Aluminium — chemistry, alloys; alumina, alums

3.2.2 · Chemistry › p-Block

80/20 core: Al ek Group 13 metal hai jo amphoteric hai (dono acids aur bases ke saath react karta hai), ek protective oxide layer banata hai (passivation), aur ek covalent-character chloride $A l_{2} C l_{6}$ deta hai. In teen ideas ko master karo aur baaki sab samajh aa jaayega.

1. Al itna special kyun hai?

2. Aluminium ki Reactions — derive karo, ratto mat

2a. Air / oxygen ke saath (passivation)

KYA: Al, $O_{2}$ se react karke ek patli, mazboot, impervious oxide film banata hai. $4 A l + 3 O_{2} \to 2 A l_{2} O_{3}$ Yeh kyun ruk jaata hai: $A l_{2} O_{3}$ ki layer dense hoti hai aur tightly chipki rehti hai, neeche ke metal ko seal karti hai → yeh passivation hi reason hai ki Al "rust nahi hota" reactive hone ke bawajood.

2b. Acids ke saath

Dilute HCl / $H_{2} S O_{4}$ ke saath: $2 A l + 6 H C l \to 2 A l C l_{3} + 3 H_{2} ↑$

2c. Alkali ke saath (amphoteric ka proof)

$2 A l + 2 N a O H + 6 H_{2} O \to 2 N a [A l (O H)_{4}] + 3 H_{2} ↑$ KYU: $O H^{-}$ protective oxide ko aluminate ke roop mein dissolve kar deta hai, fresh metal expose karta hai → reaction jaari rehti hai. Base ke saath yeh reaction ek metal ke amphoteric hone ki pehchaan hai.

2d. Thermite reaction (oxygen ke liye high affinity)

$2 A l + F e_{2} O_{3} \to A l_{2} O_{3} + 2 F e (Δ H ≪ 0)$ KYU: $A l_{2} O_{3}$ , $F e_{2} O_{3}$ se zyada stable hai; Al metal oxide ko reduce karta hai, bahut zyada heat release karta hai (molten Fe) → rails welding ke liye use hota hai. Yahan Al ek reducing agent ki tarah kaam kar raha hai.

3. $A l C l_{3}$ — dimer $A l_{2} C l_{6}$

Figure — Aluminium — chemistry, alloys; alumina, alums

4. Alumina ( $A l_{2} O_{3}$ )

Amphoteric ka proof: $A l_{2} O_{3} + 6 H C l \to 2 A l C l_{3} + 3 H_{2} O (base-like)$ $A l_{2} O_{3} + 2 N a O H + 3 H_{2} O \to 2 N a [A l (O H)_{4}] (acid-like)$

5. Alums

Common potash alum: $K_{2} S O_{4} \cdot A l_{2} (S O_{4})_{3} \cdot 24 H_{2} O$ , yaani $K A l (S O_{4})_{2} \cdot 12 H_{2} O$ .

6. Alloys (mix kyun karte hain?)

Alloy	Composition (key)	Use
Duralumin	Al + Cu + Mg + Mn	aircraft, light strong parts
Magnalium	Al + Mg	balance beams, light frames
Alnico	Al + Ni + Co (+Fe)	strong permanent magnets

Recall Feynman: ek 12-saal ke bachche ko samjhao

Aluminium ek shy-but-tough metal hai. Jaise hi yeh hawa se milta hai, woh ek invisible "armour" (oxide skin) bana leta hai jo usse protect karta hai — isliye tumhara soda can toot nahi jaata. Yeh ek "do-munh wala" dost hai: yeh acids se bhi lad sakta hai aur strong soaps (bases) se bhi — yahi hai "amphoteric." Thodi si doosri metals milaao aur yeh super strong ho jaata hai lekin feather-light rehta hai, planes ke liye perfect. Alum naam ka ek special salt dirty paani mein daalo aur woh saari floating gandagi ko pakad ke clumps bana deta hai taaki woh sink ho jaayein — saaf paani!

Flashcards

Al ki electronic configuration aur common oxidation state kya hai?

[N e] 3 s^{2} 3 p^{1}

; oxidation state +3.

Conc.

H N O_{3}

aluminium par attack kyun NAHI karta?

Yeh Al ko passivate karta hai ek inert protective oxide layer banakar.

Al ki NaOH solution ke saath reaction likhiye.

2 A l + 2 N a O H + 6 H_{2} O \to 2 N a [A l (O H)_{4}] + 3 H_{2}

A l C l_{3}

dimer

A l_{2} C l_{6}

ke roop mein kyun exist karta hai?

Monomer electron-deficient hota hai (6e); Cl lone pairs bridge karke Al ka octet complete karte hain.

A l_{2} C l_{6}

mein bridging vs terminal Cl kitne hote hain?

2 bridging, 4 terminal; har Al

s p^{3}

hai.

Aqueous

A l C l_{3}

acidic kyun hota hai?

A l^{3 +}

ki high charge density hoti hai → hydrolysis hoti hai,

H^{+}

release hota hai.

"Amphoteric" ka matlab kya hai aur kaun se Al species amphoteric hain?

Dono acids aur bases se react kare; Al,

A l_{2} O_{3}

A l (O H)_{3}

Thermite reaction likhiye aur uska use batayiye.

2 A l + F e_{2} O_{3} \to A l_{2} O_{3} + 2 F e

; rail welding (Al reducing agent hai).

Alum ka general formula kya hai?

M_{2} S O_{4} \cdot M_{2}^{'} (S O_{4})_{3} \cdot 24 H_{2} O

M^{+} M^{' 3 +} (S O_{4})_{2} \cdot 12 H_{2} O

Potash alum ka formula kya hai?

K A l (S O_{4})_{2} \cdot 12 H_{2} O

Alum paani kyun saaf karta hai?

Gelatinous

A l (O H)_{3}

floc banata hai jo suspended impurities ko trap karke settle kar deta hai.

Duralumin ki composition aur use kya hai?

Al+Cu+Mg+Mn; aircraft / strong-light parts.

Alumina kya hai aur ek notable property batao?

A l_{2} O_{3}

; amphoteric, bahut hard, high m.p. (corundum/ruby host).

Connections

Fajans Rules — $A l^{3 +}$ ki covalent character aur polarising power explain karta hai
Group 13 Elements — B, Al, Ga, In, Tl ke periodic trends
Lewis Acids and Bases — $A l C l_{3}$ electron-deficient catalyst kyun hai
Passivation and Corrosion
Coordination Compounds — $[A l (O H)_{4}]^{-}$ aluminate ion
Thermodynamics of Reduction (Ellingham) — thermite kyun kaam karta hai