The World of Metals and Non-metals: questions with answers

Sodium and potassium are soft metals that can be cut with a knife. Unlike iron and copper, these metals are not hard.

Shine alone does not identify a material as a metal. Other properties, such as malleability and electrical conduction, must also be checked. Metallic lustre is a property of the metal itself, not an added polish.

Ropes made of steel wires can support heavy loads. That is why they are used in cranes to lift heavy objects and in suspension bridges. So drawing a metal out into thin wire does not make it weak.

Steel is a mixture of the metal iron and the non-metal carbon. Ropes made of steel wires can support heavy loads. That is why they are used in suspension bridges and in cranes to lift heavy objects. So drawing a metal out into thin wire does not make it weak.

Aluminium foil is used for wrapping food items. Aluminium is used for food packaging because it is cheaper and its thin sheets can be folded easily into any shape. Iron, copper and gold are not the metals used for food foil.

The block of wood keeps its shape when gently hammered in this activity. It does not form a thin sheet or break into pieces. This shows that malleable and brittle do not describe every material.

The metal coin is sonorous because it produces a ringing sound, even though the sound is soft. The wooden block and rubber ball produce dull thuds. Sonority depends on a ringing sound, not loudness. The ringing is a property of the coin, not the floor.

The metal coin produces a ringing sound because metals are sonorous. A metal object does not need to be hollow to produce a ringing sound.

Metals are good conductors of heat. The transfer of heat from one point of a material to another is called conduction. That is what made the far end of the metal spoon hot in Activity 4.3, and it is why a metal handle grows hot. Wood is a poor conductor, which is not the same as no conduction. The wooden spoon in that activity did warm a little; it simply transferred heat poorly.

Sulfur, coal and stone are poor conductors of electricity. The bulb does not glow when each material is tested. Being hard does not make stone or coal a good conductor.

Iron and copper stand in water without changing, so not every metal reacts with water. Sodium reacts vigorously with water, so at least one metal does. Both are metals, so the rule that fits both observations is that some metals react with water and others do not.

Non-metals generally do not react with water. Sulfur put into water in Activity 4.8 shows no reaction at all. Phosphorus is kept under water because it catches fire in air, not because water changes it.

Iron needs both air and water to rust. In bottle A, silica gel keeps the air dry. In bottle B, boiling removes dissolved air from the water, and the oil layer keeps air from entering it again. The nail in bottle C touches both air and water, so it develops brown rust deposits. The glass wall does not rust.

Rusting of iron can be prevented by painting, oiling, greasing, or coating the iron with a layer of zinc metal. Coating iron with zinc is called galvanisation. Painting and oiling are separate methods, and neither of them uses zinc. Corrosion is the damage done to the metal, not a way of protecting it.

You observe many metals in your day-to-day lives because of their distinct properties. This should not give an impression that non-metals are not important in our lives. We breathe in oxygen and could not survive without it. Carbon is the building block of all life forms. Nitrogen is an essential nutrient for the growth of plants. So non-metals are just as important as metals.