Science Ncert Exemplar 2019 Solutions for Class 8 Science Chapter 4 - Materials : Metals And Non Metals

Answer:

The materials which are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity are called metals. The examples of metals are iron, copper, aluminium, calcium, magnesium, etc. Sulphur is a non-metal because it is soft and dull in appearance. It breaks down into a powdery mass on tapping with a hammer and is not sonorous and a poor conductor of heat and electricity.

Hence, the correct answer is option B.

Answer:

Malleability is the property of metals by which they can be beaten into thin sheets on beating with a hammer. Zinc is a metal.

Hence, the correct answer is option D.

Answer:

A piece of coal is generally broken into pieces on beating with a hammer. Therefore, it is a nonmetal.

Hence, the correct answer is option D.

Answer:

Ductility is a characteristic property of metals. Sulphur is a nonmetal and therefore, cannot be drawn into wires.

Hence, the correct answer is option C.

Answer:

Sodium is soft and can be cut with a knife.

Hence, the correct answer is option B.

Answer:

Mercury is the only metal which is found in liquid state at room temperature.

Hence, the correct answer is option A.

Answer:

Copper does not react with dilute hydrochloric acid even on heating but it reacts with sulphuric acid.

Hence, the correct answer is option D.

Answer:

Sodium metal is very reactive. It reacts vigorously with cold water and a lot of heat is generated in the reaction.

Hence, the correct answer is option B.

Answer:

Aluminium produces hydrogen gas on reaction with dilute hydrochloric acid as well as sodium hydroxide solution. It is confirmed by a ‘pop’ sound which is produced when a burning match stick is brought near the mouth of the test tube in which reaction takes place.

Hence, the correct answer is option C.

Answer:

Phosphorus is a very reactive non-metal and catches fire on exposure to air.

Hence, the correct answer is option A.

Answer:

Sulphur dioxide is a non-metallic oxide. When it is dissolved in water sulphurous acid is formed.
Sulphur dioxide (SO₂) + Water (H₂O) → Sulphurous acid (H₂SO₃)
The sulphurous acid turns blue litmus paper red.

Hence, the correct answer is option A.

Answer:

Copper is used as electrical conduction wires because it is solid, ductile and good conductor of electricity. Colour of copper is not responsible for its use as electrical conduction wires.

Hence, the correct answer is option B.

Answer:

Sodium and potassium are soft enough to be cut with a knife.

Answer:

Oxygen is the non-metal is essential for our life and all living beings inhale it during breathing.

Answer:

Nitrogen and phosphorus are the two non-metals which are present in fertilisers and enhance the growth of plants.

Answer:

Chlorine is used as a disinfectant to purify water.

Answer:

Iodine is a purple coloured non-metal which forms a brown solution in alcohol known as Tincture of Iodine. This is applied on wounds as an antiseptic.

Answer:

No colour is observed on adding copper turning in zinc sulphate solution as copper is not able to replace zinc from zinc sulphate solution. This is because copper is less reactive than zinc and less reactive metal cannot replace a more reactive metal.

Answer:

Metals are sonorous i.e. they produce a ringing sound when struck hard. Therefore, bells are made of metals.

Answer:

Mercury is the only metal which is found in liquid state at room temperature. Therefore, it â€‹is used for making thermometers. The level of mercury rises in accordance with the temperature measured.

Answer:

Zinc is more reactive than copper and iron. Therefore, it can displace the other two metals from their salt solutions.

Answer:

Copper statue acquired a dull green coating when exposed to moist air for long time. The green material is a mixture of copper hydroxide (Cu(OH)₂) and copper carbonate (CuCO₃). The following reaction takes place:
2Cu + H₂O + CO₂ + O₂ → Cu(OH)₂ + CuCO₃

Answer:

(a) Iron is a metal.
(b) Metals are good conductors of electricity.

Answer:

No, the bulb will not glow because wooden stick is a non-metal and non-metals are poor conductors of electricity.

Answer:

The colour of the solution in beaker A becomes yellowish green due to formation of ferrous sulphate. Also, a reddish brown layer of copper will deposit on the iron nail. This is because iron is more reactive than copper and displaces it from its salt solution.
There will be no change in the colour of the solution in beaker B because copper is less reactive than iron and cannot displace iron from its salt solution.

Answer:

The tablet itself is not made of iron metal and hence, does not look like iron. It is made of a salt of iron.

Answer:

Answer:

The incorrect statements are:
(b) Metals are good conductor of electricity but poor conductor of heat.
(d) Oxides of non-metals and metals are acidic in nature.
​(e) A less reactive metal replaces a more reactive metal from its salt solution in water.

The corrected form of incorrect statements are:
(b) Metals are good conductors of heat and electricity.
(d) Oxides of non-metals are acidic in nature while oxides of metals are basic in nature.
​(e) A more reactive metal replaces a less reactive metal from its salt solution in water.

Answer:

• Dissolve copper sulphate in about 100 mL water in a beaker. A blue coloured solution is obtained.
• Put an iron nail into this beaker.
• Keep the beaker undisturbed for some time.
• The colour of the solution in beaker becomes yellowish green due to formation of ferrous sulphate. Also, a reddish brown layer of copper will deposit on the iron nail.
• This is because iron is more reactive than copper and displaces it from its salt solution.

Answer:

The name of the product formed in the reaction of sulphur and oxygen is sulphur dioxide gas.
When sulphur dioxide is dissolved in water, sulphurous acid is formed.
The sulphurous acid turns blue litmus paper to red. Generally oxides of non-metals are acidic in nature.

Q1. What is the nature of oxides formed by non-metals?
Q2. Which acid is produced on dissolving sulphur dioxide in water?

Answer:

Answer: