CBSE Class 10 Science Practical Skills – Reactivity Series
BASIC BUILDING CONCEPTS
- Metals can be arranged on the basis of relative reactivity. The arrangement of metals in a vertical column in order of their decreasing reactivity downwards is called the reactivity series of metals.
- In reactivity series, the most reactive metal (K) is placed at the top of the series while the least reactive metal (Au) is placed at the bottom.
- A more reactive metal can displace a less reactive metal from its salt solution or compounds.
- Hydrogen which is a non-metal is also placed in reactivity series.
- Metals which lie above hydrogen in reactivity series are more reactive than hydrogen. Therefore, these metals can displace hydrogen from its compounds like acids and water.
- Metals lying below hydrogen in reactivity series are less reactive than hydrogen. These metals cannot displace hydrogen from acids and water.
- To observe the action of Zn, Fe, Cu and Al metals on the following salt solutions:
- Arrange Zn, Fe, Cu and A1 metals in the decreasing order of reactivity based on the above result.
Test tubes, test tube stand, metals-Zn granules, Fe filings, Cu turnings, Al foil and aqueous solutions of zinc sulphate, ferrous sulphate, copper sulphate and aluminium sulphate.
In a displacement reaction an ion or an atom in a compound is replaced by an ion or an atom of zinc sulphate element. It may be denoted as
X + YZ ——-> XZ + Y
The displacement reactions are based on the reactivity series, where a more reactive metal displaces a less reactive metal from its salt solution.
For three different metals A, B, C, if metal A replaces metal B from its aqueous solution then metal A is more reactive than metal B.
If metal C displaces metal B from its salt solution, but metal A displaces metal C from its salt solution it follows that the increasing order of reactivity is:
B < C < A.
When pieces of Zn are dipped in copper sulphate solution, the blue colour of copper sulphate starts fading and
reddish brown particles of copper settle at the bottom. This occurs because of the following reaction:
Some other examples of displacement reactions are as follows:
- Take four test tubes and label them as ZnSO4, FeSO4, CuSO4 and Al2(SO4)3
- Pour equal amount of their aqueous solutions into the respective test tubes.
- Add a small strip of Al foil to each of the test tubes.
- Observe the changes and record your observations.
- Repeat similar procedure using:
- Cu turnings with ZnSO4, FeSO4, CuSO4 and Al2(SO4)3 solutions.
- Fe filings with ZnSO4, FeSO4, CuSO4 and Al2(SO4)3 solutions.
- Zn granules with ZnSO4, FeSO4, CuSO4 and Al2(SO4)3 solutions.
Record your observations in the following table:
- Al is able to displace Fe, Cu and Zn from their salt solutions, therefore Al is most reactive.
- Cu is unable to displace any metal among Al, Fe and Zn from their salt solutions, therefore Cu is least reactive.
- Fe is unable to displace Zn from its salt solution, whereas Zn is able to displace Fe from its salt solution, therefore Zn is more reactive than Fe.
- The decreasing order of reactivity for these metals follow the order:
Al > Zn > Fe > Cu.
- Handle the chemicals carefully.
- Clean each metal with sand paper.
- Observe the changes carefully as few reactions may occur slowly.
- Do not taste the chemicals.
- Wash your hands properly after the experiment.
What is the aim of your experiment?
The aim of my experiment is to arrange metals Al, Fe, Cu and Zn in order of their decreasing reactivity.
Why is the reactivity of different metals different?
All metals have a different tendency to lose electrons therefore, their reactivity is different.
What does the reactivity series of metals indicate?
The reactivity series indicates that metals are arranged in decreasing order of their reactivities.
Classify the type of reaction used for determining relative reactivities of metals.
Name three metals which occur in free state.
Three metals occurring in free state are gold(Au), silver(Ag) and platinum (Pt).
Which of the following metals would liberate H2 gas from a dil. solution of HCl? Zn, Ag, Hg Why?
Zn would be able to displace hydrogen from dil. HCl solution and H2 gas is obtained as Zn is more reactive than hydrogen. On the other hand, Ag and Hg being less reactive than hydrogen do not liberate H2 gas from dil. HCl solution.
Why are ornaments made of silver and gold?
Being less reactive they are not tarnished by air and moisture.
It has been observed that on adding Zn pieces to a solution of CuSO4, the blue colour disappears. Why?
Since, Zn is more reactive than Cu, it displaces Cu from CuSO4 solution and ZnSO4 (colourless) is formed. Due to this chemical change, the blue coloured solution turns colourless.
Give the equation involved for the above chemical change.
What happen if a Cu wire is dipped into a solution of FeSO4? Why?
No reaction occurs, as Cu is less reactive than Fe, so it does not displace Fe from its salt solution.
Can we store AgNO3 in a Cu vessel?
No, we cannot store AgNO3 in a Cu vessel as Cu being more reactive than Ag, will displace Ag from its salt solution and holes will be seen in the Cu vessel.
Explain the following change observed:
M + BX ——–> MX + B
M & B are metals and BX is a salt solution.
The equation shows that metal M is more reactive than metal B and therefore, displaces B from its salt solution.
What is a salt?
A salt is basically an ionic compound which contains a cation (+ve ion) except H+ and an anion (-ve ion) except OH–.
NCERT LAB MANUAL QUESTIONS
Why does the colour of copper sulphate solution change, when an iron nail is dipped in it?
Fe is more reactive than copper and, therefore, displaces it from its salt solution changing the colour of the solution from blue to pale green.
How would you devise the procedure to show that Mg > Fe > Cu on reactivity series?
Take solution of CuSO4 in two test tubes and add Mg metal to one test tube and iron nail to the other. Colour of CuSO4 solution changes from blue to colourless in one test tube and pale green in the other test tube and Cu is deposited in both test tubes. This shows that both Mg and Fe are more reactive than Cu.
Add iron nail to a solution of MgSO4 and add Mg metal to a solution of FeSO4. It is observed that no change occurs in the test tube containing MgSO4, whereas in the test tube containing FeSO4 the colour of the solution changes and iron is displaced from its salt solution. This shows that Mg is more reactive than iron and the order of reactivity is Mg > Fe > Cu.
What is the basic principle involved in this experiment?
The basic principle involved in the experiment is the displacement reaction based on reactivity series of metals. According to this, the more reactive metal has a higher tendency to react and displace a metal, lower in the reactivity series from its salt solution.
Why does the following reaction take place?
The above reaction occurs because chlorine is more reactive than iodine and therefore, displaces iodide ions from solution.
PRACTICAL BASED QUESTIONS
Multiple Choice Questions /VSA (1 Mark)
A student took four test tubes containing solution of different colours marked I, II, III and IV as shown below. The test tubes, containing copper sulphate solution and ferrous sulphate solution,could be the tubes [Delhi 2010]
(a) I and III
(b) II and III
(c) III and IV
(d) II and IV
Two beakers A and B contain Iron (II) sulphate solution. In the beaker A a small piece of copper is placed and in the beaker B a small piece of zinc is placed. It is found that a grey deposit forms on the zinc but not on the copper. From these observations, it can be concluded. [CBSE 2012, CBSE Sample Paper 2009]
(a) Zinc is most reactive metal followed by iron and then copper.
(b) Zinc is most reactive metal followed by copper and then iron.
(c) Iron is most reactive metal followed by zinc and then copper.
(d) Iron is most reactive metal followed by copper and then zinc.
A student took four test tubes I, II, III and IV containing aluminium sulphate, copper sulphate, ferrous sulphate and zinc sulphate solutions respectively. He placed an iron strip in each of them. He found a brown deposit formed in test tube [CBSE 2012, Foreign 2009]
A student added zinc granules to copper sulphate solution taken in a test tube.
Out of the following, the correct observation (s) made by the student will be
I. Zinc granules have no regular shape.
II. Zinc granules have silvery grey colour.
III. The colour of zinc granules changed to brownish black.
(a) I only
(b) II only
(c) III only
(d) I, II and III
Out of the following pair of compounds, identify the one which forms coloured solutions
(a) Al2(SO4)3, FeSO4
(b) FeSO4, CuSO4
(c) CaCl2, ZnSO4
(d) ZnSO4, CuSO4
When an aluminium strip is kept immersed in freshly prepared ferrous sulphate solution taken in a test tube, the change which is observed is [CBSE 2012, Delhi 2008]
(a) the green solution slowly turns brown
(b) the lower end of the test tube becomes slightly warm
(c) a colourless gas with smell of burning sulphur is observed
(d) light green solution changes to blue
A piece of granulated Zinc was dropped into Copper sulphate solution. After sometime, the colour of the solution changed from [CBSE 2012, AI 2008]
(a) light green to blue
(b) blue to colourless
(c) light green to colourless
(d) blue to yellow
Iron filings were added to a solution of copper sulphate. After 10 minutes, it was observed that the blue colour of the solution changes and a layer gets deposited on iron filings. The colour of the solution and that of the coating would respectively be [AI 2007]
(a) yellow and green
(b) brown and blue
(c) red and greenish-blue
(d) green and reddish-brown
Four test tubes were taken and marked A, B, C and D respectively. 2 mL of solution of Al2(SO4)3 in water was filled in each of the four test tubes.Clean piece of metal Zinc was placed in test tube A, clean iron nail was put in test tube B, clean copper wire was placed in test tube C and a clean aluminium wire was placed in test tube D. It was observed that no change occurred in any of the test tubes. The correct inference drawn is [Delhi 2007C]
(a) Zinc is more reactive than Aluminium.
(b) Zinc is more reactive than Copper.
(c) Copper is more reactive than Aluminium.
(d) Zinc, Iron and Copper are less reactive than Aluminium.
On the basis of sequence of reactions, identify the most and least reactive elements:
A + BX ——–> AX + B ……..(i)
C + AY ———> CY + A ……(ii)
(a) A, C
(b) B, C
(c) C, A
(d) C, B
Students in a lab were assigned the experiment to study the reaction of Zn with FeSO4 solution. The following set of observations were obtained. Identify the set where all observations were correct.
The test solutions in which the reaction occurs is
(a) IV, I
(b) I, III
(c) II, III
(d) III, IV
Solutions of ferrous sulphate, zinc sulphate, copper sulphate and aluminium sulphate were separately taken in four test tubes and some iron nails were placed in each of the solutions. After few minutes, it would be observed that the colour of
(a) all the four solutions changed
(b) solutions of zinc sulphate, copper sulphate and aluminium sulphate changed and that of ferrous sulphate did not change.
(c) solutions of zinc sulphate and aluminium sulphate only changed.
(d) only copper sulphate solution changed.
Aluminium sulphate and copper sulphate solu-tions were taken in two test tubes I and II, respectively. A few pieces of iron filings were then added to both the solutions. The four students A, B, C and D recorded their observations in the form of a table as given below:
The correct set of observations have been recorded by student
In an experiment each of the metals Al, Zn, Cu and Fe are reacted with ZnSO4, CuSO4, Al2(SO4)3 and FeSO4 solutions. The results are tabulated as follows where ‘√’ means that the reaction occurs and ‘×’ means no reaction occurs.
On the basis of the above result, the order of the reactivity of the metals may be concluded as
(a) Zn > Fe > Al > Cu
(b) Al > Fe > Zn > Cu
(c) Zn > Al > Fe > Cu
(d) Al > Zn > Fe > Cu
Short Answer Questions (2 Marks)
When a strip of zinc metal is put in copper sulphate solution, the blue colour of copper sulphate fades gradually. Why?
When a strip of zinc metal is placed in copper sulphate solution, zinc being more reactive displaces copper from copper sulphate solution and thus colourless solution of zinc sulphate is formed. Due to formation of this colourless zinc sulphate solution, blue colour of copper sulphate fades gradually.
Which of the following pairs will give displacement reaction?
- FeSO4 and copper metal
- FeSO4 and aluminium metal
- Copper metal is less reactive than iron metal, so no displacement reaction will occur between FeSO4 solution and copper metal.
- Aluminium metal is more reactive than iron metal, so displacement reaction will occur between FeSO4 and aluminium metal.
On placing a piece of aluminium metal in the solution of mercuric chloride, it acquires a shining silvery surface but when it is placed in a solution of magnesium sulphate, no change is observed. Explain.
Aluminium is more reactive than mercury. Because of this it displaces mercury from mercuric chloride solution. This mercury deposits on the aluminium metal giving its surface silvery shining appearance.
Aluminium is less reactive than magnesium. Hence, aluminium cannot displace magnesium from magnesium sulphate solution and so, no change is observed.
Why does zinc react with sulphuric acid to give hydrogen gas but copper does not?
Zinc is more reactive than hydrogen. Hence, it can react with sulphuric acid to give hydrogen gas.
Copper is less reactive than hydrogen. Hence it cannot displace hydrogen from sulphuric acid.
What would you observe when you put some aluminium pieces in copper sulphate solution?
Copper sulphate solution is blue in colour. When we put some aluminium pieces in copper sulphate solution, blue colour disappears and solution becomes colourless. As well as reddish brown deposits are seen on aluminium pieces. These changes are observed because of the following reaction.