Separation techniques — filtration, distillation, chromatography, centrifugation, sublimation

1.1.3 · Chemistry › Matter, Measurement & the Mole

Core Principle: Physical Property Differences Ko Exploit Karo

Separation techniques isliye kaam karti hain kyunki mixture ke components kam se kam ek physical property mein alag hote hain. Hum ek process ke zariye us difference ko amplify karte hain, phir components ko alag-alag collect karte hain.

1. Filtration — Particle Size Se Separate Karo

Kab use karein: Solid–liquid mixtures jahan solid insoluble ho aur uske particles pore size se kaafi bade hon.

Filtration Kaise Kaam Karta Hai

1. Mixture daalo funnel mein rakhe filter paper par
2. Gravity ya pressure liquid ko pores ke through kheenchta hai
3. Solid residue (jise residue ya retentate kehte hain) filter par reh jaata hai
4. Liquid (jise filtrate kehte hain) neeche collect hota hai

Particle size kyun matter karta hai? Filter paper mein pore diameter: ~2–10 μm. Sand particles: ~50–2000 μm. Sand fit nahi ho sakta. Dissolved salt ions: ~0.003 μm. Woh aasaani se nikal jaate hain.

Filtration dissolved substances ko nahi hataata. Salt water ko filter karo = phir bhi salt water.

Step 1: Filter funnel mein daalo. Yeh step kyun? Gravity mixture ko filter ki taraf le jaati hai, separation shuru hota hai.

Step 2: Liquid ke drip hone ka wait karo. Yeh step kyun? Paani + dissolved NaCl molecules itne chhote hain ki pores se nikal jaate hain. Sand grains (200 μm) 100× zyada bade hain.

Step 3: Neeche clear liquid (filtrate = salt water) collect karo; sand ko filter paper se uthaao (residue). Yeh step kyun? Physical collection se separation complete hota hai.

Result: Sand alag ho gaya. Salt abhi bhi paani mein dissolved hai — iske liye doosri technique chahiye (evaporation ya distillation) salt ko paani se alag karne ke liye.

2. Distillation — Boiling Point Se Separate Karo

Kab use karein: Liquid–liquid mixtures (ya solid jo liquid mein dissolved ho) jahan components ke different boiling points hon — ideally simple distillation ke liye >25°C ka farq.

Distillation Kaise Kaam Karta Hai

1. Mixture ko garam karo flask mein
2. Kam BP wala component vaporize hota hai, gas baan kar upar uthta hai
3. Vapor condenser mein jaata hai (thande paani se thanda kiya hua tube)
4. Vapor thanda hota hai → condense hoke liquid ban jaata hai
5. Distillate (purified liquid) receiving flask mein collect hota hai
6. Zyada BP wala component original flask mein rehta hai

Boiling point kyun matter karta hai? BP par, vapor pressure = atmospheric pressure. Kam BP matlab molecules kam temperature par liquid phase chhodh dete hain. Ethanol (BP 78°C) wine garam karne par paani (BP 100°C) se pehle vaporize hota hai.

Mixture ke liye, kam BP wala component yeh condition pehle reach karta hai. Raoult's Law (ideal mixtures): $P_{\text{total}}=P_A^0{\chi }_A+P_B^0{\chi }_B$ jahan $P_A^0$ pure-component vapor pressure hai, ${\chi }_A$ mole fraction hai. Volatile (low-BP) component total pressure mein zyada contribute karta hai, isliye woh initially vapor phase mein dominant hota hai.

Distillation Ke Types

Simple distillation: Ek vaporization–condensation cycle. BP difference >25°C par kaam karta hai. Example: paani (100°C) ko salt se alag karna (salt vaporize nahi hota).

Fractional distillation: Fractionating column (glass beads ya rings se bhara hua) mein multiple vaporization–condensation cycles. Har cycle mein zyada volatile component aur concentrate hota hai. BP difference <25°C par kaam karta hai. Example: crude oil ko alag karna — gasoline (40–200°C), kerosene (150–300°C), diesel (250–350°C).

Step 1: Distillation flask mein wine ko ~80°C tak garam karo. Yeh step kyun? Ethanol boil hota hai; paani mostly nahi. Vapor ~60% ethanol hota hai (100% nahi kyunki yeh ek mixture hai — Raoult's Law dekho).

Step 2: Vapor upar uthta hai, condenser mein jaata hai, liquid mein thanda hota hai. Yeh step kyun? 78°C se neeche cooling ethanol vapor ko condense kar deta hai. Condenser ke around cold water jacket heat remove karta hai.

Step 3: Distillate collect karo. Yeh step kyun? Pehle fractions ethanol-enriched hote hain (~40–60%). Zyada purity ke liye distillation repeat karo.

Result: Distillate stronger alcohol hai (brandy ~40–50%). Paani flask mein rehta hai (discard karo ya re-distil karo).

Note: 95.6% ethanol–water azeotrope ki wajah se simple distillation se 100% ethanol nahi mil sakta.

3. Chromatography — Polarity/Affinity Se Separate Karo

Kab use karein: Complex mixtures (dyes, amino acids, pharmaceuticals) jahan components polarity, size, ya stationary phase ke liye affinity mein alag hon.

Chromatography Kaise Kaam Karta Hai

Do phases:

• Stationary phase: immobile material (paper, silica gel, polymer beads)
• Mobile phase: moving solvent (liquid ya gas) jo sample carry karta hai

Mechanism:

1. Sample spot karo stationary phase par (e.g., paper par ink ki dot)
2. Mobile phase flow karta hai stationary phase se (e.g., paani capillary action se paper upar chadhta hai)
3. Components partition karte hain phases ke beech polarity ke basis par:
   • Polar molecules polar stationary phase ki taraf attract hote hain → dheere chalte hain
   • Nonpolar molecules mobile phase mein rehte hain → tezi se chalte hain
4. Components spatially alag ho jaate hain kyunki woh alag rates par chalte hain

Polarity kyun matter karti hai? "Like dissolves like." Polar silica gel polar molecules ko attract karta hai (H-bonds, dipole interactions). Nonpolar molecules ki silica ke saath weak interactions hoti hain, isliye woh mobile phase mein dissolved rehte hain aur door tak travel karte hain.

$0<R_f<1$. Kam $R_f$: component stationary phase se chipka hua hai (polar). Zyada $R_f$: component mobile hai (nonpolar).

First principles se derivation: Equilibrium par, ek component phases ke beech partition coefficient $K$ ke according distribute hota hai: $K=\frac{[\text{component in mobile phase}]}{[\text{component in stationary phase}]}$ Zyada $K$ → mobile phase prefer karta hai → door travel karta hai → zyada $R_f$. $R_f\propto \frac{1}{1+k^{\prime }}$ jahan $k^{\prime }=\frac{K_d{V}_s}{V_m}$ (capacity factor, $K_d$ distribution constant hai, $V_s$ $V_m$ phase volumes hain).

Chromatography Ke Types

• Paper chromatography: Paper stationary phase hai (cellulose, polar). Solvent capillary action se chadhta hai. Sasta, jaldi. Inks, dyes, amino acids ke liye use hota hai.
• Thin-layer chromatography (TLC): Glass/plastic par silica gel. Paper se tez, better resolution.
• Column chromatography: Vertical column mein packed stationary phase; solvent gravity se neeche flow karta hai. Preparative scale (grams).
• Gas chromatography (GC): Mobile phase = inert gas (He); stationary phase = capillary ke andar liquid coating. Volatile compounds alag karta hai. Forensics, drug testing mein use hota hai.
• High-performance liquid chromatography (HPLC): High-pressure pump mobile phase ko fine stationary phase ke through force karta hai. Complex mixtures separate karta hai (pharmaceuticals, proteins).

Step 1: Paper strip ke bottom se 2 cm upar black ink dot karo. Yeh step kyun? Sabhi components ka starting point. Solvent level se upar hona chahiye.

Step 2: Paper ko solvent (paani + alcohol, 1:1) mein daalo — solvent bottom se 1 cm par hai, dot ke neeche. Yeh step kyun? Solvent capillary action se upar uthta hai, dyes ko carry karta hai. Agar dot submerged hai, toh dyes directly solvent mein dissolve ho jaate hain (koi separation nahi).

Step 3: 20 minute wait karo. Solvent 10 cm tak chadhta hai. Yeh step kyun? Alag dyes ki alag polarities hoti hain:

• Blue dye (polar): cellulose se chipkata hai, 3 cm travel karta hai → $R_f=3/10=0.30$
• Red dye (medium): 6 cm travel karta hai → $R_f=0.60$
• Yellow dye (nonpolar): 9 cm travel karta hai → $R_f=0.90$

Step 4: Positions mark karo, distances measure karo, $R_f$ calculate karo. Yeh step kyun? $R_f$ values compounds identify karti hain reference table se compare karke.

Result: Black ink teen colored bands mein alag ho gayi. Har dye ka is solvent system mein characteristic $R_f$ hota hai.

4. Centrifugation — Density Se Separate Karo

Kab use karein: Liquid mein chhote particles (cells, organelles, precipitates) ke suspensions jahan density differences hain lekin gravity settling bahut dheeri hai.

Centrifugation Kaise Kaam Karta Hai

1. Sample load karo tubes mein, rotor mein rakho
2. High speed par spin karo (e.g., 5000 RPM = 3000×g)
3. Centrifugal force denser particles ko outward (tube ke bottom ki taraf) dhakelta hai
4. Kam dense liquid (supernatant) upar rehta hai
5. Ruko, supernatant ko pipette se carefully hataao; pellet (dense particles) bottom par rehta hai

Density kyun matter karti hai? Centrifugal force $F_c=m{\omega }^{2}r$ jahan $m$ mass hai, $\omega$ angular velocity hai, $r$ radius hai. Dense particles ka volume per mass zyada hota hai, isliye greater net force experience karte hain (buoyancy hatane ke baad).

Derivation: Centrifugal acceleration: $a_c={\omega }^{2}r$ jahan $\omega =2\pi \times \text{RPM}/60$ rad/s. $\text{RCF}=\frac{a_c}{g}=\frac{(2\pi \times \text{RPM}/60{)}^2\times r}{g}$ $=\frac{4{\pi }^2\times r}{3600g}\times {\text{RPM}}^2=\frac{4\times 9.87\times r}{3600\times 9.81}\times {\text{RPM}}^2$ $=1.118\times 10^{-5}\times r(\text{cm})\times {\text{RPM}}^2$

Sedimentation velocity (Stokes' Law): $v=\frac{2r^2({\rho }_p-{\rho }_f)a_c}{9\eta }$ jahan $r$ particle radius hai, ${\rho }_p$ particle density hai, ${\rho }_f$ fluid density hai, $\eta$ viscosity hai. Bade, denser particles tezi se sediment karte hain.

Step 1: 5 mL blood centrifuge tube mein load karo, 3000 RPM par 10 min spin karo (RCF ≈ 1000×g). Yeh step kyun? RBCs, sabse dense hone ki wajah se, bahar ki taraf sabse zyada net force experience karte hain. 1000×g kaafi hai RBCs ko 10 min mein pellet karne ke liye (Stokes' Law: $v\propto ({\rho }_p-{\rho }_f)$).

Step 2: RBCs bottom par red pellet banate hain. WBCs RBCs ke upar thin white layer (buffy coat) banate hain. Plasma upar clear yellow liquid hota hai. Yeh step kyun? Density gradient: RBC (1.1) > WBC (1.07) > plasma (1.03). Centrifugal force layers ko density ke hisaab se stratify karta hai.

Step 3: Pellet disturb kiye bina carefully plasma pipette karo. Yeh step kyun? Gentle removal separation preserve karta hai. Plasma ab testing ke liye available hai (glucose, proteins, antibodies).

Result: Components density se alag ho gaye. Clinical labs mein worldwide use hota hai (CBC test).

5. Sublimation — Phase Transition Se Separate Karo

Kab use karein: Mixtures jahan ek component sublime kare aur dusre na karein (ya bahut zyada temperature par karein).

Sublimation Kaise Kaam Karta Hai

1. Mixture ko dheere garam karo
2. Sublimable component solid se directly vaporize hota hai
3. Vapor utha ke cool surface se milta hai (cold finger, watch glass with ice)
4. Vapor cool surface par solid crystals ke roop mein deposit hota hai
5. Non-subliming components original container mein rehte hain

Sublimation kyun hoti hai? Triple point se neeche temperature par, solid ka vapor pressure atmospheric pressure se zyada ho sakta hai agar intermolecular forces kamzor hon. Molecules solid lattice se directly gas phase mein nikal jaate hain. Iodine ke liye: triple point 113.7°C, 12 kPa par. Room temp (25°C) par, iodine vapor pressure ≈ 0.3 kPa — kaafi notable roop se sublime hone ke liye.

First principles se derivation: Equilibrium par, solid ki chemical potential = vapor ki chemical potential: ${\mu }_s={\mu }_g$ ${\mu }_s^0={\mu }_g^0+RT\ln P$ $T$ ke respect mein differentiate karte hue (constant $P$ par): $-\frac{S_s}{T}=-\frac{S_g}{T}+R\frac{d\ln P}{dT}$ $\frac{d\ln P}{dT}=\frac{S_g-S_s}{R}=\frac{\Delta H_{\text{sub}}}{R{T}^2}$ ($\Delta G=\Delta H-T\Delta S$ use karke aur $\Delta G=0$ at equilibrium). Integrate karte hue: $\ln P=-\frac{\Delta H_{\text{sub}}}{RT}+\text{const}$ Zyada $\Delta H_{\text{sub}}$ → kam vapor pressure → kam sublimation.

Common Subliming Substances

Step 1: Mixture evaporating dish mein rakho, uske upar funnel ulta rakho (stem cotton se band kiya hua), funnel par ice-bhari beaker rakho. Yeh step kyun? Temperature gradient create hota hai: neeche garm (heat source), upar thanda (ice). Iodine sublime hoke cool surface par redeposit hoga.

Step 2: Bunsen burner se dheere ~190°C tak garam karo. Yeh step kyun? 184°C ke upar iodine ka vapor pressure significant ho jaata hai. Solid iodine → violet vapor directly. Sand solid rehta hai (melting point 1710°C).

Step 3: Purple iodine vapor upar uthta hai, thande funnel se milta hai, funnel surface par shiny gray-black crystals ke roop mein deposit hota hai. Yeh step kyun? Cooling vapor pressure kam karti hai → equilibrium solid ki taraf shift hota hai. $\ln P=-\Delta H_{\text{sub}}/RT$ → kam $T$ → bahut kam $P$ → deposition.

Step 4: Heat band karo, thanda hone do, iodine crystals carefully collect karo. Yeh step kyun? Physical collection. Sand dish mein peeche rehta hai.

Result: Pure iodine crystals. Purity >99% (trace impurities jo bhi sublime karte hain woh reh sakte hain — zyada purity ke liye resublime karo).

Summary Table: Sahi Technique Chunna

Decision tree:

1. Solid liquid mein, insoluble? → Filtration
2. Liquids with different BP? → Distillation
3. Complex mixture, small scale? → Chromatography
4. Small particles, density difference? → Centrifugation
5. Ek component sublime karta hai? → Sublimation

Connections

• States of Matter — phase transitions (solid/liquid/gas) distillation aur sublimation ke neeche hain
• Solutions and Solubility — "like dissolves like" chromatography partitioning explain karta hai
• Intermolecular Forces — kamzor IMF → aasaan sublimation; H-bonding → chromatography mein polarity
• Vapor Pressure — distillation aur sublimation drive karta hai
• Colligative Properties — boiling point elevation solutions ki distillation ko affect karta hai
• Acids and Bases — ion-exchange chromatography charge ke hisaab se separate karta hai
• Thermodynamics — $\Delta H_{\text{sub}}$, $\Delta H_{\text{vap}}$ energy requirements determine karte hain
• Stoichiometry — separation ke baad % recovery calculate karo

Filtration ek net use karne jaisi hai. Bade LEGOs pakad jaate hain, chhote marbles nikal jaate hain. Lekin agar LEGO dust marbles ke saath mix hai, toh net help nahi karega — particles bahut chhote hain.

Distillation paani ko steam banane aur phir steam ko thandi bottle mein pakadne jaisi hai taaki woh wapas paani ban jaaye. Agar tumhare paas salty paani hota, toh salt steam nahi banta ("fly away" ke liye itna garam nahi hota), isliye bottle mein pure paani milta hai aur salt pot mein rehta hai.

Chromatography ek aisi race jaisi hai jahan kuch runners Velcro shoes mein Velcro track par hain. Chipkane wale (polar molecules) dheere ho jaate hain, non-sticky waale (nonpolar) tezi se daurte hain. Woh alag times par finish karte hain, isliye tum unhe alag kar sakte ho.

Centrifugation mudy paani ki bucket ko bahut tezi se spin karne jaisi hai. Mud bhaari hai, isliye woh neeche jaata hai. Clear paani upar rehta hai. Yeh artificial super-gravity hai.

Sublimation un khaas substances ke liye hai jo ice se seedhe steam ban jaate hain bina melt hue. Dry ice aisa karta hai! Yeh solid CO₂ hai, aur bina liquid bane gas ban jaata hai. Agar tumhare paas regular ice ke saath dry ice hoti, toh tum unhe alag kar sakte the dry ice ko "fly away" karke aur use thandi plate par collect karke.

Alternatively: "Fine Diamond Cuts Can't Scratch" order ke liye — Filtration, Distillation, Chromatography, Centrifugation, Sublimation.

Flashcards

#flashcards/chemistry

Filtration kaunsi physical property exploit karta hai? :: Particle size. Bade particles porous barrier se trap hote hain; chhote particles aur fluids nikal jaate hain.

Distillation mein distillate kya hota hai? :: Receiving flask mein vapor condense hone ke baad collect kiya gaya purified liquid.

Centrifugation mein pellet kya hota hai? :: Dense particles jo tube ke bottom mein sediment ho jaate hain.

Concept Map