Question

Ionic solid `B^+A^(-)` crystallizes in rock salt type of structure.1.296 gm ionic solid salt `B^+A^(-)` is dissolved in water to make one litre solution.The pH of the solution is measured to be 6.0.if the value of face diagonal in the unit cell of `B^+A^(-)` be `600sqrt2` pm.Calculate the density of ionic solid in gm/cc.`(T=298 K, K_b "for" BOH "is" 10^(-6)`,(Avogadro Number =`6.0xx10^(23)`))

Answer 1

Correct Answer - 4 g/cc
`pH=1/2{pK_w -pK_b- log C} implies square6=7.0-5/2-1/2"log C" " " implies " " C=0.01 M`
`:. C=1.296/("Molar mass")=1/100 " " implies ` molar mass of salt =129.6
For rock salt, `600sqrt2=sqrt2a`
a=600 pm=`600xx10^(-10) cm`
effective number of formula units z=4
Now density `=Z/N_A (M/a^3)=4/(6.0xx10^23)[129.6/((600)^3xx10^(-30))]=4` gm/cc.