DAV Solutions For Class 8 Science Chapter 3

 

DAV Solutions Class 8 Science Chapter 3 Question Answer

DAV Solutions for Class 8 Science Chapter 3 Metals and Non-Metals is given below. Here DAV Class 8 Science Chapter 3 Question Answer is provided with great explanation.

A. Fill in the blanks.

1. The property, due to which a metal piece can be hammered into thin sheets, is known as ___________.

2. Bronze is an alloy of ___________ and ___________.

3. Gold is mixed with ___________ and /or ___________ to make it hard.

4. ___________ is the only non-metal to have a natural luster.

5. ___________ is a non-metal which catches fire in air.

6. The only metal, which exists in the liquid state at room temperatures, is ___________.

Answer: (1) malleability (2) copper, tin (3) silver, copper (4) Iodine (5) Phosphorus (6) mercury

B. Match the following.

Match the following

Answer: (1) d, (2) c, (3) a, (4) b, (5) e

C. Tick the correct option.

1. The two most abundant metals, found in the earth’s crust, are-

Answer: aluminium and iron

2. The metals, used in making the alloy ‘german silver’, are-

Answer: copper + zinc + nickel

3. When a metal reacts with oxygen, the resulting oxide of the metal-

Answer: is a basic oxide

4. Out of the metals, gold, silver, copper and aluminium, the one, that is most ductile, is-

Answer: gold

5. Two of the metals, that cannot be stored either in air, or under water, are-

Answer: potassium and sodium

D. Answer the following questions in brief.

1. Name (i) one metal and (ii) one non-metal which normally exists in the liquid state.

Answer: (i) Mercury (ii) Bromine

2. State the fraction of gold present in an 18-carat gold piece.

Answer: Pure gold is 24 carats. So, 18 carat means 18 parts gold and 6 parts other elements. Hence, fraction of gold present in 18 carats = 18/24 = 3/4.

3. State the property of copper wires that makes them useful for electrical fittings.

Answer: the property of copper wires that makes them useful for electrical fittings are:

• Copper is good conductor of electric current.
• It is malleable and ductile.
• Moreover, Copper is economical too.

4. Define an alloy.

Answer: A homogenous mixture of two or more metals, or a metal and a non-metal is called an alloy.

5. List any two uses of non-metals.

Answer: Two uses of non-metals are:

• Phosphorus is used in matchbox industry and in fertilisers,
• Iodine is used as an antiseptic.
• E. Answer the following questions.

• 1. Write the balanced chemical equations for the following reactions:

  (a) sodium reacts with oxygen

  Answer: 4Na (Sodium) + O₂ (Oxygen) → 2Na₂O (Sodium Oxide)

  (b) aluminium reacts with dilute hydrochloric acid

  Answer: 2Al (s) + 6HCl (aq) → 2AlCl₃ (aq) + 3H₂ (g)

  2. Why are gold and platinum suitable for making jewellery?

  Answer: Gold and Platinum are suitable for making jewellery because-

They are highly malleable and ductile.

They retain their lustre for very long period of time.

They are least reactive metals.

• 3. ‘Sodium and potassium is stored under kerosene. Give reason.

  Answer: Sodium and Potassium are highly reactive metals. They react with air even at room temperature. They also react very vigorously with water and catches fire. Therefore, these metals are stored under kerosene or paraffin wax.

  4. Why is bronze preferred over copper metal for making statues?

  Answer: Bronze is preferred over copper metal for making statues because bronze is an alloy which is stronger, harder and more resistant to corrosion than copper (pure metal).