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I believe the title is straightforward. Evaporating water leaves behind chalk. Assuming you evaporate the same amount of (the same type of) water, does the temperature at which this happens (and so also the time it will take) matter for the amount of chalk that is left behind?

Maybe a little side-question: Does the surface or container from which evaporation happens matter?

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  • $\begingroup$ Evaporating water leaves behind chalk. Only if it had chalk previously. Anyway, I don't think temperature or the container affects at all (matter is conserved). $\endgroup$
    – jinawee
    Commented Dec 30, 2013 at 16:44
  • $\begingroup$ Yes, I man tapped or bottles water, which basically always has a certain amount of minerals in it. $\endgroup$
    – Steven Roose
    Commented Dec 30, 2013 at 20:46

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It sounds like you are basically asking about how water boiling kettles often get coated with calcium carbonate when they are used with mineral-rich water. It turns out that the calcium carbonate is actually less soluble in water at higher temperatures, and so it tends to precipitate at higher temperatures.

The minerals in the water will always be left behind. So the strict answer to your question is that the same amount of minerals will be left behind regardless of the temperature of the water or how quickly it evaporates. However, I think that the way that the calcium carbonate is deposited might depend on the temperature or the roughness of the surface.

Crystals tend to form on rough surfaces, so, if you heated the water, causing the calcium carbonate to evaporate, then it would likely to form crystals on the rough surfaces. If you let the solution evaporate at low temperature, then it would leave behind the calcium carbonate on all surfaces.

This question has a good description of the situation with the kettle: https://chemistry.stackexchange.com/questions/4094/white-powder-observed-after-boiling-water-in-electric-kettle-for-many-weeks

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  • $\begingroup$ "The minerals in the water will always be left behind." Will 100% of them be left behind? Doesn't a small amount evaporates with the water. $\endgroup$
    – Steven Roose
    Commented Dec 30, 2013 at 20:45
  • $\begingroup$ F.e. there is also chalk on the cold water tubes above our shower. The water that has been on that tube is purely condensed water, so that means that the chalk in it has been in the vaporized water. $\endgroup$
    – Steven Roose
    Commented Dec 30, 2013 at 20:48
  • $\begingroup$ I would guess that almost none of the minerals evaporates with the water. In the shower, I think a low of the steam that you see is actually tiny droplets of water, so it might just be the tiny droplets of shower water that are condensing on the pipes. $\endgroup$
    – DanHickstein
    Commented Dec 31, 2013 at 16:37
  • $\begingroup$ Well, indeed, but the vapor that comes from boiling water is also partly consisting of little water droplets, so it can also take minerals with it. $\endgroup$
    – Steven Roose
    Commented Jan 1, 2014 at 17:01
  • $\begingroup$ Oh, that's a good point. So, maybe it doesn't so much depend on the temperature directly, but on the mechanism of evaporation. I.e., if it's boiling it could produce droplets which would carry away some of the dissolved minerals. $\endgroup$
    – DanHickstein
    Commented Jan 1, 2014 at 23:30

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