A very small amount of a nonvolatile solute (that does not dissociate) is dissolved in 56.8cm^(3) of benzene (density 0.889gcm^(-3)). At room temperature, vapour pressure of this solution is 98.88mmHg while that of benzene is 100mmHg. Find the molality of this solution. If the freezing temperature of this solution is 0.73 degree lower than that of benzene what is the value of molal freezing point depression constant of benzene ?

A very small amount of a nonvolatile solute (that does not dissociate)

1.	A very small amount of a nonvolatile solute (that does not dissociate) is dissolved in 56.8cm^(3) of benzene (density 0.889gcm^(-3)). At room temperature, vapour pressure of this solution is 98.88mmHg while that of benzene is 100mmHg. Find the molality of this solution. If the freezing temperature of this solution is 0.73 degree lower than that of benzene what is the value of molal freezing point depression constant of benzene ?
Answer» <P> SOLUTION :We have , `(p^(0)-p)/(p^(0))=(N)/(N)` `(100-98.88)/(100)=(n)/(0.6474)` `{N=(56.8xx0.889)/(78)=0.6474}` `n=0.00725` Molality `=(0.00725xx1000)/(56.8xx0.889)=0.1435m` Further, `K_(f)=(DeltaT_(f))/(m)=(0.73)/(0.1435)=5.087`