CBSE Sample Paper XII Chemistry
CBSE SAMPLE PAPER
TIME: 3 HOURS MAX. MARKS: 70
- i. All questions are compulsory.
- ii. Questions 1 to 5 are very short answer type carrying 1 mark each. Answer them in one sentence each.
- iii. Questions 6 to 12 are short answer type carrying 2 marks each. Answer each of them in about 30 words.
- iv. Questions 13 to 24 are also short answer type carrying 3 marks each. Answer each of them in about 40 words.
- v. Questions 25,26&27 are long answer type carrying 5 marks each. Answer each of them in about 70 words.
- Calculators are not permitted. Use log tables if necessary.
- Why is solubility of O2 in water decreases with increase of temperature?
- Rate constant of forward reaction measured at 298K is 2.3 X 10-4 S-1. Find the
rate constant for the reverse reaction
- Write IUPAC name of the compound:
CH3 –CH –CH2 –COO CH2-CH3
- How are amines purified from non-basic impurities?
- A 1 molal aqueous solution of glucose has lower boiling point than 1 molal aqueous
solution of common salt.
- How is hydrogen sulphide prepared in the laboratory? Write only equation. Also name the apparatus used. Arrange the hydrides of group 16 in the increasing order of acidity.
- (a) What is isoelectric point of an amino acid?
(b) Write chemical equation to show the formation of peptide linkage-Gly-Ala.
- (a) Write the electrode reactions of the H2—O2 fuel cell.
(b) How many Faradays of charge are needed to reduce one mole of Manganate ion
to Permanganate ion?
- Show the shape of bonding and antibonding molecular orbitals formed by combination of (a) two s orbitals
(b) two p orbitals (side to side)
- What are co-polymers and homo-polymers? Give one example for each kind.
- Consider the molecule: HOOCCHBrCH2CHBrCOOH
(a) Draw any enantiomer pairs (b) Any diastereomeric pairs (c) A meso form.
- How will you distinguish the following pairs of organic compounds?
1-propanol & 2-methyl 2-propanol
Acetonitrile and nitroethane
- Explain the following terms:
(a) Reversible sols(b) Tyndall Effect (c) Electrodialysis
- (a) A sample of freshly cut wood from a tree contains 10mg of C-14. How much C-14 will remain in the wood sample after 5 x 104 years? t1/2 of C-14 = 5700 years.
(b) Complete the following nuclear reaction:
9Be4(a, n) ——————
- How are lipids classified? Write their functions.
- (a) What happens when zinc sulphide is heated?
(b) In a mixed oxide of metals the oxide ions, O2- forms hcp lattice. The divalent
ions A2+ occupy 1/8 of the tetrahedral voids and the trivalent ions, B3+ ions occupy
1/2 of the octahedral voids. Find formula of the compound.
- (a) Illustrate with a diagram the effect of concentration on molar conductivity of an electrolyte.
(b) Calculate the e.m.f of the following cell at 298K:
Cu(s)/Cu2+(0.01M) // Ce4+(0.05M)/ Ce3+(0.02M)
E0Cu2+/Cu = 0.34 V, E0Ce4+/Ce3+ = 1.61 V
State whether the e.m.f will increase or decrease if concentration of Ce4+ is
(a) Calculate the degree of dissociation of 0.01 M NH4OH solution when its molar
conductivity is 9.4 W cm2 mol–-1. It is given that the limiting molar conductivities of
NaCl, NH4 OH and NaOH are 126, 130 and 217 W cm2 mol-1 respectively.
- (a) Explain how [PtCl2 (NH3)2] and [Pt(NH3)6]Cl2 will differ in their electrolytic conductivity. Give the state of hybridization of Pt in these compounds.
(b) Though CO is a weak Lewis base yet it forms a number of stable metal cabonyls.Explain.
- (a)What are the advantages of liquid propellants over solid propellants?
(b) Name two examples of antiseptic dyes.
(c) Write one example each of cationic and anionic detergents.
- (a) Give reasons:
(i) H2+ ion is more stable than He2+ ion.
(ii)NF3 and BF3 are not isostructural.
(b) The sodium flame test has a characteristic yellow colour due to emission of wavelength 589 nm. What is
the mass equivalence of one photon of this wavelength?
- Poly ethylene oxide is a synthetic polymer whose formula is HO (CH2CH2O)nH,
where “n” is a large integer. You prepare a sample of this polymer for which n
=180. Calculate the freezing point depression and the osmotic pressure at 293K of a
solution of 150mg of the polymer in 5.0ml of water and comment on the utility of
the two results in characterizing the polymer.
Kf for water=1.86 Kkgmol-1
R=0.082LAtmK-1mol-1. Volume of polyethylene oxide solution = 5.1 ml.
- (a) Calculate the Gibbs energy change and equilibrium constant for the following reaction at 298 K.
SO2 (g) + 2 H2S (g) ———————–à 3 S(s) + 2 H2O (l)
Df G of SO2 = -300.19 KJ/mol, Df G of H2S = -33.56 KJ/mol,
Df G of H2O = -237.13 KJ/mol. R= 8.314 JK-1mol-1.
(b) Write the most favourable circumstances for a spontaneous change.
- The following rare data were obtained at 303 K for the following reaction:
2A + B ———————– C + D
|Experiment|| | A ||
| | B ||
| Initial rate of formation of D|
|5.0 x 10-36.0 x 10-2|
2.4 x 10-1
2.0 x 10-2
What is the rate law? Find the rate of the reaction when | A | =0.5 mol L-1 &
| B | = 0.2 mol L-1.
- (a)Account for the following:
(i)o-Nitro phenol is steam volatile while p-nitro phenol is not.
(ii) An aqueous solution of methylamine reacts with ferric chloride to obtain
brown precipitate of ferric hydroxide.
(b) Write an example of Hoffmann bromamide reaction.
- (a) Name the chief ore of tin. Explain the process of extraction of tin from this ore.
(b) Account for the following:
(a)Among the noble gases , only xenon is known to form chemical compounds.
(b)Ionization energy of Gallium is less than that of aluminium.
(b) Complete and balance the following equation:
XeF6 + H2O ——————-à
(a) Draw the molecular shape of: (i) XeF4 (ii) Peroxomonosulphuric acid
(b) Define catenation and illustrate it with reference to sulphur chemistry.
(c) Write chemical equations for the commercial preparation of HI
- (a) For some of the first row transition elements the Eo values are:
Element V Cr Mn Fe Co Ni Cu
Eo (M2+/M) -1.18 -0.91 -1.18 -0.44 -0.28 -0.25 +0.34
`Give suitable explanation for the irregular trend in these values.
(b) Give reasons for the following features of transition metal chemistry:
(i)Transition metals exhibit higher oxidation state only in their oxides and fluorides.
(ii)Transition metals have high enthalpy of atomization.
(iii)The ionic radii of tripositive ions of lanthanide elements show a steady decrease
from La3+ to Lu3+.
(a) Explain the preparation of potassium permanganate from pyrolusite ore.
(b) How does potassium dichromate react with acidified oxalic acid solution? Write
(c) Explain with suitable example the use of a transition metal as a catalyst.
- An organic compound ‘A” having molecular formula C7H8O, does not react
with sodium metal. When A is treated with HI, two compounds B and C are
formed. Compound B reacts with sodium metal and also forms salt with NaOH. B
can be brominated and the major product contains three Br atoms. Compound C
containing iodine reacts with Mg in dry ether to form Grignard reagent. The
Grignard Reagent reacts with CO2 followed by acid hydrolysis to form acetic acid.
Identify A, B & C. Show the reactions involved.
(b) How are the following distinguished?
(i)Ethanoyl chloride & Ethanoic acid (ii) Nitrobenzene and benzonitrile
(a) Write the mechanism of a reaction between a carboxylic acid and an alcohol in
(b)Give comparative account of the following towards nucleophiles:
HCHO, CH3CHO, CH3COCH3, CH3COOH
(b)Identify the compounds and reagents:
(A) NaOH/Br2à (B) CHCl3/ KOH/ Heat à (C) (D) à CH3 NH CH3