๐ Short Answer Questions – Chemistry
Q1. Define oxidation, reduction reactions with examples.
Q2. Define oxidizing agent and reducing agent with examples.
Q3. Write down 5 differences between oxidation and reduction.
Q4. Write down 3 examples of each of oxidizing and reducing agent.
Q5. Identify the oxidizing and reducing agents from the following: (i) Al (RA) (ii) Na (RA) (iii) H₂S (RA) (iv) H₂SO₄ (OA) (v) KMnO₄ (OA) (vi) Zn (RA)
Q6. Identify the oxidizing and reducing agents for the following reaction: H₂ (RA) + Cl₂ (OA) → 2HCl
Q7. Describe the construction of electrochemical cell. Write names of two types of electrochemical cells.
Q8. Differentiate between electrolytes and non-electrolytes with examples.
Q9. Differentiate between strong electrolytes and weak electrolytes with examples.
Q10. Identify strong and weak electrolytes from the following: HCl (S), KI (S), NaOH (S), H₂S (W), CH₃COOH (W), NH₄OH (W), NaCl (S), C₂H₅OH (W)
Q11. Why ionic compounds conduct electricity in molten or in aqueous solutions only?
Q12. What is electrolytic cell? Explain with diagram. Describe the construction and working of electrolytic cell.
Q13. Sketch electrolytic cell for electrolysis of molten potassium chloride and identify cathode and anode, oxidation, reduction reaction, movement of electron.
Q14. Define electrochemistry, electrochemical reactions, electrochemical cell, electrolyte, non-electrolyte, salt bridge, cell, Galvanic cell, electrolytic cell, battery, electrode, cathode, anode, oxidation, reduction, redox reactions, electrochemical equivalent, and chemical equivalent.
Q15. What is electroplating? On which principle this process works? Give its merits.
Q16. What is corrosion of metal and rusting? How it can be prevented? Or name the methods which are used to protect metal from corrosion. How cathodic protection prevent metal from corrosion?
Q17. Write down 4 applications of electrolytic cells or electrolysis.
Q18. Describe the process of nickel plating and tin plating.
Q19. Write down the composition of following alloys: Brass (Cu-Zn,[4:1]), Bronze (Cu-Sn-Zn,[9:1]), Bell metal (Cu-Sn), Monel (Ni-Cu-Fe), Amalgam (Hg-Ag-Cu-Zn), Pewter (Sn-Cu-Pb-Sb-Bi), White gold (Au-Pb-Ag-Cu, 18 karat), Duralumin (Al-Cu-Mg-Ni).
๐งช Long Answer Questions – Chemistry
Q1. State and explain Faraday’s Laws of electrolysis.
Q2. Describe the construction and working of Daniell cell and lead battery.
Q3. Describe the dry cell with diagram.
Q4. What is battery? How lead storage battery works?
Q5. Explain the process of electrolysis in electrolytic cell.
Q6. What is alloy? Explain its classification with examples.
Q7. What is electroplating? How steel object can be electroplated with zinc and silver?
Q8. Examine the following chemical equations and identify oxidation, reduction, oxidizing agent, reducing agent:
(a) Zn (RA) + Cl₂ (OA) → ZnCl₂ (Zn oxidized, Cl₂ reduced)
(b) H₂S (RA) + Br₂ (OA) → 2HBr + S (H₂S oxidized, Br₂ reduced)
(c) 2Ca (RA) + O₂ (OA) → CaO (Ca oxidized, O₂ reduced)
(d) 2Li (RA) + S (OA) → Li₂S (Li oxidized, S reduced)
Q9. Identify the alloy:
• Cu‑Zn → Brass
• Cu‑Al‑Mg‑Ni → Duralumin
• Cu‑Zn‑Sn → Bronze
• Fe‑Al‑Ni‑Co → Alnico
• Cu‑Ni‑Mn → Cupronickel
๐ฏ Q10. Pick up the Correct Answer (MCQs)
1️⃣ Alloy of Cu–Sn is called
2️⃣ Which one is alloy?
3️⃣ Value of 1 Faraday is equal to
4️⃣ Which one is non electrolyte?
5️⃣ Which one is oxidizing agent?
6️⃣ Which one is reducing agent?
7️⃣ Which one forms weak electrolyte solution with water?
8️⃣ In Daniel cell, cathode is
9️⃣ 1 g equivalent weight of Al is equal to
๐ Steel is an alloy of iron which contains:
11️⃣ The substance used for electrolysis is called …
12️⃣ When molten NaCl is electrolyzed, formed at cathode is …
13️⃣ The electrolyte in lead storage battery is …
14️⃣ Lead storage battery is a … cell.
15️⃣ Dry cell is a … cell.
16️⃣ Daniell cell is a … cell.
17️⃣ The unit of Z is …
18️⃣ Electrolytic conduction is also known as …
19️⃣ Z is called as …
2️⃣0️⃣ Correct statement …
2️⃣1️⃣ The substance used for electrolysis is called …
2️⃣2️⃣ When molten NaCl is electrolyzed, formed at cathode is …
2️⃣3️⃣ The electrolyte in lead storage battery is …
2️⃣4️⃣ Lead storage battery is a … cell.
2️⃣5️⃣ Dry cell is a … cell.
2️⃣6️⃣ Daniell cell is a … cell.
2️⃣7️⃣ The unit of Z is …
2️⃣8️⃣ Electrolytic conduction is also known as …
2️⃣9️⃣ Z is called as …
3️⃣0️⃣ Alloy formation prevents corrosion by reducing ability of …
3️⃣1️⃣ Process using current for non spontaneous redox reaction …
3️⃣2️⃣ Cell used to carry out spontaneous redox reaction …
3️⃣3️⃣ Cell producing current from spontaneous redox reaction …
3️⃣4️⃣ Electrolysis of acidified water gives …
3️⃣5️⃣ Electrochemical reactions involve …
3️⃣6️⃣ Positive ions move towards …
3️⃣7️⃣ Negative ions move towards …
3️⃣8️⃣ Cathodic protection uses which metal as anode …
3️⃣9️⃣ Best conductor of electricity when molten …
4️⃣0️⃣ Added to water to make good conductor …
4️⃣1️⃣ When molten NaCl is electrolyzed, formed at anode is …
4️⃣2️⃣ Splitting of aqueous NaCl into ions is called …
4️⃣3️⃣ Ionization is …
4️⃣4️⃣ Substance through which current flows without change in composition …
4️⃣5️⃣ Substance conducting electricity in molten/solution state …
4️⃣6️⃣ Which one is NOT a strong electrolyte?
4️⃣7️⃣ Which one is a strong electrolyte?
4️⃣8️⃣ Which one is a weak electrolyte?
⚡๐งช Solution of IX Model Test Questions
Chemistry — Test #11 ๐ Chapter #7 ๐ Electrochemistry
Chemistry — Test #11 ๐ Chapter #7 ๐ Electrochemistry
๐ฏ Colourful, Exam‑Ready Solutions
๐ฏ Clear Concepts • ✅ Confident Prep • ๐ Score Higher
๐ฏ Clear Concepts • ✅ Confident Prep • ๐ Score Higher
๐✨ Answers of Short Answer‑Questions
๐ IX Chemistry • Chapter #7 ⚡ Electrochemistry
๐ IX Chemistry • Chapter #7 ⚡ Electrochemistry
๐ฏ Clear Concepts • ๐ก Easy Explanations
✅ Exam‑Ready • ๐ Boost Confidence
✅ Exam‑Ready • ๐ Boost Confidence
Q1. Define oxidation, reduction reactions with examples.
⚡ Oxidation ⚡
๐ Definition:➕ Addition of oxygen OR ➖ removal of hydrogen
๐ Loss of electrons → increase in oxidation number
๐ Examples:
๐ฟ C + O₂ → CO₂ (Carbon oxidation, ➕O)
⛽ 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O (Octane combustion, ➕O, ➖H)
๐งช N₂H₄ + O₂ → N₂ + 2H₂O (Hydrazine oxidation; ➖H)
๐ Cu → Cu²⁺ + 2ฤ (Loss of electrons, oxidation number ↑)
๐ฑ Reduction ๐ฑ
๐ Definition:➕ Addition of hydrogen OR ➖ removal of oxygen
๐ Gain of electrons → decrease in oxidation number
๐ Examples:
๐ค CuO + C → Cu + CO (Copper oxide reduced, ➖O)
⚙️ Fe₂O₃ + 2Al → Al₂O₃ + 2Fe + heat (Ferric oxide reduced, ➖O)
๐ฟ CH₂=CH₂ + H₂ → CH₃–CH₃ (Ethene hydrogenation, ➕H)
๐งช S + 2ฤ → S²⁻ (Sulphur gains electrons, oxidation number ↓)
✨ Quick Recall:
๐ฅ Oxidation = Oxygen added / Hydrogen removed / Electrons lost / Oxidation number ↑
๐ฑ Reduction = Oxygen removed / Hydrogen added / Electrons gained / Oxidation number ↓
๐ฅ Oxidation = Oxygen added / Hydrogen removed / Electrons lost / Oxidation number ↑
๐ฑ Reduction = Oxygen removed / Hydrogen added / Electrons gained / Oxidation number ↓
Q2. Define oxidizing agent and reducing agent with examples.
๐ด Oxidizing Agent
๐ Definition: Accepts electrons (Electron acceptor) → causes oxidation.๐ Examples:
๐ฌ️ All Non metals → F₂, Cl₂, Br₂, I₂, O₂, O₃ etc.
⚗️ All Oxyacids → H₂SO₄, HNO₃ etc.
๐ฃ All Oxysalts → KMnO₄, K₂Cr₂O₇
๐ข Reducing Agent
๐ Definition: Loses electrons (Electron donor) → causes reduction.๐ Examples:
๐ฉ All Metals → Li, Na, K (Alkali metals), Mg, Al, Zn etc.
๐ง All Binary acids → HCl, H₂S etc.
⚡ Ionic hydrides → NaH, KH etc.
๐ Example of Redox Reaction: Zn + Cl₂ → ZnCl₂
๐ข Zinc → loses electrons (oxidation) → Reducing agent
๐ด Chlorine → gains electrons (reduction) → Oxidizing agent
๐ข Zinc → loses electrons (oxidation) → Reducing agent
๐ด Chlorine → gains electrons (reduction) → Oxidizing agent
Q3. Write down 5 differences between oxidation and reduction.
| ๐ฅ Oxidation | ๐ฑ Reduction |
|---|---|
| ➕ Addition of oxygen | ➕ Addition of hydrogen |
| ➖ Removal of hydrogen | ➖ Removal of oxygen |
| ๐ Loss of electrons | ๐ Gain of electrons |
| ๐ Increase in oxidation number | ๐ Decrease in oxidation number |
| ๐ด Occurs at anode | ๐ข Occurs at cathode |
Q4. Write down 3 examples of each of oxidizing and reducing agent.
| ๐ด Oxidizing Agents (Electron Acceptors) | ๐ข Reducing Agents (Electron Donors) |
|---|---|
| ๐ฌ️ All Non metals → F₂, Cl₂, Br₂, O₂, O₃ etc. | ๐ฉ All Metals → Li, Na, Mg, Al, Zn etc. |
| ⚗️ All Oxyacids → H₂SO₄, HNO₃ etc. | ๐ง All Binary acids → HCl, H₂S etc. |
| ๐ฃ All Oxysalts → KMnO₄, K₂Cr₂O₇ etc. | ⚡ Ionic hydrides → NaH, KH etc. |
Q5. Identify the oxidizing and reducing agents from the following.
| ๐ด Oxidizing Agents (OA) | ๐ข Reducing Agents (RA) |
|---|---|
| ⚗️ H₂SO₄ → Oxidizing Agent (Oxyacids accept electrons) | ๐ฉ Al → Reducing Agent (Metals donate electrons) |
| ๐ฃ KMnO₄ → Oxidizing Agent (Oxysalts are strong OA) | ๐ฉ Na → Reducing Agent (Metals lose electrons) |
| ๐ง H₂S → Reducing Agent (Binary acids act as RA) | |
| ๐ฉ Zn → Reducing Agent (Metals are RA) |
✨ Quick Recall:
๐ด Oxidizing Agents (OA) = Electron acceptors (Oxyacids, Oxysalts, Non metals)
๐ข Reducing Agents (RA) = Electron donors (Metals, Binary acids, Hydrides)
๐ด Oxidizing Agents (OA) = Electron acceptors (Oxyacids, Oxysalts, Non metals)
๐ข Reducing Agents (RA) = Electron donors (Metals, Binary acids, Hydrides)
Q6. Identify the oxidizing and reducing agents for the following reaction.
⚗️ Reaction: H₂ (RA) + Cl₂ (OA) → 2HCl
๐ Oxidation: H₂ → H⁺ (oxidation number increases from 0 to +1)
๐ Reduction: Cl₂ → Cl⁻ (oxidation number decreases from 0 to -1)
๐ Oxidation: H₂ → H⁺ (oxidation number increases from 0 to +1)
๐ Reduction: Cl₂ → Cl⁻ (oxidation number decreases from 0 to -1)
๐ข Reducing Agent: H₂ → Donates electrons → Undergoes oxidation
๐ด Oxidizing Agent: Cl₂ → Accepts electrons → Undergoes reduction
๐ด Oxidizing Agent: Cl₂ → Accepts electrons → Undergoes reduction
Q7. Describe the construction of electrochemical cell. Write names of two types of electrochemical cells.
๐ Definition:
An electrochemical cell is a device that converts chemical energy ↔ electrical energy using redox reactions.
๐ Spontaneous redox → generates current (Galvanic cell)
⚡ Non spontaneous redox → driven by current (Electrolytic cell)
An electrochemical cell is a device that converts chemical energy ↔ electrical energy using redox reactions.
๐ Spontaneous redox → generates current (Galvanic cell)
⚡ Non spontaneous redox → driven by current (Electrolytic cell)
๐️ Construction / Structure:
๐บ Vessel/pot with two electrodes
๐ด Anode → Oxidation occurs (electron loss)
๐ข Cathode → Reduction occurs (electron gain)
⚡ Each electrode reaction = half cell reaction
๐ Overall cell reaction = combination of two half cell reactions
๐๐ Electrodes connected to battery / voltmeter, with electrolyte present
๐บ Vessel/pot with two electrodes
๐ด Anode → Oxidation occurs (electron loss)
๐ข Cathode → Reduction occurs (electron gain)
⚡ Each electrode reaction = half cell reaction
๐ Overall cell reaction = combination of two half cell reactions
๐๐ Electrodes connected to battery / voltmeter, with electrolyte present
๐ Types of Electrochemical Cells:
๐ Galvanic Cell → Chemical → Electrical (spontaneous)
⚡ Electrolytic Cell → Electrical → Chemical (non spontaneous)
๐ Galvanic Cell → Chemical → Electrical (spontaneous)
⚡ Electrolytic Cell → Electrical → Chemical (non spontaneous)
Q8. Differentiate between electrolytes and non-electrolytes with examples.
⚡ Electrolytes vs Non Electrolytes
| ๐ Electrolytes | ๐ซ Non Electrolytes |
|---|---|
| ๐ง Dissociate into ions in water | ๐ง Dissolve as molecules only |
| ⚡ Conductors of electricity | ๐ซ Insulators |
| ๐ Conduct electricity in aqueous solution | ❌ Do not conduct electricity |
| ๐ Polar compounds | ๐งช Non polar compounds |
| ๐งฑ Ionic bonds | ๐ Covalent bonds |
| ๐ Form cations & anions | ๐ค Remain as neutral molecules |
| ๐ Strong (complete ionization) or weak (partial ionization) | ๐ซ No ionization at all |
| ๐ Used in batteries, electrolysis, IV fluids | ๐ฌ Used in food, pharma, organic chemistry |
| ๐ Essential for nerve impulses & muscle contraction in living organisms | ๐ซ Do not affect conductivity but may change osmotic pressure |
| ๐งช Examples → Salts (NaCl, KCl), acids (HCl, H₂SO₄), bases (NaOH) | ๐ญ Examples → Sugar, glucose, urea, chloroform, ethanol, glycerine, etc. |
Q9. Differentiate between strong electrolytes and weak electrolytes with examples.
⚡ Difference between Strong and Weak Electrolytes
| ๐ช Strong Electrolytes | ๐ฑ Weak Electrolytes |
|---|---|
| 1️⃣ The electrolytes which are highly dissociated (% dissociation high) conduct large current. | 1️⃣ The electrolytes which are poorly dissociated (% dissociation low) conduct electricity slightly. |
| 2️⃣ ⚡ Conducts electric current to large extent. | 2️⃣ ๐ซ Conducts electric current poorly. |
| 3️⃣ ๐ง Dissociates completely into ions in aqueous solution. | 3️⃣ ๐ง Dissociates partially into ions in aqueous solution. |
| 4️⃣ ๐ Solution contains maximum free ions. | 4️⃣ ๐งช Solution contains both free ions & undissociated molecules. |
| 5️⃣ ๐ High electrical conductivity. | 5️⃣ ๐ Low electrical conductivity. |
| 6️⃣ ๐ฏ Percent ionization almost 100%. | 6️⃣ ๐ Percent ionization roughly 1–10%. |
| 7️⃣ ๐ซ Ostwald’s dilution law not applicable. | 7️⃣ ✅ Ostwald’s dilution law applicable. |
| 8️⃣ ๐งช Examples: (a) Strong Acids → HCl, H₂SO₄ (b) Strong Bases → NaOH, KOH (c) All Salts → NaCl, NaNO₃ |
8️⃣ ๐งช Examples: (a) Weak Acids → HF, Acetic acid, Benzoic acid (b) Weak Bases → NH₄OH |
Q10. Identify strong and weak electrolytes from the following:
HCl (S), KI (S), NaOH (S), H₂S (W), CH₃COOH (W), NH₄OH (W), NaCl (S), C₂H₅OH (W)
HCl (S), KI (S), NaOH (S), H₂S (W), CH₃COOH (W), NH₄OH (W), NaCl (S), C₂H₅OH (W)
๐ Strong Electrolytes (Complete Ionization / 100% ionization → conduct electricity well)
๐งช HCl → Strong acid, fully ionizes
๐ง KI → Ionic salt, dissociates completely
๐งผ NaOH → Strong base, full ionization
๐ง NaCl → Common soluble salt, strong ionic compound
๐งช HCl → Strong acid, fully ionizes
๐ง KI → Ionic salt, dissociates completely
๐งผ NaOH → Strong base, full ionization
๐ง NaCl → Common soluble salt, strong ionic compound
๐ง Weak Electrolytes (Partial Ionization → poor conductors)
๐งช H₂S → Weak acid, limited ionization
๐ CH₃COOH → Weak acid (acetic acid), partial ionization
๐งช NH₄OH → Weak base, incomplete ionization
๐ท C₂H₅OH → Ethanol, mostly molecular, very weak electrolyte
๐งช H₂S → Weak acid, limited ionization
๐ CH₃COOH → Weak acid (acetic acid), partial ionization
๐งช NH₄OH → Weak base, incomplete ionization
๐ท C₂H₅OH → Ethanol, mostly molecular, very weak electrolyte
Q11. Why ionic compounds conduct electricity in molten or in aqueous solutions only?
๐ Reason of Conduction
Electricity flows when charged particles (ions/electrons) can move freely.
Electricity flows when charged particles (ions/electrons) can move freely.
๐งฑ Reason of Non-Conduction in Solid Ionic Compounds
๐ Ions held in fixed lattice positions.
⚡ No free movement of charge carriers.
๐ซ Cannot conduct electricity in solid state.
๐ Ions held in fixed lattice positions.
⚡ No free movement of charge carriers.
๐ซ Cannot conduct electricity in solid state.
๐ง Reason of Conduction in Molten / Aqueous Ionic Compounds
๐ Strong electrostatic forces broken.
๐ Ions become free to move.
⚡ Positive ions → Cathode, Negative ions → Anode.
✅ Conduct electricity efficiently.
๐ Strong electrostatic forces broken.
๐ Ions become free to move.
⚡ Positive ions → Cathode, Negative ions → Anode.
✅ Conduct electricity efficiently.
Q12. What is electrolytic cell? Explain with diagram. Describe the construction and working of electrolytic cell.
๐ Definition
An electrolytic cell is a device that uses electricity to drive a non spontaneous redox reaction.
๐ It is the apparatus where electrolysis takes place.
An electrolytic cell is a device that uses electricity to drive a non spontaneous redox reaction.
๐ It is the apparatus where electrolysis takes place.
๐️ Construction
➡️๐บ Vessel containing electrolyte (๐ง) / Electrolytic pot
➡️⚡ Two electrodes
➡️๐ Electrodes connected to battery
๐ด Anode → Oxidation occurs (loss of electrons)
๐ข Cathode → Reduction occurs (gain of electrons)
➡️๐ Battery supplies current → pushes electrons into cathode
➡️๐บ Vessel containing electrolyte (๐ง) / Electrolytic pot
➡️⚡ Two electrodes
➡️๐ Electrodes connected to battery
๐ด Anode → Oxidation occurs (loss of electrons)
๐ข Cathode → Reduction occurs (gain of electrons)
➡️๐ Battery supplies current → pushes electrons into cathode
⚙️ Working
Ionization: MX → M⁺ + X⁻ (Electrolyte splits into ions)
Cathode reaction (Reduction): M⁺ + ฤ → M (Positive ions gain electrons)
Anode reaction (Oxidation): X⁻ → X + ฤ (Negative ions lose electrons)
๐ Overall redox reaction → Reduction at cathode, oxidation at anode
Ionization: MX → M⁺ + X⁻ (Electrolyte splits into ions)
Cathode reaction (Reduction): M⁺ + ฤ → M (Positive ions gain electrons)
Anode reaction (Oxidation): X⁻ → X + ฤ (Negative ions lose electrons)
๐ Overall redox reaction → Reduction at cathode, oxidation at anode
Q13. Sketch electrolytic cell for electrolysis of molten potassium chloride and identify cathode and anode, oxidation, reduction reaction, movement of electron
Q14. Define electrochemistry, electrochemical reactions, electrochemical cell, electrolyte, non-electrolyte, salt bridge, cell, Galvanic cell, electrolytic cell, battery, electrode, cathode, anode, oxidation, reduction, redox reactions, electrochemical equivalent, and chemical equivalent.
๐ Overview
Electrochemistry studies the relationship between electricity and chemical change—how redox reactions convert chemical energy ↔ electrical energy in cells and electrolytes.
Electrochemistry studies the relationship between electricity and chemical change—how redox reactions convert chemical energy ↔ electrical energy in cells and electrolytes.
Electrochemistry
The branch of chemistry dealing with electrochemical reactions, electrolytes, and electrochemical cells—linking electricity with chemical change.
Electrochemical reactions
Chemical reactions where chemical energy converts to electrical energy or vice versa through redox processes.
Electrochemical cell
A device that uses redox reactions to convert chemical energy into electrical energy or the reverse.
Electrolytic cell
An electrochemical cell where an external voltage drives a non‑spontaneous redox reaction—electrical → chemical energy.
Galvanic (Voltaic) cell
An electrochemical cell where a spontaneous redox reaction generates electric current—chemical → electrical energy.
Electrolyte
A substance that conducts electricity in molten state or aqueous solution due to free ions; acids, bases, and salts are typical electrolytes.
Strong electrolytes
Highly dissociated; nearly complete ionization in solution—conduct current strongly.
Weak electrolytes
Poorly dissociated; partial ionization in solution—conduct current slightly.
Non‑electrolyte
Substances that do not conduct electricity in molten state or aqueous solution—remain as neutral molecules.
Electrolysis
The process where applied electric field moves ions and converts them to neutral species at electrodes—driving non‑spontaneous redox.
Electroplating
Deposition of a metal onto another metal’s surface via electrolysis.
Faraday’s first law
The mass deposited or liberated at an electrode is directly proportional to the quantity of electricity passed.
Faraday’s second law
For the same quantity of electricity, masses of different substances deposited are proportional to their chemical equivalents.
Chemical equivalent
Mass deposited/liberated by one faraday (96500 C); numerically equal to gram atomic mass divided by valency.
Battery
A group of galvanic cells connected in series to provide a usable voltage/current source.
Electrochemical equivalent (Z)
Mass of substance deposited when one coulomb of charge passes through the electrolyte.
Electrode
Conductive solid immersed in electrolyte where oxidation or reduction occurs.
Cathode
Electrode where reduction occurs (electron gain).
Anode
Electrode where oxidation occurs (electron loss).
Oxidation
Loss of electrons or increase in oxidation number.
Reduction
Gain of electrons or decrease in oxidation number.
Redox reactions
Coupled oxidation–reduction processes where electrons transfer between species.
Salt bridge
Ionic conduit connecting two half‑cells to maintain electrical neutrality and complete the circuit without mixing solutions.
Cell
A single electrochemical unit (galvanic or electrolytic) performing energy conversion via redox reactions.
Q15. What is electroplating? On which principle this process works? Give its merits.
๐ Definition
Electroplating (Thin metal coating) = Deposition of a thin layer of costly / corrosion resistant metal (Ag, Au, Cr, Ni, Cu, Sn) onto a cheaper base metal (iron, steel etc.) using electrolysis in an electrolytic cell.
Electroplating (Thin metal coating) = Deposition of a thin layer of costly / corrosion resistant metal (Ag, Au, Cr, Ni, Cu, Sn) onto a cheaper base metal (iron, steel etc.) using electrolysis in an electrolytic cell.
⚙️ Principle (Basis of Process)
๐ Electrolysis is the principle.
๐ข Cathode (–) → Base metal to be coated (iron, steel).
๐ด Anode (+) → Plating metal to be coated (Ag, Au, Ni, Cr etc.).
๐ง Electrolyte → Contains ions of plating metal.
๐ Current passes → Metal ions deposit on cathode surface.
๐ Electrolysis is the principle.
๐ข Cathode (–) → Base metal to be coated (iron, steel).
๐ด Anode (+) → Plating metal to be coated (Ag, Au, Ni, Cr etc.).
๐ง Electrolyte → Contains ions of plating metal.
๐ Current passes → Metal ions deposit on cathode surface.
๐ฏ Merits / Applications (Improves appearance, protection, and durability)
➡️๐ก️ Corrosion Protection (prevents rusting).
➡️✨ Durability & Decoration (shiny, attractive finish).
➡️๐ฐ Low Cost Articles (cheap metal looks expensive).
➡️๐ง Repair (restore worn out parts).
➡️๐ก️ Corrosion Protection (prevents rusting).
➡️✨ Durability & Decoration (shiny, attractive finish).
➡️๐ฐ Low Cost Articles (cheap metal looks expensive).
➡️๐ง Repair (restore worn out parts).
Q16. What is corrosion of metal and rusting? How it can be prevented? or Name the methods which are used to protect metal from corrosion. How cathodic protection prevent metal from corrosion?
๐ Definition of Corrosion
๐ Electrochemical redox reaction → slow, spontaneous, continuous destruction of metals.
๐ฌ️ Caused by oxygen, water, or chemical agents.
๐งฑ Converts metal → oxides, hydrated oxides, or carbonates.
➡️ Metal + air + water → Metal oxide or hydrated metal oxide or carbonate (Electrochemical redox reaction).
๐ Electrochemical redox reaction → slow, spontaneous, continuous destruction of metals.
๐ฌ️ Caused by oxygen, water, or chemical agents.
๐งฑ Converts metal → oxides, hydrated oxides, or carbonates.
➡️ Metal + air + water → Metal oxide or hydrated metal oxide or carbonate (Electrochemical redox reaction).
๐งฑ Rusting of Iron
๐ด Rusting = corrosion of iron.
๐ง️ Occurs with moist oxygen + water.
๐ค Forms reddish brown flaky deposits called rust → Fe₂O₃·nH₂O (hydrated ferric oxide).
๐ซ Rusted surface gives no protection → whole iron eventually converts to rust.
⚗️ Reaction: 4Fe + 3O₂ + 2nH₂O → 2Fe₂O₃·nH₂O (hydrated iron(III) oxide/rust).
๐ด Rusting = corrosion of iron.
๐ง️ Occurs with moist oxygen + water.
๐ค Forms reddish brown flaky deposits called rust → Fe₂O₃·nH₂O (hydrated ferric oxide).
๐ซ Rusted surface gives no protection → whole iron eventually converts to rust.
⚗️ Reaction: 4Fe + 3O₂ + 2nH₂O → 2Fe₂O₃·nH₂O (hydrated iron(III) oxide/rust).
⚙️ Mechanism of Rusting
๐ Different regions of surface act differently:
๐บ Anode (less moisture) → Fe oxidizes → Fe²⁺ ions. (Fe → Fe²⁺ + 2ฤ)
๐ป Cathode (more moisture) → O₂ reduced → OH⁻ ions. (O₂ + 2H₂O + 4ฤ → 4OH⁻)
๐ Overall redox: Fe²⁺ + O₂ + H₂O → Fe₂O₃·nH₂O (rust).
๐ Different regions of surface act differently:
๐บ Anode (less moisture) → Fe oxidizes → Fe²⁺ ions. (Fe → Fe²⁺ + 2ฤ)
๐ป Cathode (more moisture) → O₂ reduced → OH⁻ ions. (O₂ + 2H₂O + 4ฤ → 4OH⁻)
๐ Overall redox: Fe²⁺ + O₂ + H₂O → Fe₂O₃·nH₂O (rust).
๐ก️ Prevention of Corrosion
➡️⚡ Electroplating → Nickel plating, chromium plating etc.
➡️๐ก️ Protective metallic coating → Galvanizing (Zn), Tin plating.
➡️๐ Alloying → Stainless steel (Fe + Cr + Ni).
➡️๐ข Cathodic protection → Sacrificial anode (Mg, Al).
➡️๐จ Non metallic coating → Paint, oils, grease, varnish, plastic emulsion.
➡️๐งฑ Other coatings → Phosphate, concrete, Fe₃O₄.
➡️⚗️ Corrosion inhibitors → K₂CrO₄.
➡️⚡ Electroplating → Nickel plating, chromium plating etc.
➡️๐ก️ Protective metallic coating → Galvanizing (Zn), Tin plating.
➡️๐ Alloying → Stainless steel (Fe + Cr + Ni).
➡️๐ข Cathodic protection → Sacrificial anode (Mg, Al).
➡️๐จ Non metallic coating → Paint, oils, grease, varnish, plastic emulsion.
➡️๐งฑ Other coatings → Phosphate, concrete, Fe₃O₄.
➡️⚗️ Corrosion inhibitors → K₂CrO₄.
๐ฑ Cathodic Protection (Special Note)
๐ข Base metal (iron/steel) made cathode.
๐ฉ More reactive active metal (Mg, Al) used as sacrificial anode.
⚡ Sacrificial metal oxidizes instead → protects main metal from corrosion.
๐ข Base metal (iron/steel) made cathode.
๐ฉ More reactive active metal (Mg, Al) used as sacrificial anode.
⚡ Sacrificial metal oxidizes instead → protects main metal from corrosion.
Q17. Write down 4 applications of electrolytic cells or electrolysis.
➡️ ✨ Electroplating of Metals: Thin, shiny, corrosion resistant coating (e.g. Ni, Cr, Ag, Au).
➡️ ๐ง Refining of Impure Metals: Electro refining of copper and other metals for purity.
➡️ ๐งช Manufacture of Chemicals: Production of caustic soda (NaOH) from brine in Nelson’s cell.
๐ Useful by‑product → Chlorine gas (Cl₂).
➡️ ⛏️ Extraction of Metals from Ores:
๐ Sodium → extracted from molten NaCl (Down’s cell).
๐ญ Aluminum → extracted using Hall‑Heroult cell.
➡️ ๐ง Refining of Impure Metals: Electro refining of copper and other metals for purity.
➡️ ๐งช Manufacture of Chemicals: Production of caustic soda (NaOH) from brine in Nelson’s cell.
๐ Useful by‑product → Chlorine gas (Cl₂).
➡️ ⛏️ Extraction of Metals from Ores:
๐ Sodium → extracted from molten NaCl (Down’s cell).
๐ญ Aluminum → extracted using Hall‑Heroult cell.
✨ Quick Recall: Electrolysis helps in → Electroplating, Refining, Chemical manufacture, Metal extraction.
Q18. Describe the process of zinc plating and tin plating.
๐น Zinc Plating / Galvanizing
๐ Definition: Deposition of a thin layer of zinc metal on cheaper base metals (iron, steel) by electroplating (electrolysis).
⚙️ Method:
๐บ Electrolytic cell
๐ข Cathode (–) → Steel object (to be coated)
๐ด Anode (+) → Rod of pure zinc
๐ง Electrolyte → Potassium zinc cyanide solution (K₂[Zn(CN)₄]) → provides Zn²⁺ ions
๐ Battery → Connects electrodes
⚡ Working:
Zn²⁺ ions deposit on cathode → thin zinc coating.
Zinc anode dissolves → supplies Zn²⁺ ions continuously.
Result → Base metal protected from corrosion (rust).
⚡ Electrolytic Reactions:
๐ Ionization: K₂Zn(CN)₄(aq) → 2K⁺(aq) + Zn²⁺(aq) + CN⁻
๐ด Anode (Oxidation): Zn(s) → Zn²⁺(aq) + 2ฤ
๐ข Cathode (Reduction): Zn²⁺(aq) + 2ฤ → Zn(s)
๐ Overall: Zn(s) (Anode) → Zn(s) (Cathode)
๐ Definition: Deposition of a thin layer of zinc metal on cheaper base metals (iron, steel) by electroplating (electrolysis).
⚙️ Method:
๐บ Electrolytic cell
๐ข Cathode (–) → Steel object (to be coated)
๐ด Anode (+) → Rod of pure zinc
๐ง Electrolyte → Potassium zinc cyanide solution (K₂[Zn(CN)₄]) → provides Zn²⁺ ions
๐ Battery → Connects electrodes
⚡ Working:
Zn²⁺ ions deposit on cathode → thin zinc coating.
Zinc anode dissolves → supplies Zn²⁺ ions continuously.
Result → Base metal protected from corrosion (rust).
⚡ Electrolytic Reactions:
๐ Ionization: K₂Zn(CN)₄(aq) → 2K⁺(aq) + Zn²⁺(aq) + CN⁻
๐ด Anode (Oxidation): Zn(s) → Zn²⁺(aq) + 2ฤ
๐ข Cathode (Reduction): Zn²⁺(aq) + 2ฤ → Zn(s)
๐ Overall: Zn(s) (Anode) → Zn(s) (Cathode)
๐น Tin Plating
๐ Definition: Deposition of a thin layer of tin metal on base metals (iron, steel, copper) by electroplating.
⚙️ Method:
๐บ Electrolytic cell
๐ข Cathode (–) → Base metal object (iron/steel/copper)
๐ด Anode (+) → Pure tin rod
๐ง Electrolyte → Acidified stannous chloride solution (SnSO₄) → provides Sn²⁺ ions
๐ Battery → Connects electrodes
⚡ Working:
Sn²⁺ ions deposit on cathode → thin tin coating.
Tin anode dissolves → supplies Sn²⁺ ions.
Result → Base metal gains shiny, corrosion resistant surface (used in food cans, utensils).
⚡ Electrolytic Reactions:
๐ Ionization: SnSO₄(aq) → Sn²⁺(aq) + SO₄²⁻
๐ด Anode (Oxidation): Sn(s) → Sn²⁺(aq) + 2ฤ
๐ข Cathode (Reduction): Sn²⁺(aq) + 2ฤ → Sn(s)
๐ Overall: Sn(s) (Anode) → Sn(s) (Cathode)
๐ Definition: Deposition of a thin layer of tin metal on base metals (iron, steel, copper) by electroplating.
⚙️ Method:
๐บ Electrolytic cell
๐ข Cathode (–) → Base metal object (iron/steel/copper)
๐ด Anode (+) → Pure tin rod
๐ง Electrolyte → Acidified stannous chloride solution (SnSO₄) → provides Sn²⁺ ions
๐ Battery → Connects electrodes
⚡ Working:
Sn²⁺ ions deposit on cathode → thin tin coating.
Tin anode dissolves → supplies Sn²⁺ ions.
Result → Base metal gains shiny, corrosion resistant surface (used in food cans, utensils).
⚡ Electrolytic Reactions:
๐ Ionization: SnSO₄(aq) → Sn²⁺(aq) + SO₄²⁻
๐ด Anode (Oxidation): Sn(s) → Sn²⁺(aq) + 2ฤ
๐ข Cathode (Reduction): Sn²⁺(aq) + 2ฤ → Sn(s)
๐ Overall: Sn(s) (Anode) → Sn(s) (Cathode)
Q19. Write down the composition of following alloys:
๐ก Brass → Cu–Zn [4:1] → Door knobs, hand rails, pipes
๐ค Bronze → Cu–Sn–Zn [9:1] → Coins, medals, tools
๐ Bell Metal → Cu–Sn [4:1] → Casting of bells
⚪ Sterling Silver → Ag–Cu [92.5:7.5%] → Cutlery, medical tools
๐ก️ Monel → Ni–Cu–Fe [63:34:2.5] → Corrosion resistant containers
๐ช Cupronickel → Cu–Ni–Mn → Coins
๐ง Solder → Sn–Cu–Pb–Sb → Electrical circuit joining
๐ค Pewter → Sn–Cu–Pb–Sb–Bi → Ornaments
๐ White Gold (18K) → Au–Pb–Ag–Cu → Jewelry
๐ฆท Amalgam → Hg–Ag–Cu–Zn → Dental fillings
✈️ Duralumin → Al–Cu–Mg–Ni → Boats, aircrafts
๐ต Alnico → Fe–Al–Ni–Co → Magnets (loudspeakers)
๐ก Yellow Gold (22K) → 91.67% Au + Ag–Cu–Zn → Jewelry
๐ด Red Gold (18K) → 75% Au + Cu → Jewelry
⚪ White Gold (18K) → 75% Au + Cu–Ag → Jewelry
๐✨ Answers of Long Answer Questions ✨๐
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