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Chemical Reactions and Equations ( Fastracl« Revision ) > Chemical Change: It is a process of change in which new substances with new properties are Farmed. Some common chemical changes seen in our daily lives are ripening of Fruit, fermentation of Fruit juice, cooking of Food, digestion of food, burning of Fuel, respiration, etc. >» Chemical Reaction: It ls a chemical change In which one or more substances react to form one or more products of entirely different properties by undergoing a change in state, colour, temperature or due to evolution of gas. Rearrangement of atoms also takes place in a chemical reaction. >» Chemical Equation: It is a representation of a chemical reaction in terms of standard symbols and Formulae used for the reactants and the products. It comprises of reactants, products and an arrow (— ) sign. For example, magnesium ribbon burns with oxygen present in the alr to form a white powder of magnesium oxide, which can be represented as: 2Mg + QO, —> 2MgO Magnesium Oxygen Magnesium oxide (Reactants) (Product) > Balanced and Unbalanced Chemical Equations: Equation having an equal number of atoms or masses of various elements in the reactants as well as products is balanced chemical equation but that having an unequal number of both is an unbalanced chemical equation. >» Types of Chemical Reactions: Chemical reactions are of the Following types: » Combination Reaction: It is the reaction in which two or more reactants combine to form a single compound. For example, CaO(s) + H,0(!) —> Ca(OH) (aq) Calcium oxide Water Calcium hydroxide (Quick lime) (Slaked lime) > Decomposition Reaction: It is the reaction in which a single reactant breaks up to give two or more simpler products. These reactions are carried out by applying heat (thermal decomposition), light (photochemical decomposition) or electricity (electrolysis or electrolytic decomposition). For example, CaCO; (s) olla CaO(s) + C€O2(g) Calclum carbonate Calcium oxide Carbon dioxide ZAQCI(s) —SUMUM , 2Ag(s) + Cl, (g) Sitver chloride Silver (White) (Grey) Electric 2H20 (1) —s ae? 2H2 (9) + 02 (9) This reaction is known as electrolysis of water. » Displacement Reaction: It is the reaction in which one element takes the place of another elementina compound. A more reactive element displaces a less reactive element From its compound. For example, Zn(s) + CuSO,(aq) ——+ ZnSO,y(aq) + Cu(s} Zinc Copper sulphata Zinc sulphota Coppermetal (Sllvery-white) (Blue) (Colourtess) (Red-brown) These reactions are also called single displacement reactions. » Double Displacement Reaction: itis the reaction in which anlons and cations of two different reactant molecules interchange their positions to farm two extremely different compounds. For example, Pb(NO3)> (aq) + 2KI(aq) ---- 2KNO3 (aq) + Pbl, (s)L Lead nitrate Potassium Potassium Leadlodide lodide nitrate (Yellow ppt) These reactions are also called precipitation reactions. » Oxidation and Reduction Reactions or Redox Reaction: ® Oxidation: In it, a substance gains oxygen or loses hydrogen during a reaction. @ Reduction: In it, a substance loses oxygen or gains hydrogen during a reactlon. MNEMONICS Concept: Definition of oxidation and reduction Mnemonics: OIL RIG Interpretation: OIL = Oxidation Is Loss (of hydrogen) RIG = Reduction Is Gain (of hydrogen) ® Redox Reaction: In it, oxidation and reduction occur simultaneously. Redox Is the short Form of Reductlon-oxidation. Reduction CuO +H, —~+ Cu+H,0 Lo Oxidation » Exothermic Reactions: These are the reactions in which heat Is released along with the formation of products. For example, respiration. >» Endothermlc Reactions: These are the reactions in which heat Is absorbed along with the Formation of products. For example, melting of ice to form water. > Corrosion: It is the process of slow conversion of metals into their undesirable compounds by the action of molsture, water, acids and air. It causes damage to car bodles, bridges, iron railings, ships and other metal objects of daily use. The Formation of rust (reddish brown coating of hydrated iron (Ill) oxide, Fe,;O4.xH,O) on iron, green coating on copper and black coating on silver are all examples of corrosion. Corrosion can be prevented by applying a layer of ail and grease, or coating the iron article with a thick layer of zinc (Galvanisatlon). >» Rancidity: It is the phenomenon in which food items containing oils and fats when exposed to alr give an ren Practice Exercise unpleasant smell and taste. This is due to oils and Fats present in the food items getting oxidised by air, heat and Ught. The methods to prevent rancidity are: > > » Keeping Food in air-tight containers. By adding antloxidants to Food. By packaging Fat and oil containing food with nitrogen. “@) Multiple Choice Questions YQ QL Q2. Q 3. Q4. Q5. Q6. In which of the following process a chemical reaction has taken place? a. Ice melts Into water b. A wet shirt got dried in sunlight c A brown layer is formed over iron rod kept in air d. Sugar getting dissolved in water In which of the following, the identity of initial substance remalns unchanged? (CBSE 2020) a. Curdling of milk b. Formation of crystals by process of crystalUsation c. Fermentation of grapes d. Digestion of food Which of the following condition help us to determine that a chemical reaction has taken place? a. Evolution of gas b. Farmation of precipitate c. Change in colour d. All of the above Which of the following feature(s) is involved in a properly written chemical equation? a. Temperature is required b. It should be balanced c. It should have information regarding physical states d. All of the above Why is it important to balance a skeletal chemical equation? (CBSE SQP 2021 Term-1) a. To verify the law of canservation of energy. b. To verify the law of constant proportion. c. To verify the law of conservation of mass. d. To verify the law of conservation of momentum. It is important to balance the chemical equations to satisfy the law of conservation of mass. Which of the following statements of the law is incorrect? (CBSE 2021 Term-1) a. The total mass of the elements present In the reactants is equal to the total mass of the elements presents in the products. b. The number of atoms of each elements remains the same, before and after a chemical reaction. c. The chemical composition of the reactants Is the same before and after the reaction. d. Mass can neither be created nor can it be destroyed In a chemical reaction. Q7. Q8. Q9. Qo. Qu. Q iz. Q13. Which of the following correctly represents a balanced chemical equation? (CBSE SQP 2021 Term-1) a. Fe(s) + 4H30(g) ——> Fe3Q, (s) + 4H2(g) b. 3Fe(s) + 4H,0(g) —- Fe30, (s) + 4H3(g) c. 3Fe(s) +Hz0(g) —> Fe30, (5) + H2(g) d, 3Fe(s) + 4H,0(g) —-+ FeO, (s) + H2(Q) When aqueous solutions of potassium iodide and lead nitrate are mixed, an insoluble substance separates out. The chemical equation for the reaction involved is: (CBSE 2023) a. Kl+PbNO; —» Pbl+KNO; b. 2KI+Pb(NO3)2 —> Pbl, + 2KNO5 c. Kl+Pb(NOs)> ——> PbI+KNO3 d. Kl + PhNO3 Pbl; + KNO3 In order to balance the following chemical equation, the values of the coefficients x and y respectively are: (CBSE 2023) Heat xPb(NO;); ———— 2Pb0 + yNO, + 0, a. 2.4 bed? eas d. 4,2 The chemical reaction between copper and oxygen can be categorised as: (COSE 2021 Term-1) a. displacement reaction b. decamposition reaction c. combination reaction d. double displacement reaction During electrolysis of water, if the volumes of oxygen and hydrogen evolved at the electrodes are Vj and V, respectively, then Vo/V, is: ed (CBSE 2023) a.4 b. 2 & a) d. Z 2 4 Which one of the following reactions is categorised as thermal decomposition reaction? (COSE 2021 Term-1) a. 2H20(() —> 2H>2(g) + 02(g) b. 2AgBr(s) —-> 2Ap(s) + Br3(g) c. 2AgCl(s) —> 2Ag(s) + Cl3(g) d. CaCO3(s) —> CaQ(s) + CO3(g) Heated Limestone Sai X + COz HZ0 Step 2 Sloked limo Q 26. Q 27. On PWN = wom a 10. Nl. T2. 4. 15. 16. 17. 18. 13. 20. 21. 22. Assertion (A): 2H,S(g) + O3(g) — 2S(s) + 2H,O(() is a redox reaction. Reason (R): In this reaction, oxidation of H,S to S and reduction of O, to H,0 takes place. Assertion (A): Rusting can be prevented by applying a layer of oil and grease. Reason (R): The whole of iron deteriorates due to rust. Assertion (A): Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised. Reason (R): This increases the taste of the chips and helps in their digestion. Q 28. Answers | Vv (c) A brown layer is formed over iron rod kept in air (b) Formation of crystals by process of crystallisation (d) All of the above (d) AU of the above (c) To verify the law of conservation of mass. (c) The chemical composition of the reactants Is the same before and after the reaction. (b) 3Fe(s) + 4H,O(g) ——> Fes0, (s) + 4H(g) (b) 2KI + Pb (NO3)>——> Pbly + 2KNO5 (a) 2.4 2Pb(NO3)» —> 2PbO + 4NO) + O05 Hence, x= 2 and y=4. (c) Combination reaction 2Cu + 03 —> 2Cu0 Here, two substances combine to form a single substances. thus. it is a combination reaction. (c) V2 (d) CacO3(s) —+ CaO(s) + CO3(g) Reaction (a) takes place In the presence af electricity. (b) and (c) are carried out by the action of light energy. Decomposition af calcium carbonate. ie. (d) is carried out by heating, thus. it is a thermal decomposition reaction. (c) Endothermic Exothermic / ¥ (b) Only (il) (d) (il) and (Iv) (b) X= Mg: Y= MgO; Type of reaction = Combination 2Mg + 0, —> 2MgO (x) (¥) As two or mare substances combine to form a new single substance. therefore. it is a combination reaction. (b) Barium sulphate NasS0,+BaCl) —» 8aSO, + 2NaCl (Sodium (Barium (Garium sulphate) — chlaride) sulphate) (a) Substance oxidised-Fe. Reducing agent-Fe In this reaction. substance oxidised = Fe. substance reduced «= CuSO, oxidising agent « CuSOQ,, Reducing agent = Fe (b) MnO; Is reduced to MnCl, and HCl Is oxidised to Cl. (d) Helum or Nitrogen (d) Assertion (A) Is false but Reason (R) is true. Assertion (A) is false because rusting of iron is an exothermic reaction. (d) Assertion (A) is false but Reason (R) is true. Assertion Is false because burning of natural gas is an exothermic reaction. 23. (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). 24. (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). (c) Assertion (A) is true but Reason (R) is false. Reason (R) is false because light provides energy for photochemical decomposition reactlan. (a) Both Assertion (A) and Reason (R) are true and Reason (R) Is the correct explanation of Assertion (A). 27. (b) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A). 28. (c) Assertion (A) is true but Reason (R) Is false. Reason (R) is false because this process prevents the chips from getting rancid. -@ Case Study Based Questions y Case Study 1 Rishabh wanted to study displacement reactions. He knows that he needs a metal and a salt solution of a different metal. So, he takes two tubes 7, and T,, out of which in 7|, he placed a copper wire in iron sulphate solution and in 73, he placed an iron nail in copper sulphate solution as shown below: * r > rc 25. 26. +<—— Toast tubo +—— Tas! tubo —— Iron nail [— Copper wiro <—,— Copper sulphate solution Iron sulphate solution Ty T2 Read the above passage carefully and give the answer of the following questions: Ql. Based on the above passage which test tube will undergo displacement reaction? a. Ty b. Tz c. Both T, and T, d. Neither T, nor T, Q2. Identify the balanced chemical equation for reaction taking place in Tj. a. Fe(s)+ CuCl, (aq) —-— FeCl, (ag) + Cu(s) b. Cu(s)+FeSO, (aq) —-— No reaction c Fe(s)+ CuSO, (aq) ——> FeSO, (aq) + Cu(s) d. Pb(s)+ CuSO, (aq) —-— PbSO, (aq) + Cu(s) Q 3. State the change(s) that is/are observed In T}. a. White precipitate of FeSO, is farmed b. The blue colour of CuSO, changes to light green colour af FeSO, c Brown coating of copper is obtained on Iran nail d. Bath b. and c. Q4. What will happen if zinc wire is used in place of copper wire in T,? a. tt will produce zinc sulphate solution and copper metal b. It will produce zinc sulphate solution and Iron metal c It will produce Iron sulphate solution and zinc metal d. No reaction will take place Q5. What will happen if silver nitrate is used in place of iron sulphate in T,? a. No reaction will take place b. It will produce copper nitrate and iron metal c It will praduce copper nitrate and silver metal d. It will produce iron nitrate and silver metal - Answers ° 1. (b) T> 2. (c) Fe(s)+CuSO, (ag) — FeSO, (aq) + Cu(s) 3. (d) Both b. and c. 4. (b) It will produce zinc sulphate solution and Iron metal 5. (c) It will produce copper nitrate and silver metal Cu + 2AgNO3; —-> Cu(NO3), + 2Ag Case Study 2 Marble’s popularity began in ancient Rome and Greece, where white and off-white marble were used to construct a variety of structures, from hand- held sculptures to massive pillars and buildings.
Usually students get confused in the tests performed to detect different gases. “Q Very Short Answer type Questions y QL Ans. Q2. Ans. Q3. Ans. Q4. Ans. Q5. Ans. Q6. Ans. Q7. Ans. Q8. Ans. Which one is a chemical change-Rusting of iron or melting of iron? Rusting of Iron is a chemical change. Why is respiration considered as an exothermic reaction? Respiration results In oxldatlon of glucase which produces heat energy. So, it is an exothermic reaction. A magnesium ribbon Is burnt In oxygen to give a white compound X accompanied by emisslon of light. Write a balanced chemical equation, when X is dissolved in water. (NCERT EXEMPLAR) The balanced chemical equation is: MgO + H;0 ---— Mg(OH), (X) (Water) (Magnesium wwodroxide) Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and Identify the type of reaction. (NCERT EXEMPLAR) 2FeSO, (s) 8" Fe303 (5) + S05 (g) +505 (g) It Is a thermal decomposition reaction. Why do we store silver chloride in dark-coloured bottles? (NCERT EXEMPLAR) We store silver chloride In dark-coloured bottles to prevent its decomposition In the sunlight. Identify the products formed when potassium lodide is added to lead nitrate solution. Also, name the compound precipitated. Potassium nitrate (KNO3) and lead lodide (Pbl,) are produced. The compound precipitated Is lead lodide (yellow ppt). The surface of copper gets coated with black copper (Il) oxide. Why? The surface of copper turns black. when kept exposed to alr, due to its reaction with oxygen making black capper (Il) oxide. Indicate the oxidising and reducing agent in the reaction. H,S+Cl, —-> 2HCL+S HaS + Cly ss» ZHCL + S (Hycrogen (Hydrochloric sulphide) acid) Oxidising Agent— Cl, Reducing Agent— H,5 -@) Short Answer Type-! Questions YQ QL Ans. “Dil. HCL is added to Zn granules.” How will you prove that chemical change has taken place here? Support your response with two arguments. (CBSE SQP 2023-24) A chemical change has taken place can be proved with the help of following two arguments: (i) Evolution of a gas: When dilute HCl is added to Zn granules in a test tube, a colourless and odourtess gas Is evolved with bubbles. (ii) Change in temperature: It is an exothermic reaction and temperature of the test tube increases. Q2. Ans. Q3. Ans. Q4. Ans. Q5. Aclear solution of slaked lime is made by dissolving Ca(OH), in an excess of water. This solution is left exposed to air. The solution slowly goes milky as a faint white precipitate forms. Explain why a faint white precipitate forms, support your response with the help of a chemical equation. (CBSE SQP 2022-23) Slaked Ume (calclum hydroxide) reacts slowly with carbon dioxide present in the air to form calcium carbonate which results in milkiness or white ppt. Ca(OH)2 (aq) + COz (g) —> CaCO; (s) + H20 (0) (Slaked (White ppt) lime) Which among the following changes are exothermic or endothermic in nature? (NCERT EXEMPLAR) (i) Decomposition of ferrous sulphate (ii) Dilution of sulphuric acid (iii) Dissolution of sodium hydroxide in water (iv) Dissolution of ammonium chloride in water (ii) and (ii) are exothermic as heat Is released in these changes. (i) and (iv) are endothermic as heat Is absorbed In these changes. (i) Write two observations when lead nitrate is heated in a test tube. (ii) Name the type of reaction. (i) The compound turns yellow due to formation af lead oxide and reddish brown furnes evolve due to formation of nitrogen dioxide. (i) It is a thermal decomposition reaction. What Is the difference between displacement and double displacement reactions? Write equations for these reactions. . Ina displacement reaction, a more reactive element displaces aless reactive element fram its compound. While. in a double displacement reaction. two atoms or a group of atoms interchange their positions to form new compounds. For example: Displacement reaction: CuSO, (aq) + Zn (5) —> ZnSO, (oq) + Cu (5) Double displacement reaction: Na>S0, (aq) + BaCl, (ag) —> BaSO, (s) + 2NaCl (aq) COMMON ERROR: Students get confused between the displacement and double displacement reactions and interchange thelr definitions. Q6. Ans. What is observed when aqueous solutions of potassium iodide and lead nitrate are mixed together? Name the type of reaction and write the chemical equation for the reaction that occurs. (CBSE 2023) When aqueous solutions of potassium iodide and lead nitrate are mixed together a yellow precipitate of lead lodide Is observed. Itls a double displacement and precipitation reaction. Pb(NO,),+2KI—> Pbl,(L) +2KNO, (yoilow ppt} Q7. When copper powder is heated In a watch glass, a Ans. Q8. Ans TiP: Learn the definition of reducing agents. Reducing agents are those substances which have the ability of adding hydrogen or removing oxygen from other substances. black substance Is formed: (i) Why is this black substance formed? Name it. (ii) How can this black substance be reversed to its original form? (CBSE 2023) (i) This black substance is formed because oxygen Is added to copper powder and copper oxide (black substance) Is formed. (ii) If hydrogen _gas is passed over this black substance (CuO). the black coating on the surface turns brown as the reverse reaction takes place and orlginal form (copper) Is obtained. Identify the reducing agent in the following reactions: (i) HO + Fy —-~-—» HF + HOF (il) Fe,0; +3CO —--— 2Fe + 3C0, Q9. Ans. (i) Water (H20) as F3 is getting reduced to HF. (i) Carbon monoxide (CO). Identify the oxidising agent In the following reactions: (i) Pb,0, + 8HCL—-— 3PbCI, +Cl, + 4H,0 (il) 2Mg + 0, —-—> 2MgO (i) Pb30, (ii) O2 ERROR - agent and reducing agent In a reaction. COMMON [st students get confused between the oxidising 1 a @ Q Ans. Learn the concept of skeletal chemical equation and also, the difference between skeletal and balanced chemical equations. 1. Short Answer Type-!i Questions N What Is meant by skeletal type chemical equation? What does it represents? Using the equation for electrolytic decomposition of water, differentiate between a skeletal chemical equation and a balanced chemical equation. TIP: A chemical equation In which the number of atoms of reactants is not equal to the number of atoms of products Is called a skeletal chemical equation. Q 8. Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions. (i) Zine reacts with silver nitrate to produce zinc nitrate and silver. (ii) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide. (CBSE 2019) Ans. (i) This is a displacement reaction. Zinc being more reactive than silver displaces it from its salt Zn(s) + 2AgNO, (aq) — Zn(NO,), (aq) + 2Ag (s) Zinc Silver nitrate Zinc nitrate Silver (il) This Is a double displacement reaction because mutual exchange of lons takes place between the reactants. 2KI (aq) Potassiurn lodide + Pb(NO3)> (aq) Lead nitrate + 2KNO, (aq) + Pbl, (s) Potassiumnitrate Leadiodide (Yellow ppt) COMMONJERR()R - Students aften write unbalanced chemical equations. Many of them foil to write correct chemical formula of zinc nitrate or lead lodide. Q 9. Write down the balanced chemical equations for the following reactions and identify the type of reaction in each case. (i) Nitrogen gas is treated with hydrogen gas to form ammonia gas. (ii) Lead nitrate is heated strongly to form lead monoxide, nitrogen dioxide and oxygen. (iii) A copper wire is dipped in silver nitrate solution and a shining deposit of silver Is produced. (CBSE 2023) Ans. (i) Na(s) + 3H2(g) —> 2NH3(g) Type of reaction: Combination reaction 2Pb(NO,),(s) "4 2PbO(s) + 4NO, (9) + 0,(g) Type of reaction: Decomposition reaction. (iii) Cu(s) + Z2AgNO3(aq) —> 2Ap(s) + Cu(NO3)2(aq) Type of reaction: Displacement reaction. COMMON ERROR . Many students forget to answer the type of chemical reactions in this question. Q10. Write the chemical equation of the reaction in which the following changes have taken place with an example of each: (i) Change in colour. (ij) Change In temperature. (iii) Formation of precipitate. (CBSE 2015) Ans. (|) Fe(s) + CuSO,,(0q) —> FeSO, (aq) +Cu (s) The blue colour of solution changes to light green. (il) CaQ(s) + H0(() —> Ca(OH), (aq) + Heat The temperature Increases because heat Is evolved. (lll) Pb(NO5)5(aq)+ 2KI(aq)—+ Pbl,(s) + 2KNO5(aq) Lead nitrate Lead iodide (Yellaw ppt) Yellow precipitate of Pbl, is formed. QU. Name the type of chemical reaction represented by the following equations: (i) CaO + HJO ——> Ca(OH), (ii) 3BaCl, + Al, (SO,); ——> 2AlCL, + 3BaSO, (iii) 2FeSO, > Fe, 0; + SO, + SO; Ans. The type of chemical reactlons are as follows: (i) Combination reaction. () Double displacement reaction. (iii) Decomposition reaction. Q12. (i) Write the essential condition for the following reaction to take place: 2AQgBr ~---——> 2Ag + Bry Write one application of this reaction. (ii) Complete the following chemical equation of a chemical reaction: (CBSE 2015) Heat 2FesO, ——? Fe,0; FH cessnsenes FH pn snnnneae (iii) What happens when water is added to quick lime? Write chemical equation. (CBSE 2015) Sunlight Ans. (i) 2Ag8r » 2Ag + Br, Sunlight is required to decompose silver bromide Inte silver and bromine. This reaction Is used photography. in black and white (ii) 2FeSO,(5) <2» Fe,05(s) + S05 (g) + S05 (g) (iii) Slaked lime is formed with hissing sound and a large amount of heat |s evolved. CaO + H30 —-—» Ca(OH); + Heat (se ERROR: | Usually students get confused in the essential conditions and liberation of gases in the reaction. Q13. On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, a white precipitate is obtained. (1) Write a balanced chemical equation of the reaction involved. (ii) What other name can be given to this precipitation reaction? (iii) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why? (i) Balanced Chemical Equation: Na,SO3(ag) + BaCl;(aq) Sodium sulphite Barium chloride —-— BaSO3(s) + 2NaCl(oq) Barium sulphite Sodium chloride Ans. (il) This precipitation reaction is also known as double displacement reaction. (iil) BaSO5 is a salt of weak acid (H3S0;), therefore dilute HCl decomposes barium sulphite to produce sulphur dioxide gas which has the smell of burning sulphur. BaSO3(s) + 2HC\(aq) —+ BaCl (s) + H,O(l) + SO2(g) (White ppt) Barium chloride BaCl, Is soluble In water, precipitate disappears. hence white Q 14. You might have noted that when copper powder is heated ina 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. Ans. (I) When copper powder [s heated, It reacts with oxygen to form copper oxide which Is a black colour substance. (ii) The black substance Is copper oxide. (iti) Chemical Reaction: 2Cu(s) + O2(g) —> 2Cu0(s) 6 0®:@—> ©-© @:O—-@:@ Identify the types of reaction mentioned above in (i) and (ii). Give one example for each type in the form of a balanced chemical equation. (CBSE SQP 2022-23) Ans. (i) Displacement reaction. Example : Fe(s) + CuSO,,(aq) —> FeS0,,(aq) + Cu(s) (ii) Double displacement reaction Example : Na,SO, (aq) + BaCl;(aq) —+ BaSO,(s) + 2NaCl(aq) Q16. Mention with reason the colour changes observed when: (i) Silver chloride Is exposed to sunlight. (ii) Copper powder is strongly heated in the presence of oxygen. (iil) A plece of zinc Is dropped In copper sulphate solution. (CBSE 2020) Ans. G- TIP: [ Learn and understand the basic concepts of each type of chemical reaction and make a list of few examples for each. (I) White silver chloride turns grey due to the decomposition of silver chloride into silver and chlorine by sunlight. (li) A black coating Is farmed on the surface of brown copper powder because oxygen Is added to copper and copper oxide is formed. (ll) When a piece of zinc Is dropped in CuSO, solution, zinc being more reactive displaces copper from CuSO, and forms ZnSO, solution. During this process, the colour of the solution changes from blue to Light green. Q17. When potassium iodide solution is added to a solution of lead(Il) nitrate in a test tube, a precipitate is formed. (i) What Is the colour of this precipitate? Name the compound precipitated. (ii) Write the balanced chemical equation for this reaction. (iii) List two types of reactions in which this reaction can be placed. (CBSE 2019) Ans. (|) The colour of the precipitate formed is yellow and the compound precipitated is lead iodide Pbl,). (i) The balanced chemical equation for this reaction is: Pb(NO3)5 + 2K] —-—> Pbl> + 2KNO3 Leadill) Potassium Lead Potassium nitrate lodide lodide nitrate (Yellow ppt) (iii) The two types of reactions in which the given reaction can be placed are: (a) Precipitation reaction. (b) Double displacement reaction. Q18. What is redox reaction? Identify the substance oxidised and the substance reduced in the following reactions: (i) 2PbO + C —-> 2Pb+ CO, (ii) MnO, + 4HCL_—> MnCl, + 2H,0 + Cl, Ans. The reaction in which oxidation and reduction take place simultaneously Is called redox reaction. Practice a number af questions based an identifying oxidising and reducing agents. (i) Substance Oxidised: C Substance Reduced: PbO (ll) Substance Oxidised: HCL Substance Reduced: MnO, (iv) CoHa(g) + 302(g) —> 2C02(g) + 2H20(q) Ethylene + Heat + Light It ls a redox reaction/combustion reaction. (v) 2Cu (NO3)2(5) = 2CuO(s) + Op(g) + 4NO;(g) It Is a decomposition reaction. Q4. (i) Balance the following chemical equations: (a) NaOH + H,SO, > Na,SO, +H,0 (b) PbO + C———> Pb + CO, (c) Fe,0; + Al—-—- Al,0; + Fe + Heat (ii) Write the balanced chemical equations for the following reactions: (a) Barium chloride + Potassium sulphate — Barium sulphate + Potassium chloride (b) Zinc + Silver nitrate —-> Zinc nitrate + Silver (CBSE 2017) Ans. (i) (a) 2NaQH +H3S0,. += » Na,S0,+2H;0 (b) 2PbO +C =» 2Pb+C0; (c) Fe,03 + 2Al—--» Al,03+2Fe + Heat (li) (a) BaCl, +K,S0, ———> BaSO, +2KCI (b) Zn + 2AgNO, ——> Zn(NO3)>+2Ag Q5. (i) Identify the type of reactions taking place In each of the following cases and write the balanced chemical equations for the reactions. (a) Barium chloride solution is mixed with copper sulphate solution and a white precipitate Is obtained. (b) On heating copper powder in air, the surface of the copper powder turns black. (ii) What happens when hydrogen gas is passed over the heated copper oxide? Write the chemical equation involved in this reaction. Ans. (i) (a) The reaction ts double decomposition reaction. Chemical Equation: BaCl, (aq) + CuSO, (aq) ——-> BaSO,(s) + CuCl,(aq) (b) The reaction is a cambination/redox reaction. He Chemical Equation 2Cu + 02 =. 2Cu0 (ii) If hydrogen gas is passed over heated copper oxide (CuO), the black coating on the surface turns brown as the reaction takes place between CuO and H2 gas and copper Is obtained. Cutis; S, tuto (Black) (Brown) Q 6. Ametal nitrate A on heating gives yellowish brown coloured metal oxide along with brown gas Banda colourless gas C. Aqueous solution of A on reaction with potassium iodide forms a yellow precipitate of compound D. Identify A, 8, C and D. Also identify the types of both the reactions. Metal present in A is used In alloy which is used for soldering purposes. Ans. Metal nitrate ‘A'ls Pb (NO3)> 2Pb (NO3)2 (5) > 2PbO (s) + 4NO, (g) + 0» (9) Lead nitrate Load (U) oxide Nitrogen Oxygen a (Yellowish dlaxide (Colourless) brown) (Brown) AG # Pb (NO3)3 (oq) + 2KI (aq) ——> Pblz(s) + 2KNO3(0q) A Potassium Leed Potassium iodide iodide nitrate (Yellow ppt) DO So, A’ is lead nitrate , ‘6 is nitrogen dioxide, ‘C Is oxygen and 'D’ Is lead iodide. Here. the first reaction Is decomposition reaction while the second one Is double displacement reaction or a precipitation reaction. Q7. (i) Explain the following terms with one example each: (a) Corrosion (b) Rancidity (ii) Explain two ways by which food Industries prevent rancidity. ns. TiP- Carefully understand the concept of corrosian ond rancidity with examples. A (i) (a) Corrosion: It is a natural process in which metals are slowly eaten up by the action of alr. moisture or chemicals. For example, rusting is a form of corrosion in which iron is eaten up by the action of air and moisture and a reddish brown coating of iron oxide Is formed as shown in the following chemical reaction. 2Fe(s) + 3H,0 (1) —-— Fe,03 (s) + 3H, (9) (b) Rancidity: When the substance containing oils and fats are exposed to air, they get oxidised and become rancid due to which thelr smell taste and colour change. This process is known as rancidity. For example, when butter Is kept open for a long time. then its smell and taste gets changed. (ii), Rancidity can be prevented in the following ways: (a) By adding antioxidants to food contalning fats and oils. (b) By filling nitrogen gas to the packaging of fat and oll containing foods. COMMONJERR()R (s tudents often give wrong ways to prevent rancidity. oy Chapter Test Multiple Choice Questions Q1. Inthe given equation, Cu + XHNO; —> Cu(NO;), + YNO, + 2H,0 The values of X and Y are: a. 3and5 b. 8and 6 c 4and2 d. Zand] Q2. When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and sulphuric acid is formed in the solution. The reaction is an example of: a. combination reaction b. displacement reaction c. decomposition reaction d. double displacement reaction Q3. Which among the following statement(s) Is/are true? Exposure of silver chloride to sunlight for a long duration turns grey due to: (i) the formation of silver by decomposition of silver chloride (il) sublimation of silver chloride (iii) decomposition of chlorine gas from silver chloride (iv) oxidation of silver chloride a. Only (i) b. (I) and (iil) c (ii) and (iii) d. Only (iv) Q4. Identify the substance that is oxidised and the substance that is reduced in the following reaction: CuO(s) + Hz(g) —> Cu(s) + H,O0(!) a. Cud, H> b. H2, Cu0 c. H20, Cu d. Cu, H2O Assertion and Reason Type Questions Directions (Q. Nos. 5-6): Each of the fallowing questions consists of tvo statements, one is Assertion (A) and the other Is Reason (R). Give answer: a. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). b. Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A). c Assertion (A) is true but Reason (R) is false. d. Assertion (A) Is false but Reason (R) Is true. Q5. Assertion (A): Reaction between sodium sulphate and barium chloride is a double displacement and precipitation reaction. Reason (R): Reaction between sodium sulphate and barium chloride Involves the exchange of lons between the reactants and a white precipitate of barium sulphate is formed. Q6. Assertion (A): Quicklime reacts vigorously with water releasing a large amount of heat. Reason (R): A solution of quicklime is used for whitewashing walls. Case Study Based Question Q7. Reactions in which one element takes place of another element in a compound, are known as displacement reactions. In general, more reactive elements displaces a less reactive element from its compound. In all single displacement reactions, only one element displaces another element from its compound. The single displacement reactions are, however, written as just displacement reactions. Read the above passage carefully and give the answer of the following questions: (i) Copper displaces which of the following metals from its salt solution? a. ZnSO, b. FeSO, c. AgNO; d. Pb(NOS), (ii) During the experiment of dipping iron nail in copper sulphate solution, four students recorded their observation as: (A) green colour of CuSO, changes to blue colour of FeSO, (B) red brown coating Is formed on Iron nail (C) deep blue colour of CuSO, changes to Ught green colour of FeSO, (D) Greyish white coating is formed on iron nail Which of the above observations are correct? a. (A) and (B) b. (A) and (0) c. (B) and (C) d. (C) and (D) (iii) Which of the following reactions is a displacement reaction? a. CaO + H;0 —-+ Ca(OH), b. MgCO;-—> Mg + CO, c. Mg + CuSO, —> MgSO, + Cu d. H> + C1;—> 2HCL (iv) A strip of copper was placed In a beaker containing zinc sulphate solution. On observing the strip next day, it was noticed that: a. colour of copper strip has changed b. copper strip became thicker c. copper strip became thinner d. copper strip remained as It was 
