-3 drops of phenolphthalein indicator to each beaker after 10 minutes.
8. What do you observe?
9. Record all your observations in Table 5.1 of results.
10. Identify the metals that reacted with cold water.
11. Arrange the metals in decreasing order of reactivity with cold water.
12. Share your findings with the class.

Figure 5.1: Calcium reacting with water

Table 5.1: Summary of results

Results and discussion

• Why is the indicator added?
• What product is got after the reaction? Do all the metals start floating after some time?
• What conclusions can you draw from your observations about the reactivity of the elements with cold water?
• How best can we compare the reactivity of metals with water?
• Do you think in our comparison in this activity, we used a fair procedure? If you think there are some shortcomings or limitations with our procedures, suggest what should have been maintained.

From Activity 5.1, you have seen how to arrange metals in order of reactivity with cold water.

However, some metals did not react with cold water. Thus, it was difficult to come up with a proper reactivity series of the elements.

 In order to overcome the above difficulty, let us now consider how the same metals react with dilute acids.

 HOW FAST DO METALS REACT WITH ACIDS?

We already know that metals react with acids to give a salt and hydrogen gas.

 The word equation is:

Metal + Dilute acid → Salt + Hydrogen [heat is given out]

 However, the question is: Do all metals react with dilute acids in a similar way?

Let us find out in Activity 5.2.

Activity 5.2 Investigating how fast metals react with dilute hydrochloric acid

 In this activity, you will work in groups to investigate how fast metals react with dilute hydrochloric acid.

 What you need

• Metal samples: calcium, copper, iron, magnesium and zinc.
• Dilute hydrochloric acid.
• Beakers or test tubes.
• Thermometers. The Reactivity Series

What to do

1. Put dilute hydrochloric acid in five separate test tubes to a depth of about 1cm.

2. Add one spatula – end full of each test metal in the test tubes. Note and record all your observations in Table 5.2 of results.

3. Insert a thermometer in each of the test tubes and record the highest temperature reached. See Figure 5.2.

Figure 5.2: Action of acid on a metal

4. Observe the rate at which the bubbles of hydrogen are produced in each tube. Note and record all your observations in Table 5.2 of results.

5. Arrange the metals in decreasing order of reactivity with dilute hydrochloric acid.

6. Share your findings with your classmates.

 Table 5.2: Summary of results

Results and discussion

• Which metal reacted vigorously with the acid?
• Which metal gave the highest temperature?  
• Observations Product (s) if any
• Write word equations for the reaction, if any, of the metals reacted with dilute hydrochloric acid.
• What conclusions can you draw about the position of copper in relation to that of hydrogen in the reactivity series following results from Activities 5.1 and 5.2?

THE LABORATORY TEST FOR HYDROGEN

DID YOU KNOW?
 Did you know how to test for hydrogen?
There is a simple laboratory test to see if a gas is hydrogen. A burning wooden splint is introduced into a test tube of hydrogen. The gas makes a pop sound. This is because the flame ignites the hydrogen, which burns explosively in excess oxygen to make a loud pop sound.

Hydrogen + oxygen → water

From Activities 5.1 and 5.2, you have come up with the reactivity series of some metals.
We can arrange all the metals in a metal reactivity series by reacting metals with different solutions of metal ions.

Let us now examine how metals react with other metal solutions.

What happens when a metal is placed in a solution of another metal?

Activity 5.3 investigating the reaction of a solid metal with another in an aqueous solution

In this activity, you will work in groups to investigate the reaction of a solid metal with another in an aqueous solution.

What you need

• Iron nail
• Iron (II) sulphate
• Test tubes
• Sand paper
• Copper strip
• Copper (II) sulphate
• Stop clock / watch

What to do

1. With a piece of sandpaper, clean a strip of copper and an iron nail.

2. Half – fill two test tubes separately with iron (II) sulphate and copper (II) sulphate. (See Figure 5.3.)

 3. Place the iron nail in the tube containing copper (II) sulphate and the copper strip in the test tube containing iron (II) sulphate. (See Figure 5.3.)

 Figure 5.3: Action of a solid metal on an aqueous solution of another metal copper ( ) sulphate solution iron ( ) sulphate solution

·         Results and discussion

• Which test tube has a reaction taking place?
• How you are able to know that there is a reaction in that particular test tube? Observe the test tubes and note what happens in about 25 minutes.
• Explain why the reaction has occurred basing on what you know from reactions in Activities 5.1 and 5.2
• . Write a word equation for the reaction, if any, that has occurred.
• What type of reaction did occur?

Hint: You can refer to the internet or any other source.

 From the results in Activity 5.3, we see that using metals and a solution of metal ions gives a more convenient way of determining which metal is more reactive than the other.

 Group discussion

 1. from your observations in Activity 5.3:

                a) Which metal is more reactive; copper or iron?

b) Place copper in the reactivity order established in Activity 5.2.

c)  What general rule can be derived?

2. Metal Y is more reactive than metal Z. Metal Y was added to an aqueous solution of compound Z. The mixture was shaken and allowed to stand for some time as shown in Figure 5.4.

Figure 5.4: Action of metal Y on solution of compound Z

Solution of compound of Z metal Y

a) What do you think will happen to the mixture?

b) Write a general equation to support your answer in (a)

3. State two applications of the reactivity order.

4. Share your ideas with the other group members in class.

THE REACTIVITY SERIES

So far, we have seen that the results from the previous activities can help us arrange magnesium, copper, iron, calcium and zinc in order of reactivity.

NB: How to remember the first twenty elements

Please Potassium

Sir Sodium

Can Calcium

Mohammed Magnesium

At Aluminium

Zanzibar Zinc

Ignore Iron

Ladies Lead

Here Hydrogen

Comes Copper

My Mercury

Sister Silver

Grace Gold

The question is: Where in the reactivity series do we place the other elements such as sodium, potassium, aluminium, lead, carbon and gold, among others?

 To answer the above question, let us look at the following activity:

Activity 5.4 investigating more about the reactivity series of metals

In this activity, you work in pairs or groups to discover more about the reactivity series of metals.

What you need

• Library or internet (if available).
• Manila papers and markers.

What to do

1. Carry out research from the library or internet (if available) on:

• The meaning of reactivity series of metals.
• The arrangement of metals, carbon and hydrogen in the reactivity series.
• The mnemonic for the elements in the reactivity series, beginning with the most reactive.
• Why aluminium, which is more reactive than iron, can be used for things like television aerials, satellite dishes, and ladders, without protecting it.

Figure 5.5 a): Aluminium ladder

b): Satellite dishes

• Why knowledge of the reactivity series of elements is important to us.

2. Prepare a summary of your findings.

3. Share the summary of your findings with your teacher and other classmates.

 Does the reactivity of metals depend on their electronic structure?

In the previous sections, you have examined the reactions of metals with a number of reagents in order to generate a reactivity series.

 In this section, you will look at how the reactivity of a metal is related to its electronic structure.

You should remember that in Chapter 3, we looked at how to write and draw the electronic structures of elements. We also saw why elements form ions.

Now let us look at the following activity to help us understand how the electronic structure is related to the reactivity of a metal.

Activity 5.5 Investigating how the electronic structure of a metal is related to its reactivity

In this activity, you work individually or in pairs to investigate how metals react depending on their electronic structure.

 What you need

• The Periodic Table of elements.
• Library or internet (if available).
• Manila papers and markers.

 What to do

 1. Draw the electronic structure of the potassium atom, sodium atom, calcium atom, and magnesium atom.

2. a) Write the formulae and electronic structure of the most likely ion formed by each element.

b) Do all the elements lose or gain electrons to form ions? Suggest a reason for your answer.

3. a) Write the electronic structure of the neon atom and argon atom.

b) Compare the electronic structures of the ions formed in step 2 (a) and those of the neon and argon atoms.

 c) Suggest reasons why atoms of elements form ions.

 4. Carry out research from the library or internet (if available) on how the reactivity of metals is affected by the electronic structure.

Your findings should include the following:

• Whether metals react by electron loss or gain.
• How the electronic structure of a metal influences its reactivity
• Why noble gases are described as chemically inert.
• Why potassium is more reactive than sodium and magnesium is less reactive than sodium,
• How the reactivity of a metal determines its uses.

 5.Prepare a summary of your findings.

6.Share the summary of your findings with your teacher and other classmates.

 WHAT GOVERNS THE EXTRACTION OF METALS?

 The reactivity series can help us to extract some metals from their compounds.

In Activity 5.3, we saw that a more reactive metal will replace a less reactive metal in a compound. We call this type of reaction a displacement reaction.

 Let us now examine how a displacement reaction can help us to extract certain metals from their oxides

Activity 5.6. Extracting copper from copper (II) oxide using a charcoal block

In this activity, you will work in groups with help from your teacher to extract copper from copper (II) oxide using charcoal.

What you need

• Blowpipe
• Copper (II) oxide
• Water.
• Charcoal block
• Pair of tongs
• Spatula and dropper

What to do

1. Create a small cavity in the charcoal block.
2. Place about a spatula endful of copper (II) oxide in the cavity and wet it with one drop of water.
3. By means of the blowpipe, direct the Bunsen burner flame onto the copper (II) oxide in the cavity. See Figure 5.6.
4. Observe and record what happens to the oxide and the charcoal block.

Figure 5.6: Extraction of copper from copper (II) oxide

Results and discussion

• What happens to copper oxide? Describe any colour changes.
• What happens to the charcoal block? Write word equations of what takes place in the cavity.

Assessment 5.1

In groups, carry out research from the library or internet (if available) and discuss why:

a) More reactive metals, like those in groups I and II, cannot be extracted on a charcoal block.

b) Metals lower in the reactive series, like gold; can be obtained from alluvial deposits.

5.3 What are alloys?

In Senior One, we learnt that alloys are a homogeneous mixture of two or more metals or metals and non – metals. When we make alloys, there are changes in the properties of the element which are advantageous to us in our daily life.

Let us find out more in the activity that follows:

Activity 5.7 Investigating the composition and properties of alloys

In this activity, you will work in groups to investigate the composition and properties of alloys.

What you need

• Collection of articles or objects made from or containing alloys. For example , articles made of alloys like knives / spoons / forks , door locks , screws , bolts , ornaments , medals , coinage ( 100 shilling coin ) , brass band instruments and so on .

What to do

1. Examine the articles provided one by one. Note the colours of the articles. What general conclusion can you draw from their appearance?
2. . Think of other alloys outside the classroom. What do you think they are made up of?
3.  Carry out research on alloys in terms of :

a) Chemical composition.

 b) Properties.

c) Uses.

•  Explain, using an appropriate chart, the uses of alloys in relationship to their properties.
•  Compare your findings with the other groups, and then share your findings with your classmates.

Results and discussion

• What are the alloys made of?
• Are the colours / appearance of the alloys related to the colour of the main element?
• What are the properties gained in the alloying?
• What are the uses of common alloys?
• ‘Metals are more useful to us when mixed with some other elements ‘. Discuss this statement with respect to stainless steel.

Chapter Summary

 In this chapter, you have learnt that:

• Some metals react with water to produce metal hydroxides and hydrogen gas.
• Metals usually react with dilute acids to give a metal salt and hydrogen gas. For example:

Metal + Hydrochloric acid → Metal chloride + Hydrogen

• Copper does not react with dilute acids.
• Different metals have different reactivity with water and dilute acids
• The arrangement of common metals in order of their decreasing reactivity is known as an activity series or reactivity series…
• Metals above hydrogen in the activity series can displace hydrogen from dilute acids
• More reactive metals displace less reactive metals from their compounds in aqueous solutions.
• Metals form positive ions by losing electrons.
• Metals below carbon in the reactivity series can be extracted from their compounds by the use of carbon.

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