Class 12 Chemistry : Important Questions and Topics for NEB exam 2081 - Note Library

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Class 12 Chemistry : Important Questions and Topics for NEB exam 2081

Class 12 biology neb important question chapterwise unitwise neb 2080 2081

 Here are important Topics and Questions which are frequently asked question in neb class 12 exam .


ORGANIC CHEMISTRY :

SET A: Almost one sure :

  • Identification of 10, 20 and 30 alcohols by Victor Meyer’s method.
  • Separation of 10, 20 and 30 amines by Hoffmann’s method.

SET B: Name reactions:

  1. Aldol condensation reaction
  2. Cannizaro’s reaction
  3. Perkins condensation
  4. Claisen Condensation reaction.
  5. Benzoin condensation
  6. Carbylamine reaction
  7. Reimer Tiemann reaction
  8. Coupling reaction( preparation of azo dyes)
  9. Diazotization reaction
  10. Friedel- Craft’s reaction
  11. Hoffmann’s Bromamide reaction( Decarbonylation reaction)
  12. Esterification reaction
  13. Carbonylation reaction (Oxo process)
  14. Williamsan’s etherification reaction
  15. Rosenmund reduction

SET C: Test reaction:

  1. Iodoform test
  2. Silver mirror test( reaction with Tollen’s reagent)
  3. Nitrous acid test of 10, 20 and 30 amines.
  4. 2,4 – DNP test
  5. Carbylamine test ( test of primary amines)

SET D: Important reactions:

  1. Reduction of nitrobenzene in different medium.
  2. Preparation of alcohols using Grignard reagent.
  3. Oxidation of alcohols.
  4. Fermentation
  5. All reactions of chloroform.

SET E: Reactions to prepare : (with one use)

  1. DDT                      6. Picric acid
  2. BHC                      7. Urotropin
  3. Chloropicrin.      8. TNT
  4. Phenolphthalein
  5. Bakelite

SET F : Convert:

  1. 1-bromopropane to 2- bromopropane and vice- versa.
  2. 1- propanol to 2- propanol and vice versa.
  3. Methanamine to ethanamine and vice versa.
  4. Phenol to anisole(methoxy benzene) and vice versa.
  5. Ethoxy ethane to methoxy ethane.
  6. Phenol/aniline to azo-dye.
  7. Ethanal/ ethanol to 3-hydroxy butanal.
  8. Ethanol to 2- hydroxy propanoic acid.
  9. Propanone(acetone) to 2-hydroxy-2-methyl propanoic acid.
  10. Phenol to toluene.
  11. Ethanol to propanol/ propanoic acid.
  12. Methanamide to ethanamine.
Some Important  questions of Organic Chemistry:
  1. Why is chloroform stored in a dark bottle containing ethanol?
  2. Why does chloroform not give white ppt. with aq. AgNO3?
  3. Why is nucleophilic substitution reaction difficult in haloarene?
  4. Why is boiling point of ethanol greater than that of ethoxy ethane?
  5. Why is phenol more acidic than aliphatic alcohol?
  6. Why does nitrobenzene undergoes electrophilic substitution reaction at meta position? ( Explain why –NO2 group is meta directing towards electrophilic aromatic substitution)
  7. Why is chlorobenzene o/p – directing towards electrophilic substitution reaction?
  8. It is dangerous to boil a sample of ether stored for a long time, give reason.
  9. Ether is stored in a bottle containing iron wire, why?
  10. Give a suitable test to distinguish ethanamine from N-methyl methanamine.
  11. Write a chemical test to distinguish ethanoic acid(acetic acid) from methanoic acid(formic acid).
  12. Why is chloroacetic acid stronger acid than acetic acid?
  13. Why is formic acid stronger acid than acetic acid?
  14. Why amino group of aniline is protected before nitration?(Aniline can not be nitrated directly, why?)
  15. Write the functional isomers of C3H6O with their IUPAC name. Give a chemical test to distinguish them.
  16. Write an unsymmetrical ether of C3H8O. How would you prepare this ether using Williamson’s synthesis?
  17. Write down possible isomeric amines of C3H9N and give their IUPAC names.

What happens when:

  1. Sodium benzoate is heated with sodalime.
  2. Phenol is heated with zinc dust.
  3. Chlorobenzene is treated with chloral .
  4. Ethyl alcohol(ethanol) is treated with acetic acid(ethanoic acid)
  5. Phenol is treaded with aq. Br2.
  6. Aniline is treated with aq. Br2.
  7. Phenol is treated with benzene diazonium chloride.
  8. Ethoxy ethane is treated with excess HI.
  9. Methanal(formaldehyde) is treated with ammonia.
  10. Methanal / benzaldehyde is treated with NaOH .
  11. Ethanal/propanone is treated with NaOH .
  12. Aldehyde/ketone is treated with hydroxyl amine.
  13. Ethanol is heated with conc. H2SO4.
  14. Acetic acid is treated with P2O5.

APPLIED CHEMISTRY

1. Write monomers and one use of:

(a)Bakelite    (b)Nylon-6,6   (c) Polystyrene

(c)polyvinyl chloride(PVC)     (d) Teflon

2. Write example and one use of:

  • Analgesic , antipyretic, antibiotics, tranquilizer and antiseptic drug.
  • Herbicide and Pesticide
  • Germicide and Insecticide
  • Natural and synthetic dye

See note of drugs…

3. Write the flow sheet diagram for the production of cement.

4. Differentiate between OPC and PPC cement.

5. Write the flow sheet diagram for paper production.

6. Differentiate between nuclear fusion and fission reaction.

PHYSICAL CHEMISTRY :

  1. Selection of indicators.
  2. Different concepts of acids and bases and their limitations
  3. Common ion effect and solubility product principle and its application in salt analysis (precipitation reaction).
  4. Buffer solution.
  5. Electrochemical series.
  6. Standard electrodes.
  7. Hess law.
  8. Prediction of feasibility/ spontaneity of reactions in terms of free energy change, entropy change and enthalpy change.
  9. Differences between order and molecularity of reaction.
  10. Collision theory of reaction rate.
  11. Factors affecting rate of reaction.
  12. Derivation of integrated rate equation and half life for first order reaction.
Some Important questions from physical chemistry :

1. Define the terms:

  • Normality and Normality factor
  • End point and Equivalent point
  • Titration error
  • Seminormal solution and Decinormal solution
  • Indicator
  • Standard solution(primary and secondary) with example.

2. What are primary standard substances? What are the requisites for a substance to be primary standard?

3. Define molarity and normality. Write their relationship.

4. What happens when HCl is passed through saturated solution of NaOH?

5. Predict whether the aqueous solution of CuSO4/CaCl2/Na2CO3/NaCl is acidic basic or neutral. Give reason.

6.State Ostwald’s dilution law. What is the limitation of this law?

7. Define pH and pOH . Write their relation.

8. Mention one important application of standard hydrogen electrode giving example.

9. State first law of thermodynamics and point out its limitation.

10. Distinguish between intensive and extensive property with one example of each.

11. Define enthalpy of combustion and enthalpy of formation.

12. Draw energy profile diagram for exothermic and endothermic reactions.

13. Draw energy profile diagram for catalyzed and uncatalyzed reactions.( How does catalyst increases the rate of reaction?)

14. State second law of thermodynamics. Explain this law on the basis of entropy change.

15. What is meant by effective collision of reacting species? What are the essential conditions for the effective collision of reacting species?

16. Find the unit of rate constant of: zero, first, second and third order reaction.

Note : Numerical problems are most important for physical chemistry , which are not listed here

INORGANIC CHEMISTRY 

SET A: Characteristics of Transition metals:

  1. Variable oxidation state
  2. Formation of complexes
  3. Reason for coloured complexes
  4. Catalytic property
  5. Magnetic property.
  6. CFT for octahedral complex.

SET B: Extraction  of :

  1. (Blister) copper from copper pyrites.
  2. Steel (Mainly Open Hearth process)
  3. Iron from iron pyrites.
  4. Zinc from zinc blend ( sulphide ore).
  5. Mercury from cinnabar (HgS) ore.

SET C: Chemistry of:

  1. Blue vitriol ( CuSO4.5H2O)
  2. White vitriol ( ZnSO4. 7H2O)
  3. Zinc white ( ZnO)
  4. Calomel (Hg2Cl2)
  5. Corrosive sublimate (HgCl2)
Some Important  questions of Inorganic Chemistry :

1. Cu2+ complexes are colored while those of Zn2+ are colorless. Explain the reason.

2. Why Fe3+ is more stable than Fe2+ ?

3. Sc3+, Ti4+, V5+ complexes are white even though all are transition elements. Give reason.

4. What are transition metals? Why are they called so?

Those metals which have partially filled d-orbital in their elemental or common oxidation states are called transition metals. They are called transition elements because they are present between s-block and p-block elements and their properties are intermediate between the s-block and p-block elements.

5. Copper metal becomes black/green when exposed to air for long time, why?

In presence of moist air, a green layer of basic copper carbonate is formed. Hence, copper metal becomes green when exposed to air for long time.

6. What happens when copper (coin) is treated with conc. HNO3?

Copper nitrate is formed.

7. Why is zinc not considered as transition element?

Zinc is not considered a transition metal because it does not have partly filled (i.e. incomplete) d-orbital. It has 3d-orbital fulfilled , [Ar]3d104s2. It does not exhibit general characteristics of transition elements, eg. zinc forms colourless compounds.

8. What is Rinman’s green? How it is prepared? Write its one important use.

Cobalt zincate is called Rinman’s green.It is prepared by heating zinc oxide with cobalt nitrate.

It is used as green pigment.

9. What is lithopone? How it is prepared?

Zinc sulphate reacts with barium sulphide to form a white paint commercially called lithopone.

10. Write molecular formula of Philosopher’s wool. How it is prepared?

Zinc oxide (ZnO) is called philosopher’s wool. It is prepared by strongly heating zinc in air.

11. What is Nessler’s reagent? How is it prepared? Give its one use.

Alkaline solution of potassium tetra iodo mercurate (II), i.e. solution of K2HgI4 in KOH or NaOH is called Nessler’s reagent. It is prepared by treating mercuric chloride with excess of KI.

It is used to detect the presence of ammonia or ammonium salt.

12. What is the composition of stainless steel? Write its one use.

Stainless steel is the alloy of iron containing at least 10.5% chromium and other alloying elements such as nickel (1-8%). Generally, stainless steel is mixture of Fe, Cr, Ni and C.

It resist corrosion and used in making automobile parts, surgical instruments, knives, etc.

13. Freshly prepared ferrous sulphate should be used while it is used as a laboratory reagent, why?

When ferrous sulphate is exposed to air for a long time, it gets oxidized by atmospheric air to basic ferric sulphate, therefore it should be freshly prepared in the laboratory.

14. Rusting (corrosion) of iron and methods of prevention. 

The corrosion of iron is called rusting. Rust is chemically the hydrated ferric oxide [Fe2O3.xH2O].

Iron does not rust in dry air, however, the presence of moisture, carbon dioxide and oxygen are major factors for rusting of iron.General reaction of rust formation is:

Prevention:

  • By coating iron surface with a metallic film of corrosion-resistant metals such as zinc, tin, nickel, etc.
  • By a thin coating of paints, enamels, etc.
  • By treating with antirust solutions of conc. Nitric acid, phosphoric acid, etc.

15. Why do silver ornaments turn black (get tarnished) when exposed to air?

Silver gets tarnished when exposed to air containing traces of hydrogen sulphide due to formation of black ppt of silver sulphide.

16. Why does silver nitrate produce permanent black stain on the skin?

OR

Why does ink made of silver nitrate is used to mark the skin or nail during election?

In the presence of organic matter (skin) and sunlight, silver nitrate decomposes to give a permanent black stain of metallic silver. Hence, ink made of silver nitrate is used to mark the skin or nail during election.

17. What is lunar caustic? Why it is called lunar caustic?

Silver nitrate (AgNO3) is called lunar caustic. It leaves black stain when comes in contact with skin in presence of sunlight. It produces a burning sensation like caustic soda and leaves a black stain like the moon (lunar) on the skin. So, it is called lunar caustic.

18. Why is teeth filling is done with an alloy of gold and silver?

The dentist uses an alloy of gold and silver because this is harder than gold and silver alone and thus durable, strong, and affordable.

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