33.State the type of chemical reactions and chemical equations that take place in the following:
(i) Magnesium wire is burnt in air.
(ii) Electric current is passed through water.
(iii) Ammonia and hydrogen chloride gases’are mixed.

Answer.

34. 2g of ferrous sulphate crystals are heated in a dry boiling tube.
(i) List any two observations.
(ii) Name the type of chemical reaction taking place.
(iii) ‘Write the chemical equation for the reaction.
Answer.
(i) •Green colour of Fe SO4 disappears and reddish brown solid is formed.
• Smell of burning sulphur.
(ii) Decomposition reaction

Long Answer Type Questions [5 Marks] -Year 2015

35. (a) Define a balanced chemical equation. Why should an equation be balanced?
(b) Write the balanced chemical equation for the following reaction:
(i) Phosphorus burns in presence of chlorine to form phosphorus penta chloride.
(ii) Burning of natural gas.
(iii) The process of respiration.
Answer.
(a) Balanced chemical equation has an equal number of atoms of different elements in the reactants and products. According to law of conservation of mass, matter can neither be created nor be destroyed in a chemical reaction.
(b)(i) P4 (s) + 10Cl2 (g) ———> 4PCl5 (S)
(i)CH4 (g) + 2O2 (g) ———> CO2 (g) + 2H2O(l) + heat energy
(iii) C6H12O6 (s) + 6O2 (g) + 6H2O ———> 6CO2 (aq) + 12H2O (l) + energy

36.(a) Explain two ways by which food industries prevent rancidity.
(b) Discuss the importance of decomposition reaction in metal industry with three points.
Answer.
(a) (i) Rancidity can be prevented by adding antioxidants to food containing
fat and oil, e.g. butylated hydroxy anisole is added to butter as antioxidant.
(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.
(b) (i) Molten NaCl is electrolytically decomposed to form sodium metal.
(ii) Aluminium metal is obtained by electric decomposition of bauxite ore mixed with cryolite.
(iii) Carbonate ores are thermally decomposed to give metal oxide which on reduction give metal.

Short Answer Type Question[I] [2 Marks] -Year 2014

37. What is observed when a solution of potassium iodide solution is added to a solution of lead nitrate? Name the type of reaction. Write a balanced chemical equation to represent the above chemical reaction.
Answer.Yellow precipitate of lead iodide is formed. It is precipitation reaction.
Pb( NO3)2 (aq) + 2KI (aq) —-> Pbl2 (s) + 2KNO3 (aq)
It is also called double displacement reaction.

short Answer Type Question[ll] [3 Marks] -Year 2014

38.Write chemical equation reactions taking place when carried out with the help of
(a) Iron reacts with steam
(b) Magnesium reacts with dil HCl
(c) Copper is heated in air.
Answer.

Long Answer Type Question [5 Marks] -Year 2014

39.(a) Write one example for each of decomposion reaction carried out with help of
(i) Electricity (ii) Heat (iii) Light
(b) Which of the following statements is correct and why copper can displace silver from silver nitrate and silver can displace copper from copper sulphate solution.
Answer.

Short Answer Type Questions[ll] [3 Marks] -Year 2013

40. What is meant by skeltal type chemical equation? What does it represent? Using the equation for electrolytic decomposition of water, differentiate between a skeltal chemical equation and a balanced chemical equation.
Answer. The equations in which gaseous are written in atomic form instead of molecular form and equation is not balanced, are called skeltal type equation. They represent gaseous elements formed in atomic state and equation is not balanced

Short Answer Type Questions[l] [2 Marks]-Year 2012

41.Identify the type of reaction(s) in the following equations.
(i)CH4 + 2O2 CO2 + 2 H2O
(ii) Pb(NO3)2 + 2KI ——–>Pbl2 + 2KNOs
(iii) CaO +  H2O ——–> Ca(OH)2
(iv) CuSO4 + Zn ——–> ZnSO4 + Cu
Answer.
(i) Combustion reaction and oxidation reaction.
(ii)Double displacement reaction and precipitation reaction.
(iii) Combination reaction.
(iv) Displacement reaction.

42.What is the colour of ferrous sulphate crystals? How does this colour change after heating?
Answer.The colour of ferrous sulphate is pale green. The colour changes to reddish brown on heating due to formation of iron (III) oxide.
Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.
Thermal decomposition reaction:

Photochemical decomposition reaction:

43. Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Write two observations.
Answer. It is because displacement reaction takes place.
Iron displaces copper from copper sulphate solution and forms pale green
coloured solution of FeS04 and reddish brown copper metal gets deposited.
Fe(s) + CuS04(aq) ——–> FeS04(aq) + Cu(s)

44. Translate the following statement into chemical equation and then balance it Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. State the two types in which this reaction can be classified.
Answer. 3BaCl2(aq) + A12(S04)3(aq) ——–> 3BaS04(s) + 2AlCl3(aq)
It can be classified as double displacement as well as precipitation reaction.

45. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer. In decomposition reaction, a compound is broken down into simpler compounds or elements, e.g.

Combination reaction is a reaction in which two or more elements or compounds combine to form a new compound, e.g.

Thus, decomposition and combination reactions are opposite to each other.

Short Answer Type Questions[ll] [3 Marks]  -Year 2012

46. What is rancidity? Mention any two ways by which rancidity can be prevented.
Answer. The process in which taste and smell of food gets spoiled is called rancidity. It happens due to oxidation.
Prevention from rancidity:
(i) Antioxidants are added to fatty acids to prevent oxidation, e.g. chips are packed in presence of nitrogen gas which prevents spoilage by oxidation.
(ii)Food should be kept in airtight container in refrigerator.

47.Write balanced chemical equation for the reactions that take place during respiration. Identify the type of combination reaction that takes place during this process and justify the name. Give one more example of this type of reaction.
Answer. CgH1206 + 6O2 —————> 6CO2 + 6H20 + heat
It is an exothermic combination reaction because heat is evolved.
CH4(g) + 2O2(g) ————–>CO2 (g) + 2H20
Combustion of methane is another example of exothermic combination reaction.

48. What is redox reaction? Identify the substance oxidised and the substance reduced in the following reactions.
(i)2PbO + C —–> 2Pb + CO2
(ii)MnO2 + 4HCl —–> MnCl2 + 2H20 + Cl2
Answer. Those reactions in which oxidation and reduction takes place simultaneously are called redox reactions.
(i) PbO is getting reduced and C is getting oxidised.
(ii) MnOs is getting reduced and HCl is getting oxidised.

Very Short Answer Type Questions [1 Mark] -Year 2011

49.State one basic difference between a physical change and a chemical change.
Answer. In physical change, no new substance is formed, whereas in a chemical change, new substance(s) is/are formed.

50. What is meant by a chemical reaction?
Answer. The reaction representing a chemical change is called a chemical reaction.

35.AgN03(aq) + NaCl(aq)——————– > AgCl(s)4↓ + NaN03(aq)
FeS + H2S04————- > FeS04 + H2S↑
Consider the above mentioned two chemical equations with two different kinds of arrows (↑and ↓) along with product. What do these two different arrows indicate?
Ans,↑shows the gas is evolved whereas ↓shows insoluble substance (precipitate) is formed.

51. Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
Answer. It is because properties of compound (H2O) are different from properties of its constituting elements, i.e. H2and O2.

Short Answer Type Questions[l] [2 Marks] -Year 2011

52.Using a suitable chemical equation, justify that some chemical reactions are determined by:
(i) change in colour, (ii) change in temperature.
Answer.

53.(a) A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.
(b) Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer.
(a) ‘X’ is calcium oxide (CaO).
CaO(s) + H2O(l) —–> Ca(OH)2(aq) + heat
(a) It is because iron displaces copper from CuS04 to form FeS04 which is pale green.
Fe(s) + CUS04 (aq)—–> FeS04(aq) + Cu(s)
Blue                       Pale green

54.Write the balanced equation for the. following reaction and identify the type of reaction in each case.
(i) Potassium bromide + Barium iodide—-> Potassium iodide + Barium bromide.
(ii) Hydrogen(g) + Chlorine(g)—-> Hydrogen chloride(g)
Answer.

55. A zinc plate was put into a solution of copper sulphate kept in a glass container. It was found that blue colour of the solution gets fader and fader with the passage of time. After few days, when zinc plate was taken out of the solution, a number of holes were observed on it.
(i) State the reason for changes observed on the zinc plate.
(ii) Write the chemical equation for the reaction involved.
Answer.
(i) It is because zinc has displaced copper from CuS04. Zinc metal has been used to form zinc sulphate, therefore, number of holes were observed.

56. A white salt on heating decomposes to give brown fumes and a residue is left behind.
(i) Name the salt.
(ii) Write the equation for the decom-position reaction.
Answer.
(i) Lead nitrate is white salt.

57. When a solution of potassium iodide is added to a solution of lead nitrate in a test tube, a reaction takes place.
(a) What type of reaction is this?
(b) Write a balanced chemical equation to represent the above reaction.
Answer.
(a) Double displacement as well as precipitation reaction.

58. Write balanced equations for the following mentioning the type of reaction involved.
(i) Aluminium + Bromine —–> Aluminium bromide
(ii) Calcium carbonate—–> Calcium oxide + Carbon dioxide
(iii) Silver chloride—–>Silver + Chlorine
Answer.

59.(a) Why is respiration considered as an exothermic reaction?
(b) Define the terms oxidation and reduction.
(c) Identify the substance that is oxidised and reduced in the following reaction.

Answer. (a) It is because heat is evolved during respiration.
(b) Oxidation is a process in which O2 is added or H2 is removed or loss of electrons take place. Reduction is a process in which H2 is added or O2. is removed or gain of electrons take place.
(c) Zn is getting oxidised, CuO is getting reduced.

60.You might have noted that when copper powder is heated in a china dish, the surface of copper powder becomes coated with a black colour substance.
(i) How has this black coloured substance formed?
(ii) What is that black substance?
(iii) Write the chemical equation of the reaction that takes place.
Answer.
(i) Copper reacts with oxygen to form copper oxide which is black, i.e. oxidation of copper takes place.
(ii)Copper oxide

Very Short Answer Type Questions [1 Mark] -Year 2010

61. What happens chemically when quicklime is added to water filled in a bucket?
Answer. Quicklime reacts with water to form slaked lime and produces lot of heat and hissing sound.

62. On what basis is a chemical equation balanced?
Answer. A chemical reaction is balanced on the basis of law of conservation of mass.

63. What change in colour is observed when white silver chloride is left exposed to sunlight? State the type of chemical reaction in this change.
Answer. Silver chloride becomes grey. It is a photochemical decomposition reaction.

64. Write a balanced chemical equation for the reaction between sodium chloride
and silver nitrate indicating the physical state of the reactants and the products.
Answer.

Short Answer Type Questions[l] [2 Marks]

65. What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction.
Answer. White precipitate of barium sulphate is formed.
If both reactants are in solid state, then the reaction will not take place between them.

It is a double displacement as well as a precipitation reaction.

66. What is a redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced? Why?
Answer. The reactions in which oxidation (loss of electrons) and reduction (gain of electrons) take place simultaneously are called redox reactions.

Magnesium is getting oxidised because it is losing electrons to form Mg2+ and oxygen is gaining electrons to form O2-, therefore it is getting reduced.

67. Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
Answer. Any two of these observations will suggest chemical reaction has taken place.
(i) Change in state.
(ii)Change in colour.
(iii) Evolution of gas.
(iv)Change in temperature.
For example, lead nitrate is white crystalline solid which on heating gives yellowish brown solid (lead monoxide). A brown gas and a colourless gas is also evolved. It shows chemical reaction has taken place.

Very Short Answer Type Questions [1 Mark] -Year 2009

68.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.

69.Balance the following chemical equations.
Answer.

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

70. Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change?
Answer.

It is decomposition reaction.

71. 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. ,

Oxidation reactions are mostly exothermic in nature because heat is evolved in this process.

72. 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.

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.

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.

73.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.

The type of reaction is combination reaction and the product formed is magnesium oxide.

74.Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions.
Answer.

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

75.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).

(iii) Yes, it is also a double displacement reaction.

76.What do you mean by exothermic and endothermic reactions? Give examples.
Answer.Exothermic reactions are those in which heat is evolved, e.g.

Endothermic reactions are those reactions in which heat is absorbed, e.g.