Sulfur — allotropes (rhombic, monoclinic); SO₂, SO₃; H₂SO₄ (Contact process); oxoacids of S

3.2.8 · Chemistry › p-Block

1. Allotropes of Sulfur

YEH kya hain: Dono rhombic aur monoclinic sulfur mein S₈ puckered (crown-shaped) rings hote hain. Farq sirf iss baat mein hai ki rings crystal lattice mein kaise pack hoti hain — molecule mein nahi.

KYU yeh temperature matter karta hai (Feynman logic): Ek substance woh form adopt karta hai jisme free energy ( $G$ ) kam ho. Rhombic zyada tightly pack hota hai (denser, $2.06 g/cm^{3}$ ) isliye low $T$ par win karta hai (low entropy favoured). Monoclinic loose hai (density kam $1.98 g/cm^{3}$ , entropy zyada) isliye jab $T$ badhta hai to $- T S$ term ise win karaa deta hai.

Property	Rhombic (α)	Monoclinic (β)
Stable	< 369 K	369–393 K
Colour	yellow	pale/honey yellow
Density	2.06 g/cm³ (denser)	1.98 g/cm³
Molecule	S₈ crown ring	S₈ crown ring
Kaise banate hain	CS₂ se crystallise karo	S ko melt karo, slowly cool karo, decant karo

Figure — Sulfur — allotropes (rhombic, monoclinic); SO₂, SO₃; H₂SO₄ (Contact process); oxoacids of S

2. The Oxides: SO₂ aur SO₃

Preparation (KAISE): $S + O_{2} \to S O_{2} C u + 2 H_{2} S O_{4} (conc) \to C u S O_{4} + S O_{2} + 2 H_{2} O$ $N a_{2} S O_{3} + 2 H C l \to 2 N a C l + H_{2} O + S O_{2}$

Structure aur KYU bent hai: S ke paas 2 bond pairs + 1 lone pair hain → bent (angular), bond angle ≈ 119°. Resonance se bond order 1.5 milti hai (dono S–O equivalent, length ~143 pm, single aur double ke beech).

3. H₂SO₄ ka Manufacturing — Contact Process

Teen stages (KAISE):

Stage 1 — SO₂ banao: $S + O_{2} \to S O_{2} ya 4 F e S_{2} + 11 O_{2} \to 2 F e_{2} O_{3} + 8 S O_{2}$

Stage 2 — key catalytic step (process ka dil): $2 S O_{2} + O_{2} ⇌ V_{2} O_{5}, 720 K 2 S O_{3} Δ H = - 196 kJ/mol$

Stage 3 — SO₃ absorb karo (clever trick): Hum SO₃ directly paani mein NAHI dalte (ek dense uncontrollable acid mist banti hai). Iske bajay: $S O_{3} + H_{2} S O_{4} \to H_{2} S_{2} O_{7} (oleum, fuming sulfuric acid)$ $H_{2} S_{2} O_{7} + H_{2} O \to 2 H_{2} S O_{4}$

4. Oxoacids of Sulfur

Acid	Formula	S oxid. state	Key feature
Sulfurous	$H_{2} S O_{3}$	+4	sulfuric ke comparison mein ek S=O missing
Sulfuric	$H_{2} S O_{4}$	+6	2 =O, 2 –OH
Thiosulfuric	$H_{2} S_{2} O_{3}$	+2 (avg)	ek O ki jagah S
Pyrosulfuric (oleum)	$H_{2} S_{2} O_{7}$	+6	do S ke beech –O– bridge
Peroxomonosulfuric (Caro's)	$H_{2} S O_{5}$	+6	ek –O–O– peroxo link
Peroxodisulfuric (Marshall's)	$H_{2} S_{2} O_{8}$	+6	do S ke beech –O–O– bridge
Dithionous	$H_{2} S_{2} O_{4}$	+3	S–S bond

Sulfur ke do common crystalline allotropes kya hain?

Rhombic (α) aur monoclinic (β), dono S₈ crown rings se bane hain.

Rhombic ⇌ monoclinic sulfur ki transition temperature?

369 K (96 °C).

369 K se neeche kaunsa sulfur allotrope stable hota hai?

Rhombic (α) — denser (2.06 g/cm³).

Kyun rhombic low T par aur monoclinic high T par favoured hota hai?

Rhombic denser hai (lower enthalpy) isliye low T par win karta hai; monoclinic ki higher entropy hai isliye −TS term use high T par win karaa deta hai.

Plastic sulfur kis chiz se bana hota hai?

Lambi S–S chains (toote hue S₈ rings se), amorphous aur metastable.

SO₂ ki shape aur bond angle?

Bent/V-shaped, ~119°, 2 bond pairs + 1 lone pair ki wajah se; bond order 1.5.

SO₂ mein S ka oxidation state aur iska kya matlab hai?

+4; intermediate, isliye SO₂ dono oxidising aur reducing agent ho sakta hai.

Gaseous SO₃ ki shape aur S ka oxidation state?

Trigonal planar; S +6 hai.

Contact process ke teen stages ke naam batao.

(1) S ko burn karke SO₂ banao; (2) catalytic 2SO₂+O₂⇌2SO₃, V₂O₅ ke upar; (3) SO₃ ko conc. H₂SO₄ mein absorb karo → oleum → dilute karo.

Contact process mein use hone wala catalyst?

V₂O₅ (vanadium pentoxide).

Stage 2 mein moderate temperature (~720 K) kyun?

Reaction exothermic hai; low T SO₃ favour karta hai par slow hai, isliye 720 K yield–speed compromise hai.

Contact process mein high pressure kyun nahi use karte?

Conversion already ~96% 1–2 atm ke paas hai, isliye high pressure cost-effective nahi.

SO₃ ko H₂SO₄ mein absorb kyun karte hain, paani mein nahi?

Direct SO₃+H₂O ek uncontrollable acid mist/fog banata hai; oleum route controllable hai.

Oleum kya hai?

Fuming sulfuric acid, H₂S₂O₇ (SO₃ conc. H₂SO₄ mein dissolve hota hai).

H₂SO₄ mein S ka oxidation state?

+6.

Kaun sa oxoacid S–S bond rakhta hai aur S ka average state kya hai?

Dithionous acid H₂S₂O₄ (ya thiosulfate area); thiosulfuric H₂S₂O₃ mein S–S hai avg +2 ke saath.

Kaun se do oxoacids mein peroxo (–O–O–) link hota hai?

Caro's acid H₂SO₅ aur Marshall's acid H₂S₂O₈.

Cl₂ aur SO₂ bleaching mein kya farq hai?

Cl₂ oxidation se bleach karta hai (permanent); SO₂ reduction se (temporary, colour hawa mein wapas aata hai).

Recall Feynman: 12 saal ke bacche ko samjhao

Sulfur atoms LOVE karte hain ek doosre ka haath pakadna. Aath atoms ek choti crown-shaped ring mein haath milate hain (S₈). Tum yeh crowns do neat tareekon se stack kar sakte ho — ek tight (rhombic) aur ek loose (monoclinic) — bilkul jaise oranges ko do alag patterns mein stack karte hain. Inhe garam karo aur crowns toot jaate hain aur atoms lambi chains banate hain (rubbery plastic sulfur). Jab sulfur jalta hai toh oxygen pakad leta hai ek smelly gas banane ke liye (SO₂), aur thodi aur mehnat se aur ek helper se (catalyst) aur bhi zyada oxygen pakad leta hai (SO₃). Use carefully acid mein dubao aur milti hai sulfuric acid — chemicals ki "king." Factory mein poora trick yeh hai: SO₃ banane ka step heat deta hai, isliye agar bahut zyada garam karo toh yeh ulta ho jaata hai — isliye warm-not-hot rakho aur ek helper use karo jaldi karne ke liye.

Connections

Group 16 - Oxygen family - general trends
Oxygen and its oxides
Le Chateliers Principle (Contact process ke condition choices drive karta hai)
Catalysis and V2O5
Oxidation states and oxoacids
Redox titrations - thiosulfate and iodine
Allotropy - carbon and phosphorus (catenation tendencies compare karo)

1. Allotropes of Sulfur

2. The Oxides: SO₂ aur SO₃

3. H₂SO₄ ka Manufacturing — Contact Process

4. Oxoacids of Sulfur

Connections

Concept Map