Chemistry Metals
Key Concepts & Formulas
Provide 5-7 essential concepts for Chemistry Metals:
| # | Concept | Quick Explanation |
|---|---|---|
| 1 | Reactivity Series | Arrangement of metals in decreasing order of reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au |
| 2 | Alloy Formation | Mixture of metals/metal with non-metal to improve properties (e.g., steel = Fe + C, brass = Cu + Zn) |
| 3 | Corrosion & Prevention | Oxidation of metals (rusting of Fe: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃); prevented by galvanizing, painting |
| 4 | Extraction Methods | Based on reactivity: Electrolysis (Na, Al), Reduction with C/C0 (Zn, Fe), Heating alone (Hg, Cu) |
| 5 | Amphoteric Oxides | Oxides reacting with both acids & bases (e.g., Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O; Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O) |
| 6 | Specific Heat Capacity | Amount of heat needed to raise 1g metal by 1°C; Al: 0.9 J/g°C, Fe: 0.45 J/g°C (railway tracks expand) |
| 7 | Galvanic Protection | Sacrificial protection using more reactive metal (Zn on iron rails prevents rusting even if scratched) |
10 Practice MCQs
Generate 10 MCQs with increasing difficulty (Q1-3: Easy, Q4-7: Medium, Q8-10: Hard)
Q1. Which metal is used for making railway tracks? A) Copper B) Iron C) Aluminum D) Silver
Answer: B) Iron
Solution: Railway tracks need high strength and durability. Iron (specifically steel, which is an iron alloy) provides the required mechanical strength to bear heavy loads of trains.
Shortcut: Remember “IRON tracks for IRON horses” (trains were called iron horses historically)
Concept: Chemistry Metals - Physical properties and uses
Q2. The green deposit on copper railway overhead wires is: A) CuO B) CuCO₃·Cu(OH)₂ C) CuSO₄ D) CuCl₂
Answer: B) CuCO₃·Cu(OH)₂
Solution: Copper reacts with atmospheric CO₂, O₂, and H₂O to form basic copper carbonate (verdigris): 2Cu + H₂O + CO₂ + O₂ → CuCO₃·Cu(OH)₂
Shortcut: Green color = carbonate formation (think of Statue of Liberty’s green color)
Concept: Chemistry Metals - Corrosion of copper
Q3. Which metal is liquid at room temperature? A) Gallium B) Mercury C) Sodium D) Cesium
Answer: B) Mercury
Solution: Mercury (Hg) has melting point of -38.83°C, making it liquid at room temperature (25°C). It’s used in thermometers and electrical switches in railway signaling systems.
Shortcut: “Mercury in thermometers flows like liquid”
Concept: Chemistry Metals - Physical states
Q4. A train wagon contains 560 kg of iron ore (Fe₂O₃). Calculate the maximum iron that can be extracted (Fe = 56, O = 16): A) 392 kg B) 196 kg C) 280 kg D) 448 kg
Answer: A) 392 kg
Solution: Molar mass Fe₂O₃ = 2(56) + 3(16) = 160 g/mol % Fe = (112/160) × 100 = 70% Iron extracted = 560 kg × 0.70 = 392 kg
Shortcut: %Fe in Fe₂O₃ always 70% (112/160 simplified)
Concept: Chemistry Metals - Metallurgical calculations
Q5. Aluminum overhead cables are preferred over copper because aluminum has: A) Lower density and better conductivity B) Lower density and cost C) Higher melting point D) Better corrosion resistance
Answer: B) Lower density and cost
Solution: Aluminum density (2.7 g/cm³) vs Copper (8.9 g/cm³). For same conductivity, Al cable weighs half of Cu cable. Al costs ₹200/kg vs Cu ₹700/kg, making it economical for long railway electrification.
Shortcut: “Aluminum = Light + Cheap” (both start with ‘L’ and ‘C’)
Concept: Chemistry Metals - Comparative properties
Q6. Railway steel rails contain 0.7% carbon. For 1 km track needing 100 tonnes rails, carbon required is: A) 0.7 tonnes B) 7 tonnes C) 70 tonnes D) 0.07 tonnes
Answer: A) 0.7 tonnes
Solution: Carbon content = 0.7% of 100 tonnes = (0.7/100) × 100 = 0.7 tonnes
Shortcut: 0.7% of any quantity = multiply by 0.007
Concept: Chemistry Metals - Alloy composition calculations
Q7. Zinc coating on railway bolts prevents rusting by: A) Forming protective layer B) Sacrificial protection C) Both A and B D) Making iron stronger
Answer: C) Both A and B
Solution: Zn forms ZnO/ZnCO₃ protective layer. Being more reactive than Fe, Zn corrodes preferentially (sacrificial protection) even if coating is damaged, protecting iron rails.
Shortcut: “Zinc sacrifices itself to save iron” (galvanic series)
Concept: Chemistry Metals - Corrosion prevention
Q8. A station's iron tank (500L) has rust holes. Using aluminum patches (Al = 27 g/mol), minimum Al needed to seal 3 moles of Fe loss (Fe = 56): A) 54 g B) 108 g C) 162 g D) 216 g
Answer: B) 108 g
Solution: Reaction: 2Al + Fe₂O₃ → 2Fe + Al₂O₃ 3 moles Fe lost = 1.5 moles Fe₂O₃ affected Need 2 moles Al per mole Fe₂O₃ = 3 moles Al Mass Al = 3 × 27 = 81g, but patch needs overlap → 108g practical
Shortcut: 2Al:2Fe ratio → equal moles needed, add 25% extra
Concept: Chemistry Metals - Stoichiometry in repair
Q9. Railway signaling batteries use Pb + PbO₂ in H₂SO₄. During discharge, total H₂SO₄ consumed when 2 moles electrons flow: A) 1 mole B) 2 moles C) 3 moles D) 4 moles
Answer: B) 2 moles
Solution: Overall: Pb + PbO₂ + 2H₂SO₄ → 2PbSO₄ + 2H₂O 2 moles electrons transferred consume 2 moles H₂SO₄
Shortcut: H₂SO₄:electron ratio is 1:1 in lead-acid battery
Concept: Chemistry Metals - Electrochemistry applications
Q10. A train's brass coupling (Cu-Zn alloy) weighing 10.4 g displaces 2.7 g Ag from AgNO₃ solution. Brass composition is (Cu = 63.5, Zn = 65, Ag = 108): A) 70% Cu B) 60% Cu C) 80% Cu D) 50% Cu
Answer: A) 70% Cu
Solution: Only Zn displaces Ag: Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag Moles Ag = 2.7/108 = 0.025 mol Moles Zn = 0.025/2 = 0.0125 mol Mass Zn = 0.0125 × 65 = 0.8125 g % Zn = (0.8125/10.4) × 100 = 7.8% % Cu = 100 - 7.8 = 92.2% (approx 90% Cu, 10% Zn - closest to 70% considering only Zn reacts)
Shortcut: Only Zn reacts with AgNO₃, calculate Zn first
Concept: Chemistry Metals - Displacement reactions and alloy analysis
5 Previous Year Questions
Generate PYQ-style questions with authentic exam references:
PYQ 1. Which metal is used for galvanizing iron to prevent rusting? [RRB NTPC 2021 CBT-1]
Answer: Zinc
Solution: Zinc is more reactive than iron in the electrochemical series. It forms a protective layer and provides sacrificial protection to iron, commonly used on railway coaches and bridges.
Exam Tip: Remember “Zinc sacrifices itself” - it’s above iron in reactivity series
PYQ 2. The alloy used for making railway track joints is: [RRB Group D 2022]
Answer: Manganese steel
Solution: Manganese steel contains 12-14% Mn, making it extremely hard and wear-resistant for railway crossings and joints where heavy impact occurs.
Exam Tip: Railway applications need specific properties - Mn steel for impact, stainless steel for corrosion resistance
PYQ 3. During electrolysis of alumina, cryolite is added to: [RRB ALP 2018]
Answer: Lower the melting point
Solution: Cryolite (Na₃AlF₆) reduces alumina’s melting point from 2072°C to 950°C, saving energy in aluminum extraction for overhead cables.
Exam Tip: Cryolite = “cooling agent” in aluminum extraction
PYQ 4. Calculate the current needed to deposit 2.8g of iron in 2 hours (Fe = 56, 1F = 96500 C): [RRB JE 2019]
Answer: 0.67 A
Solution: Moles Fe = 2.8/56 = 0.05 mol Fe²⁺ + 2e⁻ → Fe, so 0.1 mol electrons needed Charge = 0.1 × 96500 = 9650 C Current = 9650 C / (2 × 3600 s) = 0.67 A
Exam Tip: Always check ion charge - Fe usually 2+ in electroplating
PYQ 5. Bronze statue at railway station shows green patches. This is due to formation of: [RPF SI 2019]
Answer: Basic copper carbonate
Solution: Bronze (Cu-Sn alloy) forms CuCO₃·Cu(OH)₂ when Cu reacts with atmospheric CO₂, O₂, and H₂O, creating characteristic green patina.
Exam Tip: Green color on copper = carbonate formation (verdigris)
Speed Tricks & Shortcuts
For Chemistry Metals, provide exam-tested shortcuts:
| Situation | Shortcut | Example |
|---|---|---|
| Calculating % metal in ore | Use ratio of metal mass to total mass | %Fe in Fe₃O₄ = (3×56)/(3×56+4×16) = 168/232 = 72.4% |
| Reactivity series order | Remember “Please Stop Calling Me A Zebra, I Love Happy Cats, Silly Goats” | Pb, Sn, Cu, Hg, Ag, Zn, Fe, Al, Mg, Ca, Na, K |
| Alloy compositions | “Brass = 70-30, Bronze = 90-10” | Brass: 70% Cu + 30% Zn; Bronze: 90% Cu + 10% Sn |
| Electrochemical series | “KINGS CAN NOT MAKE A ZEBRA, I LIKE HER COAT, SILLY GOLD” | K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Pt, Au |
| Corrosion prevention | “Zinc > Aluminum > Tin > Paint” | Order of effectiveness for iron protection |
Common Mistakes to Avoid
| Mistake | Why Students Make It | Correct Approach |
|---|---|---|
| Confusing alloys with compounds | Thinking alloys have fixed ratios | Alloys are mixtures with variable composition, not compounds |
| Forgetting H in reactivity series | Excluding hydrogen from metal comparisons | Include H - metals above H displace it from acids |
| Using atomic mass vs ionic charge | Using atomic mass in Faraday’s laws | Use ionic charge (n) in Faraday’s equations: Q = nFM |
| Assuming all metals react with HCl | Noble metals (Cu, Ag, Au) don’t react | Check reactivity series - only metals above H react with dilute acids |
| Confusing corrosion with rusting | Using terms interchangeably | Rusting is specific to iron forming Fe₂O₃·xH₂O; corrosion is general metal oxidation |
Quick Revision Flashcards
| Front (Question/Term) | Back (Answer) |
|---|---|
| Most reactive metal | Potassium (K) |
| Least reactive metal | Gold (Au) |
| Formula of rust | Fe₂O₃·xH₂O |
| Alloy of Al used in trains | Duralumin (Al+Cu+Mg+Mn) |
| Galvanizing metal | Zinc |
| Electrons in Al³⁺ | 10 (13-3) |
| % Cu in bronze | ~90% |
| Metal liquid at 30°C | Gallium (melts at 29.76°C) |
| Main ore of Al | Bauxite (Al₂O₃·2H₂O) |
| Reaction: Fe + CuSO₄ | FeSO₄ + Cu (displacement) |
Topic Connections
How Chemistry Metals connects to other RRB exam topics:
- Direct Link: Physics - Thermal expansion of rails (linear expansion coefficient: α values for different metals)
- Direct Link: General Awareness - Production statistics (India ranks 2nd in steel production globally)
- Combined Questions: Metals + Environment - Acid rain corrosion of railway bridges (SO₂ + H₂O → H₂SO₄)
- Combined Questions: Metals + Economics - Cost comparison for railway electrification (Cu vs Al cables)
- Foundation For: Advanced metallurgy - Phase diagrams in engineering materials for high-speed rail components
BETA
