CBSE Class 10 Science HOTs Metals and Non Metals Set 05

Chemical Properties of Metals

Question. Which of the following statements is true for an amphoteric oxide?
(a) It reacts only with acid and does not form water.
(b) It reacts with acid as well as base to form salt and hydrogen gas.
(c) It reacts with both acid as well as base to form salt and water.
(d) It reacts only with base and does not form water.
Answer: (c) It reacts with both acid as well as base to form salt and water.

Question. A student while burning a magnesium ribbon in air, collected the products in a wet watch glass. The new product obtained was
(a) magnesium oxide
(b) magnesium carbonate
(c) magnesium hydroxide
(d) magnesium chloride.
Answer: (c) magnesium hydroxide

Question. The pair(s) which will show displacement reaction is/are
(i) NaCl solution and copper metal
(ii) \( \text{AgNO}_3 \) solution and copper metal
(iii) \( \text{Al}_2(\text{SO}_4)_3 \) solution and magnesium metal
(iv) \( \text{ZnSO}_4 \) solution and iron metal.
(a) (ii) only
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (ii)
Answer: (b) (ii) and (iii)

Read the passage given below and answer the following questions :
A student, took four metals P, Q, R and S and carried out different experiments to study the properties of metals. Some of the observations were:
• All metals could not be cut with knife except metal R.
• Metal P combined with oxygen to form an oxide \( \text{M}_2\text{O}_3 \) which reacted with both acids and bases.
• Reaction with water :
P – Did not react either with cold or hot water but reacted with steam.
Q – Reacted with hot water and the metal started floating
R – Reacted violently with cold water.
S – Did not react with water at all

Question. Out of the given metals, the one which needs to be stored in kerosene is
(a) P
(b) R
(c) S
(d) Q
Answer: (b) R

Question. Out of the given metals, the metal Q is
(a) iron
(b) zinc
(c) potassium
(d) magnesium.
Answer: (d) magnesium.

Question. Metal which forms amphoteric oxides is
(a) P
(b) Q
(c) R
(d) S.
Answer: (a) P

Question. The increasing order of the reactivity of the four metals is
(a) P < Q < R < S
(b) S < R < Q < P
(c) S < P < Q < R
(d) P < R < Q < S.
Answer: (c) S < P < Q < R

Question. Which one of the following statements is true about the position of metals in the activity series of metals?
(a) Copper is below hydrogen but above lead.
(b) Iron is below lead and zinc.
(c) Zinc is below magnesium but above aluminium.
(d) Magnesium is below calcium but above aluminium.
Answer: (d) Magnesium is below calcium but above aluminium.

SA I 

Question. Why is potassium kept immersed in kerosene?
Answer: Potassium being a very reactive metal reacts violently even with cold water thus, release enormous amount of heat. Hence, it is kept immersed in kerosene.

Question. Give reason why : (a) gold and silver are used for making jewellery. (b) a few metals are used for making cooking utensils.
Answer: (a) Gold and silver are used for making jewellery because they are highly malleable, ductile, and have metallic lustre. They also do not react with atmospheric gases easily. (b) Some metals are used for making cooking utensils because they are good conductors of heat and have high melting points.

Question. What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers?
Answer: Aluminium and zinc strips will react with iron sulphate solution as they are more reactive than iron. They will displace iron from the solution, causing the pale green colour to fade.
\( 2\text{Al}_{(s)} + 3\text{FeSO}_{4(aq)} \rightarrow \text{Al}_2(\text{SO}_4)_{3(aq)} + 3\text{Fe}_{(s)} \)
\( \text{Zn}_{(s)} + \text{FeSO}_{4(aq)} \rightarrow \text{ZnSO}_{4(aq)} + \text{Fe}_{(s)} \)
Copper is less reactive than iron, so no reaction occurs in that beaker. No reaction occurs in the beaker with the iron strip and iron sulphate solution.

Question. A pale green solution of ferrous sulphate was taken in four separate test tubes marked I, II, III and IV. Pieces of Cu, Zn and Al were dropped in test tubes II, III and IV respectively. In which case(s) (a) the colour of ferrous sulphate solution will match with the colour in test tube (I)? Give reason. (b) the colour of ferrous sulphate solution will fade and black mass will be deposited on the surface of the metal?
Answer: (a) In test tube II (copper), the colour will match test tube I because copper is less reactive than iron and no reaction takes place. (b) In test tubes III (zinc) and IV (aluminium), the green colour of ferrous sulphate solution will fade and black iron metal will deposit on the surface because zinc and aluminium are more reactive than iron and displace it from the solution.

Question. Reverse of the following chemical reaction is not possible : \( \text{Zn}_{(s)} + \text{CuSO}_{4(aq)} \rightarrow \text{ZnSO}_{4(aq)} + \text{Cu}_{(s)} \) Justify this statement with reason.
Answer: Zinc is more reactive than copper, so it can displace copper from copper sulphate solution. However, copper is less reactive than zinc, so it cannot displace zinc from zinc sulphate solution. Therefore, the reverse reaction is not possible.

Question. Name a metal which : (a) is the best conductor of heat. (b) has a very low melting point. (c) does not react with oxygen even at high temperature. (d) is most ductile.
Answer: (a) Silver (b) Gallium or Caesium (c) Gold or Silver (d) Gold

Question. What is meant by amphoteric oxides? Choose the amphoteric oxides from the following : \( \text{Na}_2\text{O} \), \( \text{ZnO} \), \( \text{CO}_2 \), \( \text{Al}_2\text{O}_3 \), \( \text{H}_2\text{O} \)
Answer: Amphoteric oxides are metal oxides which show both acidic and basic properties and react with both acids and bases to form salt and water. Among the given list, \( \text{ZnO} \) and \( \text{Al}_2\text{O}_3 \) are amphoteric oxides.

SA II 

Question. Compare in tabular form the reactivities of the following metals with cold and hot water : (a) Sodium (b) Calcium (c) Magnesium
Answer:
(a) Sodium: Reacts violently with cold water to form sodium hydroxide and hydrogen gas.
(b) Calcium: Reacts less violently with cold water to form calcium hydroxide and hydrogen gas. The metal starts floating due to bubbles of hydrogen sticking to its surface.
(c) Magnesium: Does not react with cold water; it reacts with hot water to form magnesium hydroxide and hydrogen gas. It also starts floating.

Question. Give reason for the following : (i) Hydrogen gas is not evolved when most of the metals react with nitric acid. (ii) Zinc oxide is considered as an amphoteric oxide. (iii) Metals conduct electricity.
Answer: (i) Nitric acid (\( \text{HNO}_3 \)) is a strong oxidising agent. It oxidises the hydrogen produced to water and itself gets reduced to nitrogen oxides. (ii) Zinc oxide is amphoteric because it reacts with both acids and bases to produce salt and water. (iii) Metals conduct electricity because they have free electrons that can move through the lattice.

Question. (a) Why does calcium start floating when it reacts with water? Write the balanced chemical equation of the reaction. (b) Name two metals which do not react with water.
Answer: (a) Calcium starts floating because the bubbles of hydrogen gas formed during the reaction stick to the surface of the metal.
Equation: \( \text{Ca}_{(s)} + 2\text{H}_2\text{O}_{(l)} \rightarrow \text{Ca(OH)}_{2(aq)} + \text{H}_{2(g)} \)
(b) Gold and silver.

Question. State what would happen if : (i) some zinc pieces are placed in blue copper sulphate solution. (ii) some copper pieces are placed in green ferrous sulphate solution. (iii) an iron nail is dipped in a solution of copper sulphate for some time.
Answer: (i) The blue colour of copper sulphate solution fades, and a reddish-brown coating of copper is deposited on the zinc pieces. (ii) No reaction takes place as copper is less reactive than iron. (iii) The blue colour of copper sulphate solution fades and turns pale green, and a reddish-brown deposit of copper forms on the iron nail.

Question. Give reason : (a) Aluminium is a reactive metal but is still used for packing food articles. (b) Calcium starts floating when water is added to it.
Answer: (a) Aluminium reacts with oxygen in the air to form a thin, protective layer of aluminium oxide (\( \text{Al}_2\text{O}_3 \)) which prevents further corrosion. (b) Calcium starts floating because the bubbles of hydrogen gas evolved during the reaction stick to the metal surface.

LA 

Question. (a) Complete and balance the following chemical equations : (i) \( \text{Al}_2\text{O}_3 + \text{HCl} \rightarrow \) (ii) \( \text{K}_2\text{O} + \text{H}_2\text{O} \rightarrow \) (iii) \( \text{Fe} + \text{H}_2\text{O} \rightarrow \) (b) An element ‘X’ displaces iron from the aqueous solution of iron sulphate. List your observations if the element ‘X’ is treated with the aqueous solutions of copper sulphate, zinc sulphate and silver nitrate. Based on the observations arrange X, Zn, Cu and Ag in increasing order of their reactivities.
Answer: (a) (i) \( \text{Al}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\text{O} \)
(ii) \( \text{K}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{KOH} \)
(iii) \( 3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2 \)
(b) If 'X' displaces iron, it is more reactive than iron. It will also displace copper from copper sulphate and silver from silver nitrate. If 'X' also displaces zinc, it is the most reactive. Reactivity order based on activity series: Ag < Cu < Zn < X (assuming X is more reactive than Zn).

How do Metals and Non-metals React?

Question. Assertion (A) : The solution of ionic compounds are good conductors of electricity. Reason (R) : Movement of atoms of elements take place in solution.
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer: (c) (A) is true, but (R) is false.

Question. (a) Write electron dot structure of Ca (At. No. 20) and O (At. No. 8). (b) Show the formation of calcium oxide by transfer of electrons. (c) Name the ions present in this compound. (d) List four important characteristics of this compound.
Answer: (a) Calcium (2, 8, 8, 2) has 2 valence electrons. Oxygen (2, 6) has 6 valence electrons.
(b) \( \text{Ca} : \rightarrow [\text{Ca}]^{2+} + 2\text{e}^- \); \( : \ddot{\text{O}} \cdot + 2\text{e}^- \rightarrow [: \ddot{\text{O}} :]^{2-} \). Transfer: \( \text{Ca} \cdot + \cdot \ddot{\text{O}} \rightarrow [\text{Ca}]^{2+} [\text{O}]^{2-} \).
(c) Calcium ion (\( \text{Ca}^{2+} \)) and oxide ion (\( \text{O}^{2-} \)).
(d) 1. High melting and boiling points. 2. Soluble in water but insoluble in organic solvents. 3. Solid and hard. 4. Conducts electricity in molten or aqueous state.

Question. A metal ‘X’ combines with a non-metal ‘Y’ by the transfer of electrons to form a compound Z.
(i) State the type of bond in compound Z.
(ii) What can you say about the melting point and boiling point of compound Z?
(iii) Will this compound dissolve in kerosene or petrol?
(iv) Will this compound be a good conductor of electricity?
Answer: (i) Compound Z has an ionic bond because it is formed by the transfer of electrons from a metal to a non-metal.
(ii) Compound Z will have high melting and boiling points due to the strong electrostatic force of attraction between the oppositely charged ions.
(iii) No, ionic compounds are generally insoluble in organic solvents like kerosene or petrol.
(iv) Yes, it will be a good conductor of electricity in molten state or aqueous solution, although it will not conduct electricity in the solid state.

LA 

The following questions are source based/case based questions. Read the case carefully and answer the questions that follow.
The melting points and boiling points of some ionic compounds are given below :
Compound Melting Point (K) Boiling Point (K)
NaCl 1074 1686
LiCl 887 1600
CaCl2 1045 1900
CaO 2850 3120
MgCl2 981 1685
These compounds are termed ionic because they are formed by the transfer of electrons from a metal to a non-metal. The electron transfer in such compounds is controlled by the electronic configuration of the elements involved. Every element tends to attain a completely filled valence shell of its nearest noble gas or a stable octet.

Question. Show the electron transfer in the formation of magnesium chloride.
Answer: Magnesium (Atomic number 12) electronic configuration is 2, 8, 2. It loses 2 electrons to form \( Mg^{2+} \). Chlorine (Atomic number 17) electronic configuration is 2, 8, 7. It gains 1 electron to form \( Cl^{-} \).
\( Mg \rightarrow Mg^{2+} + 2e^{-} \)
\( 2Cl + 2e^{-} \rightarrow 2Cl^{-} \)
The transfer of electrons is shown as:
\( [Mg] \rightarrow [Mg]^{2+} \)
\( 2[\cdot \ddot{Cl} \cdot] \rightarrow 2[\cdot \ddot{Cl} \cdot]^{-} \)
\( \implies MgCl_2 \)

Question. List two properties of ionic compounds other than their high melting and boiling points.
Answer: (i) Ionic compounds are generally soluble in water but insoluble in organic solvents like kerosene and petrol.
(ii) They conduct electricity in the molten state or in aqueous solution but do not conduct in the solid state.

Question. While forming an ionic compound say sodium chloride how does sodium atom attain its stable configuration?
Answer: Sodium (Atomic number 11) has an electronic configuration of 2, 8, 1. It attains a stable configuration by losing one electron from its outermost M-shell to form a sodium cation (\( Na^{+} \)), which has a stable octet configuration (2, 8) like the noble gas neon.

Question. Give reasons :
(i) Why do ionic compounds in the solid state not conduct electricity?
(ii) What happens at the cathode when electricity is passed through an aqueous solution of sodium chloride?
Answer: (i) In the solid state, ions are held together by strong electrostatic forces in a fixed rigid structure and are not free to move. Therefore, they cannot conduct electricity.
(ii) In an aqueous solution of sodium chloride (brine), hydrogen gas is liberated at the cathode because \( H^{+} \) ions (from water) are more easily reduced than \( Na^{+} \) ions.
At Cathode: \( 2H^{+} + 2e^{-} \rightarrow H_2 (g) \)

Question. (a) (i) Write two properties of gold which make it the most suitable metal for ornaments.
(ii) Name two metals which are the best conductors of heat.
(iii) Name two metals which melt when you keep them on your palm.
(b) Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively.
Answer: (a) (i) Gold is highly malleable and ductile, and it is chemically inert (highly resistant to corrosion/tarnish).
(ii) Silver and copper are the best conductors of heat.
(iii) Gallium and Caesium.
(b) Calcium (20): 2, 8, 8, 2. It loses 2 electrons to form \( Ca^{2+} \). Oxygen (8): 2, 6. It gains 2 electrons to form \( O^{2-} \).
\( Ca \cdot \cdot + : \ddot{O} : \rightarrow [Ca]^{2+} [: \ddot{O} : ]^{2-} \implies CaO \)

Question. (i) Write down the electronic configuration of magnesium and oxygen.
(ii) Give two general properties of the compound formed by combination of magnesium and oxygen.
(iii) Show the formation of this compound by the transfer of electrons.
Answer: (i) Magnesium (Mg): 2, 8, 2; Oxygen (O): 2, 6.
(ii) Properties of MgO: (1) It has a high melting point. (2) It conducts electricity in molten or aqueous state.
(iii) Magnesium loses 2 electrons to oxygen:
\( Mg \cdot \cdot + : \ddot{O} : \rightarrow [Mg]^{2+} [: \ddot{O} : ]^{2-} \implies MgO \)

Occurrence of Metals

Question. An ore on treatment with dilute hydrochloric acid produces brisk effervescence. Name the type of ore with one example. What steps will be required to obtain metal from the enriched ore? Also write the chemical equations for the reactions involved in the process.
Answer: The ore is a carbonate ore (e.g., Calamine - \( ZnCO_3 \)).
Steps involved:
(1) Calcination: Heating the ore strongly in limited air to convert it into oxide.
\( ZnCO_3 (s) \xrightarrow{\text{Heat}} ZnO (s) + CO_2 (g) \)
(2) Reduction: The metal oxide is reduced to metal using a reducing agent like carbon (coke).
\( ZnO (s) + C (s) \rightarrow Zn (s) + CO (g) \)

Question. (i) Carbonate of metal ‘X’ is abundant in earth crust and its hydroxide is used in ‘white washing’. Identify metal ‘X’.
(ii) How will you convert this carbonate into its oxide? Name the process and write its equation.
Answer: (i) Metal 'X' is Calcium (Ca). The carbonate is Calcium Carbonate (\( CaCO_3 \)) and the hydroxide used for white washing is Calcium Hydroxide (\( Ca(OH)_2 \)).
(ii) Calcium carbonate is converted into calcium oxide by heating it strongly in the absence or limited supply of air. This process is called Calcination.
\( CaCO_3 (s) \xrightarrow{\text{Heat}} CaO (s) + CO_2 (g) \)

LA 

The following questions are source based/case based questions. Read the case carefully and answer the questions that follow.
Metals are required for a variety of purposes. For this we need their extraction from their ores. Ores mined from the earth are usually contaminated with many impurities which must be removed prior to the extraction of metals. The extraction of pure metal involves the following steps:
(1) Concentration of ore
(2) Extraction of metal from the concentrated ore
(3) Refining of metal

Question. Name an ore of mercury and state the form in which mercury is present in it.
Answer: Cinnabar. Mercury is present in the form of Mercuric Sulphide (\( HgS \)).

Question. What happens to zinc carbonate when it is heated strongly in a limited supply of air?
Answer: When zinc carbonate is heated strongly in a limited supply of air, it decomposes to form zinc oxide and carbon dioxide gas. This process is called calcination.
\( ZnCO_3 (s) \xrightarrow{\text{Heat}} ZnO (s) + CO_2 (g) \)

Question. The reaction of a metal A with \( Fe_2O_3 \) is highly exothermic and is used to join railway tracks.
(I) Identify the metal A and name the reaction taking place.
(II) Write the chemical equation or the reaction of metal A with \( Fe_2O_3 \).
Answer: (I) Metal A is Aluminium (Al). The reaction is known as the Thermite reaction.
(II) \( Fe_2O_3 (s) + 2Al (s) \rightarrow 2Fe (l) + Al_2O_3 (s) + \text{Heat} \)

Question. We cannot use carbon to obtain sodium from sodium oxide. Why? State the reactions taking place at cathode and anode during electrolytic reduction of sodium chloride.
Answer: Carbon cannot be used because sodium has a higher affinity for oxygen than carbon. Therefore, carbon cannot reduce sodium oxide to sodium metal. Sodium is obtained by electrolytic reduction of molten sodium chloride.
At Cathode: \( Na^{+} + e^{-} \rightarrow Na \)
At Anode: \( 2Cl^{-} \rightarrow Cl_2 + 2e^{-} \)

Question. Two ores X and Y were taken. On heating these ores it was observed that
(a) ore X gives \( CO_2 \) gas, and
(b) ore Y gives \( SO_2 \) gas.
Write steps to convert these ores into metals, giving chemical equations of the reactions that take place.
Answer: (a) Ore X is a carbonate ore. It is converted to metal oxide by calcination.
\( \text{Metal Carbonate} \xrightarrow{\text{Heat}} \text{Metal Oxide} + CO_2 \)
Example: \( ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2 \)
(b) Ore Y is a sulphide ore. It is converted to metal oxide by roasting.
\( \text{Metal Sulphide} + O_2 \xrightarrow{\text{Heat}} \text{Metal Oxide} + SO_2 \)
Example: \( 2ZnS + 3O_2 \xrightarrow{\Delta} 2ZnO + 2SO_2 \)
Reduction: The metal oxide is then reduced to metal using carbon.
\( ZnO + C \rightarrow Zn + CO \)

Question. Carbon cannot reduce the oxides of sodium, magnesium and aluminium to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.
Answer: Carbon cannot reduce these oxides because these metals (Na, Mg, Al) have a greater affinity for oxygen than carbon. These metals are placed at the top of the reactivity series. They are obtained by the electrolytic reduction of their molten ores. For example, sodium is obtained from molten NaCl.
At Cathode: \( Na^{+} + e^{-} \rightarrow Na \)
At Anode: \( 2Cl^{-} \rightarrow Cl_2 + 2e^{-} \)

Question. Write balanced chemical equations to explain what happens, when
(i) Mercuric oxide is heated.
(ii) Mixture of cuprous oxide and cuprous sulphide is heated.
(iii) Aluminium is reacted with manganese dioxide.
(iv) Ferric oxide is reduced with aluminium.
(v) Zinc carbonate undergoes calcination.
Answer: (i) \( 2HgO (s) \xrightarrow{\text{Heat}} 2Hg (l) + O_2 (g) \)
(ii) \( 2Cu_2O + Cu_2S \xrightarrow{\text{Heat}} 6Cu (s) + SO_2 (g) \)
(iii) \( 3MnO_2 (s) + 4Al (s) \rightarrow 3Mn (l) + 2Al_2O_3 (s) + \text{Heat} \)
(iv) \( Fe_2O_3 (s) + 2Al (s) \rightarrow 2Fe (l) + Al_2O_3 (s) + \text{Heat} \)
(v) \( ZnCO_3 (s) \xrightarrow{\text{Heat}} ZnO (s) + CO_2 (g) \)

Question. (a) List in tabular form three chemical properties on the basis of which we can differentiate between a metal and a non-metal.
(b) Give reasons for the following :
(i) Most metals conduct electricity well.
(ii) The reaction of iron(III) oxide [\( Fe_2O_3 \)] with heated aluminium is used to join cracked machine parts.
Answer: (a)
1. Metals form basic oxides; Non-metals form acidic or neutral oxides.
2. Metals displace hydrogen from dilute acids; Non-metals (mostly) do not.
3. Metals are electropositive (lose electrons); Non-metals are electronegative (gain electrons).
(b) (i) Metals have free mobile electrons that carry electric charge through the metal.
(ii) This is the thermite reaction. It is highly exothermic, producing iron in the molten state, which flows into and fills the cracks in machine parts or railway tracks.

Question. (a) Name two metals which are obtained from their ores by simple heating.
(b) Differentiate between calcination and roasting, taking examples of zinc ores.
(c) What is thermite reaction? State its significance.
Answer: (a) Mercury and Copper.
(b) Roasting: Heating sulphide ore in excess air (\( 2ZnS + 3O_2 \rightarrow 2ZnO + 2SO_2 \)). Calcination: Heating carbonate ore in limited air (\( ZnCO_3 \rightarrow ZnO + CO_2 \)).
(c) Thermite reaction is the reduction of a metal oxide (like \( Fe_2O_3 \)) by aluminium. Significance: It produces molten iron used for joining railway tracks or cracked machinery.

Question. (a) Describe an activity to show that metals are good conductors of electricity.
(b) Account for the following :
(i) Hydrogen gas is not evolved when a metal reacts with nitric acid.
(ii) For storing sodium metal, it is kept immersed in kerosene.
(iii) The reaction of iron(III) oxide with aluminium is used to join cracked iron parts of machines.
Answer: (a) Set up a circuit with a battery, a bulb, and two terminals. Place a metal wire between the terminals. The bulb glows, showing metals conduct electricity.
(b) (i) \( HNO_3 \) is a strong oxidizing agent. It oxidizes the \( H_2 \) produced to water and itself gets reduced to nitrogen oxides.
(ii) Sodium is highly reactive and reacts vigorously with oxygen and moisture in air, potentially catching fire.
(iii) Thermite reaction; the heat produced melts the iron produced, allowing it to fill cracks.