Short Answer TypeAn element with molar mass 27 g mol-1 forms a cubic unit cell with edge length 4.05 x 10-8 cm . If its density is 2.7 g cm-3 , what is the nature of the cubic unit cell?
Molar mass of the given element, M = 27 g mol-1 = 0.027 kg mol-1
Edge length, a = 4.05 x 10-8 cm = 4.05 x 10-10 m
Density, d = 2.7 g cm-3 = 2.7 x 103 kg m-3
Applying the relation,
Where, Z is the number of atoms in the unit cell and NA is the Avogadro number. Thus,
Since the number of atoms in the unit cell is four, the given cubic unit cell has a face-centred cubic (fcc) or cubic-closed packed (ccp) structure.
How would you account for the following?
Actinoid contraction is greater than lanthanoid contraction.
For a reaction A + B → P, the rate is given by Rate = k[A] [B]2
(i) How is the rate of reaction affected if the concentration of B is doubled?
(ii) What is the overall order of reaction if A is present in large excess?
A first order reaction takes 30 minutes for 50% completion. Calculate the time required for 90% completion of this reaction.
(log 2 = 0.3010)
Account for the following:
(i) Acidic character increases from HF to HI.
(ii) There is a large difference between the melting and boiling points of oxygen and sulphur.
(iii) Nitrogen does not form pentahalide.
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