Q13(a). Unit cell of HgCl₂ from three Bragg reflections
HgCl₂ crystallizes in orthorhombic system. Using radiation with λ = 154 pm, for the (100), (010) and (001) planes, first order reflections in an X-ray diffractometer occur at 7° 25′, 3° 28′ and 10° 23′ respectively. Calculate the dimensions of the unit cell and the number of HgCl₂ molecules in the unit cell. The density of the crystal is 5.42 g cm⁻³ and M(HgCl₂) = 271.5 g mol⁻¹.
Answer in brief
a = 596.5 pm, b = 1273.4 pm, c = 427.2 pm; Z = 3.90 ≈ 4 HgCl₂ per unit cell.
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CoversBragg's lawX-ray diffractionorthorhombic unit cellnumber of formula units Zcrystal density
All parts of Question 13
- 13(a) Unit cell of HgCl₂ from three Bragg reflections10 marks
- 13(b) Activity as the thermodynamic counterpart of pressure10 marks