INDIAN SCHOOL MUSCAT SECOND TERM EXAMINATION SUBJECT :CHEMISTRY

Transcription

1 Roll Number Code Number 4/ INDIAN SCHOOL MUSCAT SECOND TERM EXAMINATION SUBJECT :CHEMISTRY CLASS: XI Answer key Time Allotted: Hrs Max. Marks: (CH ) C + > (CH ) CH + > CH CH + > CH + (1) 1. H O due to small size and higher E.N of oxygen atom forms H- bonding (½ +½) 1. Due to similar electronic configuration. (1) 1 4. It consists of oxidized and reduced form of the same substance taking part in an oxidation and reduction half reaction. (1) 1 5. H O < NH < SO < CO (1) 1 6. i) Number of moles of KCl formed = = 0.01 moles. (1) ii) Volume of Cl produced at STP = = 0.56 L of Cl (1) 7. i) But--yn- 1-ol ii) - Methylhex--ene (1 + 1) 8. If an electron is moving with a velocity of 600 m/s which is accurate upto 0.005%, then calculate the uncertainty in its position. (h = 6.6 x 10-4 Js and mass of electron = 9.1 x 10-1 Kg) ΔV = x 600 = 0.0 m/s 100 Δx x mδv = h 4π Δx = 6.6 x x.14 x 9.1 x 10-1 x 0.0 = 1.9 x 10 - m 9. Zn Zn + + e Ag + + e Ag (½ +½) Page 1 of 6

2 E o = E 0 Cat - E 0 anode = (-0.76) = 1.56 V (½ +½) i) a) Fe (III)O b) HAu(III)Cl 4 (½ +½) ii) No, because the oxidation number of Cr has neither increased nor decreased. (½ +½) 10. i) Na O + H O NaOH (½+ ½) ii) Oxidation state = + and Covalency = 6 (½+ ½) 11. i) A chemical compound always contains exactly the same proportion of elements by mass irrespective of the method of preparation or the source from which it is prepared. (1) ii) Whenever gases combine and are produced in a chemical reaction, they do so in a simple ratio by volume, provided the volumes are measured under the same conditions of temp and pressure. (1) iii) It is defined as the sum of atomic masses of all the elements present in one formula unit of an ionic compound. (1) 1. MnO 4 + 4H + + e MnO + H O Br + H O BrO + 6H + + 6e MnO 4 + Br + H O MnO + BrO + OH 1. i) i) Distillation under reduced pressure. ii) To remove CN ion and S ion ( ) 14. i) At high pressure and low temperature. ii) Atmospheric pressure decreases with increase in altitude. As V α 1/P, size of weather balloon becomes larger. iii) It is the temperature at which a real gas obeys ideal gas laws over a range of pressure. i) a) Dispersion force b) Dipole induced dipole ii) Due to two faulty assumptions of kinetic molecular theory. The volume taken up by the molecules is negligible when compared with the volume of the container. There is no attractive or repulsive force between the molecules. Page of 6

3 iii) P + an V - nb = nrt V 15. i) Electronic configuration of Cr = 1s s p 6 s p 6 4s 1 d 5 The 19th electron lies in the 4s- subshell, n=4, l = 0, m = 0 and s = +1/ i) It is the series of lines produced in the hydrogen spectrum when the excited electrons come down to the second energy level. (1) ii) It is the three dimensional region around the nucleus in an atom in which the probability of finding an electron is maximum. (1) 16. i) a) - Chlorophenol (1) b) 5- Methylhex--enoic acid (1) ii) CH CN sp sp (½ +½) 17. It is defined as the intermixing of atomic orbitals of slightly different energies of an atom to form new set of orbitals of equivalent energies and shapes. (1) C H Unhybridised orbitals p p s s 1 sp hybridized orbital 1s 1s Ground state Exicited state Hybridised state (1) (1) 18. Element % At.mass Moles Mole ratio C H Cl (1) Empirical formula = CH Cl Page of 6

4 n = M.M/ EFM = / 49.5 = M.F = (CH Cl) = C H 4 Cl (1) 19. i) By boiling the bicarbonates the Ca and Mg present in the water decompose into their insoluble carbonates which settle at the bottom of the tank and is later removed by filtration. M(HCO ) MCO + H O + CO (1) ii) Salts in hard water forms an insoluble deposit on the inner side of the boilers (scales). These are poor conductors of heat and also reduce the life of boilers. (1) iii) Rough surfaces cause the decomposition of H O. (1) 0. i) Due to the small size of F, there is inter electronic repulsion in p subshell. (1) ii) Anion is formed by the gain of electrons. Number of electrons increases while the nuclear charge remains the same i.e; same nuclear charge attracts greater number of electrons and hence size of an anion is greater. (1) iii) Nitrogen stable half-filled configuration, therefore more is the ionization enthalpy (1) 1. i) d = PM/ RT d N = d oxide P N M N = P o M o RT RT P N M N = P o M o 5 x 8 = x M o M o = 70g i) PV = nrt V = = x V = 4.98 L. i) By treating CO of syn gas mixture with steam in the presence of iron chromate as catalyst. ii) CO + H O CO + H a) PbS + 4H O PbSO 4 + 4H O b) Ca(HCO ) + Ca(OH) CaCO + H O. i) It will save our environment. They are concerned with the environment. ii) Chlorofluoro carbons iii) Depletes ozone layer and UV rays reach earth which may cause skin cancer. iv) CF Cl + hν = Cl + CClF Cl + O ClO + O 4 Page 4 of 6

5 ClO + O Cl + O ( ) 4. i) In the ground state of an atom the electrons are filled in various orbitals in their increasing order of their energies. (1) ii) Orbitals of a given sub-shell having the same energy (1) iii) λ = h / mv v = h / λm 5 = 6.6 x 10-4 = x 10 8 m/s (½+ ½ + ½) 4.8 x 10-1 x 9.1 x 10-1 K.E = ½ mv = ½ x 9.1 x 10-1 x (1.516 x 10 8 ) = 1.05 x J (½+ ½ + ½) i) Pairing up of e - s in the orbital of a given sub- shell takes place only after each orbital is singly occupied with electron of same spin. (1) ii) It gives information about the orientation of orbitals in space. (1) iii) E 5 =.17 x =.17 x = 8.68 x 10 0 J n 5 (½ + ½ + ½) iv) r n = x n nm. r n = x 5 = 1. nm (½+ ½) 5. i) a) The combining atomic orbitals must have same or nearly same energy. b) The combining atomic orbitals must have same symmetry. c) The combining atomic orbitals must overlap to the maximum extent. (1½) ii) M.O configuration of Ne = (σ1s ) (σ*1s ) (σs ) (σ*s ) (σpz ) (πpx = πpy ) (π*px = π*py ) (σ*pz ) Bond order of Ne = ½ (10-10) = 0 5 Since B.O = 0, it does not exist. iii) T shape/ structure B.P =, L.P = i) a) Should be bonded to a highly electronegative atom. b) Electronegative atom should be small in size. (½ +½) ii) Sigma bond is formed by the axial overlapping of atomic orbitals which is greater in comparison to the side ways overlapping. (1) Page 5 of 6

6 iii) iv) In NH, the d.p of the N-H bonds are in the same direction as that of the lone pair of electrons. But in NF, the d.p of the N-F bonds are in the direction opposite to that of the l.p. (1) It is the difference between the no: of valence electrons in an isolated atom and the no: of electrons assigned to that atom in Lewis structure. (1) Helps in selecting the lowest energy structure from the various lewis structures and thus predicts the stability (1) 6. i) Steam distillation. o-nitro phenol being steam volatile distills (1) ii) 5 iii) It is a permanent effect arising due to the shifting of sigma electrons through a carbon chain in presence of an atom or group of atom (having different electronegativity) attached to a carbon chain. (1) Its effect is least in C C bond. i) O NCH CH O is more stable because NO gp has -I effect and tends to disperse the negative charge on the oxygen atom (1) ii) Overlap between empty p-orbital / unsaturated system with adjacent C H σ bond. (1) Isopropyl carbocation is more stable -six hyper conjugative structures. (1) iii) The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide is formed. (1) Na + S Na S S - +Pb + PbS (black ppt) (1) The sodium fusion extract is treated with sodium nitroprusside. Violet colour is obtained. [Fe(CN) 5 NO] - + S - [Fe(CN) 5 NOS] 4- *********************** (1½) Page 6 of 6