Question

How many grams of the following nonelectrolytes would have to be mixed with 100.0 g of p-dichlorobenzene to increase the boiling point by 3.0 deg C? To decrease the freezing point by 2.0 deg C?

a) Succinic Acid
b) Caffeine

Answer 1

Use: \(\huge \sf \Delta T =i*m*\small \underbrace{\huge K_x}_{\small x~=~b~or~f}\)

since they're asking for a non-electrolyte, so \(i=1\)

\(\large \sf \Delta T =m*\underbrace{K_x}_{\small x~=~b~or~f}\)

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Make some substitutions with molality and moles,

\(\sf m=molality=\dfrac{n_{solute}}{L_{solution}}\)

\(\sf n=moles=\dfrac{mass}{Molar~mass}\)


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\(\large \sf \Delta T =\dfrac{\dfrac{mass}{Molar~mass}}{L_{solution}}* \underbrace{ K_x}_{\small x~=~b~or~f}=\dfrac{mass_{solute}* K_x}{Molar~mass*L_{solution}}\)



\(\large \sf mass_{solute}=\dfrac{\Delta T*Molar~mass*L_{solution}}{K_x}\)