# Finding the reduced pressure to distill a solution containing 0.4 g of naphthalene in 25 g of chloroform at 50 °C

Chloroform boils at $$\pu{62 ^\circ C}$$. For a solution containing $$\pu{0.4 g}$$ of naphthalene in $$\pu{25 g}$$ of chloroform, the boiling point is elevated by $$\pu{0.45 K}$$, to avoid any decomposition during distillation chloroform has to be distilled at $$\pu{50 ^\circ C}$$, what maximum pressure can be maintained in the flask?

My approach: I found the molality of the solution to be $$0.125m$$, equating it with the formula $$\Delta T_\mathrm b=K_\mathrm b\cdot m$$ I found $$K_\mathrm b$$ to be $$3.6\ \mathrm{K\ kg/mol}$$, I am not able to proceed after this step, please provide an approach to solve the problem from here.

I also tried using the formula $$\Delta K_\mathrm b=\dfrac{R {T_\mathrm b}^2}{1000l_\mathrm v}$$ but finding out the latent heat of vaporisation did not prove to be of any help.

• Apply the Clausius-Clapeyron integral equation, as you know vapour tension at 2 temperatures(on indirectly ). Then you can calculate the tension at the 3rd temperature. – Poutnik Aug 15 '20 at 9:44
• Can you provide your approach in detail in the answer, I am not able to apply the Clausius-Clapeyron equeation – Shriom707 Aug 15 '20 at 9:45
• I can,but I will not. Try harder. If I consider the time delay of your comment and time to write and post it, you could hardly have a good look at it. Consider also the Raoult law to get the 2nd vapour tension. – Poutnik Aug 15 '20 at 9:49
• @Poutnik Is your answer 509.6 torr, I am asking this just to be sure? – Shriom707 Aug 15 '20 at 10:36
• Particular answer is of no importance, the principles and procedures are what matters. Otherwise it qualifies well for the closure as a homework-like question. – Poutnik Aug 15 '20 at 10:38