Important 3 Marks Questions for CBSE 12th Chemistry Exam

Important Questions for 12th Chemistry Exam

Question 1:

The partial pressure of ethane over a saturated solution containing 6.56 x 10-2 of ethane is 1 bar. If the solution were to contain 5.0 x 10-2 g of ethane, what will be the partial pressure of the gas.

Question 2:

(a)What are fuel cells? Explain the electrode reactions involved in working of H2-O2 fuel cell.

(b)Represent the galvanic cell in which the reaction Zn + Cu 2+ -> Zn 2+ + Cu , take place.

Question 3:

(a)Based on the nature of intermolecular forces, classify the following solids :Silicon carbide, Argon

(b)ZnO turns yellow on heating. Why ?

(c)What is meant by groups 12-16 compounds ? Give an example.

Question 4:

(a)The cell in which the following reaction occurs: 2 Fe3+ (aq) + 2 I-(aq) -> 2 Fe2+ (aq) + I2(s) has cell Eocell= 0·236 V at 298 K. Calculate the standard Gibbs energy of the cell reaction. (Given : 1 F = 96,500 C mol-1)

(b)How many electrons flow through a metallic wire if a current of 0·5 A is passed for 2 hours ? (Given : 1 F = 96,500 C mol-1)

Question 5:

(a)What type of isomerism is shown by the complex:[Co(NH3)5(SCN)]2+ ?

(b)Why is [NiCl4]2- paramagnetic while [Ni(CN)4]2- is diamagnetic ? (Atomic number of Ni = 28)

(c)Why are low spin tetrahedral complexes rarely observed

Question 6:

Write one difference in each of the following :

(a) Multimolecular colloid and Associated colloid

(b) Coagulation and Peptization

(c) Homogeneous catalysis and Heterogeneous catalysis

Question 7:

Write the dispersed phase and dispersion medium of milk.

(a) Write one similarity between physisorption and chemisorption.

(b) Write the chemical method by which Fe(OH)3 sol is prepared from FeCl3.

Question 8:

A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed.

(Given : log 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021)

Question 9:

The following compounds are given to you : 2-Bromopentane, 2-Bromo-2-methylbutane, 1-Bromopentane

(a) Write the compound which is most reactive towards SN2 reaction.

(b) Write the compound which is optically active.

(c) Write the compound which is most reactive towards -elimination reaction.

Question 10:

Write the principle of the following :

(a) Zone refining

(b) Froth floatation process

(c) Chromatography

Question 11: 

Write the structures of the monomers used for getting the following polymers :

(a) Nylon-6,6

(b) Melamine-formaldehyde polymer

(c) Buna-S

Question 12:

Define the following :

(a) Anionic detergents

(b) Limited spectrum antibiotics

(c) Antiseptics

Question 13:

Give reasons for the following :

(a) Red phosphorus is less reactive than white phosphorus.

(b) Electron gain enthalpies of halogens are largely negative.

(c) N2O5 is more acidic than N2O3.

Question 14:

Give reasons for the following :

(a) Acetylation of aniline reduces its activation effect.

(b) CH3NH2 is more basic than C6H5NH2

(c) Although -NH2 is o/p directing group, yet aniline on nitration gives a significant amount of m-nitroaniline.

Question 15:

Define the following terms given an example of each

(i) Associated colloids

(ii) Lyophilic solution

(iii) Adsorption

Question 16:

Calculate the emf of the following cell at 25ºC 3 Ag (s) | Ag+ (10–3M) || Cu2+(10–1M) | Cu (s) Given EoCell = +0.46 V and log10n = n

Question 17:

Shanti, a domestic helper of Mrs. Anuradha, fainted while mopping the floor. Mrs. Anuradha immediately took her to the nearby hospital where she was diagnosed to be severely ‘anaemic.’ The doctor prescribed an iron rich diet and multivitamins supplement to her. Mrs. Anuradha supported her financially to get the medicines. After a month, Shanti was diagnosed to be normal.

After reading the above passage, answer the following questions :

(i) What values are displayed by Mrs. Anuradha ?

(ii) Name the vitamin whose deficiency causes ‘pernicious anaemia’.

(iii) Give an example of a water soluble vitamin.

Question 18:

The rate of a reaction becomes four times when the temperature changes from 293 K to 313 K. Calculate the energy of activation (Ea) of the reaction assuming that it does not change with temperature.  [R = 8.314 J K-1 mole-1, log 4 = 0.6021]

Question 19:

For the complex [NiCl4]–2, write

(i) The IUPAC name

(ii) The hybridization type

(iii) The shape of the complex (Atomic no. of Ni = 28)

Question 20:

What is meant by crystal field splitting energy ? On the basis of crystal field theory, write the electronic configuration of d4 in terms of t2g and eg in an octahedral field when

(i) ∆0 > P

(ii) ∆0 < P

Question 21:

Give reasons for the following

(i) Ethyl iodide undergoes SN2 reaction faster than ethyl bromide.

(ii) (±) 2-Butanol is optically inactive.

(iii) C-X bond length in halobenzene is smaller than C-X bond length in CH3 – X.

Question 22:

(i) What class of drug is Ranitidine ?

(ii) If water contains dissolved Ca2+ ions, out of soaps and synthetic detergents, which will you use for cleaning clothes ?

(iii) Which of the following is an antiseptic ? 0.2% phenol, 1% phenol

Question 23:

Given reasons for the following :

(i) Oxygen is a gas but sulphur is a solid

(ii) O3 acts as a powerful oxidizing agent

(iii) BiH3 is the strongest reducing agent amongst all the hydrides of group 15 elements

Question 24:

(i) Write the IUPAC name of the complex [Cr(NH3)4Cl2]Cl.

(ii) What type of isomerism is exhibited by the complex [Co(en)3] 3+ ? (en = ethane-1,2-diamine)

Question 25:

Account for the following :

(i) Primary amines (R-NH2) have higher boiling point than tertiary amines (R3N).

(ii) Aniline does not undergo Friedel-Crafts reaction.

(iii) (CH3)2NH is more basic than (CH3)3N in an aqueous solution.

Question 26:

On the occasion of World Health Day, Dr. Satpal organized a ‘health camp’ for the poor farmers living in a nearby village. After check-up, he was shocked to see that most of the farmers suffered from cancer due to regular exposure to pesticides and many were diabetic. They distributed free medicines to them. Dr. Satpal immediately reported the matter to the National Human Rights Commission (NHRC). On the suggestions of NHRC, the government decided to provide medical care, financial assistance, setting up of super-speciality hospitals for treatment and prevention of the deadly disease in the affected villages all over India.

(i) Write the values shown by

(a) Dr. Satpal

(b) NHRC

(ii) What type of analgesics are chiefly used for the relief of pains of terminal cancer ?

(iii) Give an example of artificial sweetener that could have been recommended to diabetic patients.

Question 27:

Define the following terms :

(i) Nucleotide

(ii) Anomers

(iii) Essential amino acids

Question 28:

Calculate ∆rGº for the reaction
Mg(s) + Cu2+ (aq) → Mg2+ (aq) + Cu(s)
Given : Eºcell = + 2.71 V, 1 F = 96500 C mol-1.

Question 29:

What are emulsions ? What are their different types ? Give one example of each type

Question 30:

Given reasons for the following :

(i) (CH3)3 P = O exists but (CH3)3N = O does not.

(ii) Oxygen has less electron enthalpy with negative sign than sulphur.

(iii) H3PO2 is a stronger reducing agent than H3PO3.

Question 31:

(i) Name the method used for the refining of titanium

(ii) What is the role of Zn in the extraction of silver ?

(iii) Reduction of metal oxide to metal becomes easier if the metal obtained is in liquid state. Why?

Question 32:

  1. E0 value for the Mn3+/Mn2+ couple is positive (+1.5 V) whereas that of Cr3+/Cr2+ is negative (– 0.4 V). Why ?
  2. Transition metals form coloured compounds. Why ?
  3. Complete the following equation :
    2 MnO4− +16H+ + 5C2O42− →

Question 33:

(i) What type of isomerism is shown by [CO(NH3)5ONO]Cl2 ?

(ii) On the basis of crystal field theory, write the electronic configuration for d4 ion if ∆0< P

(iii) Write the hybridization and shape of [Fe(CN)6]3– (Atomic number of Fe = 26)

Question 34:

Write the names and structures of the monomers of the following polymers :

(i) Nylon-6,6

(ii) Bakelite

(iii) Polystyrene

Question 35:

(i) Which one of the following is a disaccharide : Starch, maltose, fructose, glucose

(ii) What is the difference between acidic amino acid and basic amino acid?

(iii) Write the name of the linkage joining two nucleotides.

Question 36:

Vapour pressure of water at 20ºC is 17.5 mm Hg. Calculate the vapour pressure of water at 20ºC when 15 g of glucose (Molar mass = 180 g mol-1) is dissolved in 150 g of water.

Question 37:

Examine the given defective crystal :

X+ Y– X+ Y– X+

Y– X+ Y– X+ Y–

X+ Y– X+ e– X+

Y– X+ Y– X+ Y–

Answer the following questions :

(i) Is the above defect stoichiometric or non-stoichiometric?

(ii) Write the term used for the electron occupied site.

(iii) Give an example of the compound which shows this type of defect.

Question 38:

How do you convert the following :

(i) Prop-1-ene to Propan-2-ol

(ii) Bromobenzene to 2-bromoacetophenone

(iii) 2-bromobutane to But-2-ene

What happens when

(i) Ethyl chloride is treated with NaI in the presence of acetone,

(ii) Chlorobenzene is treated with Na metal in the presence of dry ether,

(iii) Is methyl chloride treated with KNO2?

Write chemical equations in support of your answer.

Question 39:

Give reasons for the following :

(i) p-nitrophenol is more acidic than p-methyl phenol.

(ii) Bond length of C – O bond in phenol is shorter than that in methanol.
(iii) (CH3)3C – Br on reaction with sodium methoxide (Na+ – OCH3) gives alkene as the main product and not an ether.

Question 40:

Calculate  Eocell and ∆rGo for the following reaction at 25ºC :

A2+ + B+ → A3+ + B

Given : KC = 1010, 1 F = 96500 C mol-1

Question 41:

Define adsorption with an example. Why is adsorption exothermic in nature? Write the types of adsorption based on the nature of forces between adsorbate and adsorbent.


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