Ques 1) CaS exists in a cubic close packed arrangement of S2- ions in which Ca2+ ions occupy 1/2 of the available tetrahedral holes. How many Ca2+ and S2- ions are contained in the unit cell ?
(a) 1,1 (b) 2,4 (c)4,4 (d)4,2
Ques 2) A crystal lead (II) sulphide has NaCl stucture. In this crystal the shortest distance b/w a Pb2+ ion and S2- ion is 297 pm. What is the volume of the unit cell in the lead sulphate ?
Ques 3) K Cl crystallizes in the same type of lattice as does Na Cl . Given that r Na+ / r Cl- = 0.50 and r Na+ / r K+ = 0.70 , calculate the ratio of the side of the unit cell for K Cl and that for Na Cl :-
(a) 1.143 (b) 1.224 (c) 1.414 (d) 0.875
I am getting 0.47, which is nowhere in the options [2]
11.c
since unit cell content for ccp=4
and 1/2 tetrahedral void=4..........
so ans. is c
bye!!!gtg
23hey third is easy
2r Na+ +2 r Cl- = aNaCl
2r K+ +2 r Cl- = aKCl
so
\frac{a_{KCl}}{a_{NaCl}} = \frac{r_{K+}+r_{Cl-} }{r_{Na+}+r_{Cl-} }
divide thru out by r Na+
so ratio = \frac{\frac{1}{0.7}+ 2 }{1+2 }
= 8 / 7
= 1.143
if they hav asked reciprocal the ans is 0.875
1sorry tushar left rem two yesterday was a biut busy
2nd one ans.
side of cell,a=2*shortest distance[nacl struc. given :)]=594
so volume =a3 =2.0958*108pm3
hope it helps!!!
1oh sorry i took cm instead of pm please do correction ursewlf by using factor for picometer urself [1]
1is it clear now!!
bye gtg........
n i m not bhaiya[im in xii-but have written drop year in profile so as that i don't have any second chances in my life][1]
all the best
will be back after 17 january!
11oh yes !!!! Sorry for asking such a stupid doubt
Anyways, thanx "Jai Ho" and Qwerty [1]
23arreeyyy sorry sorry i calculated density heheehheeh...didnt u notice by the units that i hav mentioned?
