Life of Prof. Quomrul Hoque

🌱 Early Life & Vision

Born in a rural village near Patharkandi, Karimganj district, Assam, Quomrul Hoque graduated with a Master’s in History from Gauhati University.  

He keenly felt the absence of higher education opportunities in his region and resolved to change that.  

🚀 Founding Patharkandi College (1990)

On 28 October 1990, he established Patharkandi College—starting classes in a borrowed local community hall (Rabindra Bhawan) with public support.  

Through small donations (as little as 10 paise) and local material credit, he laid the foundation stone near Rajbari Pond.  

Even after securing a lecturer’s position at Nabin Chandra College in Badarpur, he invested his personal salary into developing the college infrastructure.  

🎓 Affiliation & Growth

The college received affiliation from Assam University in 1999, though it suffered setbacks after Hoque’s demise.  

In 1998, he tragically died in a car accident returning from a visit to the Directorate of Education, leaving a void at age 36.  

The institution revived in 2004 under the leadership of his younger brother, Dr Monjurul Hoque. It later gained provincial recognition and expanded its academic offerings.  

📘 Establishing the B.Ed. College (1995)

Quomrul Hoque founded the Patharkandi College of Education in 1995 to train teachers for the underserved border region.  

Recognized by the NCTE and affiliated with Assam University, this institution has since consistently ranked among the top ten in the university.  

🏆 Legacy & Honors

His contributions are commemorated at the Patharkandi College library, named the “Professor Quomrul Hoque Central Library”, and through annual awards for top students.  

The Prof. Qoumrul Hoque School of Education at the University of Science & Technology, Meghalaya, is named in his honor—recognizing his passion for accessible rural education.  

Year Milestone

📚 Pre-1990 Completed MA in History

1990 Founded Patharkandi College

1995 Established Patharkandi College of Education

1998 Died in a car accident

1999 College affiliated with Assam University

2004 Revival under his brother

2014+ Honored by USTM naming an education school after him.

🎯 Impact & Rememberance

Prof. Hoque is celebrated as a tireless educationist who devoted his earnings and time to empower rural students—especially from minority and impoverished backgrounds.  

Institutions he founded continue his legacy, producing qualified teachers and contributing significantly to the educational upliftment of Assam’s border regions.

Several personal and touching incidents from Prof. Quomrul Hoque's life reveal his deep dedication and sacrifices for education:

🧵1. Donating His Salary to the College

While he held a government lecturer post at Nabin Chandra College, Badarpur, Prof. Hoque donated almost his entire monthly salary to build infrastructure for Patharkandi College.

> He didn’t draw a separate salary from his own college—he worked there out of passion and duty to the community.

🏚️2. Living in a Cow Shed

During the early years of the college:

> He stayed in a cowshed-like structure near the college site for months—braving rain, insects, and no basic amenities—because he wanted to supervise construction personally and save money.

🧍‍♂️3. Standing on the Road to Collect Donations

He used to stand outside local markets and shops, requesting people to donate 10 or 25 paise. Sometimes:

Villagers would donate bricks, sand, bamboo, or old tin sheets, which he gratefully accepted to use for the college building.

📜4. Incident of the Letter

He once received a letter of transfer to a more comfortable government posting. But he refused to leave, saying:

"If I go, this college will stop. If I stay, even if I suffer, this college will rise. My sacrifice will make others study."

🚗5. His Final Journey

He died in a road accident in 1998 while returning from the Directorate of Education in Guwahati.

He had gone there to speed up the official processing of the college’s affiliation. His sudden death at just 36 years shocked the entire community.

HS 2 Chemistry Unit 7: Alcohols, Phenols and Ethers

 

🔷 1. Introduction to Alcohols, Phenols, and Ethers

Q1. What are alcohols, phenols, and ethers?
Ans:

• Alcohols: Organic compounds where –OH group is attached to an aliphatic carbon (e.g., CH₃OH).

• Phenols: Compounds where –OH is attached to aromatic carbon (e.g., C₆H₅OH).

• Ethers: Compounds where an alkoxy (–OR) or aryloxy (–OAr) group replaces a hydrogen atom in a hydrocarbon (e.g., CH₃OCH₃).

Key Words (with Bengali meaning):

• Hydrocarbon = হাইড্রোকার্বন

• Hydroxyl group = হাইড্রোক্সিল গ্রুপ

• Aliphatic = অ্যালিফ্যাটিক

• Aromatic = অ্যারোমেটিক

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🔷 2. Classification

Q2. How are alcohols classified based on the number of –OH groups?
Ans:

• Monohydric: One –OH group

• Dihydric: Two –OH groups

• Trihydric: Three –OH groups

• Polyhydric: More than three –OH groups

Q3. How are alcohols classified based on the type of carbon attached to –OH?
Ans:

• Primary (1°): –OH attached to a primary carbon

• Secondary (2°): –OH attached to a secondary carbon

• Tertiary (3°): –OH attached to a tertiary carbon

Key Words:

• Monohydric = এক-অ্যালকোহল

• Primary carbon = প্রাথমিক কার্বন

• Tertiary carbon = তৃতীয় কার্বন

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🔷 3. Nomenclature

Q4. What are the rules for naming alcohols in the IUPAC system?
Ans:

• Replace ‘e’ of the alkane with ‘ol’.

• Number the chain from the end closest to –OH.

• Use prefixes di-, tri- for polyhydric alcohols.

Key Words:

• IUPAC = আইইউপিএসি

• Suffix = প্রত্যয়

• Prefix = উপসর্গ

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🔷 4. Preparation of Alcohols

Q5. How are alcohols prepared from alkenes?
Ans:
(i) Acid-catalysed hydration
(ii) Hydroboration-oxidation

Q6. How are alcohols prepared from carbonyl compounds?
Ans:

• Aldehydes/ketones reduced by H₂/Ni or NaBH₄/LiAlH₄

• Carboxylic acids and esters reduced by LiAlH₄

Q7. What happens when a Grignard reagent reacts with an aldehyde/ketone?
Ans:

• It forms an alcohol after hydrolysis.

• With methanal → 1° alcohol

• With other aldehydes → 2° alcohol

• With ketones → 3° alcohol

Key Words:

• Hydration = জলায়ন

• Reduction = হ্রাস প্রক্রিয়া

• Grignard reagent = গ্রিগনার্ড বিকারক

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🔷 5. Preparation of Phenols

Q8. Mention methods of preparation of phenols.
Ans:

1. From haloarenes

2. From benzenesulphonic acid

3. From diazonium salts

4. From cumene

Key Words:

• Diazonium salt = ডায়াজোনিয়াম লবণ

• Sulphonation = সালফোনেশন

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🔷 6. Physical Properties

Q9. Why do alcohols have higher boiling points than ethers and hydrocarbons?
Ans:
Because of strong intermolecular hydrogen bonding in alcohols.

Q10. Why are lower alcohols soluble in water?
Ans:
Due to their ability to form hydrogen bonds with water.

Key Words:

• Boiling point = স্ফুটনাঙ্ক

• Solubility = দ্রাব্যতা

• Hydrogen bonding = হাইড্রোজেন বন্ধন

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🔷 7. Chemical Reactions

(a) Reactions of Alcohols

Q11. How do alcohols show acidic nature?
Ans:
They react with active metals (like Na) to form alkoxides and H₂.

Q12. What is esterification?
Ans:
Alcohols + Carboxylic acids → Esters + Water (in presence of H₂SO₄)

Q13. How do alcohols form alkenes?
Ans:
By acid-catalysed dehydration at high temperature.

Key Words:

• Ester = ইস্টার

• Alkene = অ্যালকিন

• Dehydration = জল অপসারণ

(b) Reactions of Phenols

Q14. Why are phenols more acidic than alcohols?
Ans:
Due to resonance stabilization of phenoxide ion and higher electronegativity of sp² carbon.

Q15. What is Kolbe’s Reaction?
Ans:
Phenol + NaOH → Sodium phenoxide → reacts with CO₂ → Salicylic acid

Q16. What is Reimer-Tiemann Reaction?
Ans:
Phenol + CHCl₃ + NaOH → Salicylaldehyde

Q17. Name some electrophilic substitution reactions of phenol.
Ans:

• Nitration

• Halogenation

• Sulphonation

Key Words:

• Phenoxide = ফিনোক্সাইড

• Resonance = অনুরণন

• Electrophile = ইলেক্ট্রোফাইল

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🔷 8. Preparation of Ethers

Q18. What are the two methods of preparing ethers?
Ans:

1. Dehydration of alcohols

2. Williamson synthesis (alkyl halide + sodium alkoxide)

Key Words:

• Ether = ইথার

• Dehydration = জল অপসারণ

• Williamson synthesis = উইলিয়ামসন সংশ্লেষণ

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🔷 9. Chemical Reactions of Ethers

Q19. How do ethers react with HI or HBr?
Ans:
They are cleaved into alcohol and alkyl halide via SN1 or SN2 mechanism.

Q20. What is the role of alkoxy group in aryl ethers?
Ans:
It activates the aromatic ring for electrophilic substitution (ortho-para directing).

Key Words:

• Cleavage = বিভাজন

• Alkyl halide = অ্যালকাইল হ্যালাইড

🧪 Worksheet: Alcohols, Phenols and Ethers

📘 Part A: Very Short Answer (1 mark each)

1. What is the IUPAC name of CH₃OH?

2. Write one example each of a primary, secondary, and tertiary alcohol.

3. What is the common name of C₆H₅OH?

4. What is meant by the term "esterification"?

5. Write the formula of cumene.

6. What happens when phenol is treated with zinc dust?

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📗 Part B: Short Answer (2–3 marks each)

7. Differentiate between alcohols and phenols based on structure and example.

8. Explain Kolbe’s reaction with an equation.

9. What are allylic and benzylic alcohols? Give one example each.

10. Why are phenols more acidic than alcohols?

11. Write the mechanism of acid-catalysed dehydration of ethanol.

12. What are the conditions required for the preparation of alcohol by hydroboration-oxidation?

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📙 Part C: Long Answer (5 marks each)

13. Write the chemical equations for preparation of alcohols from:
    a) Alkenes (any two methods)
    b) Carbonyl compounds
    c) Grignard reagents

14. How will you prepare phenol by the following methods?
    a) From haloarenes
    b) From diazonium salts
    c) From cumene

15. Compare the physical properties (boiling point and solubility) of alcohols, phenols and ethers. Explain the reason.

16. Describe the chemical reactions of alcohols involving:
    a) Reaction with metal
    b) Dehydration
    c) Oxidation (Primary and secondary alcohols)

17. Explain Reimer-Tiemann reaction with an example. What is the major product?

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📒 Part D: Fill in the Blanks (1 mark each)

18. Methanol is also called __________.

19. The IUPAC name of glycerol is __________.

20. In phenol, the –OH group is attached to __________ hybridised carbon.

21. In Williamson synthesis, ethers are formed by the reaction between __________ and __________.

22. Anisole is an example of __________ ether.

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📕 Part E: Match the Following (1 mark each)

A	B
23. Acidity of phenol	A. SN2 mechanism
24. Phenol + CHCl₃ + NaOH	B. 2,4,6-Tribromophenol
25. Phenol + Br₂ (in water)	C. Reimer-Tiemann Reaction
26. Alkyl halide + sodium alkoxide	D. Resonance stabilization
27. Preparation of ether	E. Williamson synthesis

📘 Part F: Key Word Matching (with Bengali meanings)

Match the English key terms with their Bengali meanings:

English Term	Bengali Meaning
28. Alcohol	A. ইথার
29. Phenol	B. ফিনল
30. Ester	C. অ্যালকোহল
31. Ether	D. ইস্টার
32. Dehydration	E. জল অপসারণ

HS 2nd year Chemistry Unit 6: Haloalkanes and Haloar

 

🔹Topic: Introduction to Haloalkanes and Haloarenes

Q1. What are haloalkanes and haloarenes? How are they classified?
Answer:
Haloalkanes and haloarenes are organic compounds where one or more hydrogen atoms in an aliphatic or aromatic hydrocarbon are replaced by halogen atoms.

• Haloalkanes: Halogen attached to sp³ carbon of an alkyl group.

• Haloarenes: Halogen attached to sp² carbon of an aromatic ring.

They are classified as:
(i) Mono, di or poly halogen compounds depending on number of halogen atoms.
(ii) According to the type of carbon (sp³/sp²) the halogen is bonded to.

Keywords with Bengali Meaning:

• Haloalkanes – হ্যালোআলকেন

• Haloarenes – হ্যালোঅ্যারিন

• Aliphatic hydrocarbon – সোজা শৃঙ্খলযুক্ত হাইড্রোকার্বন

• Aromatic hydrocarbon – সুগন্ধযুক্ত হাইড্রোকার্বন

• Halogen – হ্যালোজেন

• sp³/sp² hybridised carbon – sp³/sp² সংকরিত কার্বন

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🔹Topic: Classification of Halogenated Compounds

Q2. What are primary, secondary, and tertiary alkyl halides?
Answer:

• Primary (1°): Halogen attached to a carbon bonded to one other carbon.

• Secondary (2°): Halogen attached to a carbon bonded to two other carbons.

• Tertiary (3°): Halogen attached to a carbon bonded to three other carbons.

Keywords with Bengali Meaning:

• Primary alkyl halide – প্রাথমিক অ্যালকাইল হ্যালাইড

• Secondary alkyl halide – মাধ্যমিক অ্যালকাইল হ্যালাইড

• Tertiary alkyl halide – তৃতীয়িক অ্যালকাইল হ্যালাইড

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🔹Topic: Nomenclature

Q3. How are haloalkanes and haloarenes named in IUPAC system?
Answer:
Haloalkanes are named as substituted alkanes using prefix of halogen (fluoro-, chloro-, bromo-, iodo-) before the name of parent alkane.
Haloarenes are named by numbering the ring such that the halogen gets the lowest number.

Example:

• CH₃CH₂Cl → Chloroethane

• C₆H₅Cl → Chlorobenzene

Keywords with Bengali Meaning:

• Nomenclature – নামকরণ

• IUPAC – আইইউপিএসি

• Substituted hydrocarbon – প্রতিস্থাপিত হাইড্রোকার্বন

🧪 Class 12 Chemistry Worksheet – Chapter 6: Haloalkanes and Haloarenes (Part 1)

📘 Topic: Introduction & Classification

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Section A: Very Short Answer Questions (1 mark each)

1. What is a haloalkane?

2. What type of carbon is bonded to halogen in haloarenes?

3. What is the hybridisation of carbon in haloalkanes?

4. What is the Bengali meaning of "halogen"?

5. Name the halogenated antibiotic effective against typhoid.

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Section B: Short Answer Questions (2–3 marks each)

6. Write any two differences between haloalkanes and haloarenes.

7. Define mono, di, and poly halogen compounds with examples.

8. Classify the following alkyl halide as primary, secondary, or tertiary:
   a. CH₃CH₂CH₂Br
   b. CH₃CH(Br)CH₃
   c. (CH₃)₃CBr

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Section C: Long Answer Questions (5 marks each)

9. Explain with examples how haloalkanes are classified on the basis of the carbon atom attached to the halogen.

10. Describe the IUPAC rules for naming haloalkanes and haloarenes with at least two examples.

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Section D: Fill in the Blanks (with Bengali keyword meanings)

11. A compound where halogen is attached to an aromatic ring is called __________. (Bengali: হ্যালোঅ্যারিন)

12. Halogen bonded to a carbon with single bonds is called __________. (Bengali: স্পি³ সংকরিত কার্বন)

13. The IUPAC name of CH₃CH₂Cl is __________. (Bengali: ক্লোরোইথেন)

14. The term "haloalkane" in Bengali is __________.

15. The type of alkyl halide where halogen is bonded to a carbon attached to three alkyl groups is called __________. (Bengali: তৃতীয়িক অ্যালকাইল হ্যালাইড)

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Section E: Match the Following

Column A	Column B
1. sp² hybridised carbon	a. Haloalkane
2. Chlorobenzene	b. Tertiary halide
3. (CH₃)₃CBr	c. IUPAC name of CH₃CH₂Cl
4. 1° alkyl halide	d. C₆H₅Cl
5. Chloroethane	e. Halogen on CH₃ group

HS 2nd year Chemistry Unit 5: Coordination Compounds Coordination

 

🔹 1. What are coordination compounds?

Answer:
Coordination compounds are compounds in which a central metal atom or ion is bonded to a fixed number of ions or molecules through coordinate bonds. These surrounding molecules or ions are called ligands.

Keywords with Bengali meanings:

• Coordination compound – সমযোজিত যৌগ

• Central metal atom/ion – কেন্দ্রীয় ধাতব পরমাণু/আয়ন

• Ligand – লিগ্যান্ড (বন্ধনকারী আয়ন বা অণু)

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🔹 2. State Werner’s theory of coordination compounds.

Answer:
Werner's theory states that:

1. Metals show two types of valencies: primary (ionisable) and secondary (non-ionisable).

2. Primary valencies are satisfied by negative ions.

3. Secondary valencies are satisfied by ligands and determine the geometry.

4. The secondary valencies form specific shapes like octahedral, tetrahedral, etc.

Keywords with Bengali meanings:

• Primary valence – প্রাথমিক সঁযোগ

• Secondary valence – গৌণ সঁযোগ

• Ionisable – আয়নীয়

• Geometry – জ্যামিতিক গঠন

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🔹 3. What is the difference between a double salt and a complex?

Answer:
Double salts dissociate completely into ions in water (e.g., Mohr’s salt), whereas complexes retain their identity and do not fully dissociate (e.g., [Fe(CN)6]⁴⁻).

Keywords with Bengali meanings:

• Double salt – যৌগিক লবণ

• Complex – সমযোজিত যৌগ

• Dissociate – বিযুক্ত হওয়া

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🔹 4. Define coordination entity, central atom/ion, and ligand.

Answer:

• Coordination entity: A central atom/ion bonded to ligands in a fixed arrangement.

• Central atom/ion: Metal ion to which ligands are bonded.

• Ligand: Ions/molecules donating electron pairs to the metal ion.

Keywords with Bengali meanings:

• Coordination entity – সমযোজিত সত্ত্বা

• Ligand – লিগ্যান্ড

• Central atom – কেন্দ্রীয় পরমাণু

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🔹 5. What is coordination number and coordination sphere?

Answer:

• Coordination number: Number of ligand donor atoms directly bonded to the central metal atom.

• Coordination sphere: The central metal ion and ligands within square brackets.

Keywords with Bengali meanings:

• Coordination number – সমযোজনা সংখ্যা

• Coordination sphere – সমযোজনা বলয়

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🔹 6. Define oxidation number, homoleptic and heteroleptic complexes.

Answer:

• Oxidation number: The hypothetical charge on the central atom if all ligands are removed.

• Homoleptic complex: All ligands are of the same type.

• Heteroleptic complex: More than one type of ligand is present.

Keywords with Bengali meanings:

• Oxidation number – জারণ সংখ্যা

• Homoleptic – সমজাতীয় লিগ্যান্ড বিশিষ্ট

• Heteroleptic – বিভিন্ন লিগ্যান্ড বিশিষ্ট

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🔹 7. What are unidentate, didentate, and polydentate ligands?

Answer:

• Unidentate: Donates one pair of electrons (e.g., NH₃)

• Didentate: Donates two pairs (e.g., ethylene diamine)

• Polydentate: Donates multiple pairs (e.g., EDTA⁴⁻)

Keywords with Bengali meanings:

• Unidentate – একদন্তীয়

• Didentate – দ্বিদন্তীয়

• Polydentate – বহুদন্তীয়

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🔹 8. Explain chelation and ambidentate ligands.

Answer:

• Chelation: Formation of ring structures when a ligand binds through multiple atoms.

• Ambidentate: Ligands with two donor atoms but only one binds at a time (e.g., NO₂⁻ binds via N or O).

Keywords with Bengali meanings:

• Chelation – চেলেশন (বহুবন্ধন তৈরি)

• Ambidentate – দ্বিমুখী লিগ্যান্ড

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🔹 9. Describe the types of isomerism in coordination compounds.

Answer:

• Structural isomerism: Includes linkage, coordination, ionisation, and solvate isomerism.

• Stereoisomerism: Includes geometrical and optical isomerism.

Keywords with Bengali meanings:

• Isomerism – সমসূত্রীয়তা

• Geometrical isomerism – জ্যামিতিক সমসূত্রীয়তা

• Optical isomerism – আলোকীয় সমসূত্রীয়তা

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🔹 10. Explain the valence bond theory (VBT) for bonding in coordination compounds.

Answer:
According to VBT, metal ions hybridise orbitals (like sp³, dsp², d²sp³) to accept electron pairs from ligands, forming stable geometrical structures.

Keywords with Bengali meanings:

• Valence bond theory – সঁযোজক বন্ধন তত্ত্ব

• Hybridisation – সংকরীকরণ

• Geometry – জ্যামিতিক গঠন

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🔹 11. What is crystal field theory (CFT)?

Answer:
CFT explains bonding based on the electrostatic interaction between metal ions and ligands, causing d-orbital splitting into different energy levels.

Keywords with Bengali meanings:

• Crystal field theory – স্ফটিক ক্ষেত্র তত্ত্ব

• d-orbital splitting – d-কক্ষের বিভাজন

• Spectrochemical series – বর্ণ রসায়নিক শ্রেণি

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🔹 12. What causes colour in coordination compounds?

Answer:
The colour arises from d–d electronic transitions within the metal ion under the influence of ligands, absorbing visible light.

Keywords with Bengali meanings:

• Colour – বর্ণ

• d–d transition – d–d স্থানান্তর

• Absorption – শোষণ

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🔹 13. Describe the structure and bonding in metal carbonyls.

Answer:
Metal carbonyls have σ bonding from CO to metal and π-back bonding from metal d-orbital to CO's empty π* orbital, resulting in strong synergic bonding.

Keywords with Bengali meanings:

• Metal carbonyl – ধাতব কার্বোনাইল

• σ bond – সিগমা বন্ধন

• π-back bonding – পাই ব্যাক বন্ধন

• Synergic bonding – সহযোগী বন্ধন

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🔹 14. Mention some applications of coordination compounds.

Answer:

• Used in extraction of metals (e.g., gold, silver)

• In biological systems (e.g., haemoglobin, chlorophyll)

• Analytical chemistry (e.g., detection using EDTA)

• Medicine (e.g., cisplatin for cancer treatment)

• Electroplating and photography

Keywords with Bengali meanings:

• Extraction – নিষ্কাশন

• Biological system – জীবগত প্রক্রিয়া

• Electroplating – তড়িৎআবরণ

• Chelate therapy – চেলেট চিকিৎসা

📘 Worksheet: Coordination Compounds (Chapter 5 - Chemistry Class 12)

Name: ___________________
Class: XII  Date: _______________

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✍️ Section A – Short Answer Questions

Q1. Define coordination compounds.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keyword: Coordination compound – সমযোজিত যৌগ

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Q2. State any two postulates of Werner’s theory.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keywords: Primary valence – প্রাথমিক সঁযোগ, Secondary valence – গৌণ সঁযোগ

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Q3. Differentiate between a double salt and a coordination compound.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keywords: Double salt – যৌগিক লবণ, Dissociate – বিযুক্ত হওয়া

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Q4. What is meant by ligand? Give one example.
✒️ ____________________________________________________________________
📌 Keyword: Ligand – লিগ্যান্ড

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Q5. Define coordination number and coordination sphere.
✒️ ____________________________________________________________________
📌 Keywords: Coordination number – সমযোজনা সংখ্যা, Coordination sphere – সমযোজনা বলয়

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Q6. What is the oxidation number of the metal in [Fe(CN)6]⁴⁻?
✒️ ____________________________________________________________________
📌 Keyword: Oxidation number – জারণ সংখ্যা

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🧠 Section B – Conceptual Understanding

Q7. Explain the difference between homoleptic and heteroleptic complexes.
✒️ ____________________________________________________________________
✒️ ____________________________________________________________________
📌 Keywords: Homoleptic – সমজাতীয় লিগ্যান্ড বিশিষ্ট, Heteroleptic – বিভিন্ন লিগ্যান্ড বিশিষ্ট

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Q8. Define unidentate, didentate and polydentate ligands with examples.
✒️ ____________________________________________________________________
📌 Keywords: Unidentate – একদন্তীয়, Didentate – দ্বিদন্তীয়, Polydentate – বহুদন্তীয়

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Q9. What are chelating and ambidentate ligands? Give one example of each.
✒️ ____________________________________________________________________
📌 Keywords: Chelation – চেলেশন, Ambidentate – দ্বিমুখী লিগ্যান্ড

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Q10. Name two types of isomerism shown by coordination compounds.
✒️ ____________________________________________________________________
📌 Keywords: Geometrical isomerism – জ্যামিতিক সমসূত্রীয়তা, Optical isomerism – আলোকীয় সমসূত্রীয়তা

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🧪 Section C – Theory Based Questions

Q11. State the basic concept of Valence Bond Theory (VBT).
✒️ ____________________________________________________________________
📌 Keywords: Hybridisation – সংকরীকরণ, Valence Bond Theory – সঁযোজক বন্ধন তত্ত্ব

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Q12. Describe d-orbital splitting in Crystal Field Theory.
✒️ ____________________________________________________________________
📌 Keyword: Crystal Field Theory – স্ফটিক ক্ষেত্র তত্ত্ব, d-orbital splitting – d-কক্ষের বিভাজন

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Q13. Why are many coordination compounds coloured?
✒️ ____________________________________________________________________
📌 Keyword: d–d transition – d–d স্থানান্তর, Absorption – শোষণ

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Q14. Write a note on bonding in metal carbonyls.
✒️ ____________________________________________________________________
📌 Keywords: Metal carbonyl – ধাতব কার্বোনাইল, Synergic bonding – সহযোগী বন্ধন

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Q15. Mention any three applications of coordination compounds in daily life.
✒️ ____________________________________________________________________
📌 Keywords: Electroplating – তড়িৎআবরণ, Chelate therapy – চেলেট চিকিৎসা

HS 2nd year Chemistry Unit 4:The d- and f Block Elements The d - and f Block Element

 

🟢 Topic: Introduction to d- and f-Block Elements

Q1. What are d-block and f-block elements?
Answer:
The d-block elements are those in which the d-orbitals are progressively filled, found in groups 3 to 12 of the periodic table. The f-block elements are those in which the 4f and 5f orbitals are progressively filled. They are placed separately at the bottom of the periodic table.

Keywords with Bengali Meaning:

• d-orbitals – d-কক্ষপথগুলি

• f-orbitals – f-কক্ষপথগুলি

• progressively filled – ক্রমশ পূর্ণ হয়

• periodic table – আবর্ত সারণি

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Q2. Why are zinc (Zn), cadmium (Cd), and mercury (Hg) not considered transition metals?
Answer:
Zinc, cadmium, and mercury have completely filled d-subshells (d¹⁰ configuration) in their ground states and common oxidation states, so they are not considered transition metals.

Keywords with Bengali Meaning:

• transition metals – স্থানান্তর ধাতু

• oxidation states – জারণ অবস্থা

• ground state – ভূমিস্থিতি

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🟢 Topic: Electronic Configurations of d-Block Elements

Q3. Write the general electronic configuration of d-block elements.
Answer:
The general electronic configuration of d-block elements is (n–1)d¹⁻¹⁰ ns¹⁻². For example, Cr: [Ar] 3d⁵ 4s¹ and Cu: [Ar] 3d¹⁰ 4s¹ due to extra stability of half-filled and completely filled orbitals.

Keywords with Bengali Meaning:

• electronic configuration – তড়িৎ বিন্যাস

• half-filled – অর্ধ পূর্ণ

• completely filled – সম্পূর্ণ পূর্ণ

• stability – স্থিতিশীলতা

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Q4. Why does chromium have the configuration 3d⁵ 4s¹ instead of 3d⁴ 4s²?
Answer:
Chromium prefers 3d⁵ 4s¹ because half-filled d-orbitals (3d⁵) offer extra stability due to symmetrical distribution and exchange energy.

Keywords with Bengali Meaning:

• exchange energy – বিনিময় শক্তি

• symmetrical distribution – সমবণ্টন

• configuration – বিন্যাস

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🟢 Topic: General Properties of Transition Elements

Q5. Mention some physical properties of transition elements.
Answer:
Transition elements have high melting and boiling points, metallic lustre, high tensile strength, good conductivity, and hardness (except Zn, Cd, Hg).

Keywords with Bengali Meaning:

• metallic lustre – ধাতব দীপ্তি

• tensile strength – প্রসারণ শক্তি

• conductivity – পরিবাহিতা

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Q6. Why do transition elements have high melting and boiling points?
Answer:
Due to the involvement of (n–1)d electrons along with ns electrons in metallic bonding, which leads to stronger bonds.

Keywords with Bengali Meaning:

• metallic bonding – ধাতব বন্ধন

• boiling point – স্ফুটনাঙ্ক

• melting point – গলনাঙ্ক

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Q7. What is lanthanoid contraction?
Answer:
Lanthanoid contraction is the gradual decrease in atomic and ionic size from La to Lu due to poor shielding of f-electrons.

Keywords with Bengali Meaning:

• contraction – সংকোচন

• shielding effect – আবরণ প্রভাব

• ionic size – আয়নিক আকার

🧪 Worksheet: The d- and f-Block Elements (Part 1)

Class 12 – Chemistry | Chapter 4
Name: ___________ Roll No: ________ Date: ___________

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Section A: Very Short Answer Questions

(Answer in 1–2 sentences)

Q1. What is the general electronic configuration of d-block elements?
Ans: ___________________________________________________________

Q2. Why is Zn not considered a transition metal?
Ans: ___________________________________________________________

Q3. Which element has the configuration [Ar] 3d⁵ 4s¹ and why?
Ans: ___________________________________________________________

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Section B: Short Answer Questions

(Answer in 3–5 sentences)

Q4. What are d- and f-block elements? Mention their positions in the periodic table.
Ans:

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Q5. Why do transition metals have high melting and boiling points?
Ans:

---

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Q6. Write any three physical properties of transition elements.
Ans:

1. ---

2. ---

3. ---

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Section C: Conceptual Questions

(Think and answer in detail)

Q7. Explain why Cr has a configuration of 3d⁵ 4s¹ instead of 3d⁴ 4s².
Ans:

---

---

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Q8. What is lanthanoid contraction? What causes it?
Ans:

---

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HS 2nd year Chemistry Unit 3: Chemical Kinetics

 

🔹 Topic: Introduction to Chemical Kinetics

Q1. What does chemical kinetics study?
Ans. Chemical kinetics studies the rate of chemical reactions, factors affecting them, and the mechanism by which they occur.

Keywords:

• Chemical kinetics – রাসায়নিক গতি বিদ্যা

• Reaction rate – বিক্রিয়া হার

• Mechanism – প্রক্রিয়া

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🔹 Topic: Average and Instantaneous Rate of Reaction

Q2. Define average rate of a chemical reaction.
Ans. Average rate is the change in concentration of reactants or products divided by the time interval during which the change occurs.
$\text{Average Rate} = \frac{\Delta [R]}{\Delta t}$

Q3. Define instantaneous rate of reaction.
Ans. It is the rate of change of concentration of a reactant or product at a specific instant of time.
$\text{Instantaneous Rate} = \frac{d[R]}{dt}$

Keywords:

• Average rate – গড় হার

• Instantaneous rate – তাৎক্ষণিক হার

• Concentration – ঘনত্ব

• Time interval – সময় ব্যবধান

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🔹 Topic: Rate of Reaction and Stoichiometry

Q4. Why do we divide the rate of disappearance or appearance by stoichiometric coefficients?
Ans. Because in reactions where coefficients are not 1, rate is proportionally related and must be normalized to compare rates of different species.

Keywords:

• Stoichiometry – স্টয়কিওমেট্রি

• Disappearance – অদৃশ্য হওয়া

• Appearance – আবির্ভাব

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🔹 Topic: Rate Law and Rate Constant

Q5. What is rate law?
Ans. It expresses the rate of a reaction as a function of the concentration of reactants raised to some powers.
Example: $\text{Rate} = k[A]^x[B]^y$

Q6. What is rate constant?
Ans. Rate constant $k$ is the proportionality factor in the rate law.

Keywords:

• Rate law – হার সূত্র

• Rate constant – হার ধ্রুবক

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🔹 Topic: Order and Molecularity of Reaction

Q7. What is the order of a reaction?
Ans. The sum of the powers of concentration terms in the rate law expression.

Q8. What is molecularity?
Ans. The number of reacting species involved in an elementary step of a reaction.

Keywords:

• Order – ক্রম

• Molecularity – অণুসংখ্যা

• Elementary reaction – মৌলিক বিক্রিয়া

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🔹 Topic: Integrated Rate Equations

Q9. Derive the integrated rate law for a first-order reaction.
Ans. For a first-order reaction:
$\ln[R] = -kt + \ln[R_0]$
or
$k = \frac{2.303}{t} \log \frac{[R_0]}{[R]}$

Keywords:

• Integrated rate equation – সমন্বিত হার সমীকরণ

• First order – প্রথম ক্রম

• Logarithm – লগারিদম

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🔹 Topic: Half-life of Reactions

Q10. Define half-life of a reaction.
Ans. It is the time taken for the concentration of a reactant to reduce to half of its initial value.

• For first-order: $t_{1/2} = \frac{0.693}{k}$

Keywords:

• Half-life – অর্ধ-আয়ু

• Initial concentration – প্রাথমিক ঘনত্ব

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🔹 Topic: Temperature Dependence – Arrhenius Equation

Q11. Write and explain the Arrhenius equation.
Ans.
$k = A e^{-E_a/RT}$
It shows the effect of temperature on the rate constant. $E_a$ is the activation energy.

Keywords:

• Arrhenius equation – অ্যারেনিয়াস সমীকরণ

• Activation energy – সক্রিয়ন শক্তি

• Frequency factor – বারম্বারতা ধ্রুবক

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🔹 Topic: Catalyst and Collision Theory

Q12. What is the role of a catalyst in a reaction?
Ans. A catalyst increases the rate of reaction by providing an alternate path with lower activation energy.

Q13. What are effective collisions?
Ans. Collisions in which molecules have sufficient energy and proper orientation to form products.

Keywords:

• Catalyst – অনুঘটক

• Collision – সংঘর্ষ

• Effective collision – কার্যকর সংঘর্ষ

• Orientation – বিন্যাস

🔬 Class 12 Chemistry – Chapter 3: Chemical Kinetics

📝 Worksheet (With Bengali Keywords)

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Section A: Very Short Answer (1 mark each)

Write the answer in one sentence.

1. What is chemical kinetics?

2. What is the formula for average rate of a chemical reaction?

3. Write the expression for the instantaneous rate of a reaction.

4. What is meant by ‘rate constant’?

5. Define molecularity.

6. What is the half-life of a reaction?

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Section B: Short Answer (2-3 marks each)

Answer briefly.

7. What is the difference between average rate and instantaneous rate?

8. Why is the rate of disappearance or appearance divided by stoichiometric coefficients?

9. What is a rate law? Give an example.

10. Explain the order of a reaction with an example.

11. Write the integrated rate equation for a first-order reaction.

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Section C: Long Answer (5 marks each)

Answer in detail.

12. Derive the expression for the integrated rate law of a first-order reaction.

13. Explain the Arrhenius equation. How does temperature affect the rate of a reaction?

14. Describe the role of a catalyst in a chemical reaction. How does it affect activation energy?

15. What are effective collisions? Explain with an example.

16. Differentiate between order and molecularity of a reaction.

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Section D: Numerical Questions

17. For a first-order reaction, calculate the half-life when rate constant $k = 2.31 \times 10^{-3}\ s^{-1}$.

18. A reaction follows first-order kinetics. If 80% of the reaction is complete in 20 minutes, calculate the rate constant.

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Section E: Bengali Keyword Matching

Match the English keyword with its Bengali meaning:

English Term	Bengali Meaning
1. Reaction rate	A. অনুঘটক
2. Catalyst	B. বিক্রিয়া হার
3. Molecularity	C. লগারিদম
4. Logarithm	D. সক্রিয়ন শক্তি
5. Activation energy	E. অণুসংখ্যা

Section F: Application-Based Questions

19. In the reaction A + B → C, if the rate = k[A][B]², how will the rate change if:
    a) [B] is doubled
    b) Both [A] and [B] are halved

20. Explain how reaction mechanism relates to the rate determining step with an example.