Chapter 4: The World of Metals and Non-metals

Step 1 – Recall the property involved
Malleability is the property that allows a metal to be hammered or rolled into thin sheets. Therefore, any example of a "metal sheet" must be a substance that is (a) a metal and (b) commonly found or used in sheet form.

Step 2 – List metals that are widely rolled into sheets

• Aluminium – kitchen foil, cold-drink cans, aeroplane bodies
• Iron / Steel – roofing sheets, car bodies, ship plates
• Copper – decorative panels, electrical equipment casings
• Zinc – corrugated roofing sheets, galvanised sheets
• Tin – tin-plate used for food cans
• Lead – protective radiation shields, roofing flashings
• Gold and Silver – beaten into very thin leaves for gilding and sweets

Step 3 – Connect back to the concept
All of the above are good examples because their ability to form sheets directly demonstrates the malleability of metals discussed in the chapter.

Step 1 – Natural occurrence of the two metals

• Copper (Cu) is low in the reactivity series. Because of this it is sometimes found as shiny native copper and also in easily reducible ores such as copper oxide or carbonate.
• Iron (Fe) is much more reactive. It is never found free in the earth’s crust (except rare meteorites); it exists only as very stable oxides like $$\mathrm{Fe_2O_3}$$.

Step 2 – Temperatures early humans could reach

• Simple wood- or charcoal-fired kilns reached about $$1100\,{}^{\circ}\mathrm{C}$$.
• Melting point of copper: $$1085\,{}^{\circ}\mathrm{C}$$ (within reach).
• Melting point of iron: $$1535\,{}^{\circ}\mathrm{C}$$ (far above what those kilns could achieve).

Step 3 – Ease of extraction

Step 4 – Reasoning

1. Copper could be picked up in the metallic state; iron could not.
2. The temperature needed to smelt copper was achievable in primitive furnaces; for iron it was not.
3. The chemical steps for copper extraction are simpler than those for iron.

Conclusion

Because copper occurs in native form, has a lower melting point and can be extracted with simple low-temperature processes, humans discovered and used copper long before they learned to produce iron. Hence historians place the “Copper Age” earlier than the “Iron Age”.

Step 1 – Recall the property that allows metals to be made into wires
Metals are ductile; that is, they can be drawn out (stretched) into long, thin wires without breaking.

Step 2 – Think of places where long, thin conductors are needed
The most common need for thin conductors is in electrical and communication systems because metals also conduct electricity well.

Step 3 – Write the uses
Metal wires are therefore found in:

• Over-head power-transmission lines and underground electric cables.
• Household electrical wiring and the wiring inside electrical appliances (fans, heaters, irons, mixers, etc.).
• Telephone, television, computer-network and other communication cables.
• Strings of certain musical instruments (e.g. guitar, sitar, piano) and headphone/ear-phone leads.

All these uses depend on two key metallic properties: ductility (so the metal can be made into a wire) and high electrical conductivity (so the wire can safely carry electric current or signals).

Step 1 : Recall the property involved
Among the characteristic physical properties listed in your textbook is sonority – the ability of a substance to produce a clear, ringing sound when it is struck, scraped or allowed to fall on a hard surface.

Step 2 : Observe what happens with metals
When a metal object such as a spoon, plate or coin hits the floor it starts to vibrate rapidly and uniformly. These vibrations set the surrounding air in regular vibrations as well, giving a loud, sharp and pleasant “ting-ting” sound. Because metals are dense, elastic and have closely packed particles, very little of the sound energy is lost inside the metal; instead it is sent out as a clear ringing note. Hence metals are called sonorous.

Step 3 : Observe what happens with non-metals
Pieces of coal (carbon) or wood are examples of non-metals. They are brittle, porous and comparatively less elastic. When they fall on the floor, most of the mechanical energy is absorbed inside the irregular structure instead of being released as a regular vibration. The result is only a dull, muffled “thud” or no distinct ring at all. Therefore non-metals are described as non-sonorous.

Step 4 : State the difference clearly

• Metals → produce a clear, ringing metallic sound on being dropped – they are sonorous.
• Coal or wood (non-metals) → give a dull sound or thud – they are non-sonorous.

Thus the sound from a falling metal object is sharp and ringing, whereas the sound from a falling piece of coal or wood is dull and flat.

Step 1 ‒ Listing familiar cooking metals

• Aluminium ( symbol $$\mathrm{Al}$$ )
• Copper ( symbol $$\mathrm{Cu}$$ )
• Iron in the form of cast-iron or stainless-steel utensils ( symbol $$\mathrm{Fe}$$ )

Some other alloys that contain these metals and are also used are brass (copper + zinc) and bronze (copper + tin), but the main metallic component remains one of the three listed above.

Step 2 ‒ Why are these particular metals chosen?

1. Excellent conductors of heat.
   Heat must travel quickly from the flame to the food. Metals have free electrons; hence the thermal conductivity $$k$$ of these metals is large:
   

   Metal	Approx. thermal conductivity $$k$$ ( $$\mathrm{W\,m^{-1}K^{-1}}$$ )
   $$\mathrm{Cu}$$	390
   $$\mathrm{Al}$$	205
   Stainless steel (mainly $$\mathrm{Fe}$$)	15 – 20

2. High melting points.
   Cooking temperatures are far below the melting points of these metals, so the vessel does not melt or deform. For example, $$\mathrm{Al}$$ melts at about $$660^{\circ}\text{C}$$ and $$\mathrm{Fe}$$ at about $$1535^{\circ}\text{C}$$.
3. Malleability and ductility.
   They can be hammered or rolled into thin sheets and bent into the desired pot or pan shape without breaking.
4. They form protective oxide layers or alloys that resist corrosion.
   Aluminium quickly forms a thin, hard $$\mathrm{Al_2O_3}$$ layer that prevents further rusting, and stainless steel contains chromium that gives it rust-resistance. Thus the vessel lasts long and does not contaminate food.
5. Relatively inexpensive and easily available.

Step 3 ‒ Conclusion

Because aluminium, copper and iron (in stainless-steel form) possess the above set of properties, they are the metals most commonly used for making everyday cooking vessels.

Step 1 – Recall the property of metals.
Metals such as iron, aluminium and copper are good conductors of electricity. That is why the shaft (the pointed part) of a screwdriver is always made of steel (an iron alloy) so that electric current can pass through it when it is in contact with a live wire.

Step 2 – Identify the danger.
If the hand of the electrician were to touch the metal shaft directly, the current could travel through the body to the earth. This would give a severe electric shock because the human body contains salty water, which conducts electricity.

Step 3 – Choose a safe covering material.
Materials like plastic, rubber, wood and fibreglass are insulators (poor conductors). They do not allow electric current to pass through them easily.

Step 4 – Apply the idea to a screwdriver.
Therefore, the handle of a screwdriver is made of plastic or hard rubber. When the electrician holds the handle, the insulating material stops the current at the metal–plastic junction, keeping the electrician safe.

Step 5 – Explain the use of rubber gloves and shoes.
Exactly the same reasoning applies to rubber gloves and rubber-soled shoes:

• Rubber is an electrical insulator.
• By wearing rubber gloves, the electrician ensures that even if the hand accidentally touches a bare wire, current cannot enter the body.
• Rubber-soled shoes break the path between the body and the ground, so the current has no easy route to flow through the body to the earth.

Conclusion.
The handle is made of an insulating material (plastic/rubber), and rubber gloves and shoes are worn because rubber is a poor conductor; all these precautions prevent electric current from passing through the electrician’s body.

Step 1 • Recall what the brown deposit is
When an iron nail, a bicycle handle, or a gate is left in the open, a flaky brown layer slowly appears on its surface. This layer is called rust, and the process is known as rusting of iron.

Step 2 • Identify the chemical change that produces rust
Rust is hydrated iron(III) oxide. Chemists write its formation, in a simplified way, as

$$ ext{Iron (Fe)} + ext{Oxygen (O}_2) + ext{Water (H}_2 ext{O)} \[2pt] \longrightarrow \text{Hydrated iron(III) oxide (rust)}$$

The equation shows that both oxygen (from air) and water (usually present as moisture, rain, dew, etc.) are essential reactants.

Step 3 • Check each option against the requirement

• (i) Dry air only  →  supplies oxygen but no water ⇒ rusting cannot start.
• (ii) Water only  →  supplies water but has hardly any dissolved oxygen ⇒ rusting is extremely slow or absent.
• (iii) Both air and water  →  provides oxygen + moisture together ⇒ rusting proceeds, and the brown deposit forms.

Step 4 • Conclusion
An iron object develops brown deposits only when it is simultaneously in contact with air (oxygen) and water (moisture).

Observation to be explained

• Copper objects such as old water-pots or electric wires slowly acquire a green layer on their surface.
• Silver ornaments or utensils kept in the open air gradually turn black.

Step 1 ‒ Recall that metals react with substances present in moist air

Air is not composed of oxygen alone. It always contains some water vapour and may also carry traces of acidic gases (like $$\mathrm{CO_2}$$) or sulphur-containing gases (like $$\mathrm{H_2S}$$ from sewers, volcanic regions, decaying matter, etc.). These additional components make many metals undergo slow surface reactions called corrosion.

Step 2 ‒ Explain the green coating on copper

1. Fresh copper is bright reddish-brown. In moist air it first forms a thin layer of copper oxide: $$\mathrm{2Cu + O_2 \longrightarrow 2CuO}$$.
2. Carbon dioxide and water vapour present at the surface now react further with this $$\mathrm{CuO}$$ to give a basic copper carbonate, commonly written as $$\mathrm{CuCO_3 \cdot Cu(OH)_2}$$.
3. This substance is green; the mixture of the oxide and the basic carbonate is known as patina and it adheres firmly to copper articles.

Step 3 ‒ Explain the black coating on silver

1. Silver is much less reactive towards oxygen, so ordinary oxide formation is negligible.
2. Traces of hydrogen sulphide $$\mathrm{(H_2S)}$$ present in the atmosphere (even in concentrations as low as a few parts per billion) react with metallic silver: $$\mathrm{2Ag + H_2S \longrightarrow Ag_2S + H_2}$$.
3. $$\mathrm{Ag_2S}$$, silver sulphide, is black, so a thin film of it makes the entire article look dull and blackened. This process is popularly called tarnishing of silver.

Step 4 ‒ Summary

• The green layer on copper objects is mainly a mixture of copper carbonate and copper hydroxide, produced by the action of moist air and $$\mathrm{CO_2}$$.
• The black layer on silver objects is silver sulphide, formed when silver reacts with trace amounts of $$\mathrm{H_2S}$$ in the air.

Thus, both coatings are the result of slow atmospheric chemical reactions—different for each metal—collectively described as corrosion.

Step 1 – Recall a general rule about metal oxides
Everyday examples such as rust (iron oxide), quick-lime (calcium oxide) and magnesium oxide all show a common behaviour: when they dissolve or mix with water they turn red litmus blue. In other words, oxides formed by metals are usually basic in nature.

Step 2 – Write the equation for the formation of sodium oxide
Sodium is a metal, so on exposure to air it quickly combines with oxygen:
$$4\mathrm{Na} + \mathrm{O_2} \;\longrightarrow\; 2\mathrm{Na_2O}$$

Step 3 – Test the nature of the oxide
If a little water is added to the oxide, the following reaction takes place:
$$\mathrm{Na_2O} + \mathrm{H_2O} \;\longrightarrow\; 2\mathrm{NaOH}$$
$$\mathrm{NaOH}$$ is sodium hydroxide, a strong alkali. Alkalis turn red litmus blue and neutralise acids, properties that are characteristic of bases.

Step 4 – State the conclusion
Because sodium oxide produces a strong alkali on dissolving in water, it is classified as a basic oxide.

Step 1 · Recall how typical metals behave with water

• Very reactive metals (e.g. sodium, potassium) react even with cold water.

For sodium:

$$\mathrm{2Na + 2H_2O \;\longrightarrow\; 2NaOH + H_2\!\uparrow}$$

This reaction is fast, gives off heat and releases hydrogen gas.

• Moderately reactive metals (e.g. magnesium, aluminium, zinc) react slowly with hot water or steam, still forming a metal hydroxide/oxide and hydrogen.

Step 2 · Try the same experiment with sulfur

• Drop some powdered sulfur into a test-tube containing cold or hot water and shake.
• Observation: The yellow sulfur simply settles or floats; no bubbles, no heat, no colour change.
• Inference: There is no chemical reaction between sulfur and water.

Step 3 · Reason

• Sulfur is a non-metal.
• During a reaction with water, a substance would need to lose electrons to hydrogen (as metals do) to release $$\mathrm{H_2}$$ gas.
• Non-metals like sulfur prefer to gain electrons; water cannot supply electrons to them, so no reaction occurs.

Step 4 · Conclusion

Because sulfur does not react with water at all, its behaviour is completely different from that of reactive metals, which form hydroxides and liberate hydrogen.

Step 1 – Recall that oxygen is a very reactive non-metal.
Because of its high reactivity, oxygen takes part in many physical and chemical processes besides breathing.

Step 2 – List everyday and industrial uses.

• Combustion (burning fuels)
  Most fuels burn only in the presence of oxygen, releasing heat that we use for cooking, lighting and running engines.
  Example equation: $$\mathrm{C + O_2 \;\longrightarrow\; CO_2 + \text{heat}}$$
• Welding and metal cutting
  An oxy-acetylene torch mixes oxygen with acetylene; the very hot flame (about 3000 °C) joins or cuts metals.
• Medical use
  Hospitals keep oxygen cylinders to help patients who cannot breathe properly. Mountain climbers and scuba divers also carry oxygen tanks.
• Steel manufacture
  Molten iron contains impurities (mainly carbon). Blowing $$\mathrm{O_2}$$ through it oxidises the excess carbon to $$\mathrm{CO_2}$$, giving stronger, purer steel.
• Rocket propellant
  Liquid oxygen (LOX) is carried in rockets as an oxidiser; it reacts with the fuel so that rockets can burn even in space, where there is no air.
• Water purification & bleaching
  Ozone, $$\mathrm{O_3}$$, a form of oxygen, is bubbled through drinking water to kill germs and is used to bleach fabrics and paper.

Conclusion
Thus, besides supporting life, oxygen is crucial for burning fuels, welding, medicine, making steel, launching rockets and purifying water.

Step 1 – List the requirements for a good food-packing metal
A metal used for wrapping biscuits, chocolates, juices, etc. must

• be cheap so that the cost of packing stays low,
• be highly malleable (can be beaten into very thin sheets and bent easily),
• not rust or react quickly with food, and
• be light in weight, making transportation easy.

Step 2 – Examine each option

1. Aluminium, $$\mathrm{Al}$$
   • Low in cost compared with most metals.
   • Extremely malleable; forms thin “foil” that we can fold into any shape.
   • Forms a thin, protective oxide layer so the food does not get contaminated.
   • Very light.
2. Copper, $$\mathrm{Cu}$$
   • More expensive than aluminium.
   • Turns green (corrosion) and can react with food acids.
3. Iron, $$\mathrm{Fe}$$
   • Cheapest of all three but rusts quickly and is not as malleable; iron foil tears easily.
   • Much heavier than aluminium.
4. Gold, $$\mathrm{Au}$$
   • Highly malleable but far too costly for routine food packing.

Step 3 – Choose the metal that best fulfils all conditions
Only aluminium meets every requirement: low cost, very malleable, non-toxic, light, and non-rusting.

Conclusion
The metal commonly used for making food-packaging foils is aluminium.

Step 1 : Recall the activity series of metals
Metals that lie high in the reactivity (activity) series displace hydrogen from water very vigorously, releasing a lot of heat. The heat may be so large that either the metal itself, or the hydrogen formed, catches fire.

The usual order of reactivity of the metals given in the options is:

• Sodium > Aluminium > Zinc > Copper

Step 2 : Examine each metal one by one

1. Copper (Cu)
   Copper is far below hydrogen in the activity series. It does not react with cold water and therefore cannot catch fire.
2. Aluminium (Al)
   Aluminium is protected by a tightly-adhering oxide layer, so it reacts with water only at high temperature or when the oxide coat is removed. No fire is produced in ordinary contact with water.
3. Zinc (Zn)
   Zinc reacts slowly with steam, not with cold water, and the reaction is not explosive. Hence it does not catch fire.
4. Sodium (Na)
   Sodium lies very high in the activity series. It reacts explosively even with cold water, giving sodium hydroxide, hydrogen gas and a large amount of heat:

$$2\mathrm{Na} + 2\mathrm{H_2O} \longrightarrow 2\mathrm{NaOH} + \mathrm{H_2}\uparrow + \text{heat}$$

The heat liberated is sufficient to ignite the hydrogen gas as well as the tiny piece of sodium itself; therefore sodium appears to burst into flame the moment it touches water.

Step 3 : Identify the correct option
Among the four choices, only sodium shows this violent, fire-producing reaction with water.

Conclusion
The metal that catches fire on contact with water is sodium.

Understanding the question
The problem asks why, out of many known metals, hardly a handful (mainly gold, silver and platinum) are routinely chosen to make rings, necklaces, bangles, etc.

Step 1 – List the qualities a metal must possess to serve as jewellery

• Lustre – The metal must have a bright, shiny surface that appeals to the eye.
• Malleability – It must be soft enough to be hammered or rolled into thin sheets without cracking, so that intricate shapes can be produced.
• Ductility – It should also be capable of being drawn into very fine wires (for chains and filigree work).
• Resistance to corrosion/tarnish – Ornaments should remain shiny for years; the metal must not rust or react quickly with air, moisture or the salts in perspiration.
• Non-toxicity – The metal must not poison or irritate the skin.
• Acceptable density and hardness – A piece should not be too heavy to wear nor so soft that it bends out of shape in ordinary use.

Step 2 – Test common metals against these requirements

Step 3 – Draw the conclusion
Only a few noble metals — mainly $$\mathrm{Au}$$, $$\mathrm{Ag}$$ and $$\mathrm{Pt}$$ — satisfy all the conditions listed in Step 1. Most other metals fail in at least one crucial respect: they either corrode, lose lustre, are too hard or too brittle to shape finely, or are unsafe for prolonged skin contact.

Therefore, the set of metals that remain bright, can be worked into delicate forms and stay unchanged for years is very small, which is why only a few metals are suitable for making jewellery.

Step 1 - Unscramble the jumbled words in Column II

Step 2 - Recall the main uses of each element

• Oxygen is essential for respiration; living organisms cannot survive without it.
• Chlorine is added to water to kill germs and purify it.
• Copper is a very good conductor of electricity, so it is used in electrical wiring.
• Nitrogen is the major plant nutrient supplied through fertilisers for healthy growth.
• Gold is the most malleable and ductile metal known.

Step 3 - Match Column I with Column II

Thus the final pairing is:

• (i) → (c)
• (ii) → (e)
• (iii) → (a)
• (iv) → (d)
• (v) → (b)

Step 1 : Reaction of oxygen with magnesium

When a clean magnesium ribbon is heated in air, it burns with a dazzling white light.

Chemical equation (balanced):
$$2\,\mathrm{Mg}+\mathrm{O_2}\;\longrightarrow\;2\,\mathrm{MgO}$$

The white ash obtained is magnesium oxide. It is almost insoluble in cold water, but in the presence of a little moisture it slowly forms the hydroxide:

$$\mathrm{MgO}+\mathrm{H_2O}\;\longrightarrow\;\mathrm{Mg(OH)_2}$$

$$\mathrm{Mg(OH)_2}$$ is basic in nature. A suspension of this hydroxide in water turns red litmus paper blue.

Step 2 : Reaction of oxygen with sulfur

When powdered sulfur is heated in air, it burns with a pale blue flame and produces a choking gas.

Chemical equation (balanced):
$$\mathrm{S}+\mathrm{O_2}\;\longrightarrow\;\mathrm{SO_2}$$

Sulfur dioxide dissolves in water to give sulfurous acid:

$$\mathrm{SO_2}+\mathrm{H_2O}\;\longrightarrow\;\mathrm{H_2SO_3}$$

$$\mathrm{H_2SO_3}$$ is acidic. Its aqueous solution turns blue litmus paper red.

Step 3 : Main differences between the products

• Product with magnesium: $$\mathrm{MgO}$$ (a basic oxide of a metal).
• Product with sulfur: $$\mathrm{SO_2}$$ (an acidic oxide of a non-metal).
• Thus, metallic oxides are generally basic, whereas non-metallic oxides are generally acidic.

Step 1 : Identify the substance that forms an ash on strong heating in air

Metals such as magnesium burn with a dazzling white flame. The product is a white powder (ash).

$$\mathrm{Mg\;\; + \;O_2\;\;(from\;air)\;\xrightarrow{\;heat\;}\;MgO}$$

So the first blank is magnesium (Mg), and the ash is magnesium oxide (MgO).

Step 2 : Add water to the ash

When water is added to magnesium oxide, a new substance, magnesium hydroxide, is formed.

$$\mathrm{MgO\; + \;H_2O \;\longrightarrow \;Mg(OH)_2}$$

The second blank therefore is magnesium hydroxide (Mg(OH)₂).

Step 3 : Test the solution with litmus papers

• Magnesium hydroxide is basic in nature.
• A basic solution does not affect blue litmus paper → no change.
• A basic solution turns red litmus paper blue → already given.

Completed flow chart

Step 1 ‒ List the properties that a good “boiling-water pan” must have

• It should conduct heat quickly so that the water reaches its boiling point ( $$100\,{}^{\circ}\mathrm{C}$$ at sea level) in the least time and with minimum fuel.
• Its melting point must be much higher than $$100\,{}^{\circ}\mathrm{C}$$ so that the pan itself does not melt or get deformed.
• It must be chemically stable with hot water – it must not burn, catch fire or dissolve dangerously.
• It should be strong and easy to shape into the form of a vessel.

Step 2 ‒ Recall how metals and non-metals differ for these needs

• Metals such as iron and copper are good conductors of heat, have very high melting points and are strong.
• Non-metals (sulphur, coal, plastic, wood, cardboard) are usually poor conductors of heat and either burn or melt near or below $$100\,{}^{\circ}\mathrm{C}$$.

Step 3 ‒ Check each material one by one

Step 4 ‒ Choose between iron and copper

• Thermal conductivity of copper $$k_{\text{Cu}} \approx 390\,\mathrm{W\,m^{-1}\,K^{-1}}$$ is about 4 times that of iron $$k_{\text{Fe}} \approx 80\,\mathrm{W\,m^{-1}\,K^{-1}}$$.
• This means a copper pan transfers heat to the water much faster, saving fuel and time.
• Both metals have melting points far above $$100\,{}^{\circ}\mathrm{C}$$, but copper does not rust like iron does.

Therefore, copper is the most suitable material of the list for making a pan meant for boiling water.

Step 1 : Recall the conditions needed for rusting

• Rusting of iron is a chemical reaction that requires both oxygen from air and water (moisture).
• The simplified chemical change is expressed as  $$4\mathrm{Fe} + 3\mathrm{O_2} + 2\mathrm{H_2O} \rightarrow 2\mathrm{Fe_2O_3}\!\cdot\!\mathrm{H_2O}$$  which produces the brown flaky substance called rust.

Step 2 : Examine the medium surrounding each nail

Step 3 : Select the nail that will not rust

• The nail in oil lacks the two essentials for rusting (no water, no free oxygen).
• Therefore, this nail remains shiny and does not develop any brown rust layer.

Step 4 : State the reason clearly

The layer of oil acts as a protective barrier. It prevents both moisture and oxygen from reaching the iron surface, so the chemical reaction of rusting cannot proceed.

Step 1 – Recall the characteristic physical properties

• Metals are generally lustrous (shiny), malleable (can be beaten into sheets), ductile (can be drawn into wires), sonorous (produce a ringing sound), hard, have high melting/boiling points and are good conductors of heat and electricity.
• Non-metals are usually dull, brittle (break on hammering), non-sonorous, have comparatively low melting/boiling points and are poor conductors of heat and electricity (graphite is an important exception).

Step 2 – Match each property with the use it makes possible

Step 3 – Summarise the connection

Whenever we choose a substance for a job, we look at the property that is needed and then pick a material (metallic or non-metallic) that shows that property:

• If we need something that must conduct heat or electricity or bear heavy loads → choose a metal such as copper, aluminium or iron.
• If we need something that must be light, non-reactive, insulating or easily broken into powder → choose a non-metal such as carbon, sulphur, phosphorus or a compound mainly made of them.

Thus, the contrasting properties of metals and non-metals directly dictate their contrasting roles in the objects we use every day.

Step 1 ‒ Why is zinc coating (galvanisation) effective?

• During galvanisation the iron object is dipped in molten zinc. A thin, continuous layer of the metal $$\mathrm{Zn}$$ solidifies over iron $$\mathrm{Fe}$$.
• The zinc layer keeps air and moisture away from the surface of iron, so the usual rust-forming reaction
  $$\mathrm{4Fe\; +\; 3O_2\; +\; 2H_2O \;\longrightarrow\; 2Fe_2O_3\,\cdot\,H_2O}$$ cannot begin.
• Zinc is more reactive than iron in the metal reactivity series. Therefore, even if the coating is scratched, zinc preferentially oxidises:
  $$\mathrm{Zn \;\rightarrow\; Zn^{2+} + 2e^-}$$
  so iron still remains protected. This is called sacrificial protection.

Step 2 ‒ Could sulfur replace zinc?

• Sulfur $$\mathrm{S}$$ is a non-metal. It is brittle and cannot be spread as an even, sticking metallic layer on an iron surface.
• Because it is not a metal, sulfur cannot supply electrons the way zinc does; hence no sacrificial protection is possible if the layer is damaged.
• Any sulphur that happens to touch hot iron can form iron sulphide $$\mathrm{FeS}$$, making the metal weak instead of protecting it.
• Therefore, although sulfur itself does not react with water or oxygen, it fails to form a durable, adherent, and self-healing coating over iron.

Step 3 ‒ Conclusion

Sulfur cannot be used in place of zinc for protecting iron from rusting because it does not give a continuous, sticking layer and cannot provide sacrificial protection. Hence only a suitable reactive metal like zinc is employed.

Step 1 – Recall the property we want to use
Metals such as iron are malleable, i.e. they can be beaten or pressed into a required shape. However, the extent of malleability depends on temperature: when a metal is heated, the layers of atoms can slide over one another much more easily.

Step 2 – What happens to iron on heating?
When the ironsmith heats a piece of iron in the furnace, its temperature rises to what we call the "red-hot" stage (about 800 – 900 °C). At this high temperature the iron becomes soft and less rigid because its atoms vibrate vigorously and the bonds temporarily weaken. In symbolic form:

$$\text{Cold, hard iron} \;\xrightarrow[\text{furnace}]{\text{heat}}\; \text{Soft, red-hot iron}$$

Step 3 – Why soft iron is easier to shape
The softened iron now requires a much smaller force to change its shape. The ironsmith can therefore hammer, bend or press it into the desired tool without cracking or breaking it. If the same hammering were attempted on cold iron, it would resist deformation and might develop fractures.

Step 4 – Cooling restores hardness
After shaping, the iron is allowed to cool. As the temperature falls, the metal regains its original hardness so that the finished tool becomes strong and durable.

Conclusion
Heating is necessary because it converts hard, rigid iron into a soft, malleable form that can be forged into tools; once cooled, the tool becomes hard again.