Board Paper of Class 12-Science 2018 Chemistry (SET 1) - Solutions

• Question 1
  Analysis shows that FeO has a non-stoichiometric composition with formula Fe_0.95O. Give reason. VIEW SOLUTION

• Question 2
  CO (g) and H₂ (g) react to give different products in the presence of different catalysts. Which ability of the catalyst is shown by these reactions? VIEW SOLUTION

• Question 3
  Write the coordination number and oxidation state of Platinum in the complex [Pt(en)₂Cl₂]. VIEW SOLUTION

• Question 4
  Out of chlorobenzene and benzyl chloride, which one gets easily hydrolysed by aqueous NaOH and why? VIEW SOLUTION

• Question 5
  Write the IUPAC name of the following :
  VIEW SOLUTION

• Question 6
  Calculate the freezing point of a solution containing 60 g of glucose (Molar mass = 180 g mol^–1) in 250 g of water.
  (K_f  of water = 1.86 K kg mol^–1) VIEW SOLUTION

• Question 7
  For the reaction
  2N₂O₅ (g) → 4NO₂ (g) + O₂ (g), the rate of formation of NO₂ (g) is 2·8 × 10^–3 M s^–1. Calculate the rate of disappearance of N₂O₅ (g). VIEW SOLUTION

• Question 8
  Among the hydrides of Group-15 elements, which have the
  (a) lowest boiling point?
  (b) maximum basic character?
  (c) highest bond angle?
  (d) maximum reducing character? VIEW SOLUTION

• Question 9
  How do you convert the following?
  (a) Ethanal to Propanone
  (b) Toluene to Benzoic acid

  OR

  Account for the following:
  (a) Aromatic carboxylic acids do not undergo Friedel-Crafts reaction.
  (b) pK_a value of 4-nitrobenzoic acid is lower than that of benzoic acid. VIEW SOLUTION

• Question 10
  Complete and balance the following chemical equations:
  
  (a) ${\mathrm{Fe}}^{2+}+{\mathrm{MnO}}_4^{-}+{\mathrm{H}}^{+} \to$
  
  (b) ${\mathrm{MnO}}_4^{-}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{I}}^{-}\to$ VIEW SOLUTION

• Question 11
  Give reasons for the following:
  
  (a) Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.
  
  (b) Aquatic animals are more comfortable in cold water than in warm water.
  
  (c) Elevation of boiling point of 1 M KCl solution is nearly double than that of 1 M sugar solution. VIEW SOLUTION

• Question 12
  An element 'X' (At. mass = 40 g mol^–1) having f.c.c. structure, has unit cell edge length of 400 pm. Calculate the density of 'X' and the number of unit cells in 4 g of 'X'. (N_A = 6.022 × 10²³ mol^–1) VIEW SOLUTION

• Question 13
  A first order reaction is 50% completed in 40 minutes at 300 K and in 20 minutes at 320 K. Calculate the activation energy of the reaction. (Given : log 2 = 0·3010, log 4 = 0·6021, R = 8·314 JK^–1 mol^–1) VIEW SOLUTION

• Question 14
  What happens when
  (a) a freshly prepared precipitate of Fe(OH)₃ is shaken with a small amount of FeCl₃ solution?
  (b) persistent dialysis of a colloidal solution is carried out?
  (c) an emulsion is centrifuged? VIEW SOLUTION

• Question 15
  Write the chemical reactions involved in the process of extraction of Gold. Explain the role of dilute NaCN and Zn in this process. VIEW SOLUTION

• Question 16
  (a) E° value for Mn³⁺/Mn²⁺ couple is much more positive than that for Fe³⁺/Fe²⁺.
  (b) Iron has higher enthalpy of atomization than that of copper.
  (c) Sc³⁺ is colourless in aqueous solution whereas Ti³⁺ is coloured. VIEW SOLUTION

• Question 17
  (a) Identify the chiral molecule in the following pair :
  
  (b) Write the structure of the product when chlorobenzene is treated with methyl chloride in the presence of sodium metal and dry ether.
  (c) Write the structure of the alkene formed by dehydrohalogenation of 1-bromo-1methylcyclohexane with alcoholic KOH. VIEW SOLUTION

• Question 18
  (A), (B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula C₄H₈O. Isomers (A) and (C) give positive Tollens' test whereas isomer (B) does not give Tollens' test but gives positive Iodoform test. Isomers (A) and (B) on reduction with Zn(Hg)/conc. HCl give the same product (D).
  (a) Write the structures of (A), (B), (C) and (D).
  (b) Out of (A), (B), and (C) isomers, which one is least reactive towards addition of HCN? VIEW SOLUTION

• Question 19
  Write the structures of the main products in the following reactions :
  (i) 
  
  (ii) 
  
  (iii) 
    VIEW SOLUTION

• Question 20
  (a) Why is bithional added to soap?
  (b) What is tincture of iodine? Write its one use.
  (c) Among the following, which one acts as a food preservative?

  Aspartame, Aspirin, Sodium Benzoate, Paracetamol

  VIEW SOLUTION

• Question 21
  Define the following with an example of each:
  (a) Polysaccharides
  (b) Denatured protein
  (c) Essential amino acids

  OR

  
  (a) Write the product when D-glucose reacts with conc. HNO₃.
  (b) Amino acids show amphoteric behaviour. Why?
  (c) Write one difference between α-helix and β-pleated structures of proteins. VIEW SOLUTION

• Question 22
  (a) Write the formula of the following coordination compound: Iron(III) hexacyanoferrate(II)
  
  (b) What type of isomerism is exhibited by the complex [Co(NH₃)₅Cl] SO₄?
  
  (c) Write the hybridisation and number of unpaired electrons in the complex [CoF₆]^3–. (Atomic No. of Co = 27) VIEW SOLUTION

• Question 23
  Shyam went to a grocery shop to purchase some food items. The shopkeeper packed all the items in polythene bags and gave them to Shyam. But Shyam refused to accept the polythene bags and asked the shopkeeper to pack the items in paper bags. He informed the shopkeeper about the heavy penalty imposed by the government for using polythene bags. The shopkeeper promised that he would use paper bags in future in place of polythene bags.
  Answer the following :
  (a) Write the values (at least two) shown by Shyam.
  (b) Write one structural difference between low-density polythene and high-density polythene.
  (c) Why did Shyam refuse to accept the items in polythene bags?
  (d) What is a biodegradable polymer? Give an example. VIEW SOLUTION

• Question 24
  (a) Give reasons :

  (i) H₃PO₃ undergoes disproportionation reaction but H₃PO₄ does not.
  (ii) When Cl₂ reacts with excess of F₂, ClF₃ is formed and not FCl₃.
  (iii) Dioxygen is a gas while Sulphur is a solid at room temperature.

  
  (b) Draw the structures of the following :

  (i) XeF₄
  (ii) HClO₃

   

  OR
   

  (a) When concentrated sulphuric acid was added to an unknown salt present in a test tube a brown gas (A) was evolved. This gas intensified when copper turnings were added to this test tube. On cooling, the gas (A) changed into a colourless solid (B).

   

  (i) Identify (A) and (B).
  (ii) Write the structures of (A) and (B).
  (iii) Why does gas (A) change to solid on cooling?

  
  (b) Arrange the following in the decreasing order of their reducing character :

  HF, HCl, HBr, HI

  
  (c) Complete the following reaction :

  XeF₄ + SbF₅ →

  VIEW SOLUTION

• Question 25
  (a) Write the cell reaction and calculate the e.m.f of the following cell at 298 K:

  Sn (s) | Sn²⁺ (0.004 M) || H⁺ (0.020 M) | H₂ (g) (1 bar) | Pt (s)
  (Given : ${\mathrm{E}}_{{\mathrm{Sn}}^{2+}/\mathrm{Sn}}^0=-0.14 \mathrm{V}$)

  
  (b) Give reasons:

  (i) On the basis of E° values, O₂ gas should be liberated at anode but it is Cl₂ gas which is liberated in the electrolysis of aqueous NaCl.
  (ii) Conductivity of CH₃COOH decreases on dilution.

  
  OR
   

  (a) For the reaction

  $$\begin{gathered} 2\mathrm{AgCl} \left(\mathrm{s}\right)+{\mathrm{H}}_2 \left(\mathrm{g}\right) \left(1 \mathrm{atm}\right) \to 2\mathrm{Ag} \left(\mathrm{s}\right)+2{\mathrm{H}}^{+} \left(0.1 \mathrm{M}\right)+2{\mathrm{Cl}}^{-} \left(0.1 \mathrm{M}\right), \\ ∆\mathrm{G}°=-43600 \mathrm{J} \mathrm{at} 25°\mathrm{C} \end{gathered}$$
  Calculate the e.m.f. of the cell.
  [log 10^–n = – n]
   

  (b) Define fuel cell and write its two advantages. VIEW SOLUTION

• Question 26
  (a) Write the reactions involved in the following:

  (i) Hofmann bromamide degradation reaction
  (ii) Diazotisation
  (iii) Gabriel phthalimide synthesis

  
  (b) Give reason:

  (i) (CH₃)₂NH is more basic than (CH₃)₃N in an aqueous solution.
  (ii) Aromatic diazonium salts are more stable than aliphatic diazonium salts.

  
  OR

  
  (a) Write the structures of the main products of the following reactions:

  
  
  

  
  (b) Given a simple chemical test to distinguish between Aniline and N, N-dimethylaniline.
  
  (c) Arrange the following in the increasing order of their pK_b values:

  C₆H₅NH₂, C₂H₅NH₂, C₆H₅NHCH₃

  VIEW SOLUTION