Materials: Metals and Non-Metals

Q43. There are three materials X, Y and Z. X and Z are hard and shiny, but Y is dull and not very hard. Identify the metals and non-metals from X, Y and Z.

Ans. X and Z are metals.

Y is non-metal.

Q44. Why wires are made of aluminum and copper and not of carbon and sulphur?

Ans. Aluminum and copper are metals and can be drawn into wires. But carbon and sulphur are non-metals and hence cannot be drawn into thin wires.

Q45. How phosphorus is stored?
Or
Why is phosphorous stored in water?
Or
What will happen if phosphorus is kept in open air?
Or
Why do we store white phosphorus in water?

Ans. Phosphorus is a very reactive non-metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.

Q46. Why are wooden or plastic handles used for cooking utensils?
Or
Why can’t we hold a hot metallic pan without a plastic or wooden handle without getting hurt?

Ans. Wooden or plastic handles are used for cooking utensils because they are bad conductors of heat and protects us from being hurt while handling hot things.

Q47. Why there is difference in sound on dropping a metal coin and a piece of coal?

Ans. Metals are sonorous i.e. they produce ringing sound when struck hard whereas non-metals non-sonorous. Hence, on dropping a metal coin, ringing sound is produced but no such sound is produced in case of coal.

Q48. What does the ‘pop’ sound indicate in a reaction?

Ans. The ‘pop’ sound indicates the presence of hydrogen gas. Metals react with sodium hydroxide to produce hydrogen gas. Reactions of non-metals with bases are complex.

Q49. What is an element? Give example.

Ans. If a substance cannot be broken down further by chemical reactions, by cooling, heating, or by electrolysis, it is called ‘element’. Sulphur is an element. So is iron. Carbon, too, is an element.

Q50. “The atom of an element remains unaffected by physical changes in the element.” Explain the statement with the help of example.

Ans. The atom of an element remains unaffected by physical changes in the element. For example, an atom of liquid sulphur would be exactly the same as the atom of solid or vapour sulphur.

Q51. How are elements classified?

Ans. An important classification of elements is in terms of metals and non-metals. Most of the elements are metals. Less than 20 are non-metals. A few are metalloids which possess characters of both metals and non-metals.

Q52. Why are electric wire made of copper?
Or
Why are copper metal wires used to conduct electricity?

Ans. Copper metal wires are used to conduct electricity because:

                        i.        It is ductile and can be drawn into wires.

                       ii.        It is a good conductor of electricity.

Q53. Why can't copper displace zinc from its salt solution?
Or
Copper cannot displace zinc from its salt solution. Give reason.

Ans. A more reactive metal can replace a less reactive metal from its compound in aqueous solution. Zinc is more reactive than copper. Therefore, copper cannot displace zinc from its salt solution.

Q54. Can you store lemon pickle in an aluminium utensil? Explain.

Ans. Lemon pickle cannot be stored in aluminium utensils because lemon pickle contains acids, which can react with aluminium (metal) liberating hydrogen gas. This can lead to the spoiling of the pickle.

Q55. Complete the following reactions of iron and magnesium with oxygen.
Iron (Fe) + Oxygen (O₂) + Water (H₂O) → ?
Magnesium (Mg) + Oxygen (O₂) → ?

Ans. Iron (Fe) + Oxygen (O₂) + Water (H₂O) → Iron oxide (Fe₂O₃)

Magnesium (Mg) + Oxygen (O₂) → Magnesium oxide (MgO)

Q56. Explain reaction between sulphur and oxygen. What is the nature of its oxide formed?

Ans. When sulphur burns in air, it combines with oxygen of air to form sulphur dioxide (which is an acidic oxide).

Sulphur(S) + Oxygen(O₂)  →  Sulphur dioxide(SO₂)

                                            (An acidic oxide)

Q57. Can copper displace iron from iron sulphate solution? Give reason.
Or
Why copper cannot displace iron from iron sulphate solution?

Ans. A more reactive metal can replace a less reactive metal from its compound in aqueous solution. Copper lies below iron in the reactivity series i.e. iron is more reactive than copper. Therefore, copper cannot displace iron from its salt solutions.