MG SCHOOL SCIENCE
Class 10 Science
Chapter 1
Chemical Reactions and Equations
10Source pages
5Question groups
Class 10Science
Study tip: Open each page section to read the questions and answers. Use the search box to find topics such as oxidation, rancidity, displacement reaction, balancing equations and electrolysis.
Chapter questions and answers
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Class 10 Science - Chapter 1 Chemical Reactions and Equations Multiple Choice Questions 1. The metal that displaces copper from copper sulphate solution is (A) mercury (B) gold (C) iron (D) silver Ans. : (C) iron 2. The gas liberated at the cathode in the electrolysis of water is (A) Oxygen (B) Hydrogen (C) Chlorine (D) Nitrogen Ans. : (B) Hydrogen 3. Fe2O3 + 2 Al →Al2O3 + 2 Fe The type of above chemical reaction is (A) combination reaction (B) double displacement reaction (C) decomposition reaction (D) displacement reaction Ans. : (D) displacement reaction 4. The reactants that exchange ions by reacting with each other and form a precipitate among the following are (A) BaCl2 and Na2SO4 (B) Al2O3 and HCl (C) NaOH and H2SO4 (D) Na2O and CO2 Ans. : (A) BaCl2 and Na2SO4 5. Chips manufacturers, flush bags of chips with nitrogen gas because, to (A) prevent corrosion of chips (B) prevent chips from getting oxidised (C) make chips undergo rancidity (D) prevent the chips from getting reduced Ans. : (B) prevent chips from getting oxidised 6. A type of chemical reaction in which a single product is formed by two or more reactants is (A) chemical decomposition
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(B) chemical combination (C) chemical displacement (D) chemical double displacement Ans. : (B) chemical combination 7. Ferrous sulphate crystals lose green colour when heated. Because this compound (A) decomposes into simpler products (B) loses water molecules (C) releases sulphur dioxide gas (D) produces brown fumes Ans. : (B) loses water molecules 8. In the electrolysis of water the gases that are released at cathode and anode and their ratio respectively are, (A) Hydrogen:Oxygen ; 1:2 (B) Oxygen:Hydrogen ; 2:1 (C) Hydrogen : Oxygen ; 2:1 (D) Oxygen : Hydrogen ; 1:2 Ans. : (C) Hydrogen : Oxygen ; 2:1 9. The electrolysis of water to form hydrogen and oxygen gases is (A) an endothermic reaction (B) a displacement reaction (C) an exothermic reaction (D) a redox reaction Ans. : (A) an endothermic reaction 10. The reactants that exchange ions by reacting each other and form a precipitate among the following are (A) Aluminium oxide and hydrochloric acid (B) Sodium hydroxide and sulphuric acid (C) Aluminium oxide and hydrochloric acid (D) Barium chloride and sodium sulphate Ans. : (D) Barium chloride and sodium sulphate 11. ZnO + C →Zn + CO ; the reactants that are oxidised and reduced in this chemical reaction respectively are (A) ZnO and C (B) C and ZnO (C) Zn and CO (D) CO and Zn Ans. : (B) C and ZnO 12. 2AgCl →2Ag + Cl2; the type of this chemical reaction is (A) Combination reaction (B) Displacement reaction (C) Decomposition reaction (D) Double displacement reaction Ans. : (C) Decomposition reaction 13. The gas flushed to the bags containing chips is
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(A) Hydrogen (B) Oxygen (C) Chlorine (D) Nitrogen Ans. : (D) Nitrogen 14. In this chemical reaction [CuO + H2 →Cu + H2O], (A) hydrogen is reduced to form water (B) exchange of ions took place between the reactants (C) copper oxide is oxidised to form copper (D) copper oxide is reduced to form copper Ans. : (D) copper oxide is reduced to form copper 15. Zn + CuSO4 →ZnSO4 + Cu The above reaction is an example for (A) Endothermic reaction (B) Precipitation reaction (C) Displacement reaction (D) Double displacement reaction Ans. : (C) Displacement reaction 16. Analyse the experiment expressed in the above figure. The molecular formulae of the solution 'Y' that gives a yellow colour precipitate by reacting with KI solution and the another product that forms here respectively are (A) Pb(NO3)2 and KNO3 (B) PbI2 and KNO3 (C) Pb(NO3)2 and KI (D) Pb(NO3)2 and K2SO4 Ans. : (B) PbI2 and KNO3 17. Silver chloride turns grey when exposed to sunlight. This is because silver chloride (A) decomposes to form silver. (B) decomposes to form chlorine. (C) combines with oxygen. (D) reacts with atmospheric moisture. Ans. : (A) decomposes to form silver. 18. Observe the following chemical equations. Identify the correct statement CuSO4 + Fe →FeSO4 + Cu 2AgNO3 + Cu →Cu(NO3)2 + 2Ag (A) Copper is more reactive than iron and silver (B) Iron is less reactive than copper and silver (C) Copper is more reactive than silver but less reactive than iron (D) Silver is more reactive than copper and iron. Ans. : (C) Copper is more reactive than silver but less reactive than iron 19. An example for the chemical change among the following is (A) Dissolving of salt in water (B) Tearing of paper (C) Rusting of iron
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(D) Boiling of water Ans. : (C) Rusting of iron One Mark Questions 1. ZnO + C →Zn + CO In this reaction name the reactant i) that is oxidised and ii) that is reduced. Ans. : Oxidised reactant is : C Reduced reactant is : ZnO. 2. Manufacturers of chips, flush the packets of chips with nitrogen gas. Why? Ans. : To prevent the chips from getting oxidised. OR To prevent rancidity. 3. CuO + H2 →Cu + H2O In this reaction name the reactant i) that is oxidised ii) that is reduced. Ans. : i) Hydrogen or H2 ii) Copper Oxide or CuO. 4. Oil and fat containing food items are flushed with nitrogen. Why? Ans. : Nitrogen is an inert gas, hence it acts as antioxidant and prevents the oils and fats from oxidation. 5. Packets of chips are flushed with nitrogen gas. Why? Ans. : To prevent chips from getting oxidised / to prevent rancidity. 6. An iron nail is dropped into a test tube having copper sulphate solution. The iron nail gradually turns to brownish colour. Why? Ans. : Since iron is more reactive than copper, it displaces copper from copper sulphate solution / Displaced copper gets deposited on the iron nail. 7. Name the product produced when calcium oxide reacts with water. Ans. : Calcium hydroxide 8. What are redox reactions ? Ans. : A chemical reaction in which one reactant gets oxidised while the other gets reduced is called redox reaction. 9. How can rancidity be controlled? Ans. : • Adding antioxidants to food. • Keeping food in refrigerator. • Storing food in airtight containers. • Packaging food and oil in Nitrogen Gas. 10. How is rancidity prevented in foods containing fat or oil ? Ans. : • Adding antioxidants • Storing in airtight containers • Flushing gases like nitrogen into the packets containing fried foods. (Any two) 11. Which ions produce a white precipitate when the solution of sodium sulphate is added to the solution of barium chloride? Ans. : Ba^2+ and SO4^2- 12. What is the reason for the formation of brown coloured fume in the experiment shown through the below given figure? Ans. : Due to the evolution of nitrogen dioxide gas by the decomposition of lead nitrate
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13. What is rancidity? Ans. : The process by which fat and oil substances are oxidized, changing their smell and taste, is called rancidity. 14. Observe the given equation. Which numbers respectively will be in the positions W, X, Y and Z when this equation is balanced ? Ans. : 2, 2, 4, 1. Two Marks Questions 1. Draw the diagram of the arrangement of apparatus used to show the electrolysis of water and label the 'graphite rod'. Ans. : [Diagram of Electrolysis of water with labelled parts: Cathode, Anode, Graphite rod, Water, Plastic mug, Test tube, Oxygen, Hydrogen]. 2. The chemical reaction that takes place between sodium sulphate and barium chloride is called double displacement reaction. Why ? Write the balanced chemical equation for this reaction. Ans. : • There is an exchange of ions between the reactants sodium sulphate and barium chloride. • Na2SO4 + BaCl2 →BaSO4 + 2NaCl 3. What is the type of chemical reaction in which quicklime is obtained by lime stone (calcium carbonate)? Write a chemical equation for this reaction. Ans. : • Decomposition reaction or thermal decomposition reaction / endothermic reaction. • CaCO3 --Heat-->CaO + CO2 4. Write the balanced chemical equation for the following reactions : (i) Hydrogen + Chlorine →Hydrogen chloride (ii) Sodium + Water →Sodium hydroxide + Hydrogen. Ans. : (i) H2 + Cl2 →2HCl (ii) 2Na(s) + 2H2O(l) →2NaOH(aq) + H2(g) 5. Name the brown fumes liberated when lead nitrate is heated. Write the balanced chemical equation for this reaction. Ans. : • The brown fume coming out when lead nitrate is heated is due to the liberation of Nitrogen dioxide gas. • 2Pb(NO3)2 →2PbO + 4NO2 + O2 6. Calcium oxide reacts with water to form slaked lime. What type of Chemical reaction is this? Write the balanced chemical equation for this reaction. Ans. : • Combination Reaction / Exothermic reaction • CaO(s) + H2O(l) →Ca(OH)2(aq) + Heat 7. “Calcium oxide and carbon dioxide are produced on heating calcium carbonate.” Write the balanced chemical equation for this reaction. Mention the type of this chemical reaction. Ans. : • CaCO3 →CaO + CO2 • (Thermal) decomposition reaction / endothermic reaction 8. Add same amount of barium chloride solution to a test tube containing 5 ml of sodium sulphate solution. Then i) Which insoluble white precipitate is formed ? ii) Name the ions responsible for the formation of white precipitate. iii) Mention the type of chemical reaction that took place here.
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Ans. : i) BaSO4 / barium sulphate ii) SO4^2- →sulphate radical, Ba^2+ →Barium ion iii) Double displacement reaction / precipitation reaction. 9. Observe the test tubes A, B and C given in the following figures. i) In which test tube the iron nail undergoes rust ? Why ? ii) Iron nails present in other two test tubes do not rust. Why ? Ans. : i) Iron nail present in test tube A because both moisture and air are available. ii) In test tube B only moisture is available but not oxygen. In test tube C only air is available but not moisture. 10. What is rancidity ? Mention any two methods of preventing rancidity. Ans. : When fat and oil containing food materials oxidise, then their smell and taste change. This is called rancidity. Methods of preventing rancidity : • Adding antioxidants • Keeping fried food materials in airtight containers • Flushing bags of chips with nitrogen gas. 11. Translate the following statement into chemical equation and then balance it. 'Hydrogen gas combines with chlorine gas to form hydrogen chloride.' Ans. : H2 + Cl2 →2HCl Three Marks Questions 1. Write the balanced chemical equation for the following chemical reactions : i) Calcium carbonate --Heat-->Calcium oxide + Carbon dioxide ii) Hydrogen + Chlorine →Hydrogen chloride iii) Magnesium + Hydrochloric acid →Magnesium chloride + Hydrogen. Ans. : i) CaCO3 --Heat-->CaO + CO2 ii) H2 + Cl2 →2HCl iii) Mg + 2HCl →MgCl2 + H2 2. Which type of chemical reaction takes place when an iron nail is dipped in copper sulphate solution ? Why ? Write a balanced chemical equation for this chemical reaction. Ans. : • Chemical displacement reaction. • Because more reactive iron displaces copper from copper sulphate solution. • Fe + CuSO4 →FeSO4 + Cu. 3. Write the balanced chemical equations for the following chemical reactions. How can we confirm by observation that these chemical reactions are taking place ? a) Lead nitrate is heated. b) Sodium sulphate reacts with Barium chloride. Ans. : a)2Pb(NO3)2 →2PbO + 4NO2 + O2 (Confirmed by the formation of brown coloured fumes.) b) Na2SO4 + BaCl2 →BaSO4 + 2NaCl (Confirmed by the formation of white coloured precipitate.) 4. The reaction of Barium chloride with Aluminium sulphate solution is an example for which type of chemical reaction ? Why ? Write the balanced chemical equation for this reaction. Ans. : • It is an example for double displacement reaction / Precipitation reaction. • There is an exchange of ions between the reactants / White precipitate of Barium Sulphate is formed. • 3BaCl2 + Al2(SO4)3 →3BaSO4 + 2AlCl3. 5. Draw the diagram of the apparatus used in electrolysis of water. Label the following parts : (i) Cathode (ii) Graphite rod.
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Ans. : [Diagram of apparatus used in electrolysis of water with labels: Cathode, Graphite rod, Anode, Oxygen, Hydrogen, Water, Plastic mug, 6V Battery]. 6. The reaction of lead with Copper Chloride solution is an example for which type of chemical reaction? Why? Write the balanced chemical equation for this reaction. Ans. : • Chemical displacement reaction. • Because more reactive lead displaces copper from copper Chloride solution. • Pb(s) + CuCl2(aq) →PbCl2(aq) + Cu(s) 7. Write the balanced chemical equations for the following reactions and identify the exothermic and endothermic reaction. i) heating of ferrous sulphate crystals. ii) calcium oxide reacts with water. Ans. : i) 2FeSO4(s) --Heat-->Fe2O3(s) + SO2(g) + SO3(g) (It is an endothermic reaction) ii) CaO + H2O →Ca(OH)2 + Heat (It is an exothermic reaction) 8. Silver chloride exposed to the sunlight turns grey colour. Why? Write the balanced chemical equation for this reaction and mention the type of reaction. Ans. : White silver chloride turns grey in sunlight due to the decomposition of silver chloride into silver and chlorine by light. 2AgCl --Sunlight-->2Ag + Cl2 The above reaction is an endothermic or decomposition reaction. 9. a) Identify the substances that are oxidised and reduced in the following chemical reaction: ZnO + C →Zn + CO b) What is rancidity ? Mention any two methods to prevent rancidity. Ans. : a) ZnO — is reduced. C — is oxidised. b) When fats and oils are oxidised, they become rancid and their smell and taste change. • Substances which prevent oxidation (antioxidants) are added to food. • Keeping food in airtight containers. 10. a) Mention any two factors that help to determine that a change is a chemical reaction. b) Mention the type of chemical reaction that takes place when sodium sulphate solution is added to barium chloride solution. Write the balanced chemical equation for this reaction. Ans. : a) Factors: Formation of new substances, Change in colour, Change in state, Change in temperature, Evolution of a gas. (Any two) b) Double displacement reaction. Na2SO4 + BaCl2 →BaSO4 + 2NaCl 11. Write the chemical equations for the following reactions. i) Quicklime is reacted with water ii) Zinc pieces are added to copper sulphate solution iii) Sodium chloride solution is added to silver nitrate solution. Ans. : i) CaO + H2O →Ca(OH)2 + Heat ii) Zn + CuSO4 →ZnSO4 + Cu iii) NaCl + AgNO3 →NaNO3 + AgCl 12. In which of the following chemical reactions water insoluble precipitate will be formed ? Explain. Which water soluble products are formed in both of the reactions ? i) Barium chloride reacted with sodium sulphate. ii) Zinc reacted with hydrochloric acid.
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Ans. : • Insoluble precipitate will be formed in chemical reaction (i). • Sodium sulphate and barium chloride react to produce water insoluble white precipitate of barium sulphate. • Water soluble product formed in reaction (i) is sodium chloride and in reaction (ii) zinc chloride. 13. Write the balanced chemical equations for the following word equations. (i) Manganese oxide + hydrochloric acid →manganese chloride + chlorine + water (ii) Calcium hydroxide + carbon dioxide →calcium carbonate + water (iii) Zinc carbonate →zinc oxide + Carbon dioxide Ans. : (i) MnO2 + 4HCl →MnCl2 + 2H2O + Cl2 (ii) Ca(OH)2 + CO2 →CaCO3 + H2O (iii) ZnCO3 →ZnO + CO2 14. Convert the following chemical reactions into chemical equations. (i) Ammonia forms when nitrogen gas reacts with hydrogen gas. (ii) Sodium oxide reacts with water to form sodium hydroxide. (iii) By reacting with water potassium metal produces potassium hydroxide and hydrogen gas. Ans. : (i) 3H2 + N2 →2NH3 (ii) Na2O + H2O →2NaOH (iii) 2K + 2H2O →2KOH + H2 15. Balance the following equations: (i) Mg + N2 →Mg3N2 (ii) NaOH + H2SO4 →Na2SO4 + H2O (iii) Al(OH)3 →Al2O3 + H2O Ans. : (i) 3Mg + N2 →Mg3N2 (ii) 2NaOH + H2SO4 →Na2SO4 + 2H2O (iii) 2Al(OH)3 →Al2O3 + 3H2O 16. Convert the following chemical reactions into chemical equations. (i) Copper reacts with concentrated nitric acid. (ii) Silver nitrate solution is added to potassium bromide solution. (iii) Zinc oxide is reduced by coke. Ans. : (i) Cu + 4HNO3 →Cu(NO3)2 + 2NO2 + 2H2O (ii) KBr + AgNO3 →KNO3 + AgBr (iii) ZnO + C →Zn + CO 17. a) Magnesium ribbon burns with a dazzling white flame in the air and change into magnesium oxide. Mention the type of reactions. b) List out the observations that help us to determine that a chemical reaction has taken place. Ans. : a) Chemical combination reaction. b) Change in colour, Evolution of a gas, Change in temperature, Change in state. 18. Write the balanced chemical equations for the following reactions: a) Calcium carbonate →Calcium oxide + carbon dioxide b) Hydrogen + chlorine →Hydrogen chloride c) Magnesium + hydrochloric acid →Magnesium chloride + Hydrogen Ans. : a) CaCO3 →CaO + CO2 b) H2 + Cl2 →2HCl c) Mg + 2HCl →MgCl2 + H2
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19. a) Chemical equations have to be balanced. Why? b) Mention the measures that are followed to prevent rusting of iron. Ans. : a) According to the law of conservation of mass, the number of atoms of each element remains the same before and after a chemical reaction. b) Measures to prevent rusting: Oiling, Greasing, Painting, Galvanisation, Chrome plating, Anodisation. 20. Observe the solutions of compounds given below and answer the following questions: Pb(NO3)2, BaCl2, Na2SO4, KI. a) Which solutions are to be reacted with each other to get white precipitate? Mention the type of this reaction. b) Which positive and negative ions combine to form this precipitate ? Ans. : a) Na2SO4 and BaCl2. Type: Chemical double displacement / Precipitation reaction. b) Ba^2+ and SO4^2-. Important Questions 1. Show the formation of Na2O and MgO by the transfer of electrons. Ans. : Na →Na+ + e- ; O + 2e- →O^2- ; 2Na+ + O^2- →Na2O Mg →Mg^2+ + 2e- ; O + 2e- →O^2- ; Mg^2+ + O^2- →MgO 2. What are the general properties for ionic compounds? Ans. : • Ionic compounds are solids and are somewhat hard. • Ionic compounds have high melting and boiling points. • Compounds are generally soluble in water and insoluble in organic solvents. • Ionic compounds conduct electricity in the molten state. 3. Name any two metals those displaces hydrogen from the dilute acids and two metals those does not displaces hydrogen from the dilute acids. Ans. : • Metals more reactive than hydrogen displace it from dilute acids. Example: Sodium, Potassium, Zinc, Iron. • Metals less reactive than hydrogen do not displace it from dilute acids. Example: Copper, Silver. 4. Give reasons - (a) Platinum, Gold, Silver are used in making ornaments (b) Sodium, Potassium are stored in kerosene (c) Aluminium is used in utensils even it is more reactive. Ans. : a) Shining surface / Metallic lustre, Ductility and Malleability, Less reactivity. b) These metals are highly reactive with air and water. So they are kept in kerosene. c) Aluminium is lighter and good conductor. Aluminium forms an oxide layer to prevent itself from further corrosion. 5. Why the metal oxides are said to be basic oxides. Explain with an example. Ans. : Metal oxides when dissolved in water form alkalis which are basic in nature. Example: Sodium hydroxide is formed on dissolving sodium oxide in water: Na2O + H2O →2NaOH 6. You are given cold water and hot water in two separate test tubes. If you kept a piece of magnesium in test tube containing cold water it shrinks, while in hot water it floats. Give reason. Ans. : • Magnesium does not react with cold water. • Magnesium liberates hydrogen gas when it reacts with hot water. • It also starts floating due to the bubbles of hydrogen gas sticking to its surface. 7. Define ductility and malleability.
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Ans. : • Ductility: The ability of metals to be drawn into thin wires. • Malleability: Some metals can be beaten into thin sheets. This property is called malleability. 8. Define ionic bond and explain the formation of ionic bond taking sodium chloride as an example. Ans. : • Ionic Bond: A strong electrostatic force of attraction between positive and negative ions is called an ionic bond. • Formation of NaCl: - Sodium has atomic number 11 (configuration: 2, 8, 1). - Chlorine has atomic number 17 (configuration: 2, 8, 7). - Sodium donates 1 electron to chlorine atom to attain octet configuration, forming Na+. - Chlorine receives 1 electron from sodium, forming Cl-. - Strong electrostatic force of attraction between Na+ and Cl- forms ionic bond in NaCl. 9. Why is Aluminium oxide called an amphoteric oxide? Explain with help of chemical equations. Ans. : Aluminium oxide (Al2O3) reacts with both acids as well as bases to produce salt and water, hence it is called an amphoteric oxide. • Reacts with acid: Al2O3 + 6HCl →2AlCl3 + 3H2O • Reacts with base: Al2O3 + 2NaOH →2NaAlO2 + H2O 10. Metals are arranged in the reactivity series. Why hydrogen is kept in the series though it is not a metal? Ans. : Hydrogen is a non-metal but still placed in the reactivity series because it behaves as an electropositive element like metals (i.e. can lose electrons to form positive ions). 11. You are provided with three metals: sodium, magnesium and copper. Using only water as the reactant, how will you identify each of them? Ans. : (a) The metal which reacts violently with cold water and catches fire is sodium. (b) The metal which evolves hydrogen gas upon heating/hot water is magnesium. (c) The metal which does not react with water even on strong heating is copper. 12. Corrosion of metals is not always harmful. Illustrate. Ans. : Corrosion is generally harmful, but corrosion of aluminium is useful because a layer of aluminium oxide (Al2O3) formed as a result of chemical reaction gets deposited on the surface. It forms a protective coating and prevents further attack of water, air, acids, or alkalis. 13. Classify the following oxides as acidic, basic and amphoteric oxides: ZnO, MgO, SO2, CO2, Na2O, CaO, Al2O3. Ans. : • Acidic oxides: SO2, CO2 • Basic oxides: MgO, Na2O, CaO • Amphoteric oxides: ZnO, Al2O3
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