Directions : For question number 24, two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to this question from the codes (A), (B), (C) and (D) as given below : (A) Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A): Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements. Reason (R): The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration.
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(A) / Both, Assertion(A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (1 Mark)
Answer the following : (a) Why should chemical equations be balanced ? (b) Name the oxidising and reducing agent in the following equation : $\ce{4Na + O2 -> 2Na2O}$
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(a)To follow the law of conservation of mass (b) Oxidising agent - $\ce{O2}$/Oxygen Reducing agent - $\ce{Na}$/Sodium
Translate the following statements into chemical equation and then balance them : (a) Water is added to quicklime (b) Burning of natural gas (c) Thermal decomposition of ferrous sulphate
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(a) $\ce{CaO(s) + H2O(l) -> Ca(OH)2 + Heat}$ (1 Mark) (b) $\ce{CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)}$ (1 Mark) (c) $\ce{2FeSO4(s) ->[Heat] Fe2O3(s) + SO2(g) + SO3(g)}$ (1 Mark) (deduct ½ mark for no / incorrect balancing)
Give reasons : (i) Potato chips manufacturers fill the packet of chips with nitrogen gas. (ii) Respiration is an exothermic reaction. (iii) Silver chloride is stored in dark coloured bottles.
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(i) To prevent the chips from getting oxidised/rancid. (ii) During respiration, glucose combines with oxygen in the cells of our body and gives energy. (iii) To prevent the decomposition of silver chloride into silver and chlorine by sunlight.
(a) Name the substance oxidised and reduced in the following reaction : $\ce{ZnO + C -> Zn + CO}$ (b) Balance the following chemical reaction : $\ce{Pb(NO3)2 + KI -> PbI2 + KNO3}$ (c) Give one example each of electrolytic decomposition and decomposition by sunlight.
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(a) • Substance oxidised - $\ce{C}$ (½) • Substance reduced - $\ce{ZnO}$ (½) (b) $\ce{Pb(NO3)2 + 2 KI -> PbI2 + 2 KNO3}$ (1) (c) • $\ce{2H2O ->[electricity] 2H2 + O2}$ (½) • $\ce{2AgCl ->[sunlight] 2Ag + Cl2}$ (½) (any other example in each case)
What happens when : (a) silver chloride is kept in sunlight ? (b) lead nitrate solution is added to potassium iodide solution? (c) food materials containing fats and oils are left for a long time?
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(a)Silver chloride decomposes to form silver / white silver chloride turns grey in sunlight / (1 Mark) $\ce{2AgCl ->[Sunlight] 2Ag + Cl2}$ (b)A precipitate of lead (II) iodide is formed / yellow ppt of lead iodide is formed / (1 Mark) $\ce{2Pb(NO3)2(s) ->[heat] 2PbO(s) + 4NO2(g) + O2(g)}$ Lead nitrate Colourless Lead monoxide Yellow Nitrogen dioxide Reddish brown Oxygen (c)Fats and oils are oxidized, they become rancid, and their smell and taste change. (1 Mark)
Answer the following : (a) Write two observations when green coloured crystals of ferrous sulphate are heated in a boiling tube. (b) Why brown coloured copper powder turns black on heating ? (c) What happens when limestone is heated strongly ?
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(a) • Green colour of the crystal changes brown. (½ Mark) • Colourless gases with odour of burning sulphur. (½ Mark) (any other observation) (b) Copper changes to copper (II) oxide which is black in colour. / $\ce{2Cu(s) + O2(g) ->[Heat] 2CuO(s)}$ (Brown to Black) (1 Mark) (Award full marks if chemical equation with colour changes is written) (c) Calcium oxide (quick lime) and colourless gas ($\ce{CO2}$) is evolved / $\ce{CaCO3(s) ->[Heat] CaO(s) + CO2(g)}$ (1 Mark)
2 g of green coloured crystals of ferrous sulphate are heated in a dry boiling tube. Name the type of chemical reaction taking place. Write the balanced chemical equation for the reaction. Is this an exothermic or an endothermic reaction ?
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• Thermal decomposition reaction • $\ce{2FeSO4(s) ->[heat] Fe2O3(s) + SO2(g) + SO3(g)}$ (deduct ½ mark if no / incorrect balancing) • Endothermic reaction
Account for the following : (a) White silver chloride turns grey when exposed to sunlight. (b) Lead (II) nitrate on heating releases brown fumes. (c) Bags of oil and fat containing food items are flushed with nitrogen gas.
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• $\ce{CaSO4.1/2H2O}$ u2022 373K / 100°C Decomposition of silver chloride (AgCl) to form silver (Ag) $\ce{2AgCl(s) ->[Sunlight] 2Ag(s) + Cl2(g)}$ Decomposition of lead nitrate releases $\ce{NO2}$ / Nitrogen dioxide $\ce{2Pb(NO3)2(s) ->[Heat] 2PbO(s) + 4NO2(g) + O2(g)}$ (Lead nitrate) (Lead oxide) (Nitrogen dioxide) (Oxygen) To prevent the oxidation of fats in food items.
What happens when (i) lead (II) nitrate is heated ? (ii) iron (II) sulphate is heated ? (iii) silver chloride is exposed to sunlight ? Write balanced chemical equations of the reactions involved in support of your answer.
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(i) Brown fumes of nitrogen dioxide are formed. (½ Mark) $\ce{2Pb(NO3)2(s) ->[Heat] 2PbO(s) + 4NO2(g) + O2(g)}$ (½ Mark) (ii) Smell of burning sulphur is observed/ Colour of crystal changes. (½ Mark) $\ce{2FeSO4(s) ->[Heat] Fe2O3(s) + SO2(g) + SO3(g)}$ (½ Mark) (iii) White silver chloride turns grey. (½ Mark) $\ce{2AgCl(s) ->[Sunlight] 2Ag(s) + Cl2(g)}$ (½ Mark) (Note: Award full marks if balanced chemical equation is written)
What happens when (i) Calcium carbonate is heated ? (ii) Silver bromide is exposed to sunlight ? (iii) Lead is added to copper (II) chloride solution ? Write balanced chemical equations of the reactions involved in support of your answer.
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(i) Calcium carbonate decomposes to calcium oxide and carbon dioxide. (½ Mark) $\ce{CaCO3(s) ->[Heat] CaO(s) + CO2(g)}$ (½ Mark) (ii) Silver bromide decomposes to silver and bromine by light. (½ Mark) $\ce{2AgBr(s) ->[Sunlight] 2Ag(s) + Br2(g)}$ (½ Mark) (iii) Lead displaces copper from copper chloride solution. (½ Mark) $\ce{Pb(s) + CuCl2(aq) -> PbCl2(aq) + Cu(s)}$ (½ Mark) (Note: Award full marks if balanced chemical equation is written)
(i) $\ce{AgNO3 + NaCl -> NaNO3 + AgCl}$ (ii) $\ce{K2SO4 + BaCl2 -> BaSO4 + 2KCl}$ Which of the following options clearly describes both the reactions ?
(a)(i) is double displacement, (ii) is displacement reaction.
(b)Both, (i) and (ii) are double displacement reactions and precipitation reactions.
(c)Both, (i) and (ii) are double displacement reactions and precipitation reactions.
(d)(i) is displacement, (ii) is double displacement reaction.
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(C) / Both, (i) and (ii) are double displacement reactions and precipitation reactions. (1 Mark)
What happens when (i) potassium iodide solution is added to lead (II) nitrate solution ? (ii) zinc is added to copper (II) chloride solution ? (iii) hydrogen gas is passed over hot copper (II) oxide ? Write balanced chemical equations of the reactions involved in support of your answer.
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(i) Yellow precipitate of potassium iodide is formed. (1/2) $\ce{2KI + Pb(NO3)2->PbI2 + 2KNO3}$ (1/2) (ii) Zinc will displace copper from copper chloride. (1/2) $\ce{Zn + CuCl2 -> ZnCl2 + Cu}$ (1/2) (iii) The black coating of copper oxide will turn brown. (1/2) $\ce{CuO + H2 -> Cu + H2O}$ (1/2) (Note: Award full marks if balanced chemical equation is written)
Define the following terms : (a) Corrosion (b) Rancidity (c) Double displacement reaction
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(a) The process in which a metal is attacked by substances around it such as moisture, acids etc. (1 Mark) (b) Oxidation of fats and oils present in food resulting in change of its smell and taste. (1 Mark) (c) The reaction in which there is an exchange of ions takes place between the reactants. (1 Mark)
Define the following terms : (i) Corrosion (ii) Rancidity (iii) Exothermic reaction
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(i) The process in which a metal is attacked by substances around it such as moisture, acids etc. (1) (ii) Oxidation of fats and oils present in food resulting in change of its smell and taste. (1) (iii) Reaction in which heat/energy is released along with the formation of products. (1)
Assertion (A) : Reaction of quick lime with water is an exothermic reaction. Reason (R) : A large amount of heat is evolved on the reaction of quick lime and water.
(a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
(b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
(c)Assertion (A) is true, but Reason (R) is false.
(d)Assertion (A) is false, but Reason (R) is true.
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(A)/ Both A and R are true, and R is the correct explanation of A. (1 Mark)