NCERT CLASS 10 very Important Frequently asked VSA (1mark) of ch-1 (Chemical reactions and equations)

VSA—1 mark questions of ch-1

VSA— very short Answers

1. Is burning of a candle wax a physical change or a chemical change?

Ans: Chemical change.

2. State one basic differences between a physical change and chemical change?

Ans: In physical change, no new substance is formed. There is heat change in chemical change and a new substance is formed.

3. How do you show that respiration is a chemical change?

Ans: During respiration, energy is released. Sinse energy is released, therefore respiration is regarded as a chemical change.

4. Name and state the law which is kept in mind while we balance a chemical equation?

Ans: Law of conservation of mass is applied here. Accordingly, matter can neither be created nor destroyed. Thus during a chemical reaction the total mass of the reactants and products remains the same. 

5. Write a skeletal equation-

     Hydrogen sulphide reacts with Sulphur dioxide to form Sulphur and water.

Ans: H2S + SO2 –—› S + H2O

6. Methane on burning combines with oxygen to produce carbon dioxide and water.

Ans: CH4 + O2 —–› CO2 + H2O

7. While writing the chemical reaction for the oxidation of calcium in oxygen, a student wrote the following balance equation: Ca + O –—› CaO

Is it correct? if not, explain and write the correct balance equation.

Ans: The given equation is not molecular equation. The oxygen should be written in the molecular form. The correct equation is: 

                                                Ca + O2 –—› CaO

                                                Ca+ O2 –—› 2CaO

And balanced equation is  2Ca+O2–—› 2CaO

8. Calcium carbonate on heating forms calcium oxide and carbon dioxide. Write the equation for the reaction and indicate the evolution of gas.

Ans:  CaCO3 –—› CaO + CO2 ↑

9. AgNO3 + NaCl –—› AgCl ↓ + NaNO3

    FeS + H2SO4 –—› FeSO4 + H2S ↑

Consider the above mentioned 2 chemical equations with two different kinds of arrows (↑ and ↓) along with product. What do these two different arrows indicate?

Ans: ↓ Indicate silver chloride is precipitated

    ↑ Indicates that H2S is formed in gaseous form.

10. State which one of the following is an exothermic reaction?

    (i) Reaction - heat –—› Products

   (ii) Reaction + heat –—› Products.

Ans: (i)  Reaction - heat –—› Products

                   Is Exothermic reaction.

11. Why is photosynthesis considered an endothermic reaction?

Ans: Photosynthesis is an endothermic reaction as it takes energy from Sun.

12. The internal energy of the system increases when the following reaction is carried out: A + B –—› C

State whether the reaction is exothermic or endothermic?

Ans: Endothermic.

13. How many types of Decomposition Reactions are there and what are they?

Ans: Decomposition reactions are of 3 types

         — Thermal decomposition

         — Electrolytic decomposition 

         —  Photo chemical decomposition

           

14. State the chemical change that takes place when limestone is heated strongly.

Ans: Limestone CaCO3 decomposes on heating with evolution of CO2.

    CaCO3 —–› CaO + CO2  ↑

15. What is the substance said to be reduced in a chemical reaction? Name the substance oxidized in the following reaction: 

         ZnO + C –—› Zn + CO

Ans: when a substance is against a hydrogen atom or loses oxygen atom, it is said to be reduced. 

In the reaction,

        ZnO + C –—› Zn + CO

C (carbon) is Oxidised.

16. Give two examples from everyday life situations where redox reactions are taking place.

Ans: (a) Combustion reactions.

         (b) photosynthesis of carbohydrates.

17. Explain why sodium acts as an oxidizing agent while chlorine acts as a reducing agent in the reaction,

       2Na + Cl2 –—› 2NaCl.

Ans: Sodium (Na) loses electrons and forms Na+ ions and thus acts as oxidising agent while chlorine gains electrons and form Cl- ions and is thus a reducing agent.

18. When magnesium ribbon burns in air with a dazzling white flame and forms a white Ash, is magnesium oxidised or reduced? Justify your answer with the help of chemical equation involved.

Ans: A dazzling white light is produced when magnesium ribbon burns in air.

Magnesium is oxidised in the process because oxygen is being added up to magnesium.

        2Mg + O2 –—› 2MgO

19. Why are certain reagents like silver bromide stored in dark bottles?

Ans: Reagents or chemicals like silver bromide decomposes when exposed to light. Hence, these are stored in dark bottles.

20. What happens when sugar crystals are heated? Explain your observations.

Ans: Sugar undergoes decomposition on heating. water gets vaporated thereby leaving behind black carbon as charred material.

21. Oxidation and Reduction occurs simultaneously in a chemical reaction. Comment.

Ans: It is true that oxidation cannot take place without reduction and vice versa. As electrons do not exist free, electrons lost during oxidation must be gained during reduction.

22. Identify the component oxidised in the following reaction: 

         4Na + O2 –—› 2Na2O

Ans: Na is Oxidised.

23. In the redox reaction:

                ZnO + C –—› Zn + CO

      Name the oxidising agent.

Ans: ZnO is oxidizing agent.

24. When hydrogen is passed over heated CuO, brown copper is deposited. Which substance is reduced?

Ans: Copper oxide.

25. Give one example of a redox reaction which is also a combination reaction. Name the substance oxidised.

Ans: 2Mg + O2 –—› 2MgO.

              Mg is Oxidised.

26. When iron is exposed to air and moisture, rust is formed

4Fe + 3O2 + 3H2O –—› 2Fe2O3.3H2O

Why is it called a slow reaction? Name the reaction.

Ans: Rust is a complex compound of iron and it takes several months to form when iron is exposed to air and moisture. This is a combination reaction.

27. Why potato chips manufacturers fill the packet of chips with nitrogen gas?

Ans: To prevent potato chips from oxidation, manufacturers flush out packs with nitrogen.

28. A student has been collecting silver coins and copper coins. one day she observed a black coating on silver coins and green coating on copper coins. Write the chemical name of black and green coatings.

Ans: The phenomenon is called corrosion

(Oxidation). Black coating on silver coins is silver sulphide. Green coating on copper coins is basic copper oxide.

29. Surface of some metals lose their brightness when kept in air for a long time. Why?

Ans: Metals get corroded due to exposure to air and moisture at a rough oxide film is formed on the surface.

30. Is rancidity of phenomenon of oxidation or reduction?

Ans: Oxidation.

31. Milk becomes sour if kept for a long time. what is the type of reaction?

Ans: Decomposition reaction.

32. Which one is a chemical change— rusting of iron or melting of iron?

Ans: Rusting of iron is a chemical change.

33. Why do silver articles become black after sometime when exposed to air?

Ans: Silver gets oxidized to Ag2S due to H2S to present in air.

34. State the type of chemical reaction used for extraction of metals from their naturally occurring chlorides, or oxides.

Ans: Reduction.

35. A substance x displaces y from its solution in water. It is called displacement reaction. What other chemical name can be given to such type of reactions explain giving an example.

Ans: Zinc displaces copper from its solution of copper sulphate.

        Zn + CuSO4 –—› Cu + ZnSO4

It is also called redox reaction. Zn is oxidised to Zn2+ and copper(Cu+2) is reduced to Copper metal (Cu).

36. What is quicklime?

Ans: Quick lime is calcium oxide.

37. What is slaked lime?

Ans: Slaked lime is calcium hydroxide.

38. What is lime water?

Ans: It is a saturated solution of calcium hydroxide in water.

39. What is limestone?

Ans: limestone is calcium carbonate.

40. Is the reaction between quicklime and water exothermic or endothermic in nature?

Ans: It is exothermic in nature.

41. What is slaking of lime?

Ans: Adding water to quicklime to convert it into slaked lime is called slaking of lime.

42. Identify the type of reaction involved in the reaction between quicklime and water?

Ans: It is an example of combination reaction.

43. What is milk of lime?

Ans: A suspension of calcium hydroxide in water is called milk of lime.

44. What is green vitriol?

Ans: It is ferrous sulphate heptahydrate, FeSO4.7H2O.

45. What is the colour of fresh crystals of ferrous sulphate?

Ans: It is light green coloured.

46. Name the gases evolved when ferrous sulphate crystals are heated strongly.

Ans: Sulphur dioxide(SO2) and Sulphur trioxide (SO3).

47. What is the colour of the residue obtained when crystals of ferrous sulphate are heated strongly in air? What is its chemical composition?

Ans: The residue is red in colour. Chemically it is Iron(III) oxide or ferric oxide (Fe2O3).

48. What is the smell of the gases evolved when crystals of ferrous sulphate are heated strongly?

Ans: The mixture of gases so produced has a pungent and suffocating smell of burning sulphur.

49. What happens when crystals of ferrous sulphate are kept exposed to atmosphere for a long time?

Ans: Ferrous sulphate is oxidised to Feric sulphate by atmospheric oxygen.

50. What is the colour of ferric sulphate?

Ans: It is brownish yellow in colour.

51. How can you check, if crystals of ferrous sulphate are fresh? 

Ans: By noting its colour. If its colour is not light green, it is not fresh.

52. What is the colour of Fe2+ ions?

Ans: These are light green in colour.

53. What is the number of molecules of water of crystallization in green vitriol?

Ans: seven.

54. What is the colour of copper sulphate solution?

Ans: Copper sulphate solution is sky blue in colour.

55. What is the colour of Iron nails?

Ans: It is Steel grey in colour.

56. What is the colour of ferrous sulphate solution?

Ans: It is light green in colour. 

57. What is the colour of Iron nails after the experiment?

Ans: Iron nails become reddish brown in colour. This is due to the deposition of copper on Iron nails.

58. Can we store copper sulphate solution in an iron vessel?

 Ans: No. This is because iron reacts with copper sulphate solution as iron is more reactive than copper.

59. Why does the following reaction takes place? 

2I- +Cl2 –—› 2Cl- + I2 

Ans. Because Cl2 is more reactive than I2.

60. why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Ans: It is due to the formation of pale green FeSO4. 

61. Is Barium chloride soluble in water? If so then what is the colour of solution obtained?

Ans: Yes, Barium chloride is soluble in water. It's solution in water is colourless.

62. Is Barium sulphate soluble in water?

Ans: Barium sulphate is not soluble in water.

63. What is the colour of Barium sulphate?

Ans: Barium sulphate is white in colour.

64. Is sodium sulphate soluble in water? If so then what is the colour of the solution obtained?

Ans: Yes, sodium sulphate is soluble in water. It's solution in water is colourless.

65. Give one example of a double displacement reaction?

Ans: The reaction between a solution of Barium chloride and a solution of sodium sulphate is an example of double displacement reaction.

66. list the equipment and chemicals required to study the combination reaction between quicklime and water.

Ans: 250 ml beakers, asbestos sheet dropper, quicklime and water.

67. Why do the patients suffering from kidney stones are advised to not to take foods such as tomatoes, spinach etc. ?

Ans: As we know that calcium oxalate is mostly responsible for kidney stones. Therefore, while taking tomatoes and spinach the oxalic acid present in them react with the calcium in our diet, thus forming calcium oxalate.

68. Give two other examples of thermal decomposition reaction.

Ans: CaCO3 –—› CaO + CO2

       2Pb(NO3)2 –—› 2PbO + 4NO2 + O2

69. List the equipment and chemicals required to study the decomposition reaction of ferrous sulphate crystals.

Ans: Hard glass test tube, test tube holder, bunsen burner, asbestos sheet, fresh light green ferrous sulphate crystals, acidified potassium dichromate solution(to test SO2), blue litmus paper (to test SO2 and SO3).

70. Write two observation that we likely to observe while studying thermal decomposition of ferrous sulphate crystals.

Ans: (i) light green coloured crystals of ferrous sulphate first change to dirty white  powder and then to a reddish brown coloured powder.

         (ii) During heating, first water vapours are evolved and then on strong heating, colourless gases with a suffocating smell of burning sulphur are produced.

71. Give example of combination reactions: 

(a) Involving only metals

(b) Involving only compounds.

Ans: (a) 2Mg + O2 –—› 2MgO

         (b) CaO + H2O –—› Ca(OH)2

72. Give one example of displacement reaction in each of the following cases.

(a) A non-metal displaces a non-metal

(b) A Metal displaces a non-metal.

Ans: (a) 2KBr + Cl2 –—› 2KCl + Br2

         (b) Zn + 2HCl —–› ZnCl2 + H2

73. Out of the four types of reactions, name the type of reaction which is not a redox reaction. Give One example.

Ans: Combination, decomposition and displacement reactions can be redox reactions. Double Displacement reaction is not a redox reaction. For example,

AgNO3 + NaCl –—› AgCl + NaNO3

 

74. Give a list of equipments and chemicals required to study a displacement reaction between iron and copper sulphate solution.

Ans: Two 250 ml beakers, sandpaper, filter paper, new Iron nails, copper sulphate solution.

75. Write two observations that we likely to observe while studying the displacement reaction between iron and copper sulphate solution.

Ans: (i) Blue colour of copper sulphate solution changes to pale green colour.

         (ii) Submerged part of the Steel grey iron nail is covered with a reddish brown coating of copper on its surface.

76. What will be the nature of solution formed when calcium oxide is dissolved in water? Name the substance formed when CO2 gas is passed through this solution.

Ans: (i) It will be basic in nature.

        (ii) calcium carbonate (CaCO3).

77. What happens when a moist blue litmus paper is brought near the mouth of the test tube in which FeSO4 crystals are being heated?

Ans: It will first turn red, because SO2 and SO3 are acidic in nature. However, as SO2 is a bleaching agent, the litmus paper can also turn colourless.

78. Give a list of equipments and chemicals required to study double displacement reaction between Barium chloride and sodium sulphate solutions.

Ans: One beaker (250 ml), test tubes, test tube stand, glass rod, Barium chloride solution, sodium sulphate solution, distilled water.

79. Give two precautions that need to be taken while studying double displacement reaction between Barium chloride solution and sodium sulphate solution.

Ans: (i) use only distilled water to wash all the glass equipments.

     (ii) mix the two solutions with constant stirring.

80. List two observations, that are observed while studying a double displacement reaction between Barium chloride solution and sodium sulphate solution.

Ans: (i) The white precipitate is formed during the reaction.

      (ii) The supernatant solution is colourless.

81.  write down the formula of blue vitriol and green vitriol.

Ans: (i) blue vitriol : CuSO4.5H2O

        (ii) Green vitriol: FeSO4.7H2O.

82. list two precautions to be kept in mind while studying a decomposition reaction using ferrous sulphate crystals in the laboratory.

Ans: (i) Use of clean and dry hard glass test tube for the experiment.

        (ii) The mouth of the test tube being heated should be towards the Sink and do not inhale SO2 and SO3 directly.

83. A student took solid quicklime in a China dish added a small amount of water in it.

(a) State the type of sound produced in the reaction.

(b) Mention the type of this reaction.

Ans: (a) Quick lime starts crumbling producing a sort of crackling sound in its reaction with water.

(b) This reaction is chemical combination reaction and is exothermic in nature.

84. Name all the products formed when ferrous sulphate crystals are heated and write the colour of residue left in the test tube. write a fully balanced equation in support of your answer.

Ans: The products formed are ferric oxide, Sulphur dioxide gas and sulphur trioxide gas along with steam. The colour of residue in the test tube is reddish brown.

2FeSO4.7H2O –—› Fe2O3 + SO2 + SO3 + 14H2O

85. A student obtains a white precipitate on mixing two different salt solutions in a beaker. What could these two solutions be? Identify and name the type of this reaction.

Ans: When sodium sulphate solution mixes with barium chloride solution a white precipitate of Barium sulphate is obtained. It is a double displacement reaction, because the ions of two different salt solutions exchange to form two new salts.

86. A Student mixes solid sodium sulphate in solid Barium chloride. What change on missing the two solids would the student observe? Justify your answer and explain how he can obtain the change.

Ans: No change takes place after mixing solid sodium sulphate in solid Barium chloride. When Aqueous solutions of two soluble salts are mixed, they react by interchanging their ions and form two new salts. In this way, he can obtain a change after mixing their Aqueous solutions but not in solid forms.

87. During an experiment a student obtains white precipitate of Barium sulphate on mixing two Aqueous solutions with each other.  Name the two solutions he has mixed. Also state the type of reaction that has taken place.

Ans: He has mixed solution of sodium sulphate(Na2SO4) and Barium chloride(BaCl2). Type of reaction is double displacement reaction.

88. An iron nail is dipped in a solution of copper sulphate for about 30 minutes, state the change in colour observed. Give the reason for the change.

Ans: Reddish brown deposit on the iron nail is on account of the deposition of copper metal or iron.

           The blue colour of copper sulphate solution fades, on account of the depletion of CU2+ ions in the the copper sulphate solution. If iron nail is kept in copper sulphate solution for a few hours, the blue colour may completely disappears and instead a light green coloured solution is formed.

89. What type of chemical reaction takes place between calcium oxide and water? Justify your answer.

Ans: CaO + H2O –—› Ca(OH)2

It is a combination reaction because calcium oxide combines with water to form calcium hydroxide.

90. What happens when a solution of Barium chloride is mixed with sodium sulphate. Write the equation involved.

Ans: A white precipitate of BaSO4 is obtained and the supernatant solution is colourless.

BaCl2 + Na2SO4 —–› BaSO4 + 2Nacl

NCERT solutions of class 10 ch-1 Chemical reactions and equations.