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NCERT Exemplar · Class 10 Science Chemical Reactions and Equations

44 questions · 44 still being checked

Short Answer Questions 19–28 (part 3 of 5)

  1. Exercise 19

    Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
    (a)
    Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
    (b)
    Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
    (c)
    Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4\displaystyle \mathrm{H}_2 \mathrm{SO}_4.
    (d)
    Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.

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    NCERT’s answer
    (a)
    \(\displaystyle \mathrm{N}_2(\mathrm{~g})+3 \mathrm{H}_2(\mathrm{~g}) \xrightarrow[773 \mathrm{~K}]{\text { Catalyst }} 2 \mathrm{NH}_3(\mathrm{~g})\)
    Combination reaction
    (b)
    \(\displaystyle \mathrm{NaOH}(\mathrm{aq})+\mathrm{CH}_3 \mathrm{COOH}(\mathrm{aq}) \longrightarrow \mathrm{CH}_3 \mathrm{COONa}(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}(\mathrm{l})\)
    Double displacement reaction/Neutralisation reaction
    (c)
    \(\displaystyle \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}(\mathrm{l})+\mathrm{CH}_3 \mathrm{COOH}(\mathrm{l}) \xrightarrow{\mathrm{H}^{+}} \mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5(\mathrm{l})+\mathrm{H}_2 \mathrm{O}(\mathrm{l})\)
    Double displacement reaction/Esterificaton reaction
    (d)
    \(\displaystyle \mathrm{C}_2 \mathrm{H}_4(\mathrm{~g})+3 \mathrm{O}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{CO}_2(\mathrm{~g})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{g})+\) Heat + Light
    Redox reaction/Combustion reaction
    \[\mathrm{N_2(g) + 3H_2(g) \xrightarrow[773\,K]{catalyst} 2NH_3(g)} \] (a) Combination reaction.\[\mathrm{NaOH(aq) + CH_3COOH(aq) \rightarrow CH_3COONa(aq) + H_2O(l)} \] (b) Neutralisation (double displacement) reaction.\[\mathrm{CH_3CH_2OH + CH_3COOH \xrightarrow[\Delta]{conc.\,H_2SO_4} CH_3COOC_2H_5 + H_2O} \] (c) Esterification reaction.\[\mathrm{C_2H_4(g) + 3O_2(g) \rightarrow 2CO_2(g) + 2H_2O(l) + Heat + Light} \] (d) Combustion reaction.

  2. Exercise 20

    Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
    (a)
    Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
    (b)
    Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
    (c)
    Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
    (d)
    Ethanol is burnt in air to form carbon dioxide, water and releases heat.

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    NCERT’s answer
    (a)
    \(\displaystyle \mathrm{Fe}_2 \mathrm{O}_3(\mathrm{~s})+2 \mathrm{Al}(\mathrm{s}) \longrightarrow \mathrm{Al}_2 \mathrm{O}_3(\mathrm{~s})+2 \mathrm{Fe}(\mathrm{l})+\) Heat
    Displacement reaction/Redox reaction
    (b)
    \(\displaystyle 3 \mathrm{Mg}(\mathrm{s})+\mathrm{N}_2(\mathrm{~g}) \longrightarrow \mathrm{Mg}_3 \mathrm{~N}_2(\mathrm{~s})\)
    Combination reaction
    (c)
    \(\displaystyle 2 \mathrm{KI}(\mathrm{aq})+\mathrm{Cl}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{KCl}(\mathrm{aq})+\mathrm{I}_2(\mathrm{~s})\)
    Displacement reaction
    (d)
    \(\displaystyle \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}(\mathrm{l})+3 \mathrm{O}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{CO}_2(\mathrm{~g})+3 \mathrm{H}_2 \mathrm{O}(\mathrm{l})+\) Heat
    Redox reaction/Combustion reaction
    \[\mathrm{Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + Heat} \] (a) Displacement reaction (thermit reaction).\[\mathrm{3Mg(s) + N_2(g) \rightarrow Mg_3N_2(s)} \] (b) Combination reaction.\[\mathrm{Cl_2(g) + 2KI(aq) \rightarrow 2KCl(aq) + I_2(s)} \] (c) Displacement reaction.\[\mathrm{C_2H_5OH(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l) + Heat} \] (d) Combustion reaction.

  3. Exercise 21

    Complete the missing components/variables given as x\displaystyle x and y\displaystyle y in the following reactions
    (a)
    Pb(NO3)2(aq)+2KI(aq)⟶PbI2(x)+2KNO3(y)\displaystyle \mathrm{Pb}\left(\mathrm{NO}_3\right)_2(\mathrm{aq})+2 \mathrm{KI}(\mathrm{aq}) \longrightarrow \mathrm{PbI}_2(x)+2 \mathrm{KNO}_3(y)
    (b)
    Cu(s)+2AgNO3(aq)⟶Cu(NO3)2(aq)+x( s)\displaystyle \mathrm{Cu}(\mathrm{s})+2 \mathrm{Ag} \mathrm{NO}_3(\mathrm{aq}) \longrightarrow \mathrm{Cu}\left(\mathrm{NO}_3\right)_2(\mathrm{aq})+x(\mathrm{~s})
    (c)
    Zn(s)+H2SO4(aq)⟶ZnSO4(x)+H2(y)\displaystyle \mathrm{Zn}(\mathrm{s})+\mathrm{H}_2 \mathrm{SO}_4(\mathrm{aq}) \longrightarrow \mathrm{ZnSO}_4(x)+\mathrm{H}_2(y)
    (d)
    CaCO3( s)→xCaO(s)+CO2( g)\displaystyle \mathrm{CaCO}_3(\mathrm{~s}) \xrightarrow{x} \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g})

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    NCERT’s answer
    (a)
    \(\displaystyle x \longrightarrow\) (s)
    \(\displaystyle y \longrightarrow(\mathrm{aq})\)
    (b)
    \(\displaystyle x \longrightarrow 2 \mathrm{Ag}\)
    (c)
    \(\displaystyle x \longrightarrow\) (aq)
    \(\displaystyle y \longrightarrow(\mathrm{~g})\)
    (d)
    \(\displaystyle x \longrightarrow\) Heat
    (a)
    \(\displaystyle \mathrm{PbI_2}\) is the insoluble yellow precipitate, \(\displaystyle \mathrm{KNO_3}\) stays in solution: \(\displaystyle x=(s)\), \(\displaystyle y=(aq)\).
    (b)
    Displacement liberates the less reactive metal as a solid: \(\displaystyle x=2\mathrm{Ag}\), so \(\displaystyle x(\mathrm{s})=2\mathrm{Ag(s)}\).
    (c)
    \(\displaystyle \mathrm{ZnSO_4}\) remains dissolved, \(\displaystyle \mathrm{H_2}\) escapes: \(\displaystyle x=(aq)\), \(\displaystyle y=(g)\).
    (d)
    \(\displaystyle \mathrm{CaCO_3}\) needs continuous heating to decompose: \(\displaystyle x=\Delta\) (heat).

  4. Exercise 22

    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

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    NCERT’s answer
    (b) and (c) are exothermic as heat is released in these changes. (a) and (d) are endothermic as heat is absorbed in these changes
    \[\mathrm{2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)} \] (a) Endothermic -- decomposition needs continuous heat input.(b) Exothermic -- dilution of \(\displaystyle \mathrm{H_2SO_4}\) releases heat.(c) Exothermic -- \(\displaystyle \mathrm{NaOH}\) dissolving releases heat.(d) Endothermic -- \(\displaystyle \mathrm{NH_4Cl}\) dissolving absorbs heat, the solution cools.

  5. Exercise 23

    Identify the reducing agent in the following reactions
    (a)
    4NH3+5O2⟶4NO+6H2O\displaystyle 4 \mathrm{NH}_3+5 \mathrm{O}_2 \longrightarrow 4 \mathrm{NO}+6 \mathrm{H}_2 \mathrm{O}
    (b)
    H2O+F2⟶HF+HOF\displaystyle \mathrm{H}_2 \mathrm{O}+\mathrm{F}_2 \longrightarrow \mathrm{HF}+\mathrm{HOF}
    (c)
    Fe2O3+3CO⟶2Fe+3CO2\displaystyle \mathrm{Fe}_2 \mathrm{O}_3+3 \mathrm{CO} \longrightarrow 2 \mathrm{Fe}+3 \mathrm{CO}_2
    (d)
    2H2+O2⟶2H2O\displaystyle 2 \mathrm{H}_2+\mathrm{O}_2 \longrightarrow 2 \mathrm{H}_2 \mathrm{O}

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    NCERT’s answer
    (a)
    Ammonia \(\displaystyle \left(\mathrm{NH}_3\right)\)
    (b)
    Water \(\displaystyle \left(\mathrm{H}_2 \mathrm{O}\right)\) as \(\displaystyle \mathrm{F}_2\) is getting reduced to HF
    (c)
    Carbon monoxide (CO)
    (d)
    Hydrogen
    Hint—Reducing agents are those substances which have the ability of adding hydrogen or removing oxygen from the other substances.
    (a)
    N: \(\displaystyle -3\rightarrow+2\) in \(\displaystyle \mathrm{NH_3\rightarrow NO}\), oxidised. Reducing agent: \(\displaystyle \mathrm{NH_3}\).
    (b)
    O: \(\displaystyle -2\rightarrow0\) in \(\displaystyle \mathrm{H_2O\rightarrow HOF}\), oxidised. Reducing agent: \(\displaystyle \mathrm{H_2O}\).
    (c)
    C: \(\displaystyle +2\rightarrow+4\) in \(\displaystyle \mathrm{CO\rightarrow CO_2}\), oxidised. Reducing agent: \(\displaystyle \mathrm{CO}\).
    (d)
    H: \(\displaystyle 0\rightarrow+1\) in \(\displaystyle \mathrm{H_2\rightarrow H_2O}\), oxidised. Reducing agent: \(\displaystyle \mathrm{H_2}\).

  6. Exercise 24

    Identify the oxidising agent (oxidant) in the following reactions
    (a)
    Pb3O4+8HCl⟶3PbCl2+Cl2+4H2O\displaystyle \mathrm{Pb}_3 \mathrm{O}_4+8 \mathrm{HCl} \longrightarrow 3 \mathrm{PbCl}_2+\mathrm{Cl}_2+4 \mathrm{H}_2 \mathrm{O}
    (b)
    2Mg+O2⟶2MgO\displaystyle 2 \mathrm{Mg}+\mathrm{O}_2 \longrightarrow 2 \mathrm{MgO}
    (c)
    CuSO4+Zn⟶Cu+ZnSO4\displaystyle \mathrm{CuSO}_4+\mathrm{Zn} \longrightarrow \mathrm{Cu}+\mathrm{ZnSO}_4
    (d)
    V2O5+5Ca⟶2 V+5CaO\displaystyle \mathrm{V}_2 \mathrm{O}_5+5 \mathrm{Ca} \longrightarrow 2 \mathrm{~V}+5 \mathrm{CaO}
    (e)
    3Fe+4H2O⟶Fe3O4+4H2\displaystyle 3 \mathrm{Fe}+4 \mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Fe}_3 \mathrm{O}_4+4 \mathrm{H}_2
    (f)
    CuO+H2⟶Cu+H2O\displaystyle \mathrm{CuO}+\mathrm{H}_2 \longrightarrow \mathrm{Cu}+\mathrm{H}_2 \mathrm{O}

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    NCERT’s answer
    (a)
    \(\displaystyle \mathrm{Pb}_3 \mathrm{O}_4\)
    (b)
    \(\displaystyle \mathrm{O}_2\)
    (c)
    \(\displaystyle \mathrm{CuSO}_4\)
    (d)
    \(\displaystyle \mathrm{V}_2 \mathrm{O}_5\)
    (e)
    \(\displaystyle \mathrm{H}_2 \mathrm{O}\)
    (f)
    CuO
    (a)
    Pb: \(\displaystyle +\tfrac{8}{3}\rightarrow+2\) in \(\displaystyle \mathrm{Pb_3O_4\rightarrow PbCl_2}\), reduced. Oxidising agent: \(\displaystyle \mathrm{Pb_3O_4}\).
    (b)
    O: \(\displaystyle 0\rightarrow-2\) in \(\displaystyle \mathrm{O_2\rightarrow MgO}\), reduced. Oxidising agent: \(\displaystyle \mathrm{O_2}\).
    (c)
    Cu: \(\displaystyle +2\rightarrow0\) in \(\displaystyle \mathrm{CuSO_4\rightarrow Cu}\), reduced. Oxidising agent: \(\displaystyle \mathrm{CuSO_4}\).
    (d)
    V: \(\displaystyle +5\rightarrow0\) in \(\displaystyle \mathrm{V_2O_5\rightarrow V}\), reduced. Oxidising agent: \(\displaystyle \mathrm{V_2O_5}\).
    (e)
    H: \(\displaystyle +1\rightarrow0\) in \(\displaystyle \mathrm{H_2O\rightarrow H_2}\), reduced. Oxidising agent: \(\displaystyle \mathrm{H_2O}\).
    (f)
    Cu: \(\displaystyle +2\rightarrow0\) in \(\displaystyle \mathrm{CuO\rightarrow Cu}\), reduced. Oxidising agent: \(\displaystyle \mathrm{CuO}\).

  7. Exercise 25

    Write the balanced chemical equations for the following reactions
    (a)
    Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.
    (b)
    Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
    (c)
    Copper sulphate on treatment with potassium iodide precipitates cuprous iodide ( Cu2I2\displaystyle \mathrm{Cu}_2 \mathrm{I}_2 ), liberates iodine gas and also forms potassium sulphate.

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    NCERT’s answer
    (a)
    \(\displaystyle \mathrm{Na}_2 \mathrm{CO}_3+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{NaHCO}_3\)
    (b)
    \(\displaystyle \mathrm{NaHCO}_3+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\)
    (c)
    \(\displaystyle 2 \mathrm{CuSO}_4+4 \mathrm{KI} \longrightarrow \mathrm{Cu}_2 \mathrm{I}_2+2 \mathrm{~K}_2 \mathrm{SO}_4+\mathrm{I}_2\)
    \[\mathrm{Na_2CO_3(aq) + HCl(aq) \rightarrow NaCl(aq) + NaHCO_3(aq)} \] \[\mathrm{CO_3^{2-} + H^+ \rightarrow HCO_3^-} \] (a) One mole of \(\displaystyle \mathrm{HCl}\) gives each \(\displaystyle \mathrm{CO_3^{2-}}\) a single \(\displaystyle \mathrm{H^+}\), so it stops at \(\displaystyle \mathrm{HCO_3^-}\).\[\mathrm{NaHCO_3(aq) + HCl(aq) \rightarrow NaCl(aq) + H_2O(l) + CO_2(g)} \] (b) \(\displaystyle \mathrm{HCO_3^-}\) takes one more \(\displaystyle \mathrm{H^+}\) and \(\displaystyle \mathrm{CO_2}\) escapes.\[\mathrm{2CuSO_4(aq) + 4KI(aq) \rightarrow Cu_2I_2(s) + I_2 + 2K_2SO_4(aq)} \] (c) \(\displaystyle \mathrm{Cu^{2+}}\) is reduced to \(\displaystyle \mathrm{Cu^+}\) while \(\displaystyle \mathrm{I^-}\) is oxidised to \(\displaystyle \mathrm{I_2}\).

  8. Exercise 26

    A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

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    NCERT’s answer
    \(\displaystyle \mathrm{KCl}(\mathrm{aq})+\mathrm{AgNO}_3(\mathrm{aq}) \longrightarrow \mathrm{AgCl}(\mathrm{s})+\mathrm{KNO}_3(\mathrm{aq})\) It is a double displacement and precipitation reaction.
    \[\mathrm{KCl(aq) + AgNO_3(aq) \rightarrow AgCl(s)\downarrow + KNO_3(aq)} \] \(\displaystyle \mathrm{Ag^+}\) and \(\displaystyle \mathrm{Cl^-}\) combine to give the insoluble white precipitate; \(\displaystyle \mathrm{K^+}\) and \(\displaystyle \mathrm{NO_3^-}\) stay in solution. Answer: Double displacement (precipitation) reaction.

  9. Exercise 27

    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.

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    NCERT’s answer
    \(\displaystyle 2 \mathrm{FeSO}_4(\mathrm{~s}) \xrightarrow{\text { Heat }} \mathrm{Fe}_2 \mathrm{O}_3(\mathrm{~s})+\mathrm{SO}_2(\mathrm{~g})+\mathrm{SO}_3(\mathrm{~g})\) It is a thermal decomposition reaction
    \[\mathrm{2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)} \] Green crystals turn reddish-brown (\(\displaystyle \mathrm{Fe_2O_3}\)); \(\displaystyle \mathrm{SO_2}\) gives the burning-sulphur smell. Answer: Thermal decomposition reaction.

  10. Exercise 28

    Why do fire flies glow at night?

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    NCERT’s answer
    Fire flies have a protein which in the presence of an enzyme undergoes aerial oxidation. This is a chemical reaction which involves emission of visible light. Therefore, fire flies glow at night.
    \[\text{Luciferin} + \mathrm{O_2} \xrightarrow{\text{luciferase}} \text{oxidised luciferin} + \text{light} \] Answer: A chemiluminescent, enzyme-catalysed oxidation reaction produces the glow.