CHAPTER 3

Metals and Non-Metals

Metal

1.1      Definition: Elements which contain 1,2 or 3 electrons in their outermost orbit of their atoms are               generally metals.

1. 1. Sodium, Na (11) – 2, 8,1
      
   2. Potassium, K (19) – 2,8,8,1
      
   3. Calcium, Ca (20) – 2.8,8,2
      
   4. Magnesium, Mg (12) – 2,8,2
      
   5. Aluminium, Al (13) – 2,8,3
      

1.3    Exceptions:

1. Hydrogen, H (1) – 1
   
2. Boron, B (5) – 2,3 These are non-metals.
   

   
   1.4 Physical properties of Metals:
   The physical properties of metals are given below-
   

   1. Metals are lustrous (shiny)
      
   2. Metals are good conductors of heat and electricity.
      
   3. Metals have high melting point.
      
   4. Metals have high density (heavy for their size)
      
   5. Metals are highly malleable (can be hammered to be drawn into thin foil)
      
   6. Metals are highly ductile (can be drawn into wires)
      
   7. Metals are usually solid at room temperature (an exception is Mercury)
      
   8. Metals are opaque as a thin sheet (can’t see through metals)
      

Non-metal

2.1     Definition: Elements which contain 7,6 or 5 electrons in their outermost orbit of their atoms are generally Non-metals.

2.2    Examples of non-metals:
The examples of non-metals are given below-

    (a) Nitrogen, N (7) – 2,5

    (b) Oxygen, O (8) – 2,6

    (c) Florien, F (9) – 2,7

    (d) Chlorine, Cl (17) – 2,8,7

    (e) Phosphorous, P (15) – 2,8,5

1.4           Physical properties of Non-metals: The physical properties of Non-metals are as:

• Non-metals are not lustrous (dull appearance)
  
• Non-metals are bad/poor conductors of heat and electricity
  
• Non-metals are non-ductile solids
  
• Non-metals are brittle solids
  
• Non-metals may be solids, liquids or gases at room temperature
  
• Non-metals are transparent as a thin sheet
  
• Non-metals are not sonorous
  

  Questions (Page 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: The point wise examples are as follows:

(i)    Mercury is the metal which is liquid at room temperature

(ii)    Sodium and potassium are the metals which can be cut with a knife

(iii)    Silver is the best conductor of heat

(iv)    Mercury is poor conductor of heat.

2. Explain the meanings of malleable and ductile.

Ans: Malleable: The property of being converted into sheets/foil on hammering or alike process. Metals which can be beaten to sheets are said to be malleable.

    Ductile: The property of being drawn into thin wire. Metals which can be drawn

    into thin wires are said to be ductile.

Chemical properties of metals

3.1    What happens when metals are burnt in Air:
When When metals are burnt in air, their respective metal oxides are formed. Most of the metals show this chemical property, i.e. they combine with oxygen to form their respective metallic oxides. This can be represented in following manner:

Metal + Oxygen = Metal oxide.

Example:
(a) 2Cu + O₂ = 2CuO

(b) 4Al + 3O₂ = 2Al₂O₃

3.2    (i) It is learnt that metal oxides are basic in nature, but some metal oxides such as Aluminum oxide, Zink oxide show both acidic as well as basic behavior. Such metal oxides which react with both acids as well as bases to produce salts and water are called Amphoteric oxides. Aluminum oxides reacts with acids and bases in the following manner:

    (a) Al₂O3 + HCl = AlCl₃ + H₂O

    (b) Al₂O₃ + NaOH = NaAlO₂ + H₂O

    (ii) Most metal oxides are insoluble in water but some of these dissolve in water to form                Alkalis. Sodium oxide and Potassium oxide dissolve in water to produce Alkalis as follows:

1. Na₂O(s) + H₂O (l) = NaOH(aq)
   
2. K₂O(s) + H₂O (l) = KOH(aq)
   

3.3    What happened when Metals react with water:
In general, the reactions of metals with water produce Hydrogen(H ₂ ) gas and the Hydroxides of the metals.  Metals with moderate to low reactivity, react very slowly with water. However, they react moderately with steam when heated and give hydrogen gas and metal oxides. But all metals do not react with water.

Metal + Water = Metal oxide + Hydrogen

3.4    Metals like Potassium (K) and Sodium (Na) react violently with cold water. In case of Sodium (Na) and Potassium (K), the reaction is so violent and exothermic that the evolved Hydrogen immediately catches fire.

2Na(s) + 2H₂O(l) = NaOH(aq) + H₂(g) + Heat energy

2K (s) + 2H₂O = KOH(aq) + H₂(g) + Heat energy

3.5    The reaction of Calcium (Ca) with water is less violent. The heat evolved is not sufficient for the Hydrogen to catch fire.

Ca(s) + 2H₂O(l) = Ca(OH)₂(aq) + H₂(g)

    Calcium(Ca) starts floating because the bubbles of Hydrogen gas formed stick to the surface of the metal.

3.6    Magnesium (Mg) does not react with cold water. It reacts with hot water to form magnesium hydroxide and Hydrogen (H). It also starts floating due to the bubble of Hydrogen (H) gas sticking to its surface.

3.7    Metals like Aluminum (Al), Iron (Fe) and Zink (Zn) do not react either with cold or hot water. But they react with steam to form the metal oxide and Hydrogen (H).

Al(s) + H₂O (l) = Al₂O₃(s) + H₂(g)

Fe(s) + H₂O(l) = Fe₃O₄(s) + H₂(g)

3.8    Metals such as Lead (Pb), Copper (Cu), Silver (Ag) & Gold (Au) do not react with water at all.

3.9    What happened when Metals react with Acids:
In general, when metals react with acids, they produce a salt and Hydrogen(H) gas. Most metals react with acids, but not all. The general equation that describes the chemical reaction between a metal and an is – Metal + Acid = Salt + Hydrogen(H) gas.

3.10    Hydrogen(H) gas is not evolved when a metal reacts with Nitric acid (HNO₃)

because Nitric acid (HNO₃) is strong oxidizing agent. It oxidises the H2 produced to water and itself gets reduced to any of the Nitrogen Oxides (N₂O, NO, NO₂). But Magnesium (Mg) and Maganese (Mn) react with very dilute HNO3 to evolve Hydrogen (H) gas. Copper (Cu) does not react with dilute HCl.

3.11    How do Metals react with solutions of other Metal salts:
When more reactive metal react with solution of less reactive metal salt, more reactive metal displaces less reactive metal from its salt. Such reaction is known as displacement reaction or single displacement reaction. In general this can be written as:

Metal A + Salt solution of B = Salt solution of A + Metal B

Here, Metal ‘A’ is more reactive than Metal ‘B’

Reactivity Series

4.1    The reactivity series is a list of metals arranged in the order of their decreasing activities. After performing displacement experiments, the under mentioned series is found.

Questions (Page 46)

Q-1: Why is sodium kept immersed in kerosene oil?

Ans: Sodium is a reactive metal. If it is kept open, it will react with oxygen to explore and catch fire instantly. Sodium metal is kept immersed in kerosene to prevent their reaction with oxygen, moisture and carbon dioxide of air.

Q-2: Write equations for the reactions of

(i) iron with steam

(ii) calcium and potassium with water

Ans: The equations are mentioned as follows:

(i) Iron reacts with steam to form a magnetic oxide of Iron(Fe) and Hydrogen(H₂) liberates. The reaction is chemically written as:

3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

(ii) Calcium reacts with water to form Calcium hydroxide and Hydrogen(H). Following reaction takes place:

Ca(s) + 2H₂O(I) → Ca(OH)₂(aq) + H₂(g)

Potassium reacts with cold water violently immediately with evolution of H₂ which catches fire. Following reaction takes place:

2K(s) + 2H₂O(l) → 2KOH(aq) + 2H₂(g)

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 reactivity.
Ans:  On observation of the above table, following are found:

(i) Metal B is the most reactive as it gives displacement reaction with iron (II) sulphate.

(ii) When metal B is added to copper (II) sulphate solution, a displacement reaction will take place and as a result the blue colour of copper (II) sulphate solution will fade and a red-brown deposit of copper will be formed on metal B.

(iii)Metal B is the most reactive because it displaces Iron from its salt solution. Metal A is less reactive because it displaces Copper from its salt solution. Metal C is still less reactive because it can displace only silver from its salt solution and metal D is the least reactive because it cannot displace any metal from its salt solution. Hence, the decreasing order of reactivity of the metals 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 H2SO4.

Ans: Hydrogen (H) gas is formed when dilute HCl is added to a reactive metal. Further, following reaction takes place when Iron (Fe) reacts with H₂SO₄

Fe(s)+H₂SO₄(aq) → FeSo₄(aq)+H₂(g)

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: It is observed that Zinc (Zn) is more reactive (more electro positive) than Iron (Fe). Hence, Zinc (Zn) displaces Iron (Fe) from its salt solution. The colour of Ferrous sulphate is pale green, which turns into colourless. Following reaction takes place:

FeSO₄  + Zn → ZnSO₄  + Fe(s)

                                                             Light green      Zinc sulphate(Colourless)

5.1    How do Metals & Non-metals react: Whenever, a reaction between metal & non-metal takes place donation of electron by metal and acceptance of electron by non-metal takes place. As a result, Electrovalent Bond or Ionic Bond forms.
“An Ionic Bond or Electrovalent Bond is form by complete trans of electron from one atom to another“. As a result, Cation (+ charge) & Anion (-charge) is formed due to such donation and acceptance of electrons. Hence, this bond is named Ionic Bond or Electrovalent Bond.

5.2    Reason for formation of Ionic Bond or Electrovalent Bond: Any chemical reaction between one element to another takes place to become chemically stable. To become chemically stable, it is required to complete Octet (8 electrons in the outermost orbit( or Duet (2 electrons in the outermost orbit for elements like Hydrogen etc.) as the case may be. As Metals have mostly 1,2 or 3 electrons in their outermost orbit (Refer Para 1.1) they have tendency to donate electrons to get octet as by donating, outermost electrons viz. 1,2 or 3 are donated hence the they get their octet as just previous orbit becomes the outermost orbit. Similarly, Non-metals have tendency to accept electrons as they have 7,6 or 5 electrons in their outermost orbit. Hence, by accepting their respective required electrons, non-metals complete their octet.

5.3    Example: Na (2,8,1) + Cl (2,8,7) = NaCl

Here, it is clear from the above reaction that Sodium (Na) donates 1 electron to Chlorine (Cl) to form NaCl. This bond formed between Sodium (Na) & Chlorine (Cl) is due to donation of electron. Hence, it is a Electrovalent Bond or Ionic Bond and the compound so formed is called Electrovalent compound of Ionic Compound.

5.4    Properties of Ionic Bond: The properties of Electrovalent Bond or Ionic Bond are given as follows:

• It forms crystals.
  
• It has high melting points and high boiling points.
  
• It has higher enthalpies of fusion and vaporization than molecular compounds.
  
• It is hard and brittle.
  
• It conducts electricity when it is dissolved in water as Electrovalent/Ionic Compounds are soluble in water and insoluble in solvents such as kerosene, petrol etc.
  
• It is good insulators.
  
• It is definite shape due to strong intramolecular force.
  

Questions (Page 49)

Q-1:     (i) Write the electron-dot structures for sodium, oxygen and magnesium.

        (ii) Show the formation of Na₂O and MgO by the transfer of electrons.

        (iii) What are the ions present in these compounds?

Ans: (i) The required electron-dot structure is given below

Sodium (Na) : – Na^•
– Oxygen (O)        

Magnesium : – Mg :

(ii) The formulation is as follows:

Formation of Magnesium oxide: When Magnesium (Mg) reacts with Oxygen(O), Magnesium (Mg) atom transfers its two valence electrons to an Oxygen atom. By losing two electrons, Magnesium (Mg) atoms form a Magnesium ion (Mg²⁺) and by gaining two electrons, Oxygen (O) atom forms an oxide ion (O^2-). Following reactions takes place-

Mg + O₂ = MgO

Formation of Sodium oxide: Two Sodium (Na) atoms transfer their 2 valence electrons to an Oxygen (O) atom. By losing two electrons, two Sodium (Na) atoms form two Sodium (Na) ions ( 2Na⁺). Similarly, by gaining two electrons, Oxygen (O) atom forms an oxide ion (O^2-).

(iii) Ions present in Sodium oxide compound (Na₂O) are Sodium ions (2Na⁺) and Oxide ions (O^2-). Ions present in Magnesium oxide compound (MgO) are Magnesium ions Mg²⁺ and Oxide ions (O^2-).

Q-2: Why do ionic compounds have high melting points?

Ans: Ionic/Electrovalent compounds are the ones which have both positive and negative charges. Hence there is a strong force of attraction between them. As a result a strong bond forms between them. This requires plenty of heat to break this force of attraction. Hence, Ionic/Electrovalent compounds have high melting points.

6.1     Occurrence of metals: Metals occur on earth crust in the form of mineral & ore. Some metals also occur in sea water in the form of their salts.

    Mineral: The elements or compounds which occur naturally in earth’s crust are called mineral.

    Ore: Minerals which contain a very high percentage of a particular metal and metal can be economically extracted from it are called ore.
In other words, an ore is a mineral from which a metal can be extracted economically.

7.1    Extraction of metals: In general, metals can be classified into three categories as per their reactivity as: (a) Most reactive metals like Na, K, Ca, Mg etc. (b) Medium reactive metals like Zn, Cu, Pb etc. & (c) Non-reactive or less reactive metals.

7.2    Extraction of metals low in the activity series:
Metals which are low in the activity series are generally very unreactive. The Oxides of these metals can be reduced to metals by heating only.

    Example: Cinnabar (HgS) is an ore of Mercury (Hg). When it is heated in the air, it is first converted into Mercuric oxide (HgO) and then Mercuric oxide is reduced to Mercury on further heating. Following reaction takes place:

2HgS(s) + 3O₂(g) on heating ₌ 2HgO(s) + SO₂(g)

HgO(s) on heating = Hg(l) + O₂(g)

7.3    Extraction of metals middle of the activity series:
Metals in the middle of the activity series viz. Iron (Fe), Zink (Zn), Lead (Pb), Copper (Cu) are moderately reactive. These are usually present as Sulphides or Carbonates in nature. It is easier to obtain a metal from it’s Oxide as compared to its Sulphides & Carbonates. Hence, prior to reduction, the metal Sulphide ores are converted into Oxides by heating strongly in the present of excess air. This process is called Roasting. Carbonate containing ores are changed into Oxides by heating strongly in limited air. This process is called Calcination. The chemical reaction takes place during Roasting & Calcination of Zinc (Zn) ores are shown as follows:

    Roasting: 2ZnS(s) + 3O₂ (g) on heating = 2ZnO(s) + 2SO₂(s)

    Calcination: ZnCO₃ (s) on heating = ZnO(s) + CO₂

7.4    The metal Oxides so obtained is reduced to the corresponding metals by using suitable reducing agents such as Carbon (C).

    Example : ZnO(s) + C (s) = Zn(s) + CO(g)

    In spite of using Carbon (coke) as reducing agent to reduce metal oxides into metals, sometimes, displacement reacting can also be used for this purpose. The highly reactive metals such as Sodium (Na), Calcium (Ca), Aluminum (Al) etc. are used as reducing agents because tey can displace metals of lower reactivity from their compounds.

    Example: MnO₂(s) + Al (s) = Mn(l) + Al₂O₃(s) +Heat

    These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state.

7.5    Extraction of metals towards the Top of the activity series: Metals which are high up in the reactivity series are very reactive. Such metals cannot be obtained from their compounds by means of heating with Carbon (C) in the above discussed method as Carbon (C) can’t displace them in a reaction due to their highly reactivity. Such metals are: Sodium(Na), Potassium (K), Calcium (Ca), Magnisium (Mg), Aluminium (Al) etc. Such metals are obtained by electrolytic reduction. For example: Sodium (Na), Magnesium (Mg) & Calcium (Ca) are obtained by the electrolysis of their molten Chlorides. These metals are deposited at the Cathode (Negative charged electrode because they are positively charged due to nature of donation of electron) whereas, Chlorine is liberated at the Anode ( the positively charged electrode). Following reaction takes place:

    At Cathode: Na⁺ + e^– = Na

    At Anode: 2Cl^– = Cl₂ + 2e^–

    Similarly, Aluminum (Al) is obtained from reduction of Aluminum oxide.

8.1    Refining of Metals: Metals obtained by means of various reduction processes as mentioned above are not very pure. They contain impurities which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining and the same is/are discussed below:

(a) Electrolytic Refining: Many metals such as Copper (Cu), Zink (Zn), Tin (Sn), Nickel (Ni), Silver (Ag) etc. are refined by electrolytically. In this process, the impure metals is made the Anode and a thin strip strip of pure metals is made the Cathode. A solution of the metal salt is used as an electrolyte. On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte. An equivalent amount of pure metal from the electrolyte is deposited on the Cathode. The soluble impurities go into the solution, whereas the insoluble impurities settle down at the bottom of the Anode and are known as Anode mud.

Questions (Page 53)

Q-1: Define the following terms.

(i) Mineral

(ii) Ore

(iii)Gangue

Ans: (i) Minerals:- Minerals are compounds (also known as elements) which are found                            naturally  in the earth’s crust. Example: Alums, K₂SO₄ .Al₂(SO₄)₃ . 24H₂O, etc.

                    Example: Bauxite Al₂O₃.2H₂O is the ore of Al. Copper pyrite CuFeS₂ is the ore of Copper                          (Cu). All minerals are not considered as ores but all ores are also minerals.

Q-2: Name two metals which are found in nature in the free state

Ans: Gold and Platinum are the two metals found in free state in nature.

Q-3: What chemical process is used for obtaining a metal from its oxide?

Ans: The process of Reduction method is used to obtain metal from its oxide.

    Exampe: (a) Zinc oxide is reduced to metallic Zinc by heating with Carbon(C).

    Following reaction takes place:

ZnO + C → Zn + CO

(b) Lead oxide is reduced to Lead by heating with Carbon (C)

PbO +C → Pb + CO

9.1    Corrosion: Corrosion is a natural process by which a refined metal is converted into a more chemically-stable form such as Oxide, Hydroxide, or Sulphide. It is a gradual destruction process of materials (usually metals) by chemical and/or electrochemical reaction with their environment.

    Example: Rusting of Iron (Fe) etc.

9.2    Prevention of Corrosion: Corrosion may be prevented by the following methods
(i) By painting, (ii) Oiling, (iii) Greasing, (iv) Galvanising, (v) Chrome plating, (vi) Anoding or making allows.

10.1    Some important definitions:

    (a) Galvanisation: It is a process of applying a protective Zinc (Zn) coating to steel or iron, to prevent rusting. The Galvanized article is protected against rusting even if the Zinc (Zn) coating is broken.  Metals are generally extracted from their ores by means of the following methods:

    (b) Alloy: An alloy is a homogeneous mixture of two or mere metals or a metal and a non-metal.   It is prepared by first melting the primary metal and then dissolving the other element(s) in it in a definite proportion.

Gangue + Flux = Slag

Questions (Page: 55)

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

Ans: A more reactive metal can displace a less reactive metal from its oxide. Among Zinc, Magnesium, and Copper metals, magnesium is the most reactive, copper is the least reactive metal and zinc is less reactive. The displacement reaction will take place in the following cases

Q- 2: Which metals do not corrode easily?

Ans: Gold and platinum are the metals which do not corrode easily

Q-3: What are alloys?

Ans: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.

Exercise (Page 56)

Q-1: Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal

(b) MgCl2 solution and aluminium metal

(c) FeSO4 solution and silver metal

(d) AgNO3 solution and copper metal

Ans: (d) AgNO3 solution and copper

Copper (Cu) displaces the Silver cations (reducing them to the elemental metal), in the process Copper (Cu) itself being oxidised to Copper II cations (Cu2+) and going into solution. Hence, Silver (Ag) metal precipitating out and a Copper II nitrate solution will be remaining.

Cu (s) + 2AgNO₃ (aq) → Cu(NO₃)₂ (aq) + 2Ag (s)

Q-2: Which of the following methods is suitable for preventing an iron frying pan from rusting? (a) Applying grease

(b) Applying paint

(c) Applying a coating of zinc

(d) All of the above

Ans: Answer is (c) Applying a coat of Zinc

Though applying grease and applying paint prevents iron from rusting but these cannot be applied on frying pan hence applying a coat of Zinc is most appropriate method to prevent an iron pan from rusting.

Q-3: An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be

(a) calcium

(b) carbon

(c) silicon

(d) iron

Ans: (a) Calcium: Calcium reacts with oxygen to give Calcium oxide. Calcium oxide is soluble in water to give Calcium Hydroxide.

            (b) Carbon (C) forms carbon-oxide with oxygen which is gas hence option (b) is wrong

(c) Silicon (Si) reacts with oxygen and forms Silicon dioxide. This is insoluble in water. so option (c) is not correct.

(d) Iron (Fe) reacts with oxygen and forms Iron dioxide. This is insoluble in water. so option (d) is not correct.

Q-4: Food cans are coated with tin and not with zinc because

(a) Zinc is costlier than tin.

(b) Zinc has a higher melting point than tin.

(c) Zinc is more reactive than tin.

(d) Zinc is less reactive than tin.

Ans: Correct answer is (c)

Food cans are coated with Tin and not with Zinc because Zinc is more reactive and electro positive than Tin.

Q-5: You are given a hammer, a battery, a bulb, wires and a switch.

(a) How could you use them to distinguish between samples of metals and non-metals?

(b) Assess the usefulness of these tests in distinguishing between metals and non-metals

Ans:
(a) Metals are malleable and can be easily drown into sheets by hitting with hammer. On the other hand, non-metals are hammered, they break down and they cannot be drawn into sheets as they are non-malleable. Metals are good conductors of electricity. Hence, the bulb will glow when it is connected with a battery and wire. Similarly, non-metals are bad conductors of electricity hence it will fail to lit up the bulb on connecting with wire and battery.

(b) These experiments can be helpful to demonstrate the malleability and electric conductivity of the metals and non-metals

Q-6: What are amphoteric oxides? Give two examples of amphoteric oxides

Ans: Oxides that react with both acids and bases to form salt and water are known as amphoteric oxides. Examples:  PbO and Al₂O₃.

Q-7: Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Ans: Zinc (Zn) and Magnesium (Mg) are the two metals which will displace Hydrogen (H) from dilute acids as they are very reactive metals. Gold (Au) and Silver (Ag) are the metals which will not replace Hydrogen from dilute acids as these metals are less reactive.

Q-8: In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Ans: In the process of electrolytic refining of metal called ‘M’, An impure and thick block of metal M. is considered as anode, Thin strip or wire of pure metal M is taken as anode and A suitable salt solution of metal M is considered as the electrolyte.

Q-9: Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

(a) What will be the action of gas on (i) dry litmus paper? (ii) moist litmus paper?

(b) Write a balanced chemical equation for the reaction taking place.

Ans:
(a) When sulphur powder is burnt in the air sulphur-di-oxide is formed. (i)Sulphur-di-oxide does not have any effect on dry litmus paper. (ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO₂ with water turns to sulfurous acid.

1. The reaction took place is as:
   

   S(s) + O₂(g) → SO₂(g)
   SO₂(g)+H₂O→H₂SO₃
   

Q-10: State two ways to prevent the rusting of iron.

Ans: Rusting of Iron (Fe) can be prevented by following ways:

1.    By coating the surface of the iron with rust proof paints.

2.     By applying Oil/grease on the surface of iron objects as it will prevent the iron surface to get in contact with air consisting of moisture.

Q-11: What type of oxides are formed when non-metals combine with oxygen?

Ans: When non-metals combine with Oxygen (O) it forms either acidic or neutral oxides.

Example: N₂O₅ or N₂O₃ is an acidic oxide; CO is a neutral oxide.

Q-12: Give reasons

(a) Platinum, gold and silver are used to make jewellery.

(b) Sodium, potassium and lithium are stored under oil.

(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction

Ans: (a) Platinum, Gold and Silver are used to make jewellery for as these metals are very less reactive hence they are not affected by air, water or most chemicals. These metals have a lot of lustre and they are highly malleable and ductile in nature.

(b) Sodium (Na), Potassium (K) and Lithium (Li) readily reacts with water to produce a lot of heat energy. As a result, Hydrogen (H) evolved in the reaction and results in fire. On exposure to water they react with moisture (water droplets) present in the atmosphere. In order to prevent contact with water these metals are stored under oil.

Q-13: You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Ans: Tarnished copper vessels are cleaned with lemon or tamarind because these sour substance contains acids which dissolve the coating of Copper oxide or basic Copper (Cu) carbonate present on the surface and tarnished copper vessels. This makes them shining red-brown again. Hence they are very effective in cleaning and tarnished Copper (Cu) vessels.

Q-14: Differentiate between metal and non-metal on the basis of their chemical properties.

Ans: The difference between metal & non-metal on the basis of their chemical properties are given below:

Q-15: A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

Ans: Goldsmith used the solution called Aqua regia which is called as royal water in Latin. It is the mixture of concentrated Hydrochloric acid and concentrated Nitric acid in the ratio of 3:1. Aqua regia is capable of dissolving noble metals like Gold (Au) and Platinum. When upper-layer of dull gold ornament is dissolved it lose it’s weight.

Q-16: Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

Ans: Copper (Cu) is used to make hot water tanks and not steel (an alloy of iron) because Copper (Cu) does not reacts with either water or steam whereas iron reacts with steams to corrode the tank.