4. Materials : Metals And Non-Metals Science class 8 in English Medium ncert book solutions Text Book Exercise

Text Book Exercise

Q6. Give reasons for the following : 

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

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

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

(d) Sodium and potassium are stored in kerosene.

Answer: (a) It  mainntains the temperature of food item intact as it is a good conductor of heat.

(b) Metals are good conductors of electricity. That why immersion rods are made up of  metals.

(c) It is because copper is less reactive than zinc.

(d) It is because sodium and potassium reacts vigorously when come in contact with air or water.    

Q7. Can you store lemon pickle in an aluminium utensil? Explain.

Answer: Aluminium is a metals. Metals are more reactive with acids. That is why acidic foodstuffs like lemon pickie must not be stored in alminium utensils.  

Q8. In the following Table some substances are given in Column I. In Column II some uses are given. Match the items in column I with those in Column II.

Column I Column II

(i) Gold (a) Thermometers

(ii) Iron (b) Electric wire

(iii) Aluminium (c) Wrapping food

(iv) Carbon (d) Jewellery

(v) Copper (e) Machinary

(vi) Mercury (f) Fuel

Answer: (i) (d), (ii) (e), (iii) (c), (iv) (f), (v) (b), (vi) (a).  

Q9. What happens when :

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

(b) Iron nails are placed in copper sulphate solution? Write word equations of the reactions involved.

Answer: (a) When sulphuric acid is poured on copper plate, copper sulphate is made and hydrog en gas is evolved as pe the following chemical equation :

 Copper plate + Sulphuric acid  → Copper plate + Hydrogen

(b) When iron nails are placed in copper sulphate solution , Cu is displaced by iron. Chemical equation is as follows :

Iron nails +  Copper sulphate solution → Iron sulphate + Cooper

Q10. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.

(a) How will she find the nature of the gas ?

(b) Write down word equations of all the reactions taking place in this process.

Answer: (a) When charcoal is burnt in air , carbon dioxide gas is evolved. This gas when passed into the lime water turns it milky. This is the test of CO₂ gas.

(b) Carbon + Oxygen → Carbon dioxide gas.    

Q11. One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Answer: In polisihing , the jeweller put the gold jeweller in a mild acidic solution , whichon reaction with acid goes into the solution. So, in this process certain amount of gold is lost to the acidic solution.