# NCERT Class 10: Science-Intext Solutions

Reviewed By:
Krishna Kant Majee
M.Sc., B.Ed.

### Chapter 03-Metals and Non-metals-Intext Solutions

#### NCERT Book Page Number-40

Q.1. Give an example of a metal which:
(i) is a liquid at room temperature.
(ii) can be easily cut with a knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.

Ans. (i) Metal that exists in liquid state at room temperature → Mercury
(ii) Metal that can be easily cut with a knife → Sodium
(iii) Metal that is the best conductor of heat → Silver
(iv) Metals that are poor conductors of heat → Mercury and lead

Q.2. Explain the meanings of malleable and ductile.
Ans. Malleable : Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable.
Ductile : Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile.

#### NCERT Book Page Number- 46

Q.1. Why sodium kept immersed in kerosene oil?
Ans. Sodium is a very reactive metal and combines explosively with air (oxygen) at room temperature. It also reacts violently with cold water. So, it catches fire if it kept in open. Therefore, to prevent accidental fires and accidents, sodium is stored immersed in Kerosen oil.

Q.2. Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water

Ans. (i)$3Fe(s) + ~~~~~~4H_{2}O(g) \rightarrow~~~~Fe_{3}O_{4}(aq) + 4H_{2}(g)\uparrow$
$Iron ~~~~~~~~~~~~ Steam ~~~~~~~~~~~~ Iron (II, III) ~~~~~ Hydrogen$
(ii) $Ca(s) + ~~~~~~2H_{2}O(l) \rightarrow ~~~~~~~~ Ca(OH)_{2}(aq) + H_{2}(g) \uparrow + Heat$
$Calcium~~~~~~~~~~~~~~~~~~~~~ Calcium Hydroxide$
(iii) $2K(s) + ~~~~2H_{2}O(l) \rightarrow ~~~~~~ 2KOH(aq) + H_{2}(g) \uparrow + Heat$
$Potassium ~~~~~~~~~~~~~ Water ~~~~~~~~~~~~~~~ Potassium hydroxide Hydrogen$

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

Ans. Explanation
$A + FeSO_{4}\rightarrow$No reaction, i.e., A is less reactive than iron
$A + CuSO_{4} \rightarrow$Displacement, i.e., A is more reactive than copper
$B + FeSO_{4}\rightarrow$ Displacement, i.e., B is more reactive than iron
$B + ZnSO_{4}\rightarrow$ No reaction, i.e., B is less reactive than zinc
$C + FeSO_{4}\rightarrow$No reaction, i.e., C is less reactive than iron
$C + CuSO_{4}\rightarrow$ No reaction, i.e., C is less reactive than copper
$C + ZnSO_{4}\rightarrow$ No raction, i.e., C is less reactive than zinc
$C + AgNO_{3}\rightarrow$ Displacement, i.e., C is more reactive than silver
$D + FeSO_{4}$/$CuSO_{4}$/$ZnSO_{4}$/$AgNO_{3}$ $\rightarrow$ No reaction, i.e., D is less reactive than iron, copper, zinc, and silver.
From the above equations, we obtain:

(i) B is the most reactive metal.
(ii) If B is added to a solution of copper (II) sulphate, then it would displace copper.
$B + CuSO_{4}\rightarrow$ Displacement
(iii) The arrangement of the metals in the order of decreasing is :
B > A > C > D.

Q.4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute $H_{2}SO_{4}$.
Ans. Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal. When iron reacts with dilute H2SO4, iron (II) sulphate with the evolution of hydrogen gas is formed.
$Fe + H_{2}SO_{4}\rightarrow FeSO_{4} + H_{2}$

Q.5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Ans. Zinc is more reactive than iron. Therefore, if zinc is added to a solution of iron (II) sulphate, then it would displace iron from the solution.
$Zn(s) + FeSO_{4}(aq)\rightarrow ZnSO_{4}(aq) + Fe(s)$

#### NCERT Book Page Number -49

Q.1. (i) Write the electron-dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of $Na_{2}O and MgO by the transfer of electrons. (iii) What are the ions present in these compounds? Ans. (i) The representation of elements with valence electrons as dots around the elements is referred to as electron-dot structure from elements. (iii) The ions present in$Na_{2}O$are$ Na^{+} $and$O_{2}^{-}$ions and in MgO are$Mg^{2+}$and$O^{2-}$ions. Q.2. Why do ionic compounds have high melting points? Ans. The force of attraction in ionic bonds is very strong and it is difficult to overcome that force. Hence, ionic compounds have high melting points. #### NCERT Book Page Number-53 Q.1. Define the following terms : (i) Mineral (ii) Ore (iii) Gangue Ans. (i) A substance which naturally occurs in the earth’s crust and has a uniform composition is called mineral. (ii) A mineral from which a substance can be profitably extracted is called an ore. (iii) The impurities present in an ore are called gangue. Q.2. Name two metals which are found in nature in the free state. Ans. The metals at the bottom of the reactivity series are mostly found in free state. For example gold, silver, and platinum. Q.3. What chemical process is used for obtaining a metal from its oxide? Ans. The chemical process used for obtaining a metal from its oxide is reduction. In this process, metal oxides are reduced by using suitable reducing agents such as carbon or by highly reactive metals to displace the metals from their oxides. For example, zinc oxide is reduced to metallic zinc by heating with carbon.$ZnO(s) + C(s)\rightarrow Zn(s) + CO(g) $Manganese dioxide is reduced to manganese by treating it with aluminium powder. In this case, aluminium displaces manganese from its oxide.$3MnO_{2}(s) + 4Al(s)\rightarrow 3Mn(s) + 2Al_{2}O_{3}(s) + Heat\$

Oxides of more reactive metals are reduced by electrolysis.

#### NCERT Book Page Number-55

Q.1. Metallic oxides of zinc, magnesium and copper were with the following metals:

In which cases will you find displacement reaction is taking place?

Ans.

Q.2. Which metals do not corrode easily?

Ans. More reactive a metal is, more likely it is to be corroded. Therefore, less reactive metals are less likely to get corroded. This is why gold plating provides high resistance to corrosion.

Q.3. What are alloys?

Ans. Alloys are homogeneous mixtures of two or more elements. The elements could be two metals, or a metal and a non-metals. An alloy is formed by first the metal and then dissolving the other in it. For example, steel is an alloy of iron and carbon.