Class 12 Most Important Question Of Chemistry For NEB 2021

Here, we discuss about Most important Question of chemistry for NEB 2021 in below.

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Questions

Benzene

1. General methods of preparation of benzene.

2. Write short note on friedel craft reaction.

Haloalkanes and Haloarenes

1. Describe the lab preparation of chloroform (trichloromethane).

2. Write any three general methods of preparation of chlorobenzene. Why does it gives ortho and para products during electrophilic substitution reaction?

3. Chemical properties of chloroform

a. oxidation

b. reduction

c. action on silver powder

d. conc. Nitric acid

e. propanone

f. aqueous alkali,

g. Carbylamine reaction

h. Reimer Tiemann reaction

i. lodiform reactio

4. Starting from methyl magnesium bromide (CH,MgBr) how would you prepare a. ethanol

b. propan-2-ol

c. ethanoic acid

d. 2-methyl propan-2-ol

e. methane

Alcohol and phenol

: 1. How 1, 2 and 3 alcohol are obtained from Grignard’s reagent?

2. Write down the oxidation products of primary, secondary and tertiary alcohols. 3. What happens when ethyl alcohol is treated with conc. H.SO, under different conditions?

4. Distinction between 1, 2 and 3 alcohols by victor Mayer’s method.

5. An aromatic compound A on reduction yield parent hydrocarbon B. B on nitration gives C. C on reduction in acidic solution gives D. on coupling with diazonium salts. D gives diazoaminobenzene (p aminoazobenzene). Give name for A, B, C and D. Write the chemical reactions involved

6. Write short note on Fermentation and preparation of primary alcohol by ‘oxo’ process.

Ether

1. Describe the laboratory preparation of ethane).

2. Chemical properties of ether. Action with

a. HI

b. PCI5

C. conc. HCI

d. conc. H.SO4,

e. air f. Cl2

Aldehydes and Ketones

1. Write Short notes on:

a. Aldol condensation

b. Connizzaro’s reaction

c. Perkin reaction

d. Benzoin condensation

e. Wolf Kishner reduction

f. Clemmenson reduction

g. Rosenmund reduction

2. What happens when?

a. Benzaldehyde is refluxed with alcoholic KCN.

b. Benzaldehyde is warmed with aqueous NaOH

c. Ethanal if allowed to react with hydroxylamine.

d. Benzaldehyde is heated with ethanoic anhydride (ie. acetic anhydride) in presence of sodium ethanoate.

3. An organic compound (CHO) reacts with phenyl hydrazine to form phenyl hydrozone. The compound does not reduce Fehling’s solution but gives iodoform test. The compound on clemmenson reduction gives n-pentane. Identify the organic compound giving necessary chemical equations.

4. Write the action of

a. Ammonia with methanal

b. Acetone with hydrazine

c. Ethanal with semi carbazide

d. Propanone with sodium bisulphate.

Carboxylic acid:

1. Describe the laboratory preparation of methanoic (i.e. Formic and its purification).

3. Compound A when treated with alcoholic KCN gives compound B which on hydrolysis give compound C. Compound C when treated with PCl5, give compound D. which on further catalytically hydrogenated give compound E. compound E on Clemenson reduction give ethane, Identity A, B, C, D and E.

4. What products are obtained in following reaction NaOH PC PO LAH, NH3 CH-CH₂OH/Conc H.SQ.

Nitro Compounds:

1. Describe the laboratory preparation of nitrobenzene.

2. What happens when Nitrobenzene is subjected to reduction in

a. Acidic medium

b. Neutral medium

c. alkaline mediam

d. catalytic reduction CH₂COOH

e. Electrolytic reduction

f. metal hydride reduction.

Amino Compounds:

1. Describe the laboratory preparation of aniline.

2. How would you separate 1°, 2° and 3″ amines from their Hoffmann’s method?

Biomolecules:

1. What happens when monosaccharide, disaccharide trisaccharide is hydrolysed?

2. What is a peptide bond? Write an example of a dipeptide

3. What is meant by denaturation of protein?

4. What are differences between DNA and RNA?

5. What are reducing and non reducing sugars?

Chemical Kinetics:

1. Define rate of a chemical reaction How do concentration, temperature, catalyst and surface area of reactants affect the rate of reaction?

2. Write short notes on

a. collision theory of reaction rate.

lonic equilibrium

1. Write short notes on:

a. lonic and solubility product

b. Common ion effect.

c. Solubility product principle

d. PH and pH scale

e. Auto ionization of water

f. Ostwald dilution law

2. What are ionization constant and degree of ionization of weak electrolyte?

Chemical energetic and chemical thermodynamics:

1. State the first law of thermodynamics.

2. State second law of thermodynamics

3. Define entropy and enthalpy of a system.

4. Define free energy. Derive an expression to relate Gibb’s change with work change and entropy change?State an explain Hess law of constant heat summation.

5.How is free energy change of a reaction related to enthalpy change and entropy change?

6.How would you predict whether a reaction is spontaneous, non-spontaneous and equilibrium in term of free energy.

7.What is meant by enthalpy of formation and enthalpy of combustion? 1. How is a suitable indicator selected for a particular Acid-base

Volumetric Analysis:

a.indicator

b. end point

c. equivalent point

d. end point

e. primary standard solution

f. Titration

g. normality

h. molarity

i. decinormal solution

j. normality factor k. gram per litre. .

Electrochemistry:

  1. State faraday’s laws of electrolysis
  2. What is E.C.E (electrochemical equivalent)?
  3. How specific conductance decreases and equivalent conductance
  4. Does increases with dilution?
  5. Define the terms

a. Cell constant

b. molar conductivity

c. equivalent conductivity

Iron:

  1. What is rusting? Describe electrochemical theory of rusting of iron.List any two method of prevention of iron rust or corrosion of iron.
  2. How is steel manufactured by open hearth process? Mention its advantage over Bessemer process.
  3. Draw a net labeled sketch of blast furnace for the extraction of pig iron and write down the chemical reaction involved at different zones.

Zinc:

  1. Write the preparation properties and uses of white vitrol. 2. Write short notes on extraction of zinc.

Mercury:

  1. Write short notes on

a. Extraction of mercury

b. Purification of mercury

c. Chemistry of calomel.

In pervious blog we discuss about Class 12 Most Important Question Of Physics For NEB examination 2021.

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