The problem is that the parameters of your experiment are not very adequately defined.
When you say 1 1/2 cups of salt water, how much salt is dissolved
in that water? The amount of salt in there will have a direct bearing
on the boiling point of the water (as any good cook will you tell you),
so that will make a big difference if you intend to boil the water
That brings up other ways that the description needs to be more
specific before the question could have a definite answer . How do you
intend to evaporate it? (On the stove, by leaving it out on a warm day,
etc) What temperature will the evaporation occur at? What is the
atmospheric pressure on that particular day?
(Another key parameter is how spread out the liquid will be, e.g.
on a cookie sheet or in a glass. The atmospheric humidity and especiall
the windiness matter as well./ mbw)
I think, to find the result, you need to actually perform the
experiment. You should take the mass of a sample of reasonably pure
salt (depending on what you have available. Many consumable salts have
Potassium Iodide in them, for your diet ... reagent grade sodium
chloride would not) and through a method you decide, evaporate it and
then you'll know. You might compare different salt concentrations or
evaporating it without salt in order to see general trends.
(republished on 07/24/06)