Class 8 Science Chapter 4 Metals And Nonmetals (Oxford Book)

Class 8 Science Chapter 4 Metals and Nonmetals (Oxford Book)

1. Objective type questions

A. Choose the correct option.

1. Copper is a

a. white metal b. greenish-yellow gas

c. colourless gas d. reddish-brown metal

2. A soft metal that can be cut with a knife is

a. gold b. silver

c. potassium d. iron

3. The property of metals due to which they can be drawn into thin wires is

a. malleability b. ductility

c. sonority d. good conductors of electricity

4. Which of the following is a good conductor of heat

a. Diamond b. Silver

c. Copper d. All of these

5. The order of reactivity of metals is

a. Cu > Mg> Zn > Fe

b. Cu> Fe> Zn> Mg

c. Mg> Zn> Fe > Cu

d. Mg> Fe >Zn > Cu

6. A metal that will displace copper from copper sulphate solution is

a. mercury b. gold

c. aluminium d. silver

7. Which of following gases is produced in the reaction of a metal with an acid?

a. Sulphur dioxide b. Carbon dioxide

c. Oxygen d. hydrogen

8 Which of following is the least reactive metal?

a. Gold b. Potassium

c. Copper d. silver

9. Which of following metals is used in paints and pigments?

a. Iron b. Copper

c. Mercury d. Hydrogen

10. Which of following non-metals is used for making matchsticks and fireworks?

a. Sodium b. Silicon

c. Phosphorous d. Graphite

Ans: Objective Type Questions

d) reddish-brown metal

c) potassium

b) ductility

d) All of these

c) Mg > Zn > Fe > Cu

c) aluminium

d) hydrogen

a) Gold

c) Mercury

c) Phosphorus

B. Fill in the blanks with the correct words.

1. The property of metals due to which they produce a ringing sound when struck with

a hard object is called……(thermal conductivity/sonority).

2. A non-metal that is a good conductor of heat is………………(diamond/graphite).

3. A metal that burns with white dazzling light is……….(magnesium/sodium).

4. Metallic oxides turn……) (red/blue) litmus solution to…………(red/blue

5………….. (Sodium/Magnesium) is kept immersed in kerosene.

6. Non-metallic oxides dissolve in water to form……….(acids,bases)

Ans:

The property of metals due to which they produce a ringing sound when struck with a hard object is called sonority. (thermal conductivity/sonority)
A non-metal that is a good conductor of heat is graphite. (diamond/graphite)
A metal that burns with white dazzling light is magnesium. (magnesium/sodium)
Metallic oxides turn red litmus solution to blue. (red/blue)
Sodium is kept immersed in kerosene. (Sodium/Magnesium)
Non-metallic oxides dissolve in water to form acids. (acids/bases)

II Very short answer type questions

A. Complete the equations.

1. 4Na + O2→ ……………

2. S + O2→………………

3. CO₂ + H₂O…………………….

4. 2Na + 2H2O→ 2NaOH +…………

5. Zn + H₂SO₄ → + H₂……………….

Ans:

4Na + O₂ → 2Na₂O
S + O₂ → SO₂
CO₂ + H₂O → H₂CO₃ (Carbonic acid)
2Na + 2H₂O → 2NaOH + H₂
Zn + H₂SO₄ → ZnSO₄ + H₂

III. Short answer type questions

1. Define the following terms:

Malleability: The property of metals by which they can be beaten into thin sheets.

Ductility: The property of metals by which they can be drawn into thin wires.

Sonority: The property of metals that allows them to produce a ringing sound when struck.

2. State and explain how a particular property of metals helps in making the following:

Ans:

a. Wind chimes and musical instruments – Sonority: Metals produce a pleasant ringing sound when struck, making them ideal for wind chimes and musical instruments.

b. Electrical wires – Conductivity: Metals like copper and aluminium are good conductors of electricity, hence used in wiring.

c. Decorative articles and jewellery – Lustre and malleability: Metals like gold and silver are shiny and can be shaped easily, making them suitable for jewellery and decorative items.

d. Cooking utensils – Thermal conductivity: Metals like aluminium and copper conduct heat well, which helps in even cooking.

3. Compare the reactions of metals and non-metals with oxygen.

Metals react with oxygen to form basic oxides (e.g., Magnesium + Oxygen → Magnesium oxide).

Non-metals react with oxygen to form acidic oxides (e.g., Sulphur + Oxygen → Sulphur dioxide).

4. How does the sodium metal react with water? Give two examples of metals that do not react with water.

Sodium reacts vigorously with water to form sodium hydroxide and hydrogen gas, with heat and sometimes flames:
2Na + 2H₂O → 2NaOH + H₂↑

Metals that do not react with water:

Gold

Lead

5. Write one use of each of the following:

Steel – Used in construction and making tools.

Aluminium – Used in making utensils and aircraft parts.

Mercury – Used in thermometers.

Silicon – Used in making computer chips and solar panels.

Sulphur – Used in making fertilizers and sulphuric acid.

Diamond – Used in cutting tools and jewellery.

IV. Long answer type questions

1. How do metals and non-metals react with acids? Write and explain the chemical equation for the reaction of magnesium with sulphuric acid and aluminium with hydrochloric acid.

2. Define corrosion. Explain the corrosion process in iron, copper and silver.

Ans: Corrosion is the process of gradual destruction of metals due to chemical reactions with their environment, often with oxygen, water, or chemicals. The most common form of corrosion is rusting in iron, where iron reacts with oxygen and water to form iron oxide (rust)

Corrosion of Iron:

Iron, when exposed to oxygen and moisture (water or humidity), undergoes a chemical reaction called rusting, which is a form of corrosion. The process involves the formation of hydrated iron(III) oxide (rust).

The chemical equation for rusting:

4Fe+3O2+6H2O→4Fe(OH)34Fe + 3O2 + 6H2O → 4Fe(OH)_34Fe+3O2+6H2O→4Fe(OH)3

This is the hydrated form of iron(III) oxide, which we recognize as rust. The rust can further dehydrate to form Fe₂O₃·xH₂O.

Corrosion of Copper:

Copper, when exposed to air and moisture over time, forms a greenish-blue patina on its surface, which is a product of its corrosion. This is mainly copper(II) carbonate or copper(II) hydroxide..

The chemical equation for corrosion of copper:

2Cu+O2+2CO2+2H2O→Cu2(OH)2CO32Cu + O_2 + 2CO_2 + 2H_2O → Cu_2(OH)_2CO_32Cu+O2+2CO2+2H2O→Cu2(OH)2CO3

This forms copper carbonate (patina), which gives copper its characteristic greenish appearance.

Corrosion of Silver:

Silver tarnishes when it reacts with sulfur compounds present in the air, forming silver sulfide (Ag₂S). This tarnishing is often mistaken for rust but is a different type of corrosion.

The chemical equation for tarnishing of silver:

2Ag+H2S→Ag2S+H22Ag + H_2S → Ag_2S + H_22Ag+H2S→Ag2S+H2

The silver sulfide (Ag₂S) forms a black layer on the surface of the silver, causing it to lose its shiny appearance.

3. What is a displacement reaction? On the basis of the reactivity series of metals, predict whether these metals will react with each of the following salt solutions or not.

Metals: copper, magnesium, zinc, and iron

Salt solutions: copper sulphate, magnesium sulphate, zinc sulphate, and iron sulphate

Ans: A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution.

Reactivity Series:

Magnesium > Zinc > Iron > Copper

Predictions with Reactions:

Copper with Salt Solutions:

Copper sulphate (CuSO₄): No reaction.

Magnesium sulphate (MgSO₄): No reaction.

Zinc sulphate (ZnSO₄): No reaction.

Iron sulphate (FeSO₄): No reaction.

Magnesium with Salt Solutions:

Copper sulphate (CuSO₄):

Mg+CuSO4→MgSO4+CuMg + CuSO₄ → MgSO₄ + CuMg+CuSO4→MgSO4+Cu

(Magnesium displaces copper)

Magnesium sulphate (MgSO₄): No reaction.

Zinc sulphate (ZnSO₄):

Mg+ZnSO4→MgSO4+ZnMg + ZnSO₄ → MgSO₄ + ZnMg+ZnSO4→MgSO4+Zn

(Magnesium displaces zinc)

Iron sulphate (FeSO₄):

Mg+FeSO4→MgSO4+FeMg + FeSO₄ → MgSO₄ + FeMg+FeSO4→MgSO4+Fe

(Magnesium displaces iron)

Zinc with Salt Solutions:

Copper sulphate (CuSO₄):

Zn+CuSO4→ZnSO4+CuZn + CuSO₄ → ZnSO₄ + CuZn+CuSO4→ZnSO4+Cu

(Zinc displaces copper)

Magnesium sulphate (MgSO₄): No reaction.

Zinc sulphate (ZnSO₄): No reaction.

Iron sulphate (FeSO₄):

Zn+FeSO4→ZnSO4+FeZn + FeSO₄ → ZnSO₄ + FeZn+FeSO4→ZnSO4+Fe

(Zinc displaces iron)

Iron with Salt Solutions:

Copper sulphate (CuSO₄):

Fe+CuSO4→FeSO4+CuFe + CuSO₄ → FeSO₄ + CuFe+CuSO4→FeSO4+Cu

(Iron displaces copper)

Magnesium sulphate (MgSO₄): No reaction.

Zinc sulphate (ZnSO₄): No reaction.

Iron sulphate (FeSO₄): No reaction.

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