Class 10 Science Chapter 3: Metals and Non-Metals
Welcome to your ultimate guide for Class 10 Science Chapter 3 - Metals and Non-Metals. This chapter is a cornerstone of chemistry and introduces you to the fascinating world of metals and non-metals, their properties, reactions, and everyday applications. Let’s dive in and explore everything you need to know to master this chapter!
3.1 Physical Properties
Metals and non-metals have distinct physical properties that allow us to identify and differentiate them. Let’s explore these properties in detail.
3.1.1 Metals
Metals are generally hard, shiny, malleable, ductile, and good conductors of heat and electricity. Here are some key properties of metals:
- Metallic Lustre: Metals have a shiny surface when freshly cut or polished.
- Malleability: Metals can be beaten into thin sheets. Gold and silver are the most malleable metals.
- Ductility: Metals can be drawn into thin wires. Gold is the most ductile metal.
- Conductivity: Metals are good conductors of heat and electricity. Silver and copper are the best conductors.
- Sonority: Metals produce a ringing sound when struck, which is why they are used to make bells.
Example: Copper is used in electrical wires because it is a good conductor of electricity.
3.1.2 Non-Metals
Non-metals are generally brittle, dull, and poor conductors of heat and electricity. Here are some key properties of non-metals:
- Brittleness: Non-metals are brittle and break into pieces when hammered.
- Poor Conductors: Non-metals are poor conductors of heat and electricity, except for graphite, which conducts electricity.
- Non-Lustrous: Non-metals do not have a shiny surface, except for iodine, which is lustrous.
Did you know? Diamond, an allotrope of carbon, is the hardest natural substance known, while graphite, another allotrope of carbon, is a good conductor of electricity.
3.2 Chemical Properties of Metals
Metals exhibit various chemical properties, such as reacting with oxygen, water, acids, and other metal salts. Let’s explore these reactions in detail.
3.2.1 Reaction with Oxygen
Metals react with oxygen to form metal oxides. The reactivity of metals with oxygen varies:
- Potassium and Sodium: React vigorously with oxygen and catch fire if kept in the open.
- Magnesium and Aluminium: React with oxygen to form a protective oxide layer.
- Iron: Does not burn in air but forms iron oxide when heated.
- Copper: Forms copper(II) oxide when heated in air.
Example: When magnesium burns in air, it forms magnesium oxide:
2Mg + O2 → 2MgO
3.2.2 Reaction with Water
Metals react with water to form metal oxides and hydrogen gas. The reactivity of metals with water varies:
- Potassium and Sodium: React violently with cold water, producing hydrogen gas and heat.
- Calcium: Reacts less violently with water, producing calcium hydroxide and hydrogen gas.
- Magnesium: Reacts with hot water to form magnesium hydroxide and hydrogen gas.
- Aluminium, Iron, and Zinc: React with steam to form metal oxides and hydrogen gas.
Example: Sodium reacts with water to form sodium hydroxide and hydrogen gas:
2Na + 2H2O → 2NaOH + H2
3.2.3 Reaction with Acids
Metals react with acids to form salts and hydrogen gas. The reactivity of metals with acids varies:
- Magnesium, Aluminium, Zinc, and Iron: React with dilute acids to form salts and hydrogen gas.
- Copper: Does not react with dilute acids.
Example: Zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas:
Zn + 2HCl → ZnCl2 + H2
3.2.4 Reaction with Other Metal Salts
More reactive metals can displace less reactive metals from their salt solutions. This is known as a displacement reaction.
Example: When an iron nail is placed in a copper sulfate solution, iron displaces copper from the solution:
Fe + CuSO4 → FeSO4 + Cu
3.3 Reactivity Series
The reactivity series is a list of metals arranged in the order of their decreasing reactivity. The series helps predict the outcome of reactions between metals and other substances.
| Metal | Reactivity |
|---|---|
| Potassium (K) | Most Reactive |
| Sodium (Na) | |
| Calcium (Ca) | |
| Magnesium (Mg) | |
| Aluminium (Al) | |
| Zinc (Zn) | |
| Iron (Fe) | |
| Lead (Pb) | |
| Copper (Cu) | |
| Silver (Ag) | |
| Gold (Au) | Least Reactive |
3.4 Extraction of Metals
Metals are extracted from their ores through various processes depending on their reactivity. The extraction process involves three main steps:
- Enrichment of Ores: Removing impurities from the ore.
- Reduction of Metal Oxides: Converting metal oxides into metals using reducing agents like carbon or electrolysis.
- Refining of Metals: Purifying the extracted metal to remove impurities.
3.4.1 Extraction of Metals Low in the Reactivity Series
Metals like mercury and copper, which are low in the reactivity series, are extracted by heating their ores in air.
Example: Mercury is extracted from cinnabar (HgS) by heating it in air:
2HgS + 3O2 → 2HgO + 2SO2
2HgO → 2Hg + O2
3.4.2 Extraction of Metals in the Middle of the Reactivity Series
Metals like zinc, iron, and lead are extracted by reducing their oxides with carbon or other reducing agents.
Example: Zinc is extracted from zinc oxide by heating it with carbon:
ZnO + C → Zn + CO
3.4.3 Extraction of Metals High in the Reactivity Series
Metals like sodium, magnesium, and aluminium are extracted by electrolysis of their molten chlorides or oxides.
Example: Aluminium is extracted from aluminium oxide by electrolysis:
2Al2O3 → 4Al + 3O2
3.5 Corrosion and Its Prevention
Corrosion is the process of metals deteriorating due to their reaction with moisture and air. Rusting of iron is a common example of corrosion.
3.5.1 Prevention of Corrosion
Corrosion can be prevented by various methods, such as:
- Painting: Applying a layer of paint to prevent contact with air and moisture.
- Galvanisation: Coating iron with a layer of zinc to prevent rusting.
- Alloying: Mixing metals with other substances to improve their properties. For example, stainless steel is an alloy of iron, chromium, and nickel.
Did you know? The iron pillar in Delhi, which is over 1600 years old, has not rusted due to the unique composition of its alloy.
Exercises and Questions – Solutions
Here are the solutions to all the exercise questions from the chapter:
-
Which of the following pairs will give displacement reactions?
- (a) NaCl solution and copper metal - No reaction
- (b) MgCl2 solution and aluminium metal - No reaction
- (c) FeSO4 solution and silver metal - No reaction
- (d) AgNO3 solution and copper metal - Reaction occurs
-
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 (Correct Answer)
- (d) All of the above
-
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 (Correct Answer)
- (b) Carbon
- (c) Silicon
- (d) Iron
-
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. (Correct Answer)
- (d) Zinc is less reactive than tin.
-
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.
Metals will conduct electricity and allow the bulb to glow, while non-metals will not. Metals will also produce a ringing sound when struck with a hammer (sonorous), whereas non-metals will not.
The electrical conductivity test is reliable for distinguishing metals from non-metals. The hammer test (malleability) is useful but not always definitive, as some metals (e.g., sodium) are soft.
-
What are amphoteric oxides? Give two examples.
Amphoteric oxides are metal oxides that react with both acids and bases to form salts and water.
Examples: Aluminium oxide (Al2O3) and Zinc oxide (ZnO).
-
Name two metals that will displace hydrogen from dilute acids, and two metals that will not.
Metals that displace hydrogen: Zinc (Zn), Magnesium (Mg)
Metals that do not displace hydrogen: Copper (Cu), Silver (Ag)
-
In the electrolytic refining of a metal M, what would you take as:
- Anode: Impure metal (M)
- Cathode: Pure metal (M)
- Electrolyte: A solution of a salt of metal M
-
What will be the action of gas evolved when sulphur is heated:
- (i) On dry litmus paper? No change
- (ii) On moist litmus paper? Turns blue litmus red (Sulphur dioxide is acidic)
-
State two ways to prevent the rusting of iron.
- Painting or oiling
- Galvanization (coating with zinc)
-
What type of oxides are formed when non-metals combine with oxygen?
Non-metals form acidic oxides or neutral oxides.
-
Give reasons:
- (a) Platinum, gold, and silver are used to make jewellery.
- (b) Sodium, potassium, and lithium are stored under oil.
- (c) Aluminium is highly reactive, yet it is used to make cooking utensils.
- (d) Carbonate and sulphide ores are usually converted into oxides during the extraction process.
They are highly unreactive, resistant to corrosion, and have an attractive appearance.
They react vigorously with air and water, producing heat and hydrogen gas, which can cause fire.
Aluminium forms a protective oxide layer that prevents further reaction.
It is easier to extract metals from oxides than from carbonates or sulphides.
-
Why are tarnished copper vessels cleaned with lemon or tamarind juice?
Copper reacts with air to form copper carbonate, which makes it look dull. The acids in lemon or tamarind react with this layer and remove it, restoring the shine.
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Differentiate between metal and non-metal based on their chemical properties.
- Metals lose electrons to form positive ions; non-metals gain electrons to form negative ions.
- Metals react with acids to produce hydrogen gas; non-metals do not.
- Metals form basic oxides; non-metals form acidic oxides.
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A man posing as a goldsmith dipped gold bangles in a solution, making them shine but reducing their weight. What was the solution?
The solution was likely aqua regia (a mixture of hydrochloric acid and nitric acid), which dissolves some gold, reducing the weight.
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Why is copper used to make hot water tanks instead of steel?
Copper does not corrode in water and is an excellent conductor of heat, whereas steel (iron alloy) may rust.
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