Class 10 Science Maharashtra Textbook Solutions
2 Mar 2026Chemical reactions and equations Class 10 Science 1 Chapter 3 Questions And Answers Maharashtra Board
1. Choose the correct option from the bracket and explain the statement giving reason.(Oxidation, displacement, electrolysis, reduction, zinc, copper, double displacement, decomposition) a. To prevent rusting, a layer of …….. metal is applied on iron sheets. Answer. To prevent rusting, a layer of zinc metal is applied on iron sheets.The rusting of iron is an oxidation process. Due to corrosion of an iron a deposit of reddish substance (Fe2O3.H2O) is formed on it. This substance is called rust. To prevent corrosion, a layer of zinc metal (galvanisation) is applied on iron sheets. b. The conversion of ferrous sulphate to ferric sulphate is …….. reaction. Answer. The conversion of ferrous sulphate to ferric sulphate is an oxidation reaction.When ferric ion is formed. from ferrous ion, the positive charge is increased by one unit. while this happens the rerrous ion loses one electron. A process in which a metal or its ion loses one or more electrons is called an oxidation.2FeSO4 → Fe2(SO4)3Fe2 + SO42- → 2Fe3+ + SO42- c. When electric current is passed through acidulated water …….. of water takes place. Answer. This decomposition takes place with the help of an electric current, it is also called electrolytic decomposition. d. Addition of an aqueous solution of ZnSO4 to an aqueous solution of BaCl2 is an example of ……… reaction. Answer. Addition of an aqueous solution of ZnSO4 to an aqueous solution or BaCl2 is an example or double displacement reaction. Barium chloride reacts with zinc sulphate to form a white precipitate of barium sulphate. white precipitate is formed by exchange of ions Ba++ and SO4— between the reactants. 2. Write answers to the following. a. What is the reaction called when oxidation and reduction take place simultaneously? Explain with one example. Answer. The reaction which involves simultaneous oxidation and reduction is called an oxidation-reduction or redox reaction.In a redox reaction, one reactant gets oxidised while the other gets reduced during a reaction.Redox reaction = Reduction + Oxidation In redox reaction, the reductant is oxidized by the oxidant and the oxidant is reduced by thereductant.Example:CuO(s) + H2(g) → Cu(s) + H2OIn this reaction, oxygen is removed from copper oxide therefore it is a reduction of CuO, while hydrogen accepts oxygen to form water that means oxidation of hydrogen takes place. Thus oxidation and reduction reactions occur simultaneously. Other examples of redox reactions: b. How can the rate of the chemical reaction, namely, decomposition of hydrogen peroxide be increased? Answer. At room temperature, the decomposition of hydrogen peroxide into water and oxygen takes place slowly. However, the same reaction occurs at a faster rate on adding manganese dioxide (MnO2), powder in it. c. Explain the term reactant product giving examples. Answer. d. Explain the types of reactions with reference to oxygen and hydrogen. Illustrate with examples. Answer. With reference to oxygen and hydrogen, there are two types of reaction 1. Oxidation reaction:Examples: (1) When carbon burns in air, it forms carbon dioxide. In this reaction carbon accepts oxygen, therefore, this is an oxidation reaction.C(s) + O2(g) → CO2(g) (2) When sodium reacts with ethyl alcohol, sodium ethoxide and hydrogen gas is formed. In this reaction, hydrogen is removed from ethyl alcohol, therefore this is an oxidation reaction. (3) Acidified potassium dichromate (K2Cr2O7 / H2SO4) oxidises ethly alcohol to acetic acid. 2. Reduction reaction:Examples:(1) When hydrogen gas is passed over black copper oxide a reddish coloured layer of copper isformed.In this reaction an oxygen atom removed from CuO to form copper, hence, this is reduction. (2) when hydrogen gas is passed over red hot coke, methane is obtained.Here, hydrogen is added to coke (carbon). Hence, this is reduction. e. Explain the similarity and difference in two events, namely adding NaOH to water and adding CaO to water. Answer. Similarity : Both NaOH and CaO, when dissolved separately in water, solid NaOH dissolves releasing heat, resulting in rise in temperature. This reaction is exothermic reaction. When solid CaO dissolves in water, Ca(OH)2 is formed, large amount of heat is evolved. This reaction is also exothermic reaction. Both reactions are combination reactions and single product is obtained.NaOH(s) + H2O → NaOH(aq) + HeatCaO(s) + H2O → Ca(OH)2(aq) + HeatDifference: 3. Explain the following terms with examples. a. Endothermic reaction Answer. Endothermic reaction: The reaction in which heat is absorbed is called an endothermicreaction.when KNO3(s) dissolves in water, there is absorption of heat during the reaction and the temperature of the solution falls.KNO2(s) + H2O(l) + Heat → KNO3(aq) b. Combination reaction Answer. When two or more reactants combine in a reaction to form a single product, it is called a combination reaction.Examples:1. The ammonia gas reacts with hydrogen chloride gas to form the salt in gaseous state, immediately it condenses at room temperature and gets transformed into the solid state. 2. Magnesium burns in air to form white powder of magnesium oxide as a single product. 3. Iron reacts with sulphur to form iron sulphide. c. Balanced equation Answer. In a chemical reaction, the number of atoms of the elements in the reactants is same as the number or atoms of those elements in the product, such an equation is called a balanced equation.Example: AgNO3 + NaCl → AgCl + NaNO3In the above reaction, the number of atoms of the elements in the reactants is same as the number of atoms of elements in the products. d. Displacement reaction Answer. The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by the formation of its own ions is called displacement reaction. When zinc granules are added to the blue coloured copper sulphate solution, the zinc ions formed from zinc atoms take the place of Cu2+ ions in CuSO4, and copper atoms, formed from Cu2+ ions comes out i.e. the more reactive zinc displaces the less reactive Cu from copper sulphate. 4. Give scientific reasons. a. When the gas formed on heating limestone is passed through freshly prepared lime water, the lime water turns milky. Answer. when lime stone is heated, calcium oxide and carbon dioxide are formed. This carbon dioxide gas is passed through freshly prepared lime
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