Important 2 Marks Questions for CBSE 12th Chemistry Exam

 

Question 1:

An aqueous solution of sodium chloride freezes below 273 K. Explain the lowering in freezing points of water with the help of a suitable diagram.

Question 2:

The conductivity of 0.001 M acetic acid is 4 x 10-5 S/cm. Calculate the dissociation constant of acetic acid, if molar conductivity at infinite dilution for acetic acid is 390 S cm2/mol.

Question 3:

The standard electrode potential for Daniell cell is 1.1 V. Calculate the standard Gibbs energy for the cell reaction. (F = 96500 C mol-1)

Question 4:

Explain the following:

  1. Same substance can act both as colloids and crystalloids
  2. Artificial rain is caused by spraying salt over clouds.

Question 5:

How are the following colloidal solutions prepared?

  1. Sulphur in water
  2. Gold in water

Question 6:

Give reasons for the following

  1. Alumina is dissolved in cryolite for electrolysis instead of being electrolyzed directly.
  2. Zinc oxide can be reduced to metal by heating with carbon but Cr2O3 cannot be reduced by heating with carbon.

Question 7:

Explain the following:

  1. NO2 readily forms a dimer.
  2. BiCl3 is more stable than BiCl5.

Question 8:

What is Lanthanoid contraction? What are its two consequences?

Question 9:

Explain the following:

  1. Gabriel Phthalimide reaction
  2. Coupling reaction

Question 10:

Give medical test to distinguish between the following pairs of compounds.

  1. Aniline and Ethylamine
  2. Ethylamine and Dimethylamine

Question 11:

Explain the following terms with suitable examples:

  1. Cationic detergents
  2. Anionic detergents

Question 12:

An element occurs in bcc structure. It has a cell edge length of 250 pm. Calculate the molar mass if its density is 8.0 g cm-3. ALso calculate the radius of an atom of this element.

Question 13:

Calculate the number of unit cells in 8·1 g of aluminium if it crystallizes in a face-centred cubic (f.c.c.) structure. (Atomic mass of Al = 27 g mol-1) 

Question 14:

  1. Arrange the following compounds in the increasing order of their acid strength :
    p-cresol, p-nitrophenol, phenol
  2. Write the mechanism (using curved arrow notation) of the following reaction:
    \(CH_2=CH_2 \overset{H_3O^+}{\rightarrow} Ch_3=CH^+_2+H_2O\)

Question 15:

Write the structures of the products when Butan-2-ol reacts with the following :

  1. CrO3
  2. SOCl2

Question 16:

Draw the structures of the following :

  1. H2SO3
  2. HClO3

Question 17:

Write the name of the cell which is generally used in hearing aids. Write

the reactions taking place at the anode and the cathode of this cell.

Question 18:

Using IUPAC norms write the formula for the following :

(a) Sodium dicyanidoaurate(I)

(b) Tetraamminechloridonitrito-N-platinum(IV) sulphate

Question 19:

Write the name of the cell which is generally used in hearing aids. Write the reactions taking place at the anode and the cathode of this cell.

Question 20:

Using IUPAC norms write the formulae for the following : [1 + 1 = 2]

  1. Sodium dicyanidoaurate (I)
  2. Tetraamminechloridonitrito-N-plantinum(IV) sulphate

Question 21:

(i) Write the colligative property which is used to find the molecular mass of macromolecules.

(ii) In non-ideal solution, what type of deviation shows the formation of minimum boiling azeotropes ?

Question 22:

Write the structures of the following:

(i) (HPO3)3

(ii) XeF4

Question 23:

When a coordination compound NiCl2 · 6H2O is mixed with AgNO3, 2 moles of AgCl are precipitated per mole of the compound. Write:

(i) Structural formula of the complex

(ii) IUPAC name of the complex

Question 24:

For a reaction: 2NH3(g) \(\overset{Pt}{\rightarrow}\) N2(g) + 3H2(g)  Rate = k

(i) Write the order and molecularity of this reaction.

(ii) Write the unit of k.

Question 25:

Write the chemical equations involved in the following reactions:

(i) Kolbe’s reaction

(ii) Friedal-Crafts acetylation of anisole

Question 26:

How do you convert:

(i) Phenol to toluene

(ii) Formaldehyde to Ethanol

Question 27:

Why do transition elements show variable oxidation states ? How is the variability in oxidation states of d-block different from that of the p-block elements ?

Question 28:

(i) Write down the IUPAC name of the following complex :  [Pt(NH3)(H2O)Cl2]

(ii) Write the formula for the following complex : tris(ethane-1,2-diamine)chromium(III) chloride

Question 29:

Calculate the time to deposit 1.5 g of silver at cathode when a current of 1.5 A was passed through the solution of AgNO3. (Molar mass of Ag = 108 g mol-1, 1 F = 96500 C mol-1)

Question 30:

Write the reagents used in the following reactions

  1. C6H5–CO–CH3 \(\overset{?}{\rightarrow}\) C6H5–CH2–CH,
  2. CH3–COOH \(\overset{?}{\rightarrow}\) CH3–COCl

Question 31:

Arrange the following compounds in increasing order of their property as indicated

  1. CH3CHO, C6H5CHO, HCHO (reactivity towards nucleophilic addition reaction)
  2. 2,4-dinitrobenzoic acid, 4-methoxybenzoic acid, 4-nitrobenzoic acid (acidic character)

Question 32:

  1. Why are aquatic species more comfortable in cold water than in warm water ?
  2. What happens when we place the blood cell in saline water solution (hypertonic solution) ? Give reason.

Question 33:

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

  1. Teflon
  2. Buna-N

Question 34:

An element with density 2.8 g cm-3 forms a f.c.c. unit cell with edge length 4 × 10–8 cm. Calculate the molar mass of the element. (Given: NA = 6.022 × 1023 mol-1 )

Question 35:

(i) Write the type of magnetism observed when the magnetic moments are aligned in parallel and antiparallel directions in unequal numbers.

(ii) Which stoichiometric defect decreases the density of the cystal ?

Question 36:

Define the following terms:

  1. Molar conductivity ( Λ m)
  2. Secondary batteries

Question 37:

Write the mechanism of the following reaction:

CH3CH2OH \(\overset{HBr}{\rightarrow}\) CH3CH2Br + H2O

Question 38:

Write the equations involved in the following reactions :

  1. Reimer – Tiemann reaction
  2. Williamson synthesis

Question 39:

Write the principle behind the froth floatation process. What is the role of collectors in this process ?

Question 40:

For a chemical reaction R → P, the variation in the concentration (R) vs. time (t) plot is given as

(i) Predict the order of the reaction.
(ii) What is the slope of the curve ?

Question 41:

(a) Why does presence of excess of lithium makes LiCl crystals pink ?

(b) A solid with cubic crystal is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body-centre. What is the formula of the compound ?

Question 42:

Define thermoplastic and thermosetting polymers. Give one example of each.

Question 43:

What is a biodegradable polymer ? Give an example of a biodegradable aliphatic polyester.

Question 44:

Explain the mechanism of the following reaction CH3 – CH2 – OH \(\rightarrow[443 K]{H^+}\)  CH2 = CH2 + H2O

Question 45:

How are interhalogen compounds formed ? What general compositions can be assigned to them ?

Question 46:

Aluminium crystallizes in an fcc structure. Atomic radius of the metal is 125pm. What is the length of the side of the unit cell of the metal ?

Question 47:

The standard electrode potential (Eº) for Daniel cell is +1.1V. Calculate the ∆Gº for the reaction

Zn(s) + Cu2+(aq) → Zn2+ (aq) + Cu (s) (1F = 96500 C mol-1)

Question 48:

  1. For a reaction A + B → P, the rate law is given by
    r = k[A]1/2[B]2 What is the order of this reaction ?
  2. A first order reaction is found to have a rate constant k = 5.5 × 10–14 s –1. Find the half life of the reaction.

Question 49:

Outline the principles of refining of metals by the following methods 2

(i) Zone refining

(ii) Vapour phase refining

 


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