Solved question paper for Chemistry Mar-2017 (PSEB Class 12th)

Solved Question Paper

Chemistry Mar-2017

PSEB • Class 12th • 1st • Mar-2017

Chemistry previous year question papers on BRpaper help students looking for PSEB 12th Class Question Papers to browse Chemistry papers for board exam practice and revision. This subject section is useful for finding PSEB 12th Chemistry old question papers, PYQ-style papers, and related exam-preparation material where available, so students can study the question format, recurring topics, and marks pattern used in the Punjab board exam. If you are preparing for the Punjab School Education Board Class 12 Chemistry paper, this page can help you compare past question styles with sample paper and model paper trends, and focus on important questions more confidently. BRpaper is not the official website of Punjab School Education Board or any institution, and it does not publish official notices or academic updates.

Solved Questions

Solved
  1. Under what conditions the van't Hoff factor is greater than one ?

    Very Short Answer Mar-2017 • PSEB Class 12th

    i = observed value of CP / calculated the value of CP    (when i  > 1)

    when the solute undergoes dissociation in the soln

  2. Define order of reaction. 

    Very Short Answer Mar-2017 • PSEB Class 12th

    Rate = K[A]P  [B]q  

    Order of R x n = p + q

  3. Write down IUPAC name of  CH3-NH-CH3

    Very Short Answer Mar-2017 • PSEB Class 12th

    Amine N-methyl methen - amine 

  4. Complete the following reaction:- 

    Very Short Answer Mar-2017 • PSEB Class 12th

  5. Write down an isomer of C2H3OH.

    Very Short Answer Mar-2017 • PSEB Class 12th

    The isomer of ethanol (CH3-CH2-OH) is diethyl ether. 
    (CH3-O-CH3) this is the functional isomer of ethanol.

  6. What are food preservatives

    Very Short Answer Mar-2017 • PSEB Class 12th

    Food preservatives are chemicals that prevent food from going bad by preventing microbial growth.

     

  7. What are antacids ?

    Very Short Answer Mar-2017 • PSEB Class 12th

    Antacids are the drugs used to prevent the overproduction acid in the stomach. 

  8. What are disaccharides?

    Very Short Answer Mar-2017 • PSEB Class 12th

    Disaccharides are sugars that from when two simple sugars. ie. monasaccharides combine to from a disaccharides.

  9. The radius of Na+ ion is 95pmand that of Cl- ion is 181 pm pridict whether the Co-ordination number of Na+ ion is 6 or 4

    Short Answer Mar-2017 • PSEB Class 12th

    Radius ratio = radius of cation / radius of anion      =        95 / 181 

    Radius of cation = 95 pm,  Radius of anion = 181 pm   =  0.524

    we will check the value of co-ordination no = 0.524 lies b/w 0.732 - 0.414 

    Therefore the coordination number is 6.

  10. A first order reaction is 20% complete in 20 minutes. Calculate the time it will take the reaction to complete 80%

    Short Answer Mar-2017 • PSEB Class 12th

  11. what is gravity separation method for concentration of or eg ?

    Short Answer Mar-2017 • PSEB Class 12th

    This method of concentration of the ore is based upon the difference in specific gravities of the metallic ore and gangue particles. Generally, metal ores are heavier than the gangue associated with them.

  12. Write down difference between terylence fiberes and Buna-s-rubber (elastromes).

    Short Answer Mar-2017 • PSEB Class 12th

     

    Terylene

    Buna-s rubber

    Terylene is a fibre

    Buna-s is an elastomere

    Terylene has stronger intermolecular forces of attraction.

    Buna-s rubber has weakest intermolecular forces.

    Thread forming solids which possess high tensile strength and high modulus.

    Weak binding forces permit the polymer to be stretched.

     

  13. Express linkage isomerism in [Co (NH3) NO2] CL2

    Short Answer Mar-2017 • PSEB Class 12th

    Linkage isomerism:- This type of isomerism is found in complexes that contain ambidentate ligands.

  14. Write down any two Difference between nucleoside and necleotide

    Short Answer Mar-2017 • PSEB Class 12th

    A nucleoside is formed is formed by attachment of a base to the 1st position of a sugar ie Nucleoside = sugar + Base
    Nucleotides on the other hand, all the three basic components of nucleic acids are present in nucleotide.
    Nucleotide = Sugar + Base + Phosphoric acid

  15. Write down carbylamine reation 

    Short Answer Mar-2017 • PSEB Class 12th

    A primary amine (both aliphatic and aromatic) when warmed with chloroform and alcoholic potassium hydroxide gives isocyanides. This is called a Carbylamine reaction.
    R-NH2 + CHCl3 + 3KOH → RNC (Carbylamine) + 3KCl + 3H20.

  16. Write down reactions involved in preparation of Potassium dichromate from chromite ore?

    Short Answer Mar-2017 • PSEB Class 12th

    I.    2FeCr2O4  + 8NaOH + 7/2O2→ 4Na2Cr2O4  + Fe2O3 + 4H2O.
                               (Chromite)                    (Sodium Chromate)
    II.    2FeCr2O4 + H3SO4 → Na2Cr2O4 + Na2SO4 + H2O
              (Sodium chromate)      (Sodium dichromate)
    III.    Na2Cr2O7 + 2KCl → K2Cr2O7 + 2NaCl
          (Sodium dichromate)       (potassium dichromate).

  17. Determine the type of cubic lattice to which the crystal of the element indicated here belongs It has an edge length of 290 pm and a density 80 g cm-3 Atomic mass of element = 56amu

    Long Answer Mar-2017 • PSEB Class 12th

    It belongs to crystal lattice.

  18. 18 (i) Prove that osmotic pressure is colligative property.

    (ii) Calculate the molar concentration of urea solution if it exerts an osmotic pressure of  2.45 atmosphere at 300K. [R= 0.0821 Latm.mol-1 K-1 ]

    Long Answer Mar-2017 • PSEB Class 12th

    (i) Collative property depends only on the number of dissolve parties in soln& not on their identity. Both solhave the same freezing point, boiling point, vapour pressure & osmotic pressure because that collagative property of a solonly depend on the number of dissolved particles 

    => Colligative property is proportional to the molarity & temperature 

    (pi v = nRT) the basic equation for ideal sol   or 

    (pi = CRT)  where  ({nover v } = v)

    (pi) is osmotic pressure,

    C is concentration, V is volume, T is absolute Temperature, n is the number of males of the solute of the solution.

    (ii) (Pi = {nrt over v}) 

    Osmotic pressure = 2.45 atm

    T = 300 K

    R = gas constant = 0. 0821L

    so n/v is molar concentration that is ({n over v} = { pi over rt})

    molar concentration = 2.45 / (300 * 0.0821)

      = 2.45 / 24. 63 

      = 0. 099 mol 

  19. What is electro chemical theory of rusting of iron and give two methods of prevention of rusting of iron?

    Long Answer Mar-2017 • PSEB Class 12th

    Electrochemical theory of rusting of iron and two methods of prevention of rusting of iron.

    At  Anode: Fe(s) undergoes oxidation to release electrons.

    Fe(s) → Fe2+(aq) + 2e-

    At Cathode: O2(g) + 4H(aq) + 4e-1  →  2H2O(l)

    Electrons released at the anode move to another metal and reduce oxygen in presence of H+. It is available from H2CO3 formed from the dissolution of CO2 from air into water. H+ in water may also be available through dissolution of other acidic oxides from the atmosphere.

    RXN Fe(s) + 2H+(aq)  + 1/2O2(g) → Fe2+(aq) + H2O(l)

    Fe2+ is oxidised again to form rust.

    2Fe2+(s)  + 1/2O2(g) + 2H2O(l) → Fe2O3(s) + 4H+(aq)

    (rust)

  20. OR

    19. Write the Nernst equation and calculate the emf of following cell at 298K:-
    Ni/Ni2+ (0.01M) || Cu2+ / Cu (0.01M)
    Given E0 (Cu2+/Cu) = + 0.34V, E0(Ni2+/Ni)= -0.22V

    Long Answer Mar-2017 • PSEB Class 12th

    E0cell = (EC – Ea) =     

    Ec – Ea = 0.34 – (0.22) = 0.56V

    E0cell = 0.56 –      

    = 0.56 –     

    = 0.56 – 0.03 = 0.52  

    Ecell = 0.53V

  21. Define Tyndall effect. Differentiate between electrophoresis and electroosmosis

    Long Answer Mar-2017 • PSEB Class 12th

    Tyndall effect is the phenomenon of scattering of light of colloidal particle and hence the path of the beam becomes visible is called tyndall effect.

    Electrophoresis

    Electroosmosis

    Refers to the movement of colloidal particles under an applied electric field

    Refers to the movement of molecules of the dispersion medium under the influence of electric field where colloidal particles are not allowed to move

  22. (i) Why are interhalogen compounds more reactive than halogens.
          (ii) All the five bonds in PCl5 are not equivalent. Justify.

    Long Answer Mar-2017 • PSEB Class 12th

    (i) Interhalogens are generally more reactive than halogens except fluorine. This is because A-X bonds in interhalogens are weaker than the X-X in dihalogen molecules. Reaction of interhalogens is similar to halogens. Hydrolysis of interhalogen compounds yields halogen acid and oxy-acid.

    (ii) PCl5 has a trigonal bipyramidal structure due to SP3 hybridisation. As a result of this, two Cl atoms lie along axial line along equatorial plane. Hence all atoms which lie along the axis have different bond length than that of Cl atoms lying on the equatorial plane.

    Structure of PCl5

     

     

  23. (i) Phenol has a higher boiling point than toluene. Why?
          (ii) why alcohol easily protonated but phenGtrs'.are not protonated?

    Long Answer Mar-2017 • PSEB Class 12th

    (i) Phenol has a higher boiling point then toluene due to the presence of intermolecular hydrogen bonding in phenols. The formation of hydrogen bonds increases intermolecular forces of attraction among phenol molecules hence the increase in boiling point.

    (ii) In phenol, the lone pair of electrons on oxygen involved in delocalization is not freely available for protonation whereas in alcohols, the electrons on oxygen atom are not delocalized so they are available for protonation.

  24. (i) Write HeIl-Volhard-Zelinslry reaction.  

          (ii) Write cross aldol condensation.

          (iii) Ethanoic acid is weaker acid than benzoic acid. Why ?

    Long Answer Mar-2017 • PSEB Class 12th

    (i) Equation for the reaction Hell-Volhard-Zelinsky reaction:-

    (ii) Equation Goss-Aldol condensation reaction:-

    (iii) Stronger acids have a lower PKa value. Ethanoic acid is a weaker acid than benzoic acid due to presence of a benzene ring in benzoic acid, delocalization of electrons makes it more acidic than ethanoic acid but such stabilisation is not present in ethanoic acid.

  25. (i)Why is H 3PO3 diprotic in nature ? Draw structure.  

    (ii) Why is H2S less acidic than H2Te ?

    (iii) Give hybridization and draw structure of XeF6.

    Long Answer Mar-2017 • PSEB Class 12th

    (i) H3PO3 is dipole in nature because H atoms are attached to oxygen. As a result phosphorus acid is dibasic as it has two P-OH bonds. Similarly, phosphoric acid, H3PO4 is tribasic as it has three P-OH.

    (ii) Acidic character increases, H2Te has less bond dissociation enthalpy than H2S, hence less energy is required to break H2Te bond easily releasing [H+] hence acidity of H2Te is higher whereas H2S has high bond dissociation energy and hence its acidity is less.

    (iii) Hybridisation of this molecule is SP3d3. According to VSEPR theory, this molecule has seven electron pairs. It has octahedral structure.

  26. OR

    24. (i) How is nitric acid manufactured by Qstwald process ?

    (ii) Write down there action of Ozone with blacklead sulphide.

    (iii) Draw structure of IF .

    Long Answer Mar-2017 • PSEB Class 12th
  27. (i) Scandium (z = 21) is a transition element but zinc (z = 30) is not. Explain.

    (ii) Calculate equivalent weight of KMnO4 in acidic medium.

    (iii) What do you mean by Lanthanoid contraction? 

    Long Answer Mar-2017 • PSEB Class 12th

    (i) Transition metals are elements that form at least stable where the compound has an incomplete d subshell. Zinc is not a transition metal because it forms only Zn2+ ions with all the 3d-electrons present. The valence configuration should have at least unpaired electrons.

    (ii) Eq.wt =  = 31.6g per equivalent.

    So equivalent weight =

    = = 29gm/equivalent.

    As Mn7+in KMNO4 changes to Mn2+ in acidic medium, equivalent weight becomes

    (iii) Lanthanoid contractions is greater than expected decrease in ionic radii of the elements in the lanthanoid series, from atomic number 57, lanthanum to 71, IU resulting in smaller atomic radii.

  28. OR

    25. (i) Write down any three differences between Lanthanoids and Actinoids

    (ii) The melting and boiling points of Zy, Cd and Hg are low. Why? 

    (iii) Draw the structure of manganate ion.

    Long Answer Mar-2017 • PSEB Class 12th

    (i)

    Lanthanoids

    Actinoids

    They are generally non-radioactive

    They are radioactive 

    Most of their ions are colourless.

    They have coloured ions

    Less tendency

    High tendency

     

    (ii) Zinc has relatively low melting and boiling point. Cadmium (CD) is similar to Zinc in many aspects but forms complex compound. Mercury (Hg) has a low melting point for d-block element.

    (iii) Structure of magnetic ion:-

  29. Write the following reactions :

    (i) Williamson' s synthesis

    (ii) Mendius reaction

    (iii) Friedel Craft' s Alkylation

    (iv) Haloform reaction

    (v) Gutterman reaction

    Long Answer Mar-2017 • PSEB Class 12th

    (i) William synthesis

    R―X + R  ―  Ö Na     ―>      R―Ö―R  +  NaX

    (alkythalide)(sodium alkoxide)       (ether)

    (ii) Mendius Rxn

    RCN              +           2H2       →    RCH2NH2

    (alkylcyanide)    (hydrogen) 

    (iii) Fredal Craft Alkylation:- 

     

    (iv) Halo form Rxn:- 

    (v) Carbylamine Rxn:-

    RNH2    +   CHCl3  + 3KOH(alc)  ―>  RNC  +  3KCl  + 3H2O

     

    (vi) Gatterman Rxn:- 

     

  30. OR

    26. (i) Hydrogen atom of chloroform is acidic. Explain.

    (ii) Why is dehydrohalogenation reaction in haloalkanes termed as Beta-elimination?

    Long Answer Mar-2017 • PSEB Class 12th

    (i) Hydrogen atom of chloroform is acidic because it creates a positive charge, partial deficiency of electron with carbon, more electronegativity than H atom, hence starts to pull electrons from H.

    The presence of 3Cl aggravates the pull resulting into loss of H+. It also accepts the lone pair of electrons left by H termed back donation into its empty 3d shell thereby stabilising the negative charge on carbon.

    Structure of CHCl3

    (ii) Alkenes are generally prepared through B-elimination reaction, in which two atoms on the adjacent carbon atoms are removed in formation of a double bond. Preparations include dehydration of alcohols, dehydrohalogenation of alkyl halides and dehalogenation of alkanes.

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01 How can I find PSEB 12th Chemistry previous year question papers for 1st semester on BRpaper?

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Yes. Students often use previous Chemistry papers on this page to review question style, section flow, recurring topic areas, and the overall structure seen in past Punjab board exams.

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Past papers are often used to spot commonly tested areas in Chemistry, such as numericals and questions from organic, inorganic, or physical chemistry. They are helpful for setting revision priorities, not for guaranteeing exact repeats.

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Start by reviewing a few past Chemistry papers to understand the question pattern, then revise the chapters that appear frequently, practice numericals, and use the papers for timed self-testing before the exam.