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NCERT Exemplar · Class 10 Science Chemical Reactions and Equations

44 questions · 44 still being checked

Multiple Choice Questions 11–18 (part 2 of 5)

  1. Exercise 11

    Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is
    (a)
    1\displaystyle 1:1\displaystyle 1
    (b)
    2\displaystyle 2:1\displaystyle 1
    (c)
    4\displaystyle 4:1\displaystyle 1
    (d)
    1\displaystyle 1:2\displaystyle 2

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    NCERT’s answer
    (b)
    (b) $\displaystyle 2$:1.\[2\mathrm{H_2O} \xrightarrow{\text{electrolysis}} 2\mathrm{H_2} + \mathrm{O_2} \] Two moles of \(\displaystyle \mathrm{H_2}\) form for every one mole of \(\displaystyle \mathrm{O_2}\).

  2. Exercise 12

    Which of the following is(are) an endothermic process(es)?
    (i)
    Dilution of sulphuric acid
    (ii)
    Sublimation of dry ice
    (iii)
    Condensation of water vapours
    (iv)
    Evaporation of water
    (a) (i) and (iii)
    (b) (ii) only
    (c) (iii) only
    (d) (ii) and (iv)

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    NCERT’s answer
    (d)
    (d) (ii) and (iv).\[\mathrm{CO_2(s) \rightarrow CO_2(g)} \quad \text{absorbs heat} \] \[\mathrm{H_2O(l) \rightarrow H_2O(g)} \quad \text{absorbs heat} \] Sublimation and evaporation absorb heat to overcome intermolecular forces; diluting \(\displaystyle \mathrm{H_2SO_4}\) and condensation release heat instead.

  3. Exercise 13

    In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
    (a)
    Lead sulphate (insoluble)
    (b)
    Lead acetate
    (c)
    Ammonium nitrate
    (d)
    Potassium sulphate

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    NCERT’s answer
    (b)
    Hint— Lead sulphate being insoluble will not dissociate into \(\displaystyle \mathrm{Pb}^{2+}\) ions.
    (b) Lead acetate is soluble and furnishes \(\displaystyle \mathrm{Pb^{2+}}\), so it gives the same double displacement. \[\mathrm{Pb(CH_3COO)_2(aq)} + 2\mathrm{KI(aq)} \rightarrow \mathrm{PbI_2(s)}\downarrow + 2\mathrm{CH_3COOK(aq)} \] Lead sulphate is insoluble; ammonium nitrate and potassium sulphate carry no \(\displaystyle \mathrm{Pb^{2+}}\) at all.

  4. Exercise 14

    Which of the following gases can be used for storage of fresh sample of an oil for a long time?
    (a)
    Carbon dioxide or oxygen
    (b)
    Nitrogen or oxygen
    (c)
    Carbon dioxide or helium
    (d)
    Helium or nitrogen

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    NCERT’s answer
    (d)
    (d) Helium or nitrogen — both inert, while every other pair holds a reactive gas (\(\displaystyle \mathrm{O_2}\) in (a), (b); \(\displaystyle \mathrm{CO_2}\) in (c)). \[\mathrm{He}/\mathrm{N_2}\ \text{flush} \Rightarrow \mathrm{O_2}\ \text{excluded} \Rightarrow \text{no oxidation} \Rightarrow \text{no rancidity} \]

  5. Exercise 15

    The following reaction is used for the preparation of oxygen gas in the laboratory
    2KClO3( s)→ Catalyst  Heat 2KCl( s)+3O2( g)2 \mathrm{KClO}_3(\mathrm{~s}) \xrightarrow[\text { Catalyst }]{\text { Heat }} 2 \mathrm{KCl}(\mathrm{~s})+3 \mathrm{O}_2(\mathrm{~g})
    Which of the following statement(s) is(are) correct about the reaction?
    (a)
    It is a decomposition reaction and endothermic in nature
    (b)
    It is a combination reaction
    (c)
    It is a decomposition reaction and accompanied by release of heat
    (d)
    It is a photochemical decomposition reaction and exothermic in nature

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    (c) One reactant, two products: decomposition. Heat on the arrow is for the rate; the reaction releases heat. \[\Delta_r H = 2\,\Delta_f H(\mathrm{KCl,\,s}) - 2\,\Delta_f H(\mathrm{KClO_3,\,s}) \] \[\Delta_r H = 2\,\mathrm{mol}\times(-436.5\ \mathrm{kJ\,mol^{-1}}) - 2\,\mathrm{mol}\times(-397.7\ \mathrm{kJ\,mol^{-1}}) \] \[\Delta_r H = -77.6\ \mathrm{kJ} < 0 \] (b), (d) fail: nothing combines; no light.NCERT prints: (a) -- needing heat is not being endothermic; \(\displaystyle \Delta_r H < 0\).

  6. Exercise 16

    Which one of the following processes involve chemical reactions?
    (a)
    Storing of oxygen gas under pressure in a gas cylinder
    (b)
    Liquefaction of air
    (c)
    Keeping petrol in a china dish in the open
    (d)
    Heating copper wire in presence of air at high temperature

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    NCERT’s answer
    (d)
    (d) Heating copper wire in air. \[2\mathrm{Cu(s)} + \mathrm{O_2(g)} \xrightarrow{\Delta} 2\mathrm{CuO(s)} \] Copper combines with oxygen to give a new black compound. The other three only change state or physical form — no new substance forms.

  7. Exercise 17

    In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?
    (a)
    2H2(l)+O2(l)→2H2O(g)\displaystyle 2 \mathrm{H}_2(\mathrm{l})+\mathrm{O}_2(\mathrm{l}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{g})
    (b)
    2H2( g)+O2(l)→2H2O(l)\displaystyle 2 \mathrm{H}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{l}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})
    (c)
    2H2( g)+O2( g)→2H2O(l)\displaystyle 2 \mathrm{H}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})
    (d)
    2H2( g)+O2( g)→2H2O(g)\displaystyle 2 \mathrm{H}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \rightarrow 2 \mathrm{H}_2 \mathrm{O}(\mathrm{g})

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    NCERT’s answer
    (d)
    (d) \(\displaystyle 2\mathrm{H_2(g)} + \mathrm{O_2(g)} \rightarrow 2\mathrm{H_2O(g)}\) \(\displaystyle \mathrm{H_2}\) and \(\displaystyle \mathrm{O_2}\) are far above their boiling points at reaction temperature, so they cannot be liquids; the water formed there is likewise still vapour, not yet condensed to liquid.

  8. Exercise 18

    Which of the following are combination reactions?
    (i)
    2KClO3→ Heat 2KCl+3O2\displaystyle 2 \mathrm{KClO}_3 \xrightarrow{\text { Heat }} 2 \mathrm{KCl}+3 \mathrm{O}_2
    (ii)
    MgO+H2O⟶Mg(OH)2\displaystyle \mathrm{MgO}+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{Mg}(\mathrm{OH})_2
    (iii)
    4Al+3O2⟶2Al2O3\displaystyle 4 \mathrm{Al}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{Al}_2 \mathrm{O}_3
    (iv)
    Zn+FeSO4⟶ZnSO4+Fe\displaystyle \mathrm{Zn}+\mathrm{FeSO}_4 \longrightarrow \mathrm{ZnSO}_4+\mathrm{Fe}
    (a) (i) and (iii)
    (b) (iii) and (iv)
    (c) (ii) and (iv)
    (d) (ii) and (iii)

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    NCERT’s answer
    (d)
    (d) (ii) and (iii). \[\mathrm{MgO(s)} + \mathrm{H_2O(l)} \rightarrow \mathrm{Mg(OH)_2(s)} \qquad 4\mathrm{Al(s)} + 3\mathrm{O_2(g)} \rightarrow 2\mathrm{Al_2O_3(s)} \] Both combine two reactants into one product. (i) is decomposition (one reactant, many products); (iv) is a displacement.