Chapter 3 · Metals and Non-metals

NCERT Class 10 Science Chapter 3 Intext Questions (Page 46)

All 5 questions of NCERT Class 10 Science Chapter 3 Intext Questions (Page 46) — Metals and Non-metals — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Why ​is ​sodium ​kept ​immersed ​in ​kerosene ​oil?
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   Sodium is so reactive that it catches fire in air and moisture; kerosene keeps air and moisture away from it.

   Sodium is a highly reactive metal. Kept in the open it reacts vigorously with the oxygen of the air ($4\text{Na}+{\text{O}}_2\to 2{\text{Na}}_2\text{O}$) and with moisture ($2\text{Na}+2{\text{H}}_2\text{O}\to 2\text{NaOH}+{\text{H}}_2+\text{heat}$); so much heat is released that the metal, and the hydrogen produced, catch fire. Kerosene oil does not react with sodium and keeps air and moisture away from it, so sodium is kept immersed in kerosene to protect it from oxidation and to prevent accidental fires.

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2. Q2
   Write ​equations for ​the reactions of

   1. (i)iron ​with ​steam
   2. (ii)calcium ​and ​potassium ​with water
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   Iron reacts with steam to give ${\text{Fe}}_3{\text{O}}_4$ and hydrogen; calcium and potassium react with cold water to give hydroxides and hydrogen.

   (i) $3\text{Fe(s)}+4{\text{H}}_2\text{O(g)}\to {\text{Fe}}_3{\text{O}}_4\text{(s)}+4{\text{H}}_2\text{(g)}$; iron reacts only with steam, giving iron(II,III) oxide and hydrogen. (ii) $\text{Ca(s)}+2{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(aq)}+{\text{H}}_2\text{(g)}$ (calcium reacts with cold water less violently and floats on the hydrogen bubbles); $2\text{K(s)}+2{\text{H}}_2\text{O(l)}\to 2\text{KOH(aq)}+{\text{H}}_2\text{(g)}+\text{heat energy}$ (potassium reacts violently and the hydrogen catches fire).

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3. Q3
   Samples ​of four metals A, B, ​C and ​D were taken and added to the following solution one by one. The results obtained have been tabulated as follows. Use the ​Table above to answer the following questions about metals A, B, C and D.

   1. (i)Which is ​the most reactive metal?
   2. (ii)What would you observe if B is added to a solution of Copper(II) sulphate?
   3. (iii)Arrange the metals A, B, C and D in ​the order of decreasing ​reactivity.

   Results of adding metals A, B, C and D to four salt solutions

   Metal	Iron(II) sulphate	Copper(II) sulphate	Zinc sulphate	Silver nitrate
   A	No reaction	Displacement
   B	Displacement		No reaction
   C	No reaction	No reaction	No reaction	Displacement
   D	No reaction	No reaction	No reaction	No reaction

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   B is the most reactive; B displaces copper, so the blue colour fades and reddish-brown copper deposits on B; the order is $\text{B}>\text{A}>\text{C}>\text{D}$.

   (i) B is the most reactive metal; it is the only one that displaces iron from iron(II) sulphate. (ii) B lies above copper in the reactivity series, so when B is added to copper(II) sulphate solution a displacement reaction occurs: the blue colour of the solution fades, a reddish-brown deposit of copper forms on the surface of B, and B slowly dissolves ($\text{B}+{\text{CuSO}}_4\text{(aq)}\to {\text{BSO}}_4\text{(aq)}+\text{Cu(s)}$, taking B as divalent). (iii) Order of decreasing reactivity: B > A > C > D.

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4. Q4
   Which ​gas is produced ​when ​dilute hydrochloric acid is added ​to a reactive metal? Write ​the ​chemical ​reaction when iron reacts with ​dilute ${\text{H}}_2{\text{SO}}_4$.
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   Hydrogen gas is produced; iron with dilute sulphuric acid gives iron(II) sulphate and hydrogen.

   Hydrogen gas (${\text{H}}_2$) is produced when dilute hydrochloric acid is added to a reactive metal (a metal above hydrogen in the reactivity series). Iron with dilute sulphuric acid: $\text{Fe(s)}+{\text{H}}_2{\text{SO}}_4\text{(aq)}\to {\text{FeSO}}_4\text{(aq)}+{\text{H}}_2\text{(g)}$; iron(II) sulphate and hydrogen are formed.

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5. Q5
   What ​would you ​observe when ​zinc is added to ​a solution of ​iron(II) sulphate? Write the chemical reaction that ​takes ​place.
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   Zinc displaces iron: the pale-green solution turns colourless and iron is deposited, $\text{Zn}+{\text{FeSO}}_4\to {\text{ZnSO}}_4+\text{Fe}$.

   Zinc is more reactive than iron, so it displaces iron from iron(II) sulphate solution. Observations: the pale-green colour of the iron(II) sulphate solution slowly fades and the solution becomes colourless (zinc sulphate), a greyish-black deposit of iron forms on the surface of the zinc, and the zinc slowly dissolves. Reaction: $\text{Zn(s)}+{\text{FeSO}}_4\text{(aq)}\to {\text{ZnSO}}_4\text{(aq)}+\text{Fe(s)}$ (a displacement reaction).

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