Chapter 4: The World of Metals and Non-metals (Chemistry)

(i) Aluminium. It is cheap, light and very malleable, so thin aluminium foil is used for wrapping food.

(i) Aluminium

(iv) Sodium. It reacts very vigorously with water, producing so much heat that it catches fire; so it is stored in kerosene.

(iv) Sodium

(i) F. Aluminium and copper are metals.

(ii) F. Metal oxides are basic; their solutions turn red litmus blue. (Non-metal oxides turn blue litmus red.)

(iii) T. Oxygen is a non-metal, and living beings need it for respiration.

(iv) F. Copper vessels are used for boiling water because copper is a good conductor of heat, not because it conducts electricity.

(i) F, they are metals (ii) F, metal oxides turn red litmus blue (iii) T (iv) F, because copper is a good conductor of heat

Jewellery metals must be shiny (lustrous), very malleable and ductile (so they can be beaten into thin sheets and drawn into fine wires for designs), not react with air and water (so they do not tarnish or rust and keep their shine for years), and be rare and valuable. Only a few metals, such as gold, silver and platinum, have all these properties. Metals like iron rust, and sodium reacts with air and water, so they are unsuitable.

Jewellery needs metals that are lustrous, very malleable and ductile, and do not react with air or water (no rusting or tarnishing), like gold, silver and platinum; most metals lack these qualities.

(i) – (c) copper; (ii) – (e) gold; (iii) – (a) oxygen; (iv) – (d) nitrogen; (v) – (b) chlorine

• Magnesium (a metal) burns in oxygen with a dazzling white flame, forming a white powder (ash), magnesium oxide. Dissolved in water, it gives a solution that turns red litmus blue: the oxide is basic.
• Sulfur (a non-metal) burns in oxygen with a blue flame, forming a gas with a choking smell, sulfur dioxide. Dissolved in water, it gives a solution that turns blue litmus red: the oxide is acidic.

So metal oxides are basic and non-metal oxides are acidic.

Magnesium forms magnesium oxide, which is basic (turns red litmus blue); sulfur forms sulfur dioxide, which is acidic (turns blue litmus red).

Since the solution turns red litmus blue, it is basic, so the substance burnt must be a metal, e.g. magnesium.

• Magnesium + Air + Heat → Ash (magnesium oxide)
• Ash + Water → magnesium hydroxide solution (basic)
• Blue litmus solution → no change
• Red litmus solution → blue

Magnesium → magnesium oxide (ash) → with water, a basic solution (magnesium hydroxide); blue litmus: no change; red litmus: turns blue.

Copper (iron is the next best). A pan for boiling water must be a good conductor of heat so that the heat from the stove passes quickly to the water, and it must be strong, not melt or burn, and be malleable enough to be shaped. Copper conducts heat best among these and is malleable. Iron also works but conducts heat less well and can rust. Sulfur, coal, plastic, wood and cardboard are poor conductors of heat; plastic melts, and wood, cardboard and coal burn.

Copper (or iron): it is a good conductor of heat, strong and can be shaped; the others are poor conductors and would melt or burn.

The nail dipped in oil will not rust. Rusting needs both air (oxygen) and water (moisture). The oil forms a layer on the nail that keeps air and water away. The nail in water rusts, and the one in vinegar rusts (corrodes) even faster.

The nail in oil: the oil layer keeps out air and moisture, which are both needed for rusting.

Each use matches a property: metals conduct heat and electricity (utensils, wires), are malleable, ductile, sonorous and strong (foil, wires, bells, buildings); non-metals are poor conductors (handles, insulation), and oxygen, nitrogen and chlorine support life, plants and clean water.

No. Even though sulfur does not react with water:

• sulfur is brittle and powdery; it cannot form a smooth, strong, lasting coating and would crack and fall off;
• sulfur can react with iron and with oxygen (especially when warmed), forming iron sulfide and sulfur dioxide, which is acidic and would itself corrode the iron;
• it is a non-metal and cannot be spread as a thin metallic layer the way molten zinc can.

Zinc, a metal, forms a firm protective layer and also protects iron because it is more reactive (it corrodes instead of the iron).

No: sulfur is brittle and cannot form a lasting coating, and it can react with iron and form acidic sulfur dioxide that corrodes iron; a metal like zinc is needed.

Heating makes iron soft and more malleable. Red-hot iron can be easily hammered, bent and shaped into tools such as sickles, axes and spades without cracking. Cold iron is hard and needs much more force to shape.

Heating softens the iron and makes it more malleable, so it can be hammered and shaped into tools without breaking.