Problem

Estimate the flash point of a solution of 50 mol % water and 50 mol % ethanol.

Step-by-step solution

1. Step 1 of 4

   The flash point of a liquid is the temperature at which the liquid has sufficient vapour pressure to just form a flammable atmosphere in equilibrium with the liquid. Hence, the temperature at which the fluid ignites is called as the flash point.

   Comment

2. Step 2 of 4

   By using Antoine equation we can calculate the saturation vapor pressure

   

   From Appendix B, the flash point temperature for ethanol is.

   

   Hence,

   At the flash point temperature the saturation vapour pressure is,

   

   Comment

3. Step 3 of 4

   By using Raoult’s law we can calculate the partial pressure,

   

   Thus, the partial pressure is.

   Comment

4. Step 4 of 4

   The temperature corresponding to 57.1 mm Hg can be calculated by using Antoine’s Equation.

   From Appendix E for Ethanol,

   

   Hence, the temperature corresponding to 57.1 mm Hg is.

   Therefore, 297.6 K corresponds to that is.

   Thus, the flash point of ethanol solution is.

   Comment