1.

5.35 g of a salt A Cl(of weak base AOH) is dissolved in 250 ml of solution.The pH of the resultant solution was found to be 4.85 .Find the ionic radius of A^+ & Cl^(-) if A Cl forms CsCl type crystals having density 2.2g/cc.Given K_b(AOH)=2xx10^(-5) r_(+)/r_(-)=0.731 for this unit cell.

Answer»


Solution :`pH=1/2xx[pK_w-pK_b-log C]IMPLIES 4.85\1/2xx[14-4.7-log C]implies C=0.4`
`:. C=0.4=(5.34)/("molar mass")xx4 implies` molar mass of the salt=53.5gm/mole
Now, density`=(1xx53.5)/(6.022xx10^(23)xxa^3)=2.2 " " implies " " a=3.43xx10^(-8)` CM
and for CsCl type of crystals, `sqrt3a=2(r_(+)+r_(-))`
`implies " " r_(+)=1.26xx10^(-3)cm and r_(-)=1.71xx10^(-8) cm`


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