So i wanna dissolve different salts in water and measure the vapour pressure of the resulting solution. I am doing this to compare the freezing point depression of different cations, used with the same anion and in the same concen for the experiment, as well a smaller vapour pressure implies greater freezing point depression. How would I go about this? I know the apparatus available to us is a gas pressure sensor but not much about how to utilize it.

Note: If possible, I dont want to use Raoult's Law.

  • $\begingroup$ How are you going to find out the freezing point depression by measuring the vapour pressure? And please give your own thoughts about how this could be done. There is a big problem if you have nothing but a pressure sensor. What is it? $\endgroup$ – Karl Sep 21 '20 at 5:59
  • $\begingroup$ It seems to me he wants to relate ebulioscopy and kryoscopy via respective constants. But it seems to me like "scrabbing himself behind his right ear by the left hand" . $\endgroup$ – Poutnik Sep 21 '20 at 6:01
  • $\begingroup$ @Poutnik Ja, and like a physchem lab course where they haven't given out experiment descriptions. Novel idea, that. $\endgroup$ – Karl Sep 21 '20 at 6:07
  • $\begingroup$ @Karl I remember doing the experiment described in my answer, determining water p=f(T) curve in the first year of my undergraduate studies within the lab about laboratory techniques. ( 1984 ) $\endgroup$ – Poutnik Sep 21 '20 at 6:11
  • $\begingroup$ @Poutnik The most interesting part here was always the quantitative(ly correct) error analysis. ;-) $\endgroup$ – Karl Sep 21 '20 at 6:29

Create a vacuum enduring apparatus, equipped with a heated flask with the solution, with constrained capillary air inlet immersed into the liquid ( provides boiling centers to avoit overheating ) and pressure sensor, attached to a vacuum source.

Combination of applied heating and vacuum, there will be established "laboratory grade equilibrium", where the measure pressure is the saturated vapor tension at the measured temperature.


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