CHEMISTRY CH-1 CHEMICAL REACTION AND EQUATION QUESTION ANSWER

1

State one basic difference between a physical change and a chemical change.

1

ANS:     In physical change, no new substance is formed whereas in a chemical change a new substance(s) is/are formed.

  

2

What is meant by a chemical reaction?

1

ANS:     The reaction representing a chemical change is called chemical reaction.

  

3

AgNO₃(aq) + NaCl(aq) → AgCl(s) ↓ + NaNO₃(aq) FeS + H₂SO₄ → FeSO₄ + 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?

1

ANS:     ↑ shows the gas evolved whereas ↓ shows insoluble substance (precipitate) formed.

  

4

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?

1

ANS:     It is because properties of compound (H₂O) are different from properties of its constituting elements i.e. H₂ and O₂.

  

5

What happens chemically when quicklime is added to water filled in a bucket?

1

ANS:     Quicklime reacts with water to form slaked lime and produces lot of heat and hissing sound.      CaO(s)   +   H₂O(l)   →   Ca(OH)₂(s)   +   Heat   +   Hissing sound     Quicklime           Water                Slaked lime
(Calcium oxide)                          (Calcium hydroxide)

  

6

On what basis is a chemical equation balanced?

1

ANS:     It is based on law of conservation of mass.

  

7

Balance the given chemical equation: Al(s) + CuCl₂(aq) → AlCl₃(aq) + Cu(s)

1

ANS:     2Al(s) + 3CuCl₂(aq) → 2AlCl₃(aq) + 3Cu(s)

  

8

Balance the given chemical equation: FeSO₄(s)  Fe₂O₃(s) + SO₂(g) + SO₃(g)

1

ANS:     2FeSO₄(s) Fe₂O₃(s) + SO₂(g) + SO₃(g)

  

9

Balance the given chemical equation: Fe(s) + H₂O(g) → Fe₃O₄(s) + H₂(g)

1

ANS:     3Fe(s) + 4H2O(g) → Fe₃O₄(s) + 4H₂(g)

  

10

What change in colour is observed when white silver chloride is left exposed to sunlight ? State the type of chemical reaction in this change.

1

ANS:     Silver chloride becomes grey. It is a photochemical decomposition reaction.

  

11

Name the process in which gain of electrons takes place.

1

ANS:     Reduction is a process which involves gain of electrons.

  

12

How will you define a reducing agent?

1

ANS:     Reducing agent is a substance which can lose electrons or which can add hydrogen or remove oxygen.

  

13

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

1

ANS:     To provide an inert atmosphere to prevent chips from getting oxidised. N2 does not allow chips to
get spoiled by oxidation.

  

14Why do gold and platinum not corrode in moist air?                                                          1

ANS:     They are least reactive and do not react with substances present in moist air.

  

15	Write balanced chemical equations for the following reactions: (a) Silver bromide on exposure to sunlight decomposes into silver and bromine. (b) Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.	2
	ANS:     (a) 2AgBr(s) →2Ag(s) + Br2(g) (b) 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
16	Balance the following chemical equations: (a) BaCl2 + H2SO4 → BaSO4 + HCl (b) Ca(OH)2 + HNO3 → Ca(NO3)2 + H2O (c) Pb(NO3)2 → PbO + NO2 + O2 (d) MnO2 + HCl → MnCl2 + H2O + Cl2	2
	ANS:     (a) BaCl2 + H2SO4 → BaSO4 + 2HCl (b) Ca(OH)2 + 2HNO3 → Ca(NO3)2 + 2H2O (c) 2Pb(NO3)2 → 2PbO + 4NO2 + O2 (d) MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
17	Write the balanced equation for the following reaction and identify the type of reaction in each case. (a) Potassium bromide + Barium iodide → Potassium iodide + Barium bromide. (b) Hydrogen (g) + Chlorine(g) → Hydrogen chloride (g)	2
	ANS:     (a) 2KBr(aq) + BaI2(aq) → 2KI(aq) + BaBr2(aq) (b) H2(g) + Cl2(g) → 2HCl(g)
18	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 a few days when zinc plate was taken out of the solution, a number of holes were observed on it. (a) State the reason for changes observed on the zinc plate. (b) Write the chemical equation for the reaction involved.	2
	ANS:     (a) It is because zinc has displaced copper from CuSO4. Zinc metal has been used to form zinc sulphate, therefore, number of holes were observed. Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)                  Blue               Colourless
19	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.	2
	ANS:     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. e.g. lead nitrate is white crystalline solid, on heating gives yellowish brown solid (lead monoxide), brown gas is evolved and a colourless gas is evolved. It shows chemical reaction has taken place.
20	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.	2
	ANS:     Yellow precipitate of lead iodide is formed. It is precipitation reaction. Pb(NO3)2 (aq) + 2KI (aq) → PbI2 (s) + 2KNO3 (aq) It is also called double displacement reaction.
21	Consider the following chemical reaction X + Barium chloride →         Y        + Sodium chloride                                        (White ppt) (a) Identify ‘X’ and ‘Y’ (b) The type of reaction	2
	ANS:     (a) ‘X’ is Na2SO4 and Y is BaSO4. (b) The type of reaction Na2SO4 + BaCl2 →    BaSO4    + 2NaCl                       (White ppt)
22	Identify the type of reaction from the following equations : (a) CH4 + 2O2 → CO2 + 2H2O (b) Pb(NO3)2 + 2KI → PbI2 + 2KNO3 (c) CaO + H2O → Ca(OH)2 (d) CuSO4 + Zn → ZnSO4 + Cu	2
	ANS:     (a) Combustion reaction and oxidation reaction (b) Double displacement and precipitation reaction (c) Combination reaction (d) Displacement reaction.
23	Using balanced chemical equation explain the difference between a displacement reaction and a double displacement reaction.	2
	ANS:     In displacement reaction, more reactive metal can displace less reactive metal from its salt solution, e.g. Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s) In double displacement reactions, two compound exchange their ions to form two new compounds, e.g. NaOH + HCl → NaCl + H2O
24	Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.	2
	ANS:     Thermal decomposition reaction Photochemical decomposition reaction 2AgCl(s)→2Ag(s) + Cl2(g)
25	(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?	2
	ANS:     (a) ‘X’ is calcium oxide (CaO). CaO(s) + H2O(l) → Ca(OH)2 (aq) + Heat (b) It is because iron displaces copper from CuSO4 to form FeSO4 which is pale green. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) Blue                      Pale green
26	A white salt on heating decomposes to give brown fumes and a residue is left behind. (a) Name the salt. (b) Write the equation for the decomposition reaction.	2
	ANS:     (a) Lead nitrate is white salt. (b) 2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)
27	Define combination reaction. Give one example of a combination reaction which is also exothermic.	2
	ANS:     A reaction in which two elements or compounds combine to form a single compound is called combination reaction. CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
28	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.	2
	ANS:     White precipitate of barium sulphate is formed. If both reactants are in solid state, then the reaction will not take place between them. BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq) It is double displacement as well as precipitation reaction.
29	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: (a) What type of chemical reaction takes place in each of the two given steps? (b) Name the metal initially taken in the powder form. Write balanced chemical equations for both reactions.	2
	ANS:     (a) In first step, oxidation is taking place. In second step, redox reaction takes place. (b) Metal in the powder form is copper 2Cu(s) + O2(g) → 2CuO(s) CuO(s) + H2(g) → Cu(s) + H2O(g)
30	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.	2
	ANS:      2Mg(s) + O2(g) → 2MgO(s) The type of reaction is combination reaction and the product formed is magnesium oxide.
31	Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions: (a) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) (b) Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)	2
	ANS:     Displacement reaction is a reaction in which more reactive metal can displace less reactive metal from its salt solution. Double displacement reaction: Those reactions in which compound exchange their ions to form two new compounds are called double displacement reaction. (a) Double displacement reaction (b) Displacement reaction
32	Classify each of the following as combination, decomposition, displacement or double displacement reaction: (a) 2KNO3(s) → 2KNO2(s) + O2(g) (b) Zn(s) + 2AgNO3(aq) → Zn(NO3)2 + 2Ag(s) (c) Ni(NO3)2(aq) + 2NaOH → Ni(OH)2↓ + 2NaNO3(aq) (d) N2(g) + 3H2(g) → 2NH3(g)	2
	ANS:     (a) Decomposition reaction (b) Displacement reaction (c) Double displacement reaction and precipitation reaction (d) Combination reaction
33	In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.	2
	ANS:      Thus, silver metal can be recovered.
34	Which among the following changes are exothermic or endothermic in nature? (a) Decomposition of ferrous sulphate (b) Dilution of sulphuric acid (c) Dissolution of sodium hydroxide in water (d) Dissolution of ammonium chloride in water	2
	ANS:     (a) It is endothermic reaction. (b) It is exothermic process. (c) It is exothermic process. (d) It is endothermic process.
35	Name the reducing agent in the following reaction: 3MnO2 + 4Al → 3Mn + 2Al2O2 State which is more reactive, Mn or Al and why?	2
	ANS:     ‘Al’ is reducing agent. ‘Al’ is more reactive than Mn  ‘Al’ displaces Mn from its oxide.
36	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?	2
	ANS:     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.
37	What is an oxidation reaction? Give an example of oxidation reaction. Is oxidation an exothermic or an endothermic reaction ?	2
	ANS:     The reaction in which oxygen or electronegative element is added, hydrogen or electropositive element is removed or loss of electrons takes place, is called an oxidation reaction. e.g. Fe2+ → Fe3+ + e– (Loss of electron) C + O2 → CO2 + Heat Oxidation reactions are mostly exothermic in nature because heat is evolved in this process.
38	Give two examples from everyday life situations where redox reactions are taking place.	2
	ANS:     Two examples of redox reactions are: (i) Rusting of Iron: 4Fe + 3O2  →2Fe2O3 is a redox reaction. Fe is getting oxidised to Fe3+ ion whereas O2 is getting reduced to O2– ion. (ii) Combustion Reaction: Burning of coal is a redox reaction. C(s) + O2(g) → CO2(g) + Heat C is getting oxidised to C4+ ion in CO2 whereas O2 is getting reduced to O2– ion in CO2.
39	2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g). Is it a redox reaction or not? If yes, why?	2
	ANS:     It is a redox reaction because ferrous (Fe2+) is getting oxidised to Iron(III) (Fe3+) whereas SO42– is getting reduced to SO2

40	Write the chemical equation of the reaction in which the following changes have taken place with an example of each: (a) change in colour (b) change in temperature (c) formation of precipitate	3
	ANS:     (a) Cu (s) + 2AgNO3 (aq) → Cu(NO3)2(aq) + 2Ag The solution will become blue in colour and shiny silver metal will be deposited. (b) NaOH + HCl → NaCl + H2O + Heat The temperature will increase because heat will be evolved. (c) Pb(NO3)2 (aq) + 2KI (aq) →   PbI2 (s) + 2KNO3 (aq)                                                     Yellow ppt Yellow precipitate of PbI2 will be formed.
41	(a) Write the essential condition for the following reaction to take place: AgBr → 2Ag + Br2 Write one application of this reaction. (b) Complete the following chemical equation of a chemical reaction: 2FeSO4  →Fe2O3 + .... + .... (c) What happens when water is added to quick lime. Write chemical equation.	3
	ANS:     (a) 2AgBr  →2Ag + Br2 This reaction is used in photography. (b) 2FeSO4  →Fe2O3 + SO2 + SO3 (c) Slaked lime is formed with hissing sound and lot of heat is evolved. CaO + H2O → Ca(OH)2 + Heat
42	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.	3
	ANS:     The equations in which gaseous are written in atomic form instead of molecular form and equation is not balanced are called skeltal type chemical equation. The represent gaseous elements formed in atomic state and equation is not balanced. H2O  →H + O (Skeltal equation) Hydrogen and oxygen are written in atomic forms and equation is not balanced. 2H2O → 2H2 + O2 (Balanced chemical equation) H2O → H2 + O2 is Skeltal equation.
43	Write chemical equation for the reactions taking place when (a) Iron reacts with steam (b) Magnesium reacts with dil. HCl (c) Copper is heated in air.	3
	ANS:     (a) 3Fe (s) + 4H2O (g) → Fe3O4 (s) + 4H2 (g) (b) Mg + 2HCl → MgCl2 + H2 (c) 2Cu + O2  →2CuO (s)
44	Write balanced equations for the following, mentioning the type of reaction involved. (a) Aluminium + Bromine → Aluminium bromide (b) Calcium carbonate → Calcium oxide + Carbon dioxide (c) Silver chloride → Silver + Chlorine	3
	ANS:     (a) 2Al(s) + 3Br2(g) → 2AlBr3(s) (b) CaCO3(s) → CaO(s) + CO2(g) (c) 2AgCl(s)  →2Ag(s) + Cl2(g)
45	Name the type of chemical reaction represent by the following equation: (a) CaO + H2O → Ca(OH)2 (b) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3 (c) 2FeSO4  →Fe2O3 + SO2 + SO3	3
	ANS:     (a) Combination reaction (b) Double displacement reaction (precipitation) (c) Decomposition reaction.
46	State the type of chemical reactions with chemical equations that take place in the following: (a) Magnesium ribbon is burnt in air. (b) Electric current is passed through water. (c) Ammonia and hydrogen chloride gases are mixed.	3
	ANS:     (a) 2Mg (s) + O2 (g) → 2MgO (s) Combination reaction (Redox reaction). (b) 2H2O (l)  →2H2 (g) + O2 (g) Electrical decomposition reaction. (c) NH3 (g) + HCl (g) → NH4Cl (s) Combination reaction.
47	2 g of ferrous sulphate crystals are heated in a dry boiling tube. (a) List any two observations. (b) Name the type of chemical reaction taking place. (c) Write the chemical equation for the reaction.	3
	ANS:     (a) Green colour of FeSO4 disappears and reddish brown Fe2O3 is formed.Smell of burning sulphur. (b) Decomposition reaction (c) 2FeSO4 (s) →Fe2O3 (s) + SO2 (g) + SO3 (g)
48	When you have mixed the solutions of lead(II) nitrate and potassium iodide. (a) What was the colour of the precipitate formed and can you name the precipitate ? (b) Write the balanced chemical equation for this reaction. (c) Is this also a double displacement reaction?	3
	ANS:     (a) The colour of the precipitate is yellow. The name of compound formed as a precipitate is lead iodide (PbI2). (b) Pb(NO3)2 (aq) + 2KI(aq) → PbI2(s) + 2KNO3(aq) (c) Yes, it is also a double displacement reaction.
49	The following diagram displays a chemical reaction. Observe carefully and answer the following questions: (a) Identify the type of chemical reaction that will take place and define it. How will the colour of the salt change? (b) Write the chemical equation of the reaction that takes place. (c) Mention one commercial use of this salt.	3
	ANS:     (a) Photochemical decomposition reaction. Those reactions in which a compound breaks down into simple substances in presence of light are called photochemical decomposition reaction. The colour of salt will change from white to grey. (b) 2AgCl(s)  → 2Ag(s) + Cl2(g) (c) Silver chloride is used in photography.
50	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.	3
	ANS:     C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + Heat energy It is exothermic combination reaction because heat energy is being evolved. CH4(g) + 2O2(g) → CO2(g) + 2H2O Combustion of methane is another example of exothermic combination reaction.
51	2 g of lead nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame. Now answer the following: (a) State the colour of the fumes evolved and the residue left. (b) Name the type of chemical reaction that has taken place stating its balanced chemical equation.	3
	ANS:     (a) Brown coloured fumes of NO2 gas are evolved and yellowish brown residue is formed. (b) Decomposition reaction has taken place as, 2Pb(NO3)2(s) 2PbO(s) + 4NO2(g) + O2(g)
52	What is meant by: (a) Displacement reaction (b) Reduction reaction (c) Combination reaction. Write balanced chemical equation for each reaction:	3
	ANS:     (a) Displacement reaction: The reaction in which more reactive element can displace less reactive element from its salt solution, e.g. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) (b) Reduction reaction: The reaction in which H2 is added or O2 is removed or gain of electrons takes place, e.g. Fe3+ + e– → Fe2+ (c) Combination reaction: Those reactions in which two elements or compounds react to form single compound. e.g. N2(g) + 3H2(g) → 2NH3(g)
53	Define the term decomposition reaction. Give one example each of thermal decomposition and electrolytic decomposition.	3
	ANS:     Decomposition reactions: Those reactions in which a compound splits up into two or more simpler substances are called decomposition reactions.  Thermal decomposition: CaCO3(s)  → CaO(s) + CO2(g)  Electrolytic decomposition:   2H2O (l)  → 2H2(g) + O2(g)
54	(a) Classify the following reactions into different types: (i) AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) (ii) CaO(s) + H2O(l) → Ca(OH)2(aq) (iii) 2KClO3(s)  → 2KCl(aq) + 3O2(g) (b) Which of the above reaction(s) is/are precipitation reaction(s)? Why is a reaction called precipitation reaction?	3
	ANS:     (a) (i) Precipitation reaction (Double displacement reaction) (ii) Combination reaction (iii) Decomposition reaction (b) (i) is precipitation reaction because one of the products formed is insoluble in water.
55	What is meant by (a) precipitation reaction, (b) exothermic reaction, (c) oxidation reaction. Write balanced chemical equations for an example of each.	3
	ANS:     (a) Precipitation reaction: The reaction in which two compounds exchange their ions and the product formed is insoluble in water is called precipitation reaction, e.g. AgNO3(aq) + KI(aq) → AgI(s) + KNO3(aq) (b) Exothermic reaction: The reaction in which heat is evolved, e.g. C + O2 → CO2 + Heat (c) Oxidation reaction: The reaction in which O2 is added or H2 is removed or loss of electrons takes place, e.g. 2Cu + O2 → 2CuO
56	A reddish brown coloured metal, used in electrical wires, when powdered and heated strongly in an open china dish, its colour turns black. When hydrogen gas is passed over this black substance, it regains its original colour. Based on the above information answer the following questions. (a) Name the metal and the black coloured substance formed. (b) Write balanced chemical equations for both the reactions.	3
	ANS:     (a) Reddish brown metal is copper. When it is heated in china dish in presence of oxygen, black coloured copper oxide is formed. (b) 2Cu(s) + O2(g) → 2CuO(s) When hydrogen gas is passed over heated copper oxide reddish brown copper metal is formed, e.g. CuO(s) + H2(g) Cu(s) + H2O(g)
57	What is redox reaction? Identify the substance oxidised and the substance reduced in the following reactions: (a) 2PbO + C → Pb + CO2 (b) MnO2 + 4HCl → MnCl2 + 2H2O + Cl2	3
	ANS:     Those reaction in which oxidation and reduction takes place simultaneously are called redox reactions. (a) PbO is getting reduced and C is getting oxidised. (b) MnO2 is getting reduced. HCl is getting oxidised.
58	(a) Why is respiration considered an exothermic reaction? (b) Define the terms-oxidation and reduction. (c) Identify the substance that is oxidised and reduced in the reaction: CuO(s) + Zn(s) → Cu(s) + ZnO(s)	3
	ANS:     (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.
59	What is rancidity? Mention any two ways by which rancidity can be prevented.	3
	ANS:     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.

60	(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 pentachloride. (ii) burning of natural gas. (iii) the process of respiration.	5
	ANS:     (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) (ii) CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) + Heat energy (iii) C6H12O6(aq) + 6O2 (q) → 6CO2 (aq) + 6H2O (l) + Heat energy
61	(a) Write one example for each of decomposion reaction (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.	5
	ANS:     (a) (i) 2H2O → 2H2 (g) + O2 (ii) CaCO3  → CaO + CO2 (iii) 2AgBr  → 2Ag + Br2 (b) Copper can displace silver from AgNO3 because copper is more reactive than Ag, e.g. Cu + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag (s)
62	A metal nitrate ‘A’ on heating gives yellowish brown coloured metal oxide along with brown gas ‘B’ and a colourless gas ‘C’. Aqueous solution of ‘A’ on reaction with potassium iodide forms a yellow precipitate of compound ‘D’. Identify ‘A, B, C, D’. Also identify the types of both the reactions. Metal present in ‘A’ is used in alloy which is used for soldering purposes.	5
	ANS:     Metal nitrate ‘A’ is Pb(NO3)2. ‘A’ is lead nitrate, ‘B’ is nitrogen dioxide, ‘C’ is oxygen and ‘D’ is lead iodide. (i) is decomposition reaction and (ii) is double displacement reaction (Precipitation reaction)
63	(a) Explain two ways by which food industries present rancidity. (b) Discuss the importance of decomposition reaction in metal industry with three points.	5
	ANS:     (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 gives metal.

64	Rohan suggested to his principal not to use yellow colour on school buses. He read article in newspaper that “Sudden decline in IQ levels of children and unexplained retardation or hyperactivity among them can now be traced to unacceptably high levels of lead in their blood sugar levels. The health hazard has been traced to high levels of lead in domestic paints used on the walls of schools, residences, school buses, swings in playground and toys”. (a) What is meant by IQ and what is a cause of decline IQ in children? (b) Which compound of lead is used in yellow paint of school buses? (c) What values are possesed by Rohan who wants to use lead free paints on vehicles? (d) Should we continue yellow colour on school buses? Give reason. Suggest alternative.	4
	ANS:     (a) IQ stands for Intelligence Quotient. High levels of lead in blood sugar level is a cause of decline IQ in children. (b) Lead chromate. (c) He is concerned about the health of children and wants to prevent them from toxic effects of lead. (d) No, yellow colour should be discontinued as it contains compound of lead. White paints or lead free paints should be used.
65	Anjali told her chemistry teacher that biofuels should be used instead of fossil fuels. She read in science magazine that “Researchers have found that one of most common bacteria E. coli can digest simple sugars from plant waste and turn it into valuable biofuel. It can convert a renewable non-food plant (i.e. Jatropha) to fuel. We need to put it in our feed stock, the bacteria converts feed stock into fuel which is oil that you just scrap off the tap. Biofuels, made from plants and animal fat, are alternative to petroleum based fuels.” (a) What is biofuel? (b) What are advantages of biofuel? (c) Is preparation of biofuel a chemical or physical process? (d) Why is biofuel better than petroleum products? (e) What values are possesed by Anjali who wants to use biofuel?	4
	ANS:     (a) The fuel obtained from plants and animal waste is called biofuel. (b) It is low cost, low carbon and high performance renewable fuel. (c) It is a chemical process. (d) It creates less pollution as compared to petroleum products. (e) She is nature loving and concerned about conservation of energy by using renewable source of energy.
66	Kavita uses colours to celebrate Holi with friends which are oxidised metals or industrial dyes mixed with engine oil. The doctors say these are toxic and can cause skin allergies, eye irritation and even blindness, e.g. black colour which may damage kidney and cause learning disability, purple colour which may cause Bronchial asthma and allergies. On the other hand, Komal uses edible colours which are obtained from natural substances like red colour which is prepared by red pomegranate peels boiled with water or rose petals can also be used, blue colour which are obtained by indigo plant put in water and green colour can be made from thin paste of mint and spinach leaves or heena. (a) What are the harmful effects of chemicals present in colours of Holi? (b) What are the positive effects of edible colours? (c) How is edible herbal gulal prepared? (d) What compound is contained in black colour and purple colour? (e) What values are possessed by Komal using herbal colour and not throwing coloured water on people?	4
	ANS:     (a) It can cause skin allergies, kidney problems and asthma. (b) These are not harmful for our body and are skin friendly. (c) It is prepared by dry flowers. (d) Black colour contain lead oxide and purple colour contains chromium iodide. (e) Komal saves herself as well as others from harmful effects of chemicals by using natural colours.
67	Sohan uses Kangri which makes use of charcoal or firewood and it keeps people of cold places like Srinagar, Gulmarg etc. warm. Mohan is an electrical engineer, has created a Kangri that converts solar power into thermal energy. It comes with inlet battery, inverter circuit and a solar panel as an attachment which is readily available. It requires moderate intensity of sunlight which traps and transfers it to the battery inlet of Kangri which gets charged and by virtue of attached inverter releases heat. (a) What is a source of energy in solar Kangri? Is it renewable or non-renewable source of energy? (b) Can we use it in place of heaters in rural and urban areas? (c) How chemical reaction takes place in Kangri? (d) What values shown by Mohan who uses solar Kangri?	4
	ANS:     (a) It is sunlight which charges battery which is attached to inverter releasing heat. It is renewable source of energy. (b) Yes, it can be used in rural areas where electricity is not available and also in urban areas to save electricity. (c) When charcoal or firewood is burnt in present of oxygen chemical reaction takes place in which carbon monoxide and heat are evolved. (d) Mohan is concerned about environment and wants to save it from air pollution.