CBSE Class 10 Science (Chemistry) Practical Skills – Types of Reactions
CBSE Class 10 Science Practical Skills –
Types of Reactions
Basic Building Concepts
A chemical reaction is a chemical transformation or change in which one or more substances called the reactants are converted to one or more different substances called the products.
Types of Chemical Reactions
There are four types of chemical reactions:
1. Combination Reactions: Combination reactions are those reactions in which two or more elements or compounds combine to form a more complex compound.
2.Decomposition Reactions:
Decomposition reactions are those reactions in which a single compound breaks down into its components or simpler compounds.
3. Displacement Reactions: Displacement reactions are those reactions in which more reactive element takes up the place of another element in a compound and sets the less reactive one free.
4. Double Displacement Reactions:
In a double displacement reaction, ions of two compounds switch places to form two new compounds. Two reactants yield two products.
EXPERIMENT 3(a)
Aim
To perform and observe the action of water on quicklime and classify the reaction.
Materials Required
Calcium oxide, water, beaker, glass rod, dropper, red litmus paper, test tube, filter paper, funnel.
Theory
Quicklime reacts with water to form calcium hydroxide. As in this reaction two substances – quicklime and water combine to form a new substance, therefore, this reaction is called combination reaction. This chemical change can be represented by the given chemical equation:
Procedure And Observation Table
The experimental procedure is described in the table:
Two compounds, viz. quicklime and water combine to form calcium hydroxide. Therefore, this reaction is an example of combination reaction.
Precautions
Quicklime can cause severe burns, therefore, it should be handled with spatula.
As the reaction between quicklime and water is exothermic, water should be poured over quicklime slowly.
The filtrate collected should be clear.
EXPERIMENT 3(b)
Aim
To perform and observe the action of heat on crystals of ferrous sulphate and classify the reaction.
Material Required
Ferrous sulphate crystals, test tubes, test tube holder, blue limus paper.
Theory
The crystals of ferrous sulphate are green in colour. When these crystals are heated, following reaction takes place.
Ferrous sulphate crystals (FeS04.7H20) lose water when heated and the colour of crystals changes. It then decomposes to ferric oxide(Fe203), sulphur dioxide (S02) and sulphur trioxide (S03). Ferric oxide is solid while S02 and S03 are gases. Both S02 and S03 are acidic and hence, these gases turn the blue litmus red. Sulphur dioxide can reduce an acidified solution of potassium dichromate. This reaction can be utilised to confirm the presence of sulphur dioxide.
Procedure And Observation Table
The experimental procedure is given in the following table
On heating, ferrous sulphate decomposes to give ferric oxide, sulphur dioxide and sulphur trioxide. This decomposition reaction.
Precautions
While heating ferrous sulphate, keep the mouth of test tube away from you and your classmates.
EXPERIMENT 3(c)
Aim
To perform and observe the reaction of iron nails kept in copper sulphate solution and classify the reaction.
Materials Required
Iron nails, copper sulphate solution, test tubes, test tube stand, sandpaper and thread.
Theory
When an iron nail is immersed in copper sulphate solution, following reaction takes place:
Procedure
(2) Take two iron nails and clean them by rubbing with sandpaper.
(2) Take two test tubes and mark them as ‘A’ and ‘B’.
(3) In each test tube, pour about 10 ml of copper sulphate solution.
(4) Tie one iron nail with a thread and immerse this carefully in the copper sulphate solution in test tube A for about 20 minutes. Keep aside one nail for comparison.
(5) After 20 minutes, take out the iron nail from the copper sulphate solution.
(6) Compare the intensity of blue colour of copper sulphate solutions of both the test tubes ‘A’ and ‘B\
(7) Also, compare the colour of iron nail dipped in copper sulphate solution with one kept aside.
Observations
The initial colour of copper sulphate solution was blue which after immersing iron nails turns to light green.
The initial colour of iron nail was grey. After immersing the nail into copper sulphate solution, a brown coating developed over it. Because of this coating iron nail appears reddish brown.
Results
On keeping the iron nails in copper sulphate solution, a displacement reaction takes place. In this displacement reaction, iron displaces copper and two new products ferrous sulphate and copper are formed.
Precautions
The iron nails should be cleaned by rubbing them with a sandpaper.
The test tube containing iron nails and copper sulphate solution should not be disturbed.
EXPERIMENT 3(d)
Aim
To perform and observe the reaction between sodium sulphate and barium chloride solutions and classify the reaction.
Materials Required
Sodium sulphate solution, barium chloride solution, test tubes, beaker.
Theory
When the solutions of sodium sulphate and barium chloride are mixed, a white precipitate of barium sulphate is formed. Chemical equation for this chemical change can be given as follows:
Procedure
(1) Take 5 ml of sodium sulphate solution in a test tube and mark it as ‘A’.
(2) Take 5 ml of barium chloride solution in another test tube and mark it as ‘B’.
(3) Mix the solutions of test tubes ‘A’ and ‘B’ in a beaker.
(4) With the help of a clean glass rod, stir the mixture kept in beaker.
(5) Record your observation.
Observation
On mixing the solutions of sodium sulphate and barium chloride, a white precipitate is formed.
Results
On mixing the solutions of sodium sulphate and barium chloride, a double displacement reaction takes place.
In this reaction sodium sulphate and barium chloride exchange ions and new products barium sulphate (white ppt) and sodium chloride are formed.
Precautions
Test tubes, beaker and glass rod should be cleaned.
Equal volumes of sodium sulphate and barium chloride solutions should be used.
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INTERACTIVE SESSION
Question 1:
What is the aim of your experiment?
Answer:
The aim of my experiment is to study the various types of chemical reactions.
Question 2:
How many types of chemical reactions are there?
Answer:
There are basically four types of chemical reactions, Combination reaction, Decomposition reaction, Displacement reaction and Double displacement reaction.
Question 3:
What type of reaction is combustion of hydrogen?
Answer:
It is a combination reaction.
Question 4:
Give the equation involved in the above process.
Answer:
2H2(g) + O2(g)→ 2H2O(l)
Question 5:
Can the above reaction be classified as a redox reaction?
Answer:
Yes, it can be classified as a redox reaction.
Question 6:
If we add Ag to an aqueous solution of CuS04, what happens and why?
Answer:
No change is observed because Ag being less reactive than Cu is unable to displace it from its salt solution.
Question 7:
What would happen if dil. HCl is added to (CH3COO)2Pb (lead acetate)?
Answer:
A white precipitate of PbCl2 will be obtained.
Question 8:
Give the equation involved and identify the type of chemical reaction.
Answer:
The equation involved is
(CH3COO)2Pb(aq) + 2HCl(aq) → 2CH3COOH(aq) + PbCl2(s)
This is a double displacement reaction.
Question 9:
Identify the type of chemical reaction occurring in the forward and backward processes of
CaC03 ⇌ΔCaO + C02.
Answer:
The forward reaction is a decomposition reaction while the backward reaction is a combination reaction.
Question 10:
What type of reaction is
Na2C03(aq) + 2HCl(aq)→ 2NaCl(aq) + H20(l) + C02(g)?
Answer:
It is a double displacement reaction.
Question 11:
How is it a double displacement reaction?
Answer:
In this reaction, the CO2−3 ions and Cl– ions are interchanging their positions, and H2C03 which is formed undergoes decomposition to give H20 and C02 as
H2C03(aq) ⇌H20(aq) + CO2(g)
Question 12:
Why do displacement reactions occur?
Answer:
Displacement reactions occur due to the difference in reactivities of the elements. A more reactive element (metal or non-metal) displaces a less reactive element (metal or non-metal) from its salt solution.
LAB MANUAL QUESTIONS
Question 1:
Fill in the blanks:
(а) Sodium sulphate and barium chloride are ___________ (ionic/covalent) compounds.
(b) As the white precipitate of barium sulphate is formed___________________ (immediately/sometime after mixing the two solutions), the reaction between____________________ (ionic/covalent)
compounds is (instantaneous/slow).
Answer:
(a) ionic
(b) immediately, ionic, instantaneous.
Question 2:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer:
The colour of copper sulphate solution changes when an iron nail is dipped in it because Fe is more reactive than Cu and can displace it from its salt solution.
Practical Based Questions
Multiple Choice Questions/VSA
1. A student took solid quicklime in a china dish and added a small amount of water. He heard [AI 2010]
(a) a popping sound
(b) a crackling sound
(c) a hissing sound
(d) no sound at all
2. On heating ferrous sulphate crystals, one would get
(a) sweet smell
(b) rotten egg smell
(c) irritating choking smell
(d) none of the above
3. Hydrated ferrous sulphate is commonly known as
(a) blue vitriol
(b) green vitriol
(c) yellow vitriol
(d) brown vitriol
4. On passing C02 gas through the product formed by the reaction between CaO and H20, solution becomes
(a) red
(b) pink
(c) black
(d) white
5. On heating ferrous sulphate in a test tube it undergoes
(а) combination reaction
(b) decomposition reaction
(c) displacement reaction
(d) double displacement reaction
6. An iron nail is placed in a solution of copper sulphate. The nail is taken out after 10 minutes. The nail will be found to be covered with
(a) brown deposit
(b) black deposit
(c) white deposit
(d) yellow deposit
7. CaO is commonly known as
(a) lime water
(b) slaked lime
(c) quicklime
(d) lemon water
8. The solid residue obtained on heating ferrous sulphate in a glass tube is
(a) ferrous sulphide
(b) ferrous oxide
(c) ferric oxide
(d) ferrous sulphite
9. Which of the following information about the reaction of CaO with water is not true?
(a) CaO reacts with water vigorously.
(b) During the reaction the test tube becomes hot.
(c) CaO reacts with water to form slaked lime.
(d) During the reaction dazzling white is produced.
10. When iron nails are kept in the solution of copper sulphate, the colour of the solution changes from
(a) green to yellow
(b) blue to green
(c) green to blue
(d) yellow to green
11. Precipitate formed on mixing the solutions of barium chloride-and sodium sulphate is of
(a) barium sulphate
(b) sodium chloride
(c) barium sulphite
(d) sodium sulphite
12. In ferrous sulphate, the valency of iron is
(a) 1
(b) 2
(c) 3
(d) 4
13. Which of the following represents a combination reaction?
(a) Reaction of zinc metal with copper sulphate solution
(b) Heating of lead nitrate
(c) Reaction between silver nitrate and sodium chloride
(d) Burning of magnesium in air.
Short Answer Questions
1. What is the difference between burning of magnesium ribbon in air and heating of ferrous sulphate crystals? Write equations for these reactions.
2. Why does a moist blue litmus paper turn red when it is brought near the mouth of the test tube in which ferrous sulphate crystals are being heated?
3. What happens when:
(a) solutions of sodium sulphate and barium chloride are mixed?
(b) an iron nail is dipped in copper sulphate solution for 20 minutes?
4. What precautions would you take while handling quicklime?
5. What will be the nature of solution formed when calcium oxide is dissolved in water? Name the substance formed when carbon dioxide gas is passed through this solution.
ANSWER KEY
Multiple Choice Questions/VSA
(c)
(c)
(b)
(d)
(b)
(a)
(c)
(c)
(d)
(b)
(a)
(b)
(d)
Short Answer Questions
(1)
(2) On heating ferrous sulphate crystals (FeS04.7H20) it decomposes to ferric oxide, sulphur dioxide and sulphur trioxide. Ferric oxide is solid while sulphur dioxide and sulphur trioxide are gases. Both sulphur dioxide and sulphur trioxide are acidic and hence these gases turn the moist blue litmus red.
3(a) When solutions of sodium sulphate and barium chloride are mixed, a white precipitate of barium sulphate is formed.
4. (i) Quicklime can cause severe bums, therefore it should be handled with a spatula.
(ii) As reaction between quicklime and water is exothermic, water should be poured over quicklime slowly.
5. On dissolving calcium oxide in water, calcium hydroxide is formed. When a drop of this liquid is put on a red litmus paper, it turns blue. This shows calcium hydroxide is basic in nature. When carbon dioxide gas is passed through calcium hydroxide (lime water), it turns milky due to formation of calcium carbonate.
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