Gifted Issues Discussion homepage Forums Recommended Resources More advanced evaporation experiment?

DD has an assignment of two evaporation experiments (salt water, observing how the salt doesn't evaporate with the water, and sugar water and food coloring, observing how the water leaves behind colored crystals). Of course we've done similar experiments years ago, and she's asking for something new. I'd like it to be related still. Anyone know of a good experiment or two where we could practice the scientific method and do something a bit more advanced? TIA!

Same setups, but make real experiments. Questions relating to rate of absorption, chemical composition (like acidic vs. base) or other liquids like rubbing alocohol, temperature, size of crystals formed in different conditions, types of growths accumulators (like string, paper, metal), lots of variables. Personally my favorite would be how to grow the biggest crystals.

A few to add to Zen Scanner's great ideas:

Rate of evaporation as a function of surface area (e.g., 1 cup of salty water poured into bowl versus cake pan versus jelly roll pan).

Rate of evaporation as a function of initial salt concentration (include a supersaturated solution made by boiling water and adding salt until no more will dissolve. Bonus - I think this will also make the biggest crystals).

Can you make colored salt crystals, too? (I don't really know). If not - why not. (Maybe the sugar is an organic molecule and so is the dye, but the salt is inorganic). Or maybe you can make them colored. I don't know!

Rate of evaporation of salt solution with a layer of oil over the top - probably pretty slow, and what does that say about the local effect of a large oil spill?

pH variation during evaporation (I don't know if there is any variation!)

This would be a tougher one - but rate of evaporation in a room made humid using a humidifier versus rate of evaporation in dryer air.

What if there is a mixture of salt and sugar in the solution? Maybe you could do some sort of relative saltiness/sweetness taste test to see if one or the other precipitates out faster. Again - I have no idea on this one.

Have fun!
Sue

Thanks! I had been thinking about rate of evap with some of these variables, but I am not the scientist in the family. I think she's going to like these; we'll probably try surface area and supersaturated!

Good luck... and be sure not to grow sugar crystals using a super-saturated solution in an antique Ball jar.