{"id":86882,"date":"2019-08-20T11:36:15","date_gmt":"2019-08-20T06:06:15","guid":{"rendered":"https:\/\/www.cbselabs.com\/?p=86882"},"modified":"2021-09-18T15:17:57","modified_gmt":"2021-09-18T09:47:57","slug":"cbse-previous-year-question-papers-class-12-chemistry-2012-delhi","status":"publish","type":"post","link":"https:\/\/www.cbselabs.com\/cbse-previous-year-question-papers-class-12-chemistry-2012-delhi\/","title":{"rendered":"CBSE Previous Year Question Papers Class 12 Chemistry 2012 Delhi"},"content":{"rendered":"

CBSE Previous Year Question Papers Class 12 Chemistry 2012 Delhi<\/h2>\n

Time allowed: 3 hours
\nMaximum Marks: 70<\/p>\n

CBSE Previous Year Question Papers Class 12 Chemistry 2012 Delhi Set I<\/h3>\n

Question 1.
\nWhat is meant by ‘doping’ in a semiconductor? [1]<\/p>\n

Question 2.
\nWhat is the role of graphite in the electrometallurgy of aluminium? [1]
\nAnswer:
\nGraphite is used as anode and useful for the reduction of Al2<\/sub>O3<\/sub> into Al.<\/p>\n

Question 3.
\nWhich one of PCl–<\/sup>4<\/sub> and PCl+<\/sup>4<\/sub>\u00a0is not likely to exist and why? [1]<\/p>\n

Question 4.
\nGive the IUPAC name of the following compound.
\n\"CBSE
\nAnswer:
\n3-Bromo-2-methylpropene<\/p>\n

Question 5.
\nDraw the structural formula of a 2-methyl-propan-2ol molecule. [1]
\nAnswer:
\n\"CBSE<\/p>\n

Question 6.
\nArrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions:
\nethanol, propanal, propanone, butanone.
\nAnswer:
\nButanone < Propanone < Proponal < Ethanol<\/p>\n

Question 7.
\nArrange the following in the decreasing order of their basic strength in aqueous solutions: [1]
\nCH3<\/sub>NH2<\/sub>, (CH3<\/sub>)2<\/sub>NH, (CH3<\/sub>)3<\/sub>N and NH3<\/sub>
\nAnswer:
\n(CH3<\/sub>)2<\/sub>NH > CH3<\/sub>NH2<\/sub> > (CH3<\/sub>)3<\/sub>N > NH3<\/sub><\/p>\n

Question 8.
\nDefine the term, ‘homopolymerisation’ giving an example. [1]
\nAnswer:
\nPolymerisation involving the presence of only one monomer is called homopolymerisation.
\ne.g., polyethene is a homopolymer
\n\"CBSE<\/p>\n

Question 9.
\nA 1.00 molal aqueous solution of trichloroacetic acid (CCl3<\/sub>COOH) is heated to its boiling point. The solution has a boiling point of 100.18 \u00b0C. Determine the Van’t Hoff factor for trichloroacetic acid. (Kb<\/sub> for water = 0.512 K kg mol-1<\/sup>) [2]
\nOR
\nDefine the following terms:
\n(i) Mole fraction
\n(ii) Isotonic solutions
\n(iii) Van’t Hoff factor
\n(iv) Ideal solution
\nAnswer:
\n\"CBSE
\n(i) The ratio of the number of moles of a component in a mixture to the total number of moles in the mixture is called the mole fraction of that component. It is denoted by ‘x’.<\/p>\n

(ii) Two solutions having the same molar concentration are said to be isotonic solutions. e.g., All intravenous injections must be isotonic with body fluids.<\/p>\n

(iii) The ratio of observed colligative property to the calculated colligative property is called the Van’t Hoff factor. It is denoted by ‘i’.<\/p>\n

(iv) Solutions that follow Raoult’s law at all temperatures and concentrations are called ideal solutions.<\/p>\n

Question 10.
\nWhat do you understand by the ‘order of a reaction’? Identify the reaction order from each of the following units of reaction rate constant: [2]<\/p>\n

    \n
  1. L-1<\/sup> mol s-1<\/sup><\/li>\n
  2. L mol-1<\/sup> s-1<\/sup><\/li>\n<\/ol>\n

    Answer:
    \nThe sum of the powers to which the concentration of reactants are raised in the rate law expression is called the order of a reaction.<\/p>\n

      \n
    1. Zero-order reaction<\/li>\n
    2. Second-order reaction.<\/li>\n<\/ol>\n

      Question 11.
      \nName the two groups into which the phenomenon of catalysis can be divided. Give an example of each group with the chemical equation involved. [2]
      \nAnswer:
      \nCatalysis can be positive, that is, it increases the rate of the reaction or negative i.e., decreases the rate of reaction. Depending on the phase of the reactants and the catalyst, catalysis can be:
      \n(i) Homogenous Catalysis: The reactants and catalyst are in the same phase.
      \n\"CBSE<\/p>\n

      (ii) Heterogeneous catalysis: The reactants and catalyst are in a different phase.
      \n\"CBSE<\/p>\n

      Question 12.
      \nWhat is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out. [2]
      \nAnswer:
      \nThe process of setting of colloidal particles is called coagulation of sol. Methods of coagulation are:
      \n(i) Electrophoresis: In this process, the colloidal particles move towards oppositely charged electrodes and get discharged and precipitated.<\/p>\n

      (ii) Mixing two Oppositely Charged Sols: Equal proportions of oppositely charged sols are mixed, they get neutralized and get precipitated.<\/p>\n

      (iii) Dialysis: Electrolytes are removed from the sol and colloid becomes unstable and gets coagulated.<\/p>\n

      Question 13.
      \nDescribe the principle involved in each of the following processes. [2]
      \n(i) Mond process for refining of Nickel.
      \n(ii) Columnchfomatographyforpurificationofrare elements.
      \nAnswer:
      \n(i) Nickel combined with carbon monoxide to form a volatile complex which is further decomposed to get back a pure nickel.
      \n\"CBSE<\/p>\n

      (ii) The basic principle involved in column chromatography is that different elements present in a mixture are adsorbed on adsorbent at different extents.<\/p>\n

      Question 14.
      \nExplain the following giving an appropriate reason in each case. [2]
      \n(i) O2<\/sub> and F2<\/sub> both stabilize higher oxidation states of metals but O2<\/sub> exceeds F2<\/sub> in doing so.
      \n(ii) Structures of xenon fluorides cannot be explained by Valence Bond approach.
      \nAnswer:
      \n(i) Due to the difference in the atomic size of oxygen and fluorine and the property of oxygen to form multiple bonds with metals, O2<\/sub> exceeds F2<\/sub>, stabilize higher oxidation states.<\/p>\n

      (ii) For explaining the structures of xenon fluorides, we need to use VSEPR and hybridization theories because, in VBT, covalent bonds are formed by overlapping of a half-filled atomic orbital. But xenon has fully filled electronic configuration.<\/p>\n

      Question 15.
      \nComplete the following chemical equations: [2]
      \n\"CBSE
      \nAnswer:
      \n\"CBSE<\/p>\n

      Question 16.
      \nWhat is meant by
      \n(i) peptide linkage
      \n(ii) biocatalysts? [2]
      \nAnswer:
      \n(i) Peptides linkage is the amide bond that helps to connect amino acids to form proteins. It is formed between -COOH and -NH2<\/sub> group of two amino acids with the loss of water molecule.<\/p>\n

      (ii) Biocatalysts are enzymes that catalyse the biochemical reactions in the bodies of living organisms, e.g., Amylase.<\/p>\n

      Question 17.
      \nWrite any two reactions of glucose which cannot be explained by the open chain structure of the glucose molecule. [2]
      \nAnswer:
      \nTwo reactions which can’t be explained by the open chain structure of glucose are:<\/p>\n