How can I boil water at a temperature less than 100 degree Celcius? I need to boil a water-based solution at a temperature lower than 100C.
What kind of liquid should i add to the water to make this happen?
 A: When you add a soluble substance to the water, the boiling temperature will, in general, increase. Probably the best way to boil your water-based solution is to reduce the pressure. You put it into a vessel and reduce the pressure by pumping. A known lab demonstration is also to reduce the pressure by condensation of the air due to cooling in a connected part of the closed vessel. You could also think of using a different solvent to water like alcohol with a lower boiling temperature.
A: lower the air pressure, at the top of mount everest you can boil water at about 71 celcius, but this will of course be hard to replicate at normal atmospheric pressure
" For comparison, on top of Mount Everest, at 8,848 m (29,029 ft) elevation, the pressure is about 34 kPa (255 Torr)[8] and the boiling point of water is 71 °C (160 °F)." - wikipedia
A: Here is how to answer these type of questions:
first understand, when you have an ideal solution you have to take into account both the vapor pressure of the solvent,A, and solute B. so total vapor pressure above solution will be given by $P_{Total} =P_A^*X_A+P_B^*X_B$ where $P^*_A and P_B^*$ represent the vapor pressure of the pure substances A and B. Now we know that in the boiling process the vapor pressure above liquid must equal to the atm pressure. that's where $P_{Total}$ comes in. Being a sum of two pressures it has the potential to exceed the atm. pressure and thus lower the boiling point. This directly leads to your answer;
.In order to boil at a lower temperature than water, the vapor pressure of the solution (water + liquid) must be greater than water(this is where we use the concept of $P_{total}$ discussed earlier). In order to make this solution, you must add a liquid that is both soluble in water and chemically similar to water(thus becoming a really good approximation to an ideal solution). It must have a higher vapor pressure than water(so that the general principle that volatile substances contribute most to vapor pressure over a solution is satisfied) and a boiling point lower than 100°C. One possible liquid is ethanol, with a boiling point of 78.3°C
