Chapter 3 · Metals and Non-metals

NCERT Class 10 Science Chapter 3 Intext Questions (Page 55)

All 3 questions of NCERT Class 10 Science Chapter 3 Intext Questions (Page 55) — Metals and Non-metals — in the book's order, each with its answer and a step-by-step solution.

1. Q1
   Metallic oxides of ​zinc, magnesium ​and ​copper were ​heated with ​the following ​metals. In which cases will you find ​displacement reactions taking place?

   Metal oxides heated with metals (cells to be filled in)

   Metal	Zinc	Magnesium	Copper
   Zinc oxide
   Magnesium oxide
   Copper oxide

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   Displacement occurs in three cases: zinc oxide with magnesium, copper oxide with zinc, and copper oxide with magnesium.

   Displacement reactions take place in three cases, where the metal is more reactive than the metal in the oxide (reactivity order Mg > Zn > Cu): (1) zinc oxide heated with magnesium, $\text{ZnO}+\text{Mg}\to \text{MgO}+\text{Zn}$; (2) copper oxide heated with zinc, $\text{CuO}+\text{Zn}\to \text{ZnO}+\text{Cu}$; (3) copper oxide heated with magnesium, $\text{CuO}+\text{Mg}\to \text{MgO}+\text{Cu}$. In the other six cases (ZnO with Zn or Cu; MgO with Zn, Mg or Cu; CuO with Cu) there is no displacement, because the metal is either the same as, or less reactive than, the metal in the oxide.

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2. Q2
   Which ​metals ​do not ​corrode ​easily?
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   Gold and platinum, and largely silver, do not corrode easily because they are very unreactive.

   Metals at the bottom of the reactivity series, the noble metals gold and platinum (and, to a large extent, silver), do not corrode easily, because they do not react with the oxygen, moisture, carbon dioxide and acids in their surroundings. Gold and silver do not react with oxygen even at high temperatures, which is why these metals are used for jewellery. (Silver does tarnish slowly, forming black silver sulphide with sulphur compounds in the air.)

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3. Q3
   What are alloys?
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   An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal, such as brass.

   An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. It is prepared by first melting the primary metal, then dissolving the other elements in it in definite proportions, and cooling the mixture to room temperature. Alloying is done to improve the properties of a metal; for example, iron mixed with about 0.05 per cent carbon becomes hard and strong steel, and iron with nickel and chromium gives stainless steel, which does not rust. Examples: brass (Cu and Zn), bronze (Cu and Sn), solder (Pb and Sn), stainless steel (Fe, Ni and Cr); an alloy containing mercury is called an amalgam. Alloys have lower electrical conductivity and lower melting points than the pure metals.

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