Section A
Q1.
(a) NaCl (molecular weight : 58.5) consists of a face-centred cubic lattice of Na^+ ions interlocked with a similar lattice of Cl^- ions and has a density of 2.17 g/cm^3. Draw the unit cell structure of NaCl. (i) Calculate the number of Na^+ and Cl^- ions that are present in a unit cell. (ii) Calculate the volume of the unit cell. (iii) The first-order reflection from the d_{100} planes of NaCl occurs at 5.9°. Calculate the wavelength of X-ray.
(b)
For the reaction A → B + C the following data were obtained : t in sec
0
900
1800
conc. of A
50.8
19.7
7.62
Prove that the reaction is of the first order.
(c) What would be the value of the principal quantum number, if an electron in a hydrogen atom was in the orbital of energy -0.242 × 10-18 J? Given : k = 2.179 × 10-18 J.
(d) Calculate the work done when 1 mole of He expands isothermally and reversibly from a volume of 1 litre to a volume of 10 litres at 25°C.