4. Materials : Metals And Non-Metals Science class 8 in English Medium ncert book solutions Additional Questions With Solutions

Additional Questions With Solutions

Q14: Identify following oxides are metallic or non-metallic.

(i) An oxide turns red litmus into blue.

(ii) An oxide turns blue litmus into red.

Ans: (i)  Metallic oxide.   (ii)   Non-metallic oxide.

Q15: Name the metal which reacts vigorously with water.

Ans: Sodium

Q16: Write the name of a non-metal which is a good conductor of electricity.

Ans: Graphite.

Q17: Define displacement reaction with example.

Ans: When a highly reactive metal react with a compound of it replaces the metal from compound such a reaction is called displacement reaction.

                   Example: CuSO₄ + Fe ® FeSO₄ + Cu (­)

(Here Fe is a highly reactive metal and Cu is a less reactive metal)

Q18: Write three physical properties of metals.

Ans: Three physical properties of metals.

(i) Metals are ductile.

(ii) Metals are malleable.

(iii) Metals are sonorous.

Ques: Write the name of a metal which found liquid at room temperature.

Ans: mercury.

Q19: Name the metals which can be cut with knife.

Ans: Sodium and Potassium.

Q20: What happens when:

(i) Dilute sulphuric acid is poured on a copper plate?

Ans: when sulphuric acid is poured on copper plate copper sulphate is made and hydrogen gas is evolved as per the following chemical equation.

copper plate +sulphuric acid → copper sulphate + hydrogen.

(ii) Iron nails are placed in copper sulphate solution

Ans: When iron nails are placed in copper sulphate solution Cu is displaced by iron and colour of solution changes.

(iii) Write word equations of the reactions involved.

Ans: Chemical eqution is as follows;

  Iron nails + sulphate → Iron sulphate + copper.

Q21. Give reasons for the following :

(i) Aluminium foils are used to wrap food items.

Ans: It maintains the temperature of food item intact as it is a good conductor of heat.

(ii) Immersion rods for heating liquids are made up of metallic substances.

Ans: Metals are good conductor of electricity. That is why immersion rods are made up of metals.

(iii) Copper cannot displace zinc from its salt solution.

Ans: It is because copper is less reactive than zinc.

(iv) Sodium and potassium are stored in kerosene.

Ans: It is because sodium and potassium reacts vigorously when come in contact with air or water.

Q22: Why is lemon pickle not stored in an aluminium utensil? Explain.

Ans: As lemon pickle contains acid which highly reactive to aluminium that resulting in destroyed of utensil.

Q23: Write the equation of rusting of iron.

Ans: 3Fe +2H₂O + O₂ → Fe₃O₄ + 2H₂

Q24: What is the product formed, when sulphur reacts in air (O2)?

Ans: It is sulphur dioxide (SO₂).

Q25: What is formed when sulphur dioxide is dissolved in water? Also write the eqution.

Ans: Sulphurous acid is formed.

So₂ + H₂O  → H₂SO₃ (Sulphurous acid)

Q26: What is the reactivity of non – metals with water?

Ans: Non-metals do not react with water.