Chapter 17: Group 2 Elements — Short Questions
Overview
Ye short questions wahi 10 topics cover karte hain jo MCQs mein the, lekin yahan 2-3 line ka concept-based jawab dena hota hai, sirf option choose nahi karna. Har topic ke sawalat isi tarteeb mein aa rahe hain jaise chapter mein hain.
17.1 — Properties Aur Trends (Q1–6)
Q1 (Alkaline earth metals kyun kehte hain): Inki metallic nature hai, earth’s crust mein paye jate hain, aur inke oxides aur hydroxides paani mein alkaline (basic) hote hain.
Q2 (Electron config aur similar properties): General config ns² hai. Chunke sab elements ka outer config same hai, sab 2 electrons khokar M²⁺ banate hain, isliye similar chemical behaviour dikhate hain.
Q3 (Metallic radius Be se Ba tak): Radius barhta hai neeche jaate hue: Be=112pm, Mg=160pm, Ca=197pm, Sr=215pm, Ba=222pm — har step par naya electron shell add hone ki wajah se.
Q4 (First ionization energy kam kyun hoti hai): Size barhta hai aur inner electrons ki shielding barhti hai, isliye outer electrons nucleus se kamzor attract hote hain — kam energy chahiye unhe nikalne ke liye (Be=900 → Ba=503 kJ/mol).
Q5 (Electrode potential ka trend): E° neeche jaate hue zyada negative hota hai (Be=−1.97V → Ba=−2.91V), matlab electron chhodne ki tendency (reducing agent hone ki khasiyat) barhti hai.
Q6 (Be sabse kam reactive, Ba sabse zyada kyun): Be sabse chota, sabse zyada ionization energy, aur mazboot protective oxide layer rakhta hai — isliye kam reactive. Ba sabse bara, sabse kam ionization energy, kamzor metallic bonding rakhta hai — isliye electrons aasani se nikalte hain, sabse zyada reactive.
17.2.1 — Oxygen Ke Saath Reactions (Q7–12)
Q7 (General equation): 2M + O₂ → 2MO
Q8 (Be kam reactive oxygen ke saath kyun): Be sirf 600°C se upar react karta hai, aur jaldi se thin, strong, adherent BeO layer ban jaati hai jo metal ko protect kar leti hai.
Q9 (Mg + oxygen equation): 2Mg(s) + O₂(g) → 2MgO(s)
Q10 (Ca brick-red flame, Mg white flame kyun): Flame ka color depend karta hai electron transitions par — jab excited electrons neeche energy level par wapis aate hain to light emit karte hain. Ca ke transitions laal light emit karte hain, jabke Mg ki intense combustion bright white flame deti hai.
Q11 (Oxides ki basic character kyun barhti hai): Cation bara hota hai neeche jaate hue, uski charge density (polarizing power) kam hoti hai, isliye M-O bond zyada ionic ban jata hai. Ye oxide ko paani ke saath react karne mein aasani deta hai, isliye basicity barhti hai.
Q12 (Oxide ion + paani ka equation): O²⁻(s) + H₂O(l) → 2OH⁻(aq)
17.2.2 — Water Ke Saath Reactions (Q13–18)
Q13 (Be paani/steam se kyun react nahi karta): Be par ek mazboot, chipakne wali oxide layer hoti hai jo paani ke molecules ko metal tak pohanchne se rokti hai, isliye heat karne par bhi react nahi karta.
Q14 (Mg + cold water): Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g) (bohot dheere reaction)
Q15 (Mg + steam): Mg(s) + H₂O(g) → MgO(s) + H₂(g)
Q16 (Ca + cold water): Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
Q17 (Ca(OH)₂ sparingly soluble kyun): Ca(OH)₂ ki lattice enthalpy hydration enthalpy ke muqablay mein still thodi significant hai, isliye poora nahi ghulta; jo extra bacha rehta hai wo white precipitate ki soorat mein reh jata hai.
Q18 (Hydroxides ki basic character kyun barhti hai): Neeche jaate hue zyada soluble ho jate hain (zyada OH⁻ ions release hote hain), aur bare cations ki polarizing power kam hoti hai jisse M-OH bond zyada ionic hota hai — dono effects basicity ko barhaate hain.
17.2.3 — Acids Ke Saath Reactions (Q19–23)
Q19 (General equation): M(s) + 2HCl(aq) → MCl₂(aq) + H₂(g)
Q20 (Be dheere react karta hai kyun): Be ki protective oxide layer pehle todni parti hai isse pehle ke acid metal ki surface par attack kare — isliye reaction dheeme ho jati hai, chahe Be chemically react kar sakta ho.
Q21 (Mg + HCl aur H₂SO₄):
Mg+2HCl→MgCl2+H2Mg+H2SO4→MgSO4+H2Mg + 2HCl \rightarrow MgCl_2 + H_2 \qquad Mg + H_2SO_4 \rightarrow MgSO_4 + H_2
Q22 (Ca + H₂SO₄ reaction jaldi kyun rukti hai): Jo CaSO₄ banta hai wo sparingly soluble hai; ye metal ki surface par protective coating bana deta hai jo acid aur metal ke darmiyan contact rok deta hai, isliye reaction slow ho kar ruk jati hai.
Q23 (Ca + HCl equation): Ca(s) + 2HCl(aq) → CaCl₂(aq) + H₂(g)
17.3 — Group 2 Vs Group 1 Comparison (Q24–29)
Q24 (Valence electrons compare karna): Group 1: 1 electron (ns¹), Group 2: 2 electrons (ns²)
Q25 (Group 1 zyada reactive kyun): Group 1 ko sirf ek electron nikalna hai aur unki ionization energy kam hai, isliye aasani se oxidize hote hain. Group 2 ko do electrons nikalne hain jo zyada energy chahte hain, isliye thora kam reactive hote hain.
Q26 (Hardness compare karna): Group 1 bohot naram hote hain (chaaqu se kaat sakte hain) kyunke har atom sirf ek electron metallic bonding mein deta hai. Group 2 zyada sakht hote hain kyunke har atom do electrons deta hai, jisse bonding mazboot hoti hai.
Q27 (Oxides ka general formula compare karna): Group 1: M₂O (jaise Na₂O, bohot strongly basic). Group 2: MO (jaise CaO, basic lekin Group 1 se kam strongly).
Q28 (Hydroxides ki solubility/basic strength compare karna): Group 1 hydroxides highly soluble aur strong bases hain. Group 2 hydroxides kam soluble hain (lekin neeche jaate hue barhti hai) aur generally kam basic hote hain.
Q29 (Group 2 ke melting/boiling points zyada kyun hote hain): Group 2 metal atoms do delocalized electrons dete hain metallic bond mein (Group 1 ke muqablay mein ek), jisse zyada mazboot electrostatic attraction paida hoti hai metal ions aur delocalized electrons ke darmiyan, isliye melting/boiling points zyada hote hain.
17.4 — Carbonates Aur Nitrates Ki Thermal Decomposition (Q30–35)
Q30 (Thermal decomposition ki definition): Ye ek reaction hai jisme heat lagane se ek compound do ya zyada simpler substances mein toot jata hai; ye generally endothermic hoti hai (bonds todne ke liye energy chahiye).
Q31 (Carbonate decomposition general equation): MCO₃(s) → MO(s) + CO₂(g)
Q32 (Thermal stability kyun barhti hai neeche jaate hue): Cation bara ho jata hai neeche jaate hue, uski polarizing power kam hoti hai, isliye carbonate ion ko kam distort karta hai. Isse carbonate ke bonds zyada stable rehte hain, isliye decompose hone ke liye zyada temperature chahiye.
Q33 (Ca(NO₃)₂ ka decomposition equation): 2Ca(NO₃)₂(s) → 2CaO(s) + 4NO₂(g) + O₂(g)
Q34 (Polarizing power ki definition aur asar): Ye ek cation ki anion ke electron cloud ko distort karne ki ability hai. Chote, zyada charged cations (jaise Be²⁺) mein zyada polarizing power hoti hai; ye carbonate ion ko zyada distort karte hain, jisse bond kamzor hoke kam temperature par decomposition ho jata hai.
Q35 (Increasing thermal stability order): BeCO₃ < MgCO₃ < CaCO₃ < SrCO₃ < BaCO₃
17.5 — Sulphates Aur Hydroxides Ki Solubility (Q36–41)
Q36 (Enthalpy of hydration ki definition): Ye energy hai jo release hoti hai jab gaseous ions paani ke molecules se gher liye jate hain (hydrated ho jate hain). Ye hamesha exothermic (negative value) hoti hai; chote, zyada charge density wale ions zyada energy release karte hain.
Q37 (Lattice enthalpy ki definition): Ye energy hai jo chahiye hoti hai ek solid ionic compound ko uske gaseous ions mein todne ke liye. Ye hamesha endothermic hoti hai; ye ions ke charges aur sizes par depend karti hai.
Q38 (Hydroxides ki solubility trend + example): Barhti hai neeche jaate hue — jaise Mg(OH)₂ sparingly soluble, Ba(OH)₂ quite soluble — kyunke neeche jaate hue lattice enthalpy ki kami hydration enthalpy se zyada hoti hai.
Q39 (Sulphates ki solubility trend + example): Ghatti hai neeche jaate hue — jaise MgSO₄ soluble, BaSO₄ essentially insoluble — kyunke is bare anion ke liye neeche jaate hue hydration enthalpy ki kami lattice enthalpy se zyada significant hoti hai.
Q40 (Hydroxides aur sulphates ke trends ulte kyun hain): Hydroxides (chota anion) ke liye lattice enthalpy change hawi hoti hai — cation size barhne par lattice enthalpy hydration enthalpy se tezi se girti hai, solubility ko favour karti hai. Sulphates (bara anion) ke liye hydration enthalpy change hawi hoti hai — hydration enthalpy lattice enthalpy se tezi se girti hai, solubility ko disfavour karti hai.
Q41 (Enthalpy of solution ki definition aur role): Ye overall energy change hai jab solid ionic substance paani mein ghulta hai; ye lattice enthalpy (endothermic) aur hydration enthalpy (exothermic) ka sum hai. Zyada negative (ya kam positive) ∆H_soln generally zyada solubility ko favour karta hai.
17.6 — Complex Ion Formation (Q42–46)
Q42 (Complex ion ki definition): Ye ek ion hai jisme central metal ion coordinate (dative) bonds ke zariye kai electron-donating species (ligands) — jaise H₂O, NH₃, Cl⁻, OH⁻ — se juda hota hai.
Q43 (Coordination number ka matlab): Ye coordinate bonds ki tadaad hai jo central metal ion aur uske ligands ke darmiyan bante hain. Common values: 2, 4, 6.
Q44 (Be ka coordination 4, Mg ka 6 kyun): Be sabse chota Group 2 ion hai, uski charge density bohot zyada hai, isliye sirf 4 water molecules hi qareeb se pack ho sakte hain — [Be(H₂O)₄]²⁺. Mg bara hai, isliye 6 water molecules samane ki jagah hoti hai — [Mg(H₂O)₆]²⁺.
Q45 (Ca-EDTA complex ka formula): [Ca(EDTA)]²⁻ (bantay: Ca²⁺(aq) + EDTA⁴⁻(aq) → [Ca(EDTA)]²⁻(aq))
Q46 (Ca-EDTA complex ka practical use): Water softening mein use hota hai hard water se Ca²⁺ aur Mg²⁺ ions hataane ke liye; EDTA medically bhi toxic metal ions jism se nikalne ke liye use hoti hai.
17.7 — Extraction Aur Purification (Q47–52)
Q47 (Seawater se Mg nikalne ka process): Dow Process — ek multi-step chemical/electrochemical process jo seawater ke Mg²⁺ ions se magnesium metal nikalta hai.
Q48 (Mg(OH)₂ precipitation equation): Mg²⁺(aq) + Ca(OH)₂(s) → Mg(OH)₂(s) + Ca²⁺(aq)
Q49 (Electrolysis step equation): Mg²⁺(l) + 2Cl⁻(l) → Mg(l) + Cl₂(g) (Cathode par Mg, anode par Cl₂)
Q50 (Quicklime production equation): CaCO₃(s) →(heat) CaO(s) + CO₂(g)
Q51 (CO₂ musalsal kyun hataya jata hai): Limestone ka decomposition reversible hai closed container mein. CO₂ ko musalsal hataane se equilibrium right taraf shift ho jaati hai (Le Chatelier’s principle ke mutabiq), jisse zyada aur tez CaO banti hai.
Q52 (Quicklime ki furnace aur temperature): Lime kiln use hoti hai, limestone ko 900-1000°C tak heat kiya jata hai (calcination process).
17.8 — Group 2 Compounds Ke Uses (Q53–58)
Q53 (CaCO₃ ke do construction uses): Building material ki tarah, cement/concrete banane mein, aur paper/plastics mein filler ki tarah.
Q54 (Mg(OH)₂ antacid kyun use hota hai): Milk of Magnesia stomach ka extra acid neutralize karta hai aur mild laxative ki tarah kaam karta hai; iski kam solubility isay jism ke andar use karne ke liye safe banati hai.
Q55 (BaSO₄ ‘barium meal’ mein safe kyun hai): BaSO₄ highly insoluble hai, isliye ye digestive system se guzar jaata hai bina bloodstream mein absorb hue, isliye safe hai chahe barium ions otherwise toxic hon; ye X-rays ke liye opaque bhi hai, isliye clear imaging deta hai.
Q56 (CaO environment protect karne mein use): CaO (CaCO₃ ke saath) flue gas desulphurization mein use hota hai, power plant emissions se acidic SO₂ hatane ke liye, jo acid rain rokne mein madad karta hai.
Q57 (Ca aur Mg compounds agriculture mein kaise use hote hain): CaCO₃/Ca(OH)₂ acidic soil mein daale jate hain excess acidity neutralize karne aur pH barhane ke liye. Ca cell wall development ke liye zaroori hai, Mg chlorophyll ka central atom hai (photosynthesis ke liye); calcium nitrate aur magnesium sulphate bhi fertilizers ki tarah use hote hain.
Q58 (MgSO₄/Epsom salts ka medical use): Epsom salts (MgSO₄·7H₂O) laxative ki tarah aur therapeutic baths mein muscles relax karne ke liye use hoti hai.
Sabse Zaroori Tip (Short Questions Ke Exam Ke Liye):
Short questions mein har answer 2-4 lines mein hona chahiye, jisme concept + reason dono ho. Balanced equations ko exactly sahi likhna zaroori hai — half marks equation likhne se milte hain, sirf explanation kaafi nahi hoti.