why do some liquids leave sticky spots when they evaporate? And why some of these so hard to clean??

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why do some liquids leave sticky spots when they evaporate? And why some of these so hard to clean??

In: Chemistry

It happen when something dissolved in the liquid can’t evaporate and is left behind.

A common example is soda that is primary a mixture of water and sugar. The water will evaporate and will leave the sugar behind with some water and a bit of other stuff. So what is left behind is syrup that is hard to remove.

If you have just water or add pure alcohol that also can evaporate nothing is left behind.