Class 10th science last 10 year papers chapter wise chapter 1 chemical reaction and equation part 5

 57.When the powder of a common metal is heated in an open china dish, its colour turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original colour. Based on the above information, answer the following questions.

(i) What type of chemical reaction takes place in each of the two given steps?
(ii) Name the metal initially taken in the powder form. Write balanced chemical equations for both reactions.
Answer.
(i) In first step, oxidation takes place.In second step, redox reaction takes place.
(ii)Metal in the powder form is copper.
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Very Short Answer Type Questions [1 Mark] -Year 2009

58.In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?
Answer.It is because water contains hydrogen and oxygen in the ratio of 2 : 1.

59.Balance the following chemical equations.
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-46

Short Answer Type Questions[l] [2 Marks] -Year 2009

60. Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change?
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-47
It is decomposition reaction.

61. What is an oxidation reaction? Give an example of oxidation reaction. Is oxidation an exothermic or an endothermic reaction?
Answer. The reaction in which oxygen or electronegative element is added or hydrogen or electropositive element is removed or loss of electrons takes place, is called an oxidation reaction, e.g. ,
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-48
Oxidation reactions are mostly exothermic in nature because heat is evolved in this process.


62. Describe an activity to demonstrate the change that takes place when white silver chloride is kept in sunlight. State the type of chemical reaction which takes place.
Answer.
Aim: To demonstrate the change that takes place when white silver chloride is kept in sunlight.
Materials Required: AgNO3(aq), NaCl(aq), test tubes.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-49
Procedure:
1. Take 5 ml of silver nitrate solution in a test tube.
2. Prepare sodium chloride solution in another test tube.
3. Add sodium chloride solution into test tube containing silver nitrate solution.
4. Observe the colour of silver chloride formed chloride to grey silver metal Dry it with the help of filter papers and place it on the watch glass.
5. Place the watch glass under sunlight for sometime.
6. Observe the colour of the silver chloride after sometime. Observation: White silver chloride turns grey in sunlight because silver metal is formed.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-50
Explanation: Silver chloride is photosensitive. It decomposes in presence of sunlight to form silver metal and chlorine gas.
Conclusion: Decomposition of silver chloride in presence of sunlight is photochemical decomposition reaction.


63.When magnesium ribbon burns in air or oxygen, a product is formed. State the type of chemical reaction and name the product formed in the reaction. Write balanced chemical equation of this reaction.
Answer.

chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-51
The type of reaction is combination reaction and the product formed is magnesium oxide.

64.Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions.
Answer.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-52
Displacement reaction is a reaction in which more reactive metal can displace less reactive metal from its salt solution.
Double displacement reaction are those reactions in which compounds exchange their ions to form two new compounds (?) Double displacement reaction (ii) Displacement reaction


65.When you have mixed the solutions of lead(II) nitrate and potassium iodide,
(i) what was the colour of the precipitate formed and can you name the precipitate?
(ii) write the balanced chemical equation for this reaction.
(iii) is this also a double displacement reaction?
Answer.
(i) The colour of the precipitate is yellow. The name of compound formed as a precipitate is Pbl2 (lead iodide).
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-53
(iii) Yes, it is also a double displacement reaction.

66.What do you mean by exothermic and endothermic reactions? Give examples.
Answer.Exothermic reactions are those in which heat is evolved, e.g.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-54
Endothermic reactions are those reactions in which heat is absorbed, e.g.
chemical-reactions-and-equations-chapter-wise-important-questions-class-10-science-55

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