JEE Advance - Chemistry (1993)

• 1

  The dipole moment of CH₃F is greater than of CH₃Cl

  回答

  (B)

  FALSE
• 2

  Upon mixing 45.0 ml. of 0.25 M lead nitrate solution with 25.0 ml. of 0.10M chromic sulphate solution, precipitation of lead sulphate takes place. How many moles of lead sulphate are formed? Also, calculate the molar concentrations of the species left behind in the final solution. Assume that lead sulphate is completely insoluble.

  回答

  (E)

  Moles of PbSO4 formed = 0.0075 moles, [Pb2+] = 0.05357 M, [NO3-] = 0.3214 M, [Cr3+] = 0.0714 M
• 3

  The light radiations with discrete quantities of energy are called ______.

  回答

  (C)

  Photons
• 4

  Wave functions of electrons in atoms and molecules are called ______.

  回答

  (B)

  orbitals
• 5

  The 2p_x, 2p_y and 2p_z orbitals of atom have identical shapes but differ in their _____.

  回答

  (D)

  Orientation in space
• 6

  In a given electric field, $$\beta-particles $$ are deflected more than $$\alpha-particles$$ in spite of $$\alpha-particles$$ having larger charge.

  回答

  (A)

  TRUE
• 7

  Estimate the difference in energy between 1st and 2nd Bohr orbit for a hydrogen atom. At what minimum atomic number, a transition from n = 2 to n = 1 energy level would result in the emission of X-rays with $$\lambda = 3.0 \times {10^{ - 8}}$$? Which hydrogen atom like species does this atomic number correspond to?

  回答

  (A)

  10.22 eV, 2, He+
• 8

  What transition in the hydrogen spectrum would have the same wavelength as the Balmer transition n = 4 to n = 2 of He⁺ spectrum?

  回答

  (C)

  n = 2 to n = 1
• 9

  The decreasing order of electron affinity of F, Cl, Br is F > Cl > Br

  回答

  (B)

  FALSE
• 10

  The basic nature of the hydroxides of group 13 (Gr. III B) decreases progressively down the group.

  回答

  (B)

  FALSE
• 11

  Pick out the isoelectronic structures from the following
  I. $$CH_3^+$$
  II. $$H_3O^+$$
  III. $$NH_3$$
  IV. $$CH_3^-$$

  回答

  (D)

  II, III and IV
• 12

  The dipole moment of KCl is 3.336 $$\times$$ 10^-29 Coulomb meters which indicates that it is a highly polar molecule. The interatomic distance between K⁺ and Cl^- in this molecule is 2.6 $$\times$$ 10^-10. Calculate the dipole moment of KCl molecule if there were opposite charges of one fundamental unit located at each nucleus. Calculate the percentage ionic character of KCl.

  回答

  (D)

  80.11 %
• 13

  In the van der Waal's equation (P + $${{{n^2}a} \over {{V^2}}}$$)(V - nb) = nRT the constant 'a' reflects the actual volume of the gas molecules.

  回答

  (B)

  FALSE
• 14

  A gas bulb of 1 litre capacity contains 2.0 $$\times$$ 10²¹ molecules of nitrogen exerting a pressure of 7.57 $$\times$$ 10³ Nm^-2. Calculate the root mean square (r.m.s) speed and the temparature of the gas molecules. If the ratio of the most probable speed to the root mean square speed is 0.82, calculate the most probable speed for these molecules at this temparature.

  回答

  (A)

  vrms = 494.2 m/s, T = 274.2 K, vmp = 405.2 m/s
• 15

  Ca²⁺ has a small ionic radius than K⁺ because it has ______.

  回答

  (C)

  a higher effective nuclear charge
• 16

  Give briefly the isolation of magnesium from sea water by the Dow process. Give equations for the steps involved.

  回答

  (B)

  Electrolysis of molten magnesium chloride.
• 17

  What weight of the non-volatile solute, urea(NH₂ - CO - NH₂) needs to be dissolved in 100g of water, in order to decrease the vapour pressure of water by 25%? What will be the molality of the solution?

  回答

  (C)

  111.1 g, 18.52 m
• 18

  The standard reduction potential for the half-cell
  $$NO_3^-$$ + 2H⁺ (aq) + e $$\to$$ NO₂ (g) + H₂O is 0.78 V
  (i) Calculate the reduction potential in 8 M H⁺
  (ii) What will be the reduction potential of the half-cell in a neutral solution? Assume all the other species to be at unit concentration.

  回答

  (A)

  (i) 0.887 V, (ii) -0.046 V
• 19

  Chromium metal can be plated out from an acidic solution containing CrO₃ according to the following equation
  CrO₃ (aq) + 6H⁺ (aq) + 6e^- $$\to$$ Cr(s) + 3H₂O
  Calculate (i) how many grams of chromium will be plated out by 24,000 coulombs and (ii) how long will it take to plate out 1.5 g of chromium by using 12.5 amp current.

  回答

  (A)

  i) 2.155 g Cr, ii) 1336.15 s
• 20

  A first order reaction A $$\to$$ B, requires activation energy of 70 kJ mol^-1. When 20% solution of A was kept at 25^oC for 20 minutes, 25% decomposition tooks place. What will be the percentage decomposition in the same time in a 30% solution maintained at 40^oC? Assume that activation energy remains constant in this range of temperature.

  回答

  (B)

  67.17%