Chapter 3: Metals and Non-metals

Solution

Mercury (Hg) is the only metal that is liquid at room temperature (melting point: −39°C). Gallium and caesium have very low melting points but are solid at room temperature (they can melt in your hand on a warm day).

Solution

Malleability is the property of metals that allows them to be hammered or rolled into thin sheets without breaking. Gold and silver are the most malleable metals. Aluminium foil used in kitchens is an everyday example of malleability.

Solution

Graphite (an allotrope of carbon) is the only non-metal that is a good conductor of electricity. This is because graphite has free electrons in its layered structure that can carry electric current. This is why graphite is used in making electrodes and pencil leads.

Solution

Sodium and potassium are highly reactive metals. They react vigorously with oxygen in the air (catch fire) and with moisture/water (produce hydrogen which can ignite). Storing them in kerosene oil cuts off contact with air and moisture, preventing dangerous reactions.

Solution

Amphoteric oxides react with both acids and bases. Al₂O₃ (aluminium oxide) and ZnO (zinc oxide) are amphoteric:

Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O (reacts with acid)

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (reacts with base)

Na₂O and MgO are basic oxides. SO₂ is an acidic oxide (non-metal oxide).

Solution

Only metals above hydrogen in the reactivity series can displace hydrogen from dilute acids. Copper (Cu) is below hydrogen, so it cannot react with dilute HCl or dilute H₂SO₄.

Zinc, iron, and magnesium are all above hydrogen and readily react with dilute acids.

Solution

In ionic bonding, the metal loses electrons (forms cation) and the non-metal gains electrons (forms anion). The electrons are therefore transferred from metal to non-metal. The resulting electrostatic attraction between oppositely charged ions forms the ionic bond.

Solution

Roasting is the process of heating a sulphide ore strongly in the presence of excess air to convert it into its metal oxide. Example:

2ZnS(s) + 3O₂(g) →^Δ 2ZnO(s) + 2SO₂(g)

Calcination is heating a carbonate ore in limited air. Smelting is reduction with carbon. Refining is purification of crude metal.

Solution

Galvanisation is the process of coating iron or steel with a thin layer of zinc to protect it from rusting. The zinc layer prevents moisture and air from reaching the iron. Even if the zinc layer is scratched, zinc corrodes preferentially (it is more reactive than iron), providing sacrificial protection.

Galvanised iron is used for buckets, pipes, roofing sheets, etc.

Solution

Brass = Copper + Zinc. It is harder than either copper or zinc alone and is used for taps, door fittings, and musical instruments.

Bronze = Copper + Tin. Steel = Iron + Carbon. Solder = Lead + Tin.

Solution

Solder is an alloy of lead (Pb) and tin (Sn). It has a low melting point, which makes it ideal for welding (soldering) electrical wires and electronic components without damaging them.

Solution

Pure gold (24-carat) is very soft and unsuitable for making jewellery. To increase hardness, gold is alloyed with copper or silver. 22-carat gold contains 22 parts gold and 2 parts copper or silver out of 24 parts by mass.

Solution

(a) Metals are good conductors of electricity:

In metals, the outermost electrons are loosely held and form a 'sea' of free (delocalised) electrons. When a potential difference is applied, these electrons can move freely through the metal lattice, carrying electric charge. This makes metals excellent conductors. Silver is the best conductor, followed by copper and aluminium.

(b) Non-metals are generally brittle:

Non-metals (in solid state) are held together by weak intermolecular forces (or covalent bonds in a molecular lattice). They lack the 'sea of electrons' and metallic bonding that gives metals their malleability. When stress is applied, non-metals cannot deform — they shatter or break. Exception: Diamond (a form of carbon) is extremely hard due to its extended covalent network, but it too is brittle, not malleable.

Solution

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Iron is more reactive than copper and displaces it. CuSO₄ (blue) is replaced by FeSO₄ (green). A reddish-brown coating of copper appears on the iron nail.

Solution

In the solid state, ions are held in fixed positions in a rigid crystal lattice and cannot move — so they cannot carry electric charge.

When melted or dissolved in water, the ions become free to move and can carry charge through the liquid, allowing the compound to conduct electricity.

Solution

Highly reactive metals (K, Na, Ca, Mg, Al) are at the top of the reactivity series. No common reducing agent (like carbon or CO) can reduce them. Therefore, they are extracted by electrolytic reduction — passing electricity through their molten chlorides or oxides.

Example: 2NaCl(molten) →^electricity 2Na + Cl₂

Solution

The thermite reaction is a displacement reaction in which aluminium reduces iron oxide to produce molten iron and aluminium oxide, releasing a huge amount of heat.

Balanced equation:

Fe₂O₃(s) + 2Al(s) → Al₂O₃(s) + 2Fe(l) + Heat

The reaction is so exothermic that the iron produced is in the molten state.

Application: The thermite reaction is used to weld broken railway tracks (thermite welding). The molten iron fills the gap between the broken tracks and solidifies, joining them firmly.

Solution

Decreasing order of reactivity: Mg > Zn > Fe > Cu > Au

Justification:

• Mg > Zn: Mg displaces Zn from ZnSO₄ solution: Mg + ZnSO₄ → MgSO₄ + Zn
• Zn > Fe: Zn displaces Fe from FeSO₄ solution: Zn + FeSO₄ → ZnSO₄ + Fe
• Fe > Cu: Fe displaces Cu from CuSO₄ solution: Fe + CuSO₄ → FeSO₄ + Cu
• Cu > Au: Cu can displace Au from AuCl₃: 3Cu + 2AuCl₃ → 3CuCl₂ + 2Au. Gold is the least reactive — it does not react with any acid except aqua regia.

Solution

Magnesium (Mg): Atomic number = 12. Electronic configuration: 2, 8, 2. It has 2 valence electrons.

Chlorine (Cl): Atomic number = 17. Electronic configuration: 2, 8, 7. It has 7 valence electrons (needs 1 more to complete octet).

Formation:

• Mg loses 2 electrons → Mg²⁺ (achieves noble gas configuration of Ne: 2, 8)
• Each Cl gains 1 electron → Cl⁻ (achieves noble gas configuration of Ar: 2, 8, 8)
• Two Cl atoms are needed to accept the 2 electrons from Mg.

Result: Mg²⁺ + 2Cl⁻ → MgCl₂

The bond formed is an ionic bond (electrovalent bond), held together by the electrostatic force of attraction between Mg²⁺ and Cl⁻ ions.

Solution

This is called sacrificial protection or cathodic protection.

Zinc is more reactive than iron (higher in the reactivity series). When the zinc coating is broken and both zinc and iron are exposed to moisture and air:

• Zinc oxidises (corrodes) preferentially instead of iron.
• Zinc acts as a sacrificial anode — it 'sacrifices' itself to protect iron.
• As long as zinc is present, iron will not rust, even if the zinc layer is damaged.

This is why galvanised iron is preferred over painted iron for long-term corrosion protection.

Solution

Aluminium reacts with oxygen in air to form a thin but very tough layer of aluminium oxide (Al₂O₃) on its surface. This oxide layer is non-reactive and prevents further reaction of the metal underneath with air, water, or food. This makes aluminium safe and durable for cooking utensils despite its high reactivity.

Solution

Aqua regia (Latin for 'royal water') is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in 3:1 ratio. It is one of the few reagents that can dissolve gold and platinum.

Neither HCl nor HNO₃ alone can dissolve gold, but together they produce nascent chlorine and nitrosyl chloride which attack gold:

Au + 3HCl + HNO₃ → AuCl₃ + 2H₂O + NO

Solution

Electrolytic Refining of Copper:

Setup:

• Anode: Thick block of impure copper
• Cathode: Thin strip of pure copper
• Electrolyte: Acidified copper sulphate solution (CuSO₄)

Process:

When electric current is passed:

At anode (impure copper): Cu atoms lose electrons and dissolve into solution as Cu²⁺ ions.

Cu → Cu²⁺ + 2e⁻

At cathode (pure copper): Cu²⁺ ions from the solution gain electrons and deposit as pure copper.

Cu²⁺ + 2e⁻ → Cu

The impurities from the anode (like gold, silver, platinum) do not dissolve and settle at the bottom of the tank as anode mud — which is commercially valuable!

Over time, the anode gets thinner and the cathode gets thicker with pure copper.

Solution

Case 1: Copper + Silver nitrate

Copper is more reactive than silver (Cu is above Ag in the reactivity series). So copper will displace silver:

Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)

Observation: The colourless AgNO₃ solution turns blue (due to Cu(NO₃)₂), and a shiny silver deposit appears on the copper.

Case 2: Silver + Copper sulphate

Silver is less reactive than copper. A less reactive metal cannot displace a more reactive metal. No reaction occurs.

Ag(s) + CuSO₄(aq) → No reaction

Solution

The ability of carbon to reduce a metal oxide depends on the metal's position in the reactivity series relative to carbon.

Zinc oxide + Carbon → Zinc + CO ✓

Zinc is less reactive than carbon. Carbon can remove oxygen from ZnO because it has a stronger affinity for oxygen than zinc does.

Aluminium oxide + Carbon → No reaction ✗

Aluminium is more reactive than carbon. Al holds onto oxygen more strongly than carbon can pull it away. Therefore, carbon cannot reduce Al₂O₃.

For highly reactive metals like Al, Na, K, Mg, and Ca, electrolytic reduction (electrolysis of molten salts) is the only practical method of extraction.