Types of Reactions – Combination, Decomposition, Displacement, Double displacement

Types of Reactions

In this article, we have discussed step by step procedure to perform CBSE Class 10 Science Practicals experiment Types of Reactions. It will help you understand the different types of reactions viz combination, displacement, decomposition, double displacement reaction on the following actions – water on quicklime, iron nails in CuSO₄, heat on FeSO₄, a reaction between NaSO₄ and BaCl₂.

Table of Contents

CombinationDecompositionDisplacementDouble Displacement

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Aim

Performing and observing the actions of-

1. Water on quicklime
2. Heat on ferrous sulphate crystals
3. Iron nails dipped in copper sulphate solution
4. Reaction between sodium sulphate and barium chloride solution

On the following reactions-

1. Combination reaction
2. Decomposition reaction
3. Displacement reaction
4. Double displacement reaction

Experiment 3(A) – Combination

Materials Required

1. Quick lime (Calcium oxide)
2. Borosil beaker
3. Glass rod
4. Distilled water
5. Dropper
6. Test tube
7. Litmus paper strips

Theory

When calcium oxide is mixed in water it dissolves and forms calcium hydroxide (basic in nature). During this reaction, a lot of heat is liberated and therefore it is called an exothermic reaction. The equation is as follows:

CaO(s) + H₂O(l) → Ca(OH)₂ (aq) + Heat ………(1)

Due to the basic nature of calcium hydroxide, it turns red litmus paper blue in colour. When carbon dioxide gas is passed through the calcium hydroxide the solution turns milky white.

Ca(OH)₂ (aq) + CO₂ → CaCO₃ + H₂O

In the reaction (1) slaked lime is formed by combining two products viz, quick lime and water. Therefore when two or more than two substances combine to give a single product it is termed as combining reaction. The reactions accompanied by the evolution of heat are called exothermic reactions.

Procedure

1. Wash a borosil beaker with distilled water and dry it.
2. Take a small amount of calcium oxide (quick lime) and slowly add water to it.
3. Wash and take a clean glass rod to stir the mixture of quick lime and water.
4. Touch the beaker carefully from outside.
5. Observe the change.
6. With the help of dropper take a few drops of the mixture from the beaker and place it on red and blue litmus paper strips.
7. Wait and observe.

Observation

Result and Conclusion

From the above experiment we can conclude that the reaction occurred between calcium oxide (Quick lime) and water combine to produce one single product slaked lime (Ca(OH)₂) is called combination reaction as well as an exothermic reaction.

Precautions to be taken during the Experiment

• Take a small amount of compound such as quick lime to perform the experiment.
• Since the reaction is exothermic avoid touching the mixture directly.
• Carefully pour water to the borosil beaker containing calcium oxide (quick lime).
• Calcium oxide causes severe burns and therefore it should be handled with a spatula.
• Use good quality glass beaker during the experiment because if the beaker is of poor quality then there are chances of crack on the beaker due to the exothermic reaction.

Viva Voce

1. Quick lime is also known as _________.

Ans: Calcium oxide (CaO).

2. What type of reaction takes place between quicklime and water?

Ans: Combination reaction.

3. What is the name of the product that is obtained after the combination reaction?

Ans: Slaked lime (Ca(OH)₂)

4. Combination reaction that takes place between quicklime and water is also known as _______.

Ans: Exothermic reaction.

5. How to prepare lime water?

Ans: It is a mixture of calcium oxide and water.

Experiment 3(B) – Decomposition

Materials Required

1. Ferrous sulphate crystals
2. Test tube holder
3. Boiling tube
4. Bunsen burner
5. Safety glass
6. Litmus paper strips

Theory

Ferrous sulphate crystals are ferrous sulphate heptahydrate with a chemical formula FeSO₄.7H₂O and are green in colour.

On eating the ferrous sulphate heptahydrate it loses seven water molecules to form anhydrous ferrous sulphate (FeSO₄) and is white in colour. The reaction is as follows:

Heat

FeSO₄.7H₂O → FeSO₄(s) + 7H₂O ………….(1)

(Green colour) (white colour)

Ferrous sulphate when heated is decomposed to ferric oxide, sulphur trioxide, and sulphur dioxide. The reaction is as follows:

Heat

FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g) ………….(2)

(White colour) (brown colour) (colourless) (colourless)

In the reaction (2) one substance FeSO₄ (Ferrous sulphate) splits into three substances ferric oxide (Fe₂O₃), sulphur dioxide (SO₂), and sulphur trioxide (SO₃) due to heat. Therefore this reaction is called decomposition reaction or also known as a thermal decomposition reaction.

We can combine reaction (1) and (2) and write it as follows:

2FeSO₄.7H₂O(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g) + 14H₂O(g)

Procedure

1. Wash a boiling tube with distilled water and dry it.
2. Take 2 grams of ferrous sulphate crystals in the tube.
3. Make a note of the colour of the crystals.
4. Use a test tube holder to hold the boiling tube.
5. Heat the boiling tube on the bunsen burner as shown in the figure.
6. Observe the colour of the residue got and smell the odour of the gases evolved.
7. Tiny colourless water droplets are seen near the neck of the tube.
8. Gently turn it towards your nose and smell for any gas evolved.
9. Wet blue and red litmus paper strips.
10. Hold the litmus paper strips near the mouth of the boiling tube.
11. Observe the change
12. Classify the type of reaction.

Observation

Result and Conclusion

From the above experiment 3 (B) we can conclude that the reaction occurred on heating ferrous sulphate crystals is decomposition reaction which decomposes to produce Fe₂O₃, SO₂, and SO₃. Since this decomposition reaction is carried out by heating it is also known as a thermal decomposition reaction.

Precautions to be taken during the Experiment

• Do not keep the mouth of the boiling tube towards yourself.
• Do not smell the gas by directly getting it under your nose but gently turn it towards your nose and blow it with your hand.
• Wearing safety glasses is important while you are performing this experiment.
• Thoroughly wash the boiling tube with distilled water and dry it before using it.
• Use good quality boiling tube while heating the ferrous sulphate crystals.
• Take care to keep the sulphur dioxide and sulphur trioxide gas coming in contact with your eyes as they cause irritation to eyes.

Viva Voce

1. Can you write the formula of ferrous sulphate crystals?

Ans: FeSO₄.7H₂O.

2. Ferrous sulphate crystals are also called ______.

Ans: Green vitriol.

3. Name the two gases evolved during the decomposition reaction.

Ans: Sulphur dioxide and sulphur trioxide.

4. What is the colour of the residue left in the boiling tube after the decomposition reaction?

Ans: Brown.

5. Decomposition reaction is also known as ______.

Ans: Thermal decomposition reaction.

Experiment 3(C) – Displacement

Materials Required

1. Test tube stand
2. Two test tubes
3. Two iron nails
4. Measuring cylinder
5. Beaker
6. Sandpaper
7. Copper sulphate solution
8. Laboratory stand with clamp
9. Distilled water
10. Thread

Theory

As per the reactivity series, the more reactive metals displace the less reactive metals. When iron is compared with copper, it is placed above copper in activity series. Therefore the metals placed above are more reactive whereas the metals placed below are less reactive.

When iron nails are placed in CuSO₄ iron displaces copper from copper sulphate to form ferrous sulphate. The iron nails get deposited with a brownish red substance of the copper metal. The reaction is as follows:

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Metallic iron displaces copper ion (Cu²⁺) from its salt is an example of a chemical displacement reaction. Metallic iron is converted to ferrous iron, the cupric ion is converted to metallic copper. The reaction is as follows:

Fe(s) + Cu²⁺(aq) → Fe²⁺(aq) +Cu(s)

Experimental Setup:

Image (instead of A and B use P and Q)

Procedure

1. Wash two test tube with distilled water and dry them.
2. Label the test tube as P and Q.
3. Add 20mL of distilled water in the test tube and mix copper sulphate crystals in P.
4. Transfer 10Ml of solution from P to Q.
5. Take two iron nails by cleaning them with sandpaper.
6. Take one iron nail and dip it in the CuSO₄ in test tube P for 15 minutes.
7. Take another iron nail and dip it in the CuSO₄ in test tube Q for 15 minutes.
8. Observe the intensity of the blue colour of CuSO₄ before and after the experiment performed in test tube P and Q.
9. Record your results.

Observation

Result and Conclusion

From the above experiment 3 (C) we can conclude that the reaction occurred when iron nails were dipped in the copper sulphate solution for 15 minutes the colour of the solution changes to green and brownish red copper metal is deposited on the nail. Therefore this is a displacement reaction.

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Precautions to be taken during the Experiment

• Clean the iron nails by sandpaper before dipping in a copper sulphate solution.
• Make dilute CuSO₄ for the experiment otherwise, the colour change will not be seen in its concentrated form.
• Use good quality boiling tube.

Viva Voce

1. When iron nails are dipped in the copper sulphate solution the colour of the solution changes. Why?

Ans: Copper is less reactive when compared to iron. Therefore iron has the ability to displace it from its salt solution.

2. What is the basic principle of this experiment?

Ans: More reactive metals displace less reactive metals.

3. What is the cause for displacement reaction?

Ans: Difference in reactivities of metals causes displacement reaction.

4. Can you name the metal that deposits reddish brown substance on the iron nails when dipped in CuSO₄?

Ans: Copper metal.

5. What do you mean by reactivity series of metals?

Ans: Metals arranged in the decreasing order of their reactivities.

Experiment 3(D) – Double Displacement

Materials Required

1. Test tube stand
2. Measuring cylinder
3. Two test tubes
4. Glass rod
5. Conical flask
6. Barium chloride solution
7. Sodium sulphate solution

Theory

Reactions occurring in the solution by exchanging ionic compounds to form new compounds are called double displacement reactions. The ionic compounds considered as reactants are water soluble. One of the products is formed as a precipitate or as a gas which is water soluble.

When two solutions viz sodium sulphate and barium chloride are mixed, double displacement reaction as below occurs.

Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(s)

Sulphate ions from the solution of sodium sulphate are displaced by chloride ions and the chloride ions from the solution of barium chloride are displaced by sulphate ions.

Procedure

1. Take two test tubes, wash them with distilled water and dry them.
2. Label the test tube as P and Q.
3. Pour 5mL of barium chloride in the test tube P and observe the colour.
4. Pour 5mL of sodium sulphate in the test tube Q and observe the colour.
5. Take a conical flask and pour the solutions from both the test tube into it.
6. Stir the mixture added to the conical flask with a glass rod.
7. Keep it undisturbed for some time.
8. Observe the change in colour of the solution.
9. Record your results in the below-given table.

Observation

Result and Conclusion

From the above experiment 3 (D) we can conclude that the reaction occurred on mixing the solutions of barium chloride and sodium sulphate produce a white precipitate compound by exchanging their ions. This reaction is known as a double displacement reaction.

Precautions to be taken during the Experiment

• The test tube, glass rod, and conical flask should be washed with distilled water and dried before the experiment.
• The volume of sodium sulphate and barium chloride should be equal.
• Do not try to taste or touch the chemicals.
• While combining the solutions in the mixture pour sodium sulphate first and then slowly add barium chloride to it.

Viva Voce:

1. Barium sulphate is soluble in water. True or false?

Ans: False

2. Sodium sulphate and barium chloride are ionic compounds. True or false?

Ans: True.

3. The reaction between sodium sulphate and barium chloride is called a double displacement reaction. Why?

Ans: Because they exchange their ions.

4. Can you define double displacement reaction?

Ans: The reactions where two compounds exchange their salts to form an insoluble compound.

5. What happens when you mix sodium sulphate with barium chloride?

Ans: A white precipitate is formed.