Science Buddies: "Ask an Expert"

Why is it that in three cups of water used for evporation Lake water evrorated first tap water secound and then salt warter last? Why did it happen this way, Please help this is due next Tue and we need to ask an expert and this is the place to do it.
Thank you for your time

Hi,

I think to find the answer to your question you need to research Raoult’s Law:

http://www.chemguide.co.uk/physical/pha ... onvol.html

http://www.sparknotes.com/chemistry/sol ... tion1.html

So, if I understand your situation correctly, the lake water had the least salt in it (you can tell by the amount of residue left after all the water evaporated), the salt water had the most, and the tap water was in between. This implies (according to Raoult’s law) that the lake water had the highest vapor pressure, the salt water the lowest vapor pressure. The highest vapor pressure evaporates fastest. End of story.

I hope this helps. Good luck on the project!

Best regards,

Barrett L Tomlinson