Navigating through the CBSE Class 10 Science curriculum requires an in-depth understanding of metallic bonding, electropositive nature, the reactivity series, extraction of metals (metallurgy), and corrosion prevention. Chapter 3 of Class 10 Chemistry, “Metals and Non-metals”, explores the chemical behavior of elements. It investigates how metals react with oxygen, water, acids, and salt solutions; explains the formation and properties of ionic compounds through electron transfer; details the extraction of metals from carbonate and sulphide ores via calcination and roasting; and explores the engineering significance of alloys. To help students master every aspect of this high-weightage chapter, this comprehensive solutions guide offers textbook-accurate, highly structured, and pedagogically sound responses strictly aligned with the latest CBSE evaluation standards.
Every question presented in the official NCERT textbook—ranging from all five in-text question sets (Pages 40, 46, 49, 53, and 55) to the complete chapter-end exercises (Questions 1 to 16 on Pages 56–57)—has been solved with exhaustive detail. Short-answer conceptual responses follow the official 30–40 word limit, while 3-mark and 5-mark reactions use structured chemical equations with states of matter. Key scoring terms, balanced reactions, and practical safety protocols have been highlighted to ensure students secure maximum marks in their CBSE Board Examinations.
Master Formula & Concept Summary Tables
1. The Reactivity Series of Metals
| Metal | Chemical Symbol | Reactivity Level | Reaction with Oxygen / Water / Acids |
|---|---|---|---|
| Potassium | K | Most Reactive | Reacts violently with cold water; catches fire in air; kept in kerosene. |
| Sodium | Na | Highly Reactive | Reacts vigorously with cold water; catches fire in air; kept in kerosene. |
| Calcium | Ca | Highly Reactive | Reacts with cold water; floats as H₂ bubbles stick to its surface. |
| Magnesium | Mg | Moderately Reactive | Reacts with hot water; floats as H₂ bubbles stick to its surface. |
| Aluminium | Al | Moderately Reactive | Reacts with steam; forms a protective oxide layer (Al₂O₃). |
| Zinc | Zn | Moderately Reactive | Reacts only with steam; oxide is amphoteric in nature. |
| Iron | Fe | Moderately Reactive | Reacts slowly with steam; does not burn, but iron filings burn vigorously. |
| Lead | Pb | Less Reactive | Does not react with water; reacts very slowly with dilute acids. |
| [Hydrogen] | [H] | Non-Metal Reference | Reference element. Metals above displace H₂ gas from dilute acids. |
| Copper | Cu | Low Reactivity | Does not react with water or dilute HCl; forms black CuO on heating. |
| Mercury | Hg | Low Reactivity | Extracted by simple thermal roasting of its cinnabar ore (HgS). |
| Silver | Ag | Noble Metal | Does not react with oxygen or dilute acids; tarnishes with H₂S gas (Ag₂S). |
| Gold | Au | Least Reactive | Found in free native state; dissolves only in Aqua Regia. |
| Platinum | Pt | Least Reactive | Highly unreactive noble metal; used for jewellery and electrodes. |
2. Important Alloys and Their Compositions
| Alloy Name | Primary Composition (Constituents) | Key Properties | Common Uses / Applications |
|---|---|---|---|
| Brass | Copper (Cu ~70%) + Zinc (Zn ~30%) | Malleable, corrosion-resistant, acoustic resonance. | Making musical instruments, decorative items, hardware fittings. |
| Bronze | Copper (Cu ~90%) + Tin (Sn ~10%) | Hard, brittle, resistant to corrosion, low electrical conductivity. | Making statues, medals, coins, heavy-duty industrial bearings. |
| Solder | Lead (Pb ~50%) + Tin (Sn ~50%) | Low melting point, excellent tensile bonding. | Welding and joining electrical wires and electronic circuit components. |
| Stainless Steel | Iron (Fe ~74%) + Nickel (Ni ~8%) + Chromium (Cr ~18%) + Carbon (C ~0.1%) | Does not rust, hard, strong, resistant to acids. | Manufacturing surgical instruments, kitchen cookware, cutlery. |
| Amalgam | Mercury (Hg) + any other metal (e.g., Na or Ag) | Homogeneous paste / alloy of mercury. | Silver amalgam used in dental fillings; sodium amalgam as reducing agent. |
| 22 Carat Gold | Gold (Au 22 parts) + Copper or Silver (Cu/Ag 2 parts) | Harder than pure 24-carat soft gold; wear-resistant. | Manufacturing durable jewellery and ornaments. |
3. Differences Between Calcination and Roasting
| Parameter / Feature | Calcination | Roasting |
|---|---|---|
| Type of Ore Used | Applied primarily to Carbonate Ores and Hydrated Ores. | Applied primarily to Sulphide Ores. |
| Presence of Air | Done in the absence or limited supply of air/oxygen. | Done in the presence of excess air/oxygen. |
| Gas Evolved | Releases Carbon Dioxide gas (CO₂). | Releases Sulphur Dioxide gas (SO₂). |
| Chemical Equation | ZnCO₃(s) —(Heat)→ ZnO(s) + CO₂(g)↑ | 2ZnS(s) + 3O₂(g) —(Heat)→ 2ZnO(s) + 2SO₂(g)↑ |
NCERT In-Text Questions: Set 1 (Page No. 40)
Question 1 Give an example of a metal which: [BOARD EXAM FAVORITE] (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.
Answer:
- (i) Mercury (Hg) is the only metal that exists in liquid state at room temperature (25°C).
- (ii) Sodium (Na) and Potassium (K) are soft alkali metals with low densities that can be sliced easily with a knife.
- (iii) Silver (Ag) and Copper (Cu) are the best conductors of heat.
- (iv) Lead (Pb) and Mercury (Hg) are comparatively poor conductors of heat.
Question 2 Explain the meanings of malleable and ductile. [BOARD EXAM FAVORITE]
Answer:
- Malleable: The physical property of a metal that allows it to be beaten, hammered, or rolled into thin sheets without breaking. Gold (Au) and Silver (Ag) are the most malleable metals.
- Ductile: The physical property of a metal that enables it to be drawn or stretched into thin wires. Gold is the most ductile metal (1 gram of gold can be drawn into a 2 km long wire).
NCERT In-Text Questions: Set 2 (Page No. 46)
Question 1 Why is sodium kept immersed in kerosene oil? [BOARD EXAM FAVORITE]
Answer: Sodium is an extremely reactive alkali metal with a very low ignition temperature.
When exposed to open air, it reacts violently with atmospheric oxygen and moisture, generating intense heat and catching fire spontaneously: 4Na(s) + O₂(g) → 2Na₂O(s) + Heat
To prevent accidental contact with air and moisture, and to prevent dangerous fires, sodium is always stored safely immersed in kerosene oil.
Question 2 Write equations for the reactions of: [BOARD EXAM FAVORITE] (i) Iron with steam. (ii) Calcium and potassium with water.
Answer: (i) Reaction of Iron with Steam: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)↑ (Iron forms magnetic iron oxide and liberates hydrogen gas).
(ii) Reactions with Water:
- Potassium with Cold Water (Violent & Exothermic):
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)↑ + Heat Energy(The evolved H₂ gas catches fire immediately). - Calcium with Cold Water (Less Violent):
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)↑(Calcium floats because hydrogen gas bubbles stick to its surface).
Question 3 Samples of four metals A, B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows: [BOARD EXAM FAVORITE]
| 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 |
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.
Answer:
- (i) Most Reactive Metal: Metal B is the most reactive metal because it is capable of displacing Iron from Iron(II) sulphate solution.
- (ii) Observation with Copper(II) sulphate: Since Metal B is more reactive than Iron, and Iron is more reactive than Copper, Metal B will displace Copper from Copper(II) sulphate solution. The blue color of the copper sulphate solution will fade, and a reddish-brown deposit of copper metal will form on metal B.
- (iii) Decreasing Order of Reactivity:
B > A > C > D(B is most reactive as it displaces Fe; A displaces Cu; C displaces Ag; D displaces none).
Question 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.
Answer: Hydrogen gas (H₂) is produced when dilute hydrochloric acid is added to a reactive metal.
Reaction of Iron with Dilute H₂SO₄: Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)↑ (Iron displaces hydrogen to form pale-green Iron(II) sulphate and hydrogen gas).
Question 5 What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place. [BOARD EXAM FAVORITE]
Answer: Zinc is more reactive than Iron (as it lies above iron in the reactivity series).
When zinc is added to a pale-green solution of Iron(II) sulphate:
- The pale-green colour of the solution gradually fades and becomes completely colourless due to the formation of Zinc sulphate.
- Greyish-black iron metal is displaced and deposits on the zinc strip.
Chemical Reaction: Zn(s) + FeSO₄(aq) [Pale Green] → ZnSO₄(aq) [Colourless] + Fe(s) [Grey Deposit]
NCERT In-Text Questions: Set 3 (Page No. 49)
Question 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? [BOARD EXAM FAVORITE]
Answer: (i) Electron-Dot Structures:
- Sodium (Na, Atomic No. 11 = 2, 8, 1): Has 1 valence electron
Na • - Magnesium (Mg, Atomic No. 12 = 2, 8, 2): Has 2 valence electrons
• Mg • - Oxygen (O, Atomic No. 8 = 2, 6): Has 6 valence electrons
: Ö :
(ii) Formation by Transfer of Electrons:
================================================================================ ELECTRON TRANSFER FORMATION: -------------------------------------------------------------------------------- 1. Formation of Sodium Oxide (Na₂O): Two sodium atoms each lose 1 electron to achieve octet: 2Na (2,8,1) → 2Na⁺ (2,8) + 2e⁻ One oxygen atom gains 2 electrons to complete its octet: O (2,6) + 2e⁻ → O²⁻ (2,8) Structure: [Na⁺]₂ [ :Ö: ]²⁻ ===> Na₂O 2. Formation of Magnesium Oxide (MgO): One magnesium atom loses 2 electrons: Mg (2,8,2) → Mg²⁺ (2,8) + 2e⁻ One oxygen atom gains 2 electrons: O (2,6) + 2e⁻ → O²⁻ (2,8) Structure: [Mg²⁺] [ :Ö: ]²⁻ ===> MgO ================================================================================
(iii) Ions Present:
- In Na₂O: Cation =
Sodium ion (Na⁺), Anion =Oxide ion (O²⁻) - In MgO: Cation =
Magnesium ion (Mg²⁺), Anion =Oxide ion (O²⁻)
Question 2 Why do ionic compounds have high melting points? [BOARD EXAM FAVORITE]
Answer: Ionic compounds are composed of oppositely charged cations and anions bound together by exceptionally strong electrostatic forces of attraction in a three-dimensional crystal lattice.
A very large amount of thermal heat energy is required to overcome and break these strong inter-ionic bonds, which accounts for their very high melting and boiling points (e.g., NaCl melts at 1074 K).
NCERT In-Text Questions: Set 4 (Page No. 53)
Question 1 Define the following terms: [BOARD EXAM FAVORITE] (i) Mineral (ii) Ore (iii) Gangue
Answer:
- (i) Mineral: Naturally occurring inorganic elements or compounds found in the Earth’s crust formed by geological processes (e.g., clay, mica).
- (ii) Ore: A naturally occurring mineral from which a metal can be extracted profitably, easily, and economically on a commercial scale (e.g., Bauxite is the ore of Aluminium).
- (iii) Gangue: The unwanted, worthless earthy impurities (such as sand, rock, clay, limestone, and soil) associated with commercially mined ore.
Question 2 Name two metals which are found in nature in the free state.
Answer: Gold (Au) and Platinum (Pt) (as well as Silver) are found in nature in the free, native uncombined state due to their very low chemical reactivity.
Question 3 What chemical process is used for obtaining a metal from its oxide? [BOARD EXAM FAVORITE]
Answer: The chemical process used is Reduction:
- 1. Reduction using Carbon (Coke): For moderately reactive metals (like Zinc, Iron, Lead):
ZnO(s) + C(s) → Zn(s) + CO(g)↑ - 2. Reduction using Reactive Metals (Thermite Process): Using Aluminium powder for Manganese and Iron oxides:
Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat - 3. Electrolytic Reduction: For highly reactive metals (Sodium, Magnesium, Aluminium) where carbon cannot reduce their oxides due to the metals’ high affinity for oxygen.
NCERT In-Text Questions: Set 5 (Page No. 55)
Question 1 Metallic oxides of zinc, magnesium and copper were heated with the following metals. In which cases will you find displacement reactions taking place? [BOARD EXAM FAVORITE]
| Metal | Zinc | Magnesium | Copper |
|---|---|---|---|
| Zinc oxide | No reaction | Displacement | No reaction |
| Magnesium oxide | No reaction | No reaction | No reaction |
| Copper oxide | Displacement | Displacement | No reaction |
Answer: Based on the reactivity series (Magnesium > Zinc > Copper):
- Magnesium is the most reactive: it will displace metals from Zinc oxide and Copper oxide.
- Zinc is more reactive than copper: it will displace copper from Copper oxide.
- Copper is least reactive: it cannot displace zinc or magnesium from their oxides.
Question 2 Which metals do not corrode easily?
Answer: Noble metals such as Gold (Au) and Platinum (Pt) (and to a large extent Titanium and Silver) do not corrode easily because they lie at the bottom of the reactivity series and do not react with atmospheric oxygen, moisture, or carbon dioxide.
Question 3 What are alloys? [BOARD EXAM FAVORITE]
Answer: An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, prepared by melting the primary metal and dissolving other elements in definite proportions, followed by cooling to room temperature. Examples: Brass (Cu + Zn), Bronze (Cu + Sn), Stainless Steel (Fe + Ni + Cr + C).
NCERT Chapter-End Exercises (Page No. 56-57)
Question 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
Answer: (d) AgNO₃ solution and copper metal Explanation: Copper is more reactive than Silver in the reactivity series. Therefore, Copper displaces Silver from Silver Nitrate solution: Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
Question 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
Answer: (c) Applying a coating of zinc (or using non-corrosive cookware) Explanation: While grease and paint prevent rusting, they burn, melt, and contaminate food upon heating. Applying a zinc layer (galvanization) or using stainless steel is the proper non-toxic method for cooking utensils.
Question 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
Answer: (a) Calcium Explanation: Calcium reacts with oxygen to form Calcium Oxide (CaO), an ionic compound with an extremely high melting point (2850 K). CaO dissolves readily in water to form slaked lime, Ca(OH)₂.
Question 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.
Answer: (c) Zinc is more reactive than tin. Explanation: Zinc is more reactive than Tin. If food cans are coated with zinc, it can react with organic food acids to form toxic, poisonous zinc compounds. Tin is unreactive and safe for food storage.
Question 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. [BOARD EXAM FAVORITE]
Answer: (a) Experimental Procedure:
- 1. Hammer Test (Malleability): Strike the sample with the hammer. If the sample flattens into a thin sheet without breaking, it is malleable (Metal). If it shatters into powder/pieces, it is brittle (Non-metal).
- 2. Circuit Test (Electrical Conductivity): Connect the battery, bulb, wires, and switch to form a circuit, leaving two test clips. Place the sample between the clips. If the bulb glows, the sample is a conductor (Metal). If the bulb does not glow, it is an insulator (Non-metal).
(b) Assessment of Usefulness: These tests are generally useful but have limitations due to physical exceptions:
- Exceptions: Graphite (an allotrope of carbon, non-metal) conducts electricity and would glow in the circuit test. Sodium and potassium (metals) are too soft to hammer into sheets. Therefore, chemical properties provide a more conclusive classification.
Question 6 What are amphoteric oxides? Give two examples of amphoteric oxides. [BOARD EXAM FAVORITE]
Answer: Amphoteric oxides are metal oxides that react with both acids as well as bases to produce salt and water.
Two Examples:
- Aluminium Oxide (Al₂O₃)
- Zinc Oxide (ZnO)
================================================================================ AMPHOTERIC CHEMICAL EQUATIONS OF ALUMINIUM OXIDE: -------------------------------------------------------------------------------- 1. Reaction with Acid (acting as a basic oxide): Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l) 2. Reaction with Base (acting as an acidic oxide): Al₂O₃(s) + 2NaOH(aq) → 2NaAlO₂(aq) [Sodium Aluminate] + H₂O(l) ================================================================================
Question 7 Name two metals which will displace hydrogen from dilute acids, and two metals which will not. [BOARD EXAM FAVORITE]
Answer:
- Metals that displace Hydrogen (lying above Hydrogen in reactivity series): Zinc (Zn) and Magnesium (Mg) (or Iron, Sodium).
- Metals that do NOT displace Hydrogen (lying below Hydrogen in reactivity series): Copper (Cu) and Silver (Ag) (or Gold).
Question 8 In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte? [BOARD EXAM FAVORITE]
Answer:
- Anode (+ terminal): A thick block/slab of Impure Metal M.
- Cathode (- terminal): A thin strip of Pure Metal M.
- Electrolyte: An aqueous, acidified solution of a soluble salt of Metal M (e.g., Acidified Copper Sulphate for refining copper).
Question 9 Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it. (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. [BOARD EXAM FAVORITE]
Answer: (a) Action of the evolved gas (Sulphur Dioxide, SO₂):
- (i) On Dry Litmus Paper: No color change occurs because non-metal acidic gases cannot dissociate into H⁺ ions in the complete absence of moisture.
- (ii) On Moist Litmus Paper: Turns moist blue litmus paper RED because SO₂ gas dissolves in the water film to form Sulphurous Acid (H₂SO₃):
SO₂(g) + H₂O(l) → H₂SO₃(aq)
(b) Balanced Chemical Equations:
- Burning of Sulphur:
S(s) + O₂(g) → SO₂(g) - Acid Formation:
SO₂(g) + H₂O(l) → H₂SO₃(aq)
Question 10 State two ways to prevent the rusting of iron.
Answer:
- Galvanisation: Coating iron articles with a thin protective layer of molten Zinc (Zn). Even if the surface is scratched, zinc corrodes preferentially, protecting the iron.
- Alloying (Making Stainless Steel): Mixing molten iron with Chromium (18%), Nickel (8%), and Carbon (0.1%) to form stainless steel, which is rust-proof and corrosion-resistant.
Question 11 What type of oxides are formed when non-metals combine with oxygen?
Answer: When non-metals combine with oxygen, they form Acidic Oxides (which dissolve in water to form acids, e.g., SO₂, CO₂, NO₂) or Neutral Oxides (which show neither acidic nor basic properties, e.g., CO, H₂O, N₂O).
Question 12 Give reasons: [BOARD EXAM FAVORITE] (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.
Answer:
- (a) Platinum, Gold, and Silver for Jewellery: They have a brilliant, lustrous shine, are highly malleable and ductile, and lie at the bottom of the reactivity series, meaning they do not corrode, tarnish, or react with air and moisture.
- (b) Sodium, Potassium, and Lithium stored in Oil: They are hyper-reactive alkali metals with low ignition temperatures that react violently with air and moisture, catching fire. Oil creates an airtight barrier.
- (c) Aluminium used for Cooking Utensils: Although reactive, aluminium reacts with atmospheric oxygen to form a tenacious, non-porous, protective oxide layer of Aluminium Oxide (Al₂O₃) on its surface that prevents further corrosion. It is also an excellent conductor of heat and light in weight.
- (d) Ores converted into Oxides: It is far easier and thermodynamically favorable to reduce a metal oxide to free metal using carbon or aluminium than to directly reduce metal carbonates or sulphides.
Question 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. [BOARD EXAM FAVORITE]
Answer: When copper vessels are exposed to moist air, copper reacts slowly with atmospheric CO₂ and moisture to form a green, basic coating of Basic Copper Carbonate [CuCO₃·Cu(OH)₂], which tarnishes the shiny surface.
Lemon and tamarind juices contain citric acid and tartaric acid. When applied to the vessel:
- The acid chemically reacts with and neutralizes the basic copper carbonate.
- Soluble copper salts are formed and washed away with water, restoring the shiny reddish-brown copper surface.
Question 14 Differentiate between metal and non-metal on the basis of their chemical properties. [BOARD EXAM FAVORITE]
Answer:
| Parameter | Metals | Non-Metals |
|---|---|---|
| Nature of Ion Formed | Electropositive (lose electrons to form cations, e.g., Na⁺, Mg²⁺). | Electronegative (gain electrons to form anions, e.g., Cl⁻, O²⁻). |
| Nature of Oxides | Form Basic Oxides (e.g., Na₂O, MgO) or Amphoteric Oxides (Al₂O₃). | Form Acidic Oxides (e.g., SO₂, CO₂) or Neutral Oxides (CO, H₂O). |
| Reaction with Dilute Acids | Displace Hydrogen gas from dilute mineral acids (Metal + Acid → Salt + H₂↑). | Do not displace hydrogen gas from dilute acids. |
| Reaction with Water | React with water/steam to form metal hydroxide/oxide and release H₂ gas. | Do not react with water or steam to evolve hydrogen gas. |
| Action as Redox Agents | Act as strong Reducing Agents (electron donors). | Act as strong Oxidizing Agents (electron acceptors). |
Question 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? [BOARD EXAM FAVORITE]
Answer: The fraudulent goldsmith used a solution called Aqua Regia (Latin for “Royal Water”).
- Composition of Aqua Regia: It is a freshly prepared mixture of concentrated Hydrochloric Acid (HCl) and concentrated Nitric Acid (HNO₃) in a 3:1 ratio by volume.
- Chemical Action: Aqua Regia is a fuming corrosive liquid that can dissolve noble metals like Gold and Platinum. When the bangles were dipped, the outer layer of gold dissolved into the acid solution, exposing the clean shiny inner layer but drastically reducing the total weight and mass of the gold.
Question 16 Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron). [BOARD EXAM FAVORITE]
Answer: Copper is used for making hot water tanks instead of steel for two reasons:
- Chemical Reactivity with Steam/Water: Copper lies below hydrogen in the reactivity series and does not react with water, hot water, or steam at any temperature. In contrast, steel contains iron, which reacts with steam at high temperatures (
3Fe + 4H₂O → Fe₃O₄ + 4H₂↑), causing rapid rusting and structural weakness. - Thermal Conductivity: Copper is a far better conductor of heat than steel, ensuring efficient heat transfer.
Frequently Asked Questions (FAQs) – Class 10 Chemistry Chapter 3
Question 1: What is an amphoteric oxide? Answer: An amphoteric oxide is a metal oxide that reacts with both acids and bases to produce salt and water (e.g., Al₂O₃ and ZnO).
Question 2: What is the Thermite reaction, and where is it used? Answer: The Thermite reaction is the highly exothermic reduction of Iron(III) oxide by Aluminium powder (Fe₂O₃ + 2Al → 2Fe(l) + Al₂O₃ + Heat), producing molten iron used for welding railway tracks and cracked machinery.
Question 3: What is Galvanisation? Answer: Galvanisation is the metallurgical process of coating iron or steel articles with a thin layer of molten Zinc (Zn) to protect them from rusting.
Question 4: What is an amalgam? Answer: An amalgam is an alloy in which one of the constituent metals is Mercury (Hg), such as dental silver amalgam or sodium amalgam.
Question 5: What is the composition of 22-carat gold? Answer: 22-carat gold consists of 22 parts of pure gold alloyed with 2 parts of either Copper (Cu) or Silver (Ag) to increase its hardness for making jewellery.
Question 6: Why is pure 24-carat gold not used for making ornaments? Answer: Pure 24-carat gold is extremely soft and malleable, making it prone to bending, deforming, and scratching easily unless hardened with copper or silver.
Question 7: What is the difference between an ore and a mineral? Answer: All ores are minerals, but all minerals are not ores. An ore is a specific mineral from which a metal can be extracted profitably and economically.
Question 8: What is gangue? Answer: Gangue refers to the commercially worthless, unwanted rocky, sandy, and earthy impurities mixed with mined ore.
Question 9: What is Anodising? Answer: Anodising is an electrolytic process of growing a thick, corrosion-resistant protective layer of Aluminium Oxide (Al₂O₃) on the surface of aluminium articles.
Question 10: Name two non-metals that are lustrous and liquid at room temperature. Answer:
- Lustrous non-metal: Iodine (I₂)
- Liquid non-metal: Bromine (Br₂)
Question 11: Which non-metal is an electrical conductor? Answer: Graphite, an allotrope of carbon, conducts electricity due to free delocalized electrons in its hexagonal layered lattice.
Question 12: What is the hardest natural substance known? Answer: Diamond, an allotrope of carbon with a rigid three-dimensional tetrahedral covalent network, is the hardest natural substance.
Question 13: Why does aluminium not corrode easily despite being reactive? Answer: Aluminium quickly forms a self-passivating, airtight, non-porous surface layer of Aluminium Oxide (Al₂O₃) that seals the underlying metal from further air contact.
Question 14: What is Aqua Regia? Answer: Aqua Regia is a fuming, corrosive mixture of concentrated Hydrochloric acid and concentrated Nitric acid in a 3:1 volume ratio, capable of dissolving noble metals like gold and platinum.
Question 15: Why are ionic compounds hard and brittle? Answer: Ionic compounds are hard due to strong electrostatic attractions between positive and negative ions; they are brittle because applying mechanical shear aligns like charges together, causing mutual repulsion and shattering the crystal.
Mastering the NCERT Solutions for Class 10 Science Chapter 3, “Metals and Non-metals”, equips students with the chemical equations, metallurgy principles, and ionic dot structures required for the CBSE Board Examination. Review the reactivity series, amphoteric oxide reactions, and the 15 board-level FAQs above to secure full marks in your chemistry evaluations.