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These are complete exercise solutions for Samacheer Kalvi 9th Science Chapter — Applied Chemistry. Solve each question yourself first, then verify your method and answer below. Focus on balanced equations, industrial processes, and composition-based comparisons — these are the most frequently tested areas.
Key Concepts (Quick Recap)
- Metals: Shiny (lustrous), malleable, ductile, good conductors of heat and electricity, form cations, high melting/boiling points. Examples: Fe, Cu, Al, Au, Na.
- Non-metals: Dull, brittle, poor conductors, form anions, low melting/boiling points. Examples: C, S, O, N, Cl. Exceptions: mercury (liquid metal), graphite (conductive non-metal), diamond (hard non-metal).
- Metalloids: Elements with properties intermediate between metals and non-metals. Examples: Silicon (Si), Germanium (Ge), Arsenic (As).
- Metallurgy: The process of extracting metals from their ores. Steps: concentration of ore → extraction of metal → refining.
- Corrosion: Gradual deterioration of metals by reaction with the environment. Rusting of iron: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O.
- Corrosion prevention: Painting, greasing, galvanisation (zinc coating), alloying, electroplating, sacrificial protection (Mg/Zn blocks on ships).
- Alloys: Homogeneous mixtures of two or more metals (or a metal + non-metal) designed to improve properties. Examples: Steel (Fe + C), Brass (Cu + Zn), Bronze (Cu + Sn), Stainless steel (Fe + Cr + Ni + C).
- Chemical industry: Converts raw materials into useful products — fertilizers, cement, glass, ceramics, soaps, detergents.
- Fertilizers: Chemical substances added to soil to supply nutrients. NPK fertilizers provide Nitrogen, Phosphorus, Potassium. Urea (46% N), Superphosphate (P), Muriate of potash (K).
- Cement: Portland cement = clinker + gypsum. Clinker = limestone + clay heated at 1400–1500°C.
- Glass: Made by heating sand (SiO₂) with soda ash (Na₂CO₃) and limestone (CaCO₃). Types: soda-lime glass, borosilicate (Pyrex), lead crystal.
- Ceramics: Products made from clay, hardened by heating. Includes pottery, bricks, tiles, porcelain.
I. Choose the Correct Answer
Q1. Which of the following is a liquid metal at room temperature? (a) Sodium (b) Mercury ✓ (c) Gallium (d) Aluminium
Answer(b) ✓ — Mercury (Hg) is the only metal that is liquid at room temperature (melting point −39°C). Gallium melts at 30°C, just above room temperature.
Q2. The most abundant metal in the earth's crust is: (a) Iron (b) Copper (c) Aluminium ✓ (d) Zinc
Answer(c) ✓ — Aluminium is the most abundant metal (8.3% by weight) in the earth's crust, followed by iron.
Q3. Galvanisation is the process of coating iron with: (a) Copper (b) Chromium (c) Zinc ✓ (d) Tin
Answer(c) ✓ — Galvanisation involves coating iron/steel with a thin layer of zinc. Zinc is more reactive than iron and acts as a sacrificial coating — it oxidises first, protecting the iron beneath.
Q4. An alloy of copper and zinc is called: (a) Bronze (b) Brass ✓ (c) Steel (d) Solder
Answer(b) ✓ — Brass = Cu + Zn. Bronze = Cu + Sn. Steel = Fe + C.
Q5. The chemical formula of rust is: (a) FeO (b) Fe₂O₃ (c) Fe₂O₃·xH₂O ✓ (d) Fe₃O₄
Answer(c) ✓ — Rust is hydrated iron(III) oxide, Fe₂O₃·xH₂O. The 'x' represents variable water content. Fe₂O₃ alone is anhydrous iron oxide, not rust.
Q6. Which of the following is a non-metal that conducts electricity? (a) Sulphur (b) Phosphorus (c) Graphite ✓ (d) Nitrogen
Answer(c) ✓ — Graphite (an allotrope of carbon) has delocalised electrons that allow it to conduct electricity despite being a non-metal.
Q7. The main component of NPK fertilizers is: (a) Sodium, Phosphorus, Potassium (b) Nitrogen, Phosphorus, Potassium ✓ (c) Nitrogen, Phosphorus, Calcium (d) Nitrogen, Potassium, Calcium
Answer(b) ✓ — NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K) — the three primary macronutrients required by plants.
Q8. Portland cement is made by heating limestone and clay to about: (a) 500°C (b) 1000°C (c) 1400–1500°C ✓ (d) 2500°C
Answer(c) ✓ — The mixture of limestone and clay is heated in a rotary kiln at 1400–1500°C to form clinker, which is then ground with gypsum to make cement.
Q9. Which of the following is an alloy of copper and tin? (a) Brass (b) Bronze ✓ (c) Stainless steel (d) Duralumin
Answer(b) ✓ — Bronze = Cu + Sn (copper + tin). It is harder than pure copper and resistant to corrosion; used for statues, coins, and bearings.
Q10. The process of extracting metals from their ores is called: (a) Corrosion (b) Metallurgy ✓ (c) Alloying (d) Calcination
Answer(b) ✓ — Metallurgy encompasses all processes involved in the extraction of metals from ores — concentration, extraction, and refining.
Q11. Soda-lime glass is made from: (a) Sand + limestone + soda ash ✓ (b) Sand + boron oxide + soda ash (c) Sand + lead oxide + potash (d) Sand + alumina + lime
Answer(a) ✓ — Soda-lime glass = SiO₂ (sand) + CaCO₃ (limestone) + Na₂CO₃ (soda ash). It is the most common type of glass (windows, bottles).
II. Fill in the Blanks
1. The most abundant metal in the earth's crust is aluminium. 2. The only metal that is liquid at room temperature is mercury. 3. The chemical formula of rust is Fe₂O₃·xH₂O (hydrated iron oxide). 4. An alloy of iron, chromium, and nickel is called stainless steel. 5. The process of coating iron with a thin layer of zinc is called galvanisation. 6. The nitrogen-rich fertilizer commonly used is urea (CO(NH₂)₂, 46% N). 7. The raw materials for manufacturing cement are limestone and clay. 8. Gypsum (CaSO₄·2H₂O) is added to clinker to slow down the setting time of cement. 9. The hardest naturally occurring non-metal is diamond. 10. A metal that displaces hydrogen from cold water is sodium (or potassium/calcium).
III. True or False
1. All metals are solid at room temperature.
AnswerFalse — Correction: Mercury is a liquid metal at room temperature. Gallium melts just above room temperature (30°C).
2. Non-metals are generally good conductors of electricity.
AnswerFalse — Correction: Non-metals are generally poor conductors. Exception: graphite (a non-metal) conducts electricity.
3. Rusting of iron requires both oxygen and moisture.
AnswerTrue ✓ — Iron rusts only when both oxygen and water/moisture are present. Dry air or water alone will not cause rusting.
4. Alloys are chemical compounds.
AnswerFalse — Correction: Alloys are homogeneous mixtures (not compounds) of two or more metals or a metal and a non-metal. The elements in an alloy can be separated by physical means.
5. Bronze is harder than pure copper.
AnswerTrue ✓ — Adding tin to copper increases hardness, making bronze more durable than pure copper.
6. Nitrogen-fixing bacteria convert atmospheric nitrogen into nitrates in the soil.
AnswerTrue ✓ — Rhizobium bacteria in root nodules of legumes convert N₂ into ammonia/nitrates (biological nitrogen fixation).
7. Borosilicate glass has a low thermal expansion coefficient and is heat-resistant.
AnswerTrue ✓ — Borosilicate glass (Pyrex) contains boron oxide, making it resistant to thermal shock.
8. Ceramic materials are generally good conductors of electricity.
AnswerFalse — Correction: Ceramics are insulators — they are poor conductors of heat and electricity.
IV. Match the Following
Set 1:
| Column I | Column II |
|---|
| 1. Brass | (d) Cu + Zn |
| 2. Bronze | (a) Cu + Sn |
| 3. Stainless steel | (e) Fe + Cr + Ni + C |
| 4. Solder | (c) Pb + Sn |
| 5. Duralumin | (b) Al + Cu + Mg + Mn |
Set 2:
| Column I | Column II |
|---|
| 1. Urea | (e) Nitrogen fertilizer (46% N) |
| 2. Superphosphate | (a) Phosphorus fertilizer |
| 3. Muriate of potash | (b) Potassium fertilizer (KCl) |
| 4. Gypsum | (d) Added to cement to slow setting |
| 5. Clinker | (c) Intermediate product in cement manufacture |
V. Short Answers
Q1. Differentiate between metals and non-metals.
Answer
| Property | Metals | Non-metals |
|---|
| Physical state | Solid (except Hg — liquid) | Solid, liquid (Br₂), or gas |
| Lustre | Shiny (metallic lustre) | Dull (except iodine) |
| Malleability | Malleable (can be hammered into sheets) | Brittle |
| Ductility | Ductile (can be drawn into wires) | Non-ductile |
| Conductivity | Good conductors of heat and electricity | Poor conductors (except graphite) |
| Melting/Boiling point | Generally high | Generally low (except C, Si) |
| Tensile strength | High | Low |
| Ion formation | Form cations (positive ions) | Form anions (negative ions) |
| Examples | Fe, Cu, Al, Au, Na | C, S, O, N, Cl, P |
Q2. What is corrosion? Write the equation for rusting of iron.
Answer
Corrosion is the gradual deterioration of metals by chemical reaction with environmental substances — moisture, oxygen, acids, and salts.
Rusting of iron: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O Iron + Oxygen + Water → Hydrated iron(III) oxide (rust)
Rusting requires both oxygen and moisture. In dry air or boiled water (no dissolved O₂), iron does not rust.
Q3. List the methods of preventing corrosion.
Answer
1. Painting: Coating metal surfaces with paint prevents contact with air and moisture. 2. Greasing/oiling: Applying oil or grease on moving parts prevents rusting. 3. Galvanisation: Coating iron/steel with a thin layer of zinc (zinc acts as a sacrificial anode). 4. Alloying: Mixing iron with chromium and nickel to form stainless steel (resistant to corrosion). 5. Electroplating: Depositing a thin layer of a less reactive metal (Cr, Ni) on iron by electrolysis. 6. Sacrificial protection: Attaching a more reactive metal (Mg, Zn) to iron structures — the reactive metal corrodes first (used on ships, pipelines).
Q4. What are alloys? Why are alloys preferred over pure metals?
Answer
An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, prepared by melting and mixing the components.
Why alloys are preferred: 1. Greater hardness: Bronze (Cu + Sn) is harder than pure copper. 2. Corrosion resistance: Stainless steel (Fe + Cr + Ni) resists rusting, unlike pure iron. 3. Lower melting point: Solder (Pb + Sn) melts at a lower temperature than either metal alone. 4. Improved strength: Steel (Fe + C) is stronger than pure iron. 5. Better appearance: Jewellery gold is alloyed with Cu/Ag for durability. 6. Reduced cost: Brass (Cu + Zn) is cheaper than pure copper for many applications.
Q5. What are fertilizers? Name the types with examples.
Answer
Fertilizers are chemical substances added to soil to supply essential nutrients (N, P, K) for plant growth.
Types: 1. Nitrogenous fertilizers: Supply nitrogen. Examples: Urea CO(NH₂)₂ (46% N), Ammonium nitrate NH₄NO₃ (35% N), Ammonium sulphate (NH₄)₂SO₄. 2. Phosphatic fertilizers: Supply phosphorus. Examples: Superphosphate Ca(H₂PO₄)₂, Triple superphosphate. 3. Potassic fertilizers: Supply potassium. Examples: Muriate of potash KCl, Potassium sulphate K₂SO₄. 4. Complex/NPK fertilizers: Supply N, P, K together. Examples: Ammonium phosphate, NPK mixtures.
Q6. Differentiate between natural and synthetic fertilizers.
Answer
| Feature | Natural (Organic) Fertilizers | Synthetic (Chemical) Fertilizers |
|---|
| Source | Animal waste, plant residue | Chemically manufactured |
| Examples | Manure, compost, bone meal | Urea, superphosphate, NPK |
| Nutrient content | Low, variable | High, precise |
| Effect on soil | Improves soil structure | May degrade soil with overuse |
| Decomposition | Slow release | Quick release |
| Cost | Low | Higher |
VI. Detailed Answers
Q1. Explain the process of metallurgy — from ore to metal.
Answer
Metallurgy is the science and technology of extracting metals from their ores. It involves three main stages:
1. Concentration of Ore (Enrichment): Removing gangue (unwanted impurities like sand, rock) from the ore.
- Gravity separation: Heavier ore particles settle; lighter gangue washes away (for oxide ores).
- Froth floatation: Sulphide ores are wetted by pine oil and float as froth; gangue sinks.
- Magnetic separation: Magnetic ores (magnetite) are separated from non-magnetic gangue using magnets.
2. Extraction of Metal from Concentrated Ore:
Answer
ZnO + C → Zn + CO↑ (at high temperature) Fe₂O₃ + 3C → 2Fe + 3CO↑
Al₂O₃ (molten) →(electrolysis)→ 2Al (at cathode) + 3O₂ (at anode)
2ZnS + 3O₂ →(heat)→ 2ZnO + 2SO₂↑
ZnCO₃ →(heat)→ ZnO + CO₂↑
- For moderately reactive metals (Zn, Fe, Pb, Cu): Reduction by carbon (smelting).
- For highly reactive metals (Na, K, Ca, Al): Electrolytic reduction.
- Roasting (for sulphide ores): Heating in presence of excess air.
- Calcination (for carbonate ores): Heating in limited air.
3. Refining of Metal: Purifying the extracted metal. Most common method: Electrolytic refining.
Answer
- Impure metal = anode, pure metal = cathode, electrolyte = salt solution of the metal.
- On passing current, impure metal dissolves at anode and pure metal deposits at cathode.
- Example: CuSO₄ solution for copper refining.
Q2. Describe the manufacture of cement with equations.
Answer
Raw materials: 1. Limestone (CaCO₃) 2. Clay (aluminosilicates — contains SiO₂, Al₂O₃, Fe₂O₃) 3. Gypsum (CaSO₄·2H₂O) — added at the final stage
Manufacturing process:
Step 1: Mixing Limestone and clay are crushed and mixed in a 3:1 ratio. Water is added to form a slurry (wet process) or the mixture is ground dry (dry process).
Step 2: Heating (Kiln) The mixture is fed into a rotary kiln and heated to 1400–1500°C. Reactions:
- CaCO₃ →(heat)→ CaO + CO₂↑ (decomposition of limestone)
- CaO + SiO₂ → CaSiO₃ (calcium silicate)
- CaO + Al₂O₃ → Ca₃Al₂O₆ (calcium aluminate)
The product forms grey nodules called clinker.
Step 3: Grinding Clinker is cooled and ground with 2–3% gypsum (CaSO₄·2H₂O). Gypsum slows down the setting time of cement so it doesn't set too quickly when mixed with water.
Step 4: Storage and Packing The fine grey powder is Portland cement. It is stored in silos and packed in bags.
Setting of cement: When cement is mixed with water, it undergoes hydration — a complex set of chemical reactions that produce a hard, stone-like mass.
Q3. Describe the manufacture and types of glass.
Answer
Raw materials for soda-lime glass: 1. Sand (SiO₂) — silica, the glass former 2. Soda ash (Na₂CO₃) — lowers the melting point 3. Limestone (CaCO₃) — provides stability and durability
Manufacturing process: The raw materials are finely ground, mixed, and heated in a furnace at 1400–1600°C.
Reactions:
- Na₂CO₃ →(heat)→ Na₂O + CO₂↑
- CaCO₃ →(heat)→ CaO + CO₂↑
- Na₂O + SiO₂ → Na₂SiO₃ (sodium silicate)
- CaO + SiO₂ → CaSiO₃ (calcium silicate)
The molten glass is then shaped by blowing, pressing, or rolling, and slowly cooled (annealed) to remove internal stresses.
Types of glass:
| Type | Composition | Properties | Uses |
|---|
| Soda-lime glass | SiO₂ + Na₂O + CaO | Common, easily shaped, less heat-resistant | Windows, bottles, jars |
| Borosilicate glass (Pyrex) | SiO₂ + B₂O₃ + Na₂O + Al₂O₃ | Low thermal expansion, heat-resistant | Labware, cookware |
| Lead crystal glass | SiO₂ + PbO + K₂O | High refractive index, sparkling | Decorative items, lenses |
| Safety glass (laminated) | Two glass layers + PVB plastic layer | Does not shatter into sharp pieces | Windshields, car windows |
| Toughened glass | Heat-treated soda-lime glass | 4–5× stronger, crumbles into small pieces when broken | Shower doors, phone screens |
Q4. Explain the chemical industry and its products.
Answer
The chemical industry converts raw materials (minerals, air, water, petroleum) into useful products through chemical processes.
Major sectors and products:
1. Fertilizer industry:
- Nitrogenous: Urea CO(NH₂)₂, Ammonium nitrate NH₄NO₃
- Phosphatic: Superphosphate, Triple superphosphate
- Potassic: Muriate of potash (KCl)
- NPK complex fertilizers
2. Cement industry:
- Portland cement from limestone + clay
- Used in construction, roads, dams
3. Glass industry:
- Soda-lime glass, borosilicate glass, lead crystal
- Used in packaging, construction, labware
4. Ceramic industry:
- Products from clay — bricks, tiles, pottery, porcelain
- Made by shaping clay and firing at high temperature
5. Metallurgical industry:
- Extraction of Fe, Al, Cu, Zn, etc. from ores
- Production of alloys (steel, brass, bronze, duralumin)
6. Petrochemical industry:
- Products from petroleum and natural gas
- Plastics, synthetic fibres, detergents, rubber
7. Pharmaceutical industry:
- Drugs, medicines, antiseptics, disinfectants
Environmental considerations:
- Chemical industries release pollutants (SO₂, NOₓ, heavy metals, effluents).
- Must follow environmental regulations — treat effluents, use scrubbers, and adopt green chemistry practices.
- Sustainable practices: recycling, waste minimisation, use of renewable feedstocks.
Common Mistakes
1. Calling alloys "compounds" — Alloys are homogeneous mixtures, not chemical compounds. The elements in an alloy retain their individual properties and can be separated. 2. Confusing brass and bronze — Brass = Cu + Zn; Bronze = Cu + Sn. Mnemonic: "Brass has Zinc (Z), Bronze has Tin (T)." 3. Writing rust as Fe₂O₃ instead of Fe₂O₃·xH₂O — Rust is hydrated iron oxide. The water of hydration is essential. Fe₂O₃ alone is anhydrous and is not rust. 4. Forgetting that both O₂ and H₂O are needed for rusting — Iron does not rust in dry air (no moisture) or in boiled water (no O₂). Both conditions must be present. 5. Confusing galvanisation with electroplating — Galvanisation = coating with zinc by dipping in molten zinc. Electroplating = depositing a metal layer by electrolysis. Both protect, but the processes differ. 6. Confusing roasting and calcination — Roasting = heating sulphide ore in excess air (converts to oxide + SO₂). Calcination = heating carbonate ore in limited air (converts to oxide + CO₂). 7. Saying graphite is a metal because it conducts — Graphite is a non-metal (allotrope of carbon). Its conductivity comes from delocalised electrons, not metallic bonding.
Exam Checklist
- [ ] Metals vs non-metals — at least 6 differentiating properties with examples
- [ ] Metallurgy steps: concentration → extraction → refining, with methods (froth floatation, roasting, calcination, smelting, electrolytic reduction, electrolytic refining)
- [ ] Balanced equations: rusting of iron, roasting of ZnS, calcination of ZnCO₃, smelting of Fe₂O₃
- [ ] Corrosion definition, equation, and 6 prevention methods
- [ ] Alloy compositions: brass, bronze, stainless steel, solder, duralumin, nichrome
- [ ] Cement manufacture — raw materials, process (kiln → clinker → grinding with gypsum), key equations
- [ ] Glass types — soda-lime, borosilicate, lead crystal, composition and uses
- [ ] Fertilizer types — nitrogenous, phosphatic, potassic, NPK — with examples and formulas
- [ ] Key exceptions: mercury (liquid metal), graphite (conductive non-metal), diamond (hard non-metal)
Internal Links
- [Applied Chemistry Chapter Guide](/school/tamil-nadu-state-board/class/9/science/applied-chemistry)
- [All Class 9 Science Solutions](/school/tamil-nadu-state-board/class/9/science/solutions)
- [Class 9 Science Subject Guide](/school/tamil-nadu-state-board/class/9/science)
