Question

to an activity to motivate that the sugar dissolve in water is a solution

Answer 1

The weight of the water + glass + sugar is the same as the weight of the glass containing the mixture after the sugar was stirred in.

Answer 2

The sugar cube in the hot water dissolves the fastest. Sugar will dissolve faster when you stir the solution quickly because the act of stirring increases kinetic energy which increases the temperature.

Filtering has no obvious effect on the salt-water, but a noticeable one on the sand-water. Tap water is a solution of various chemicals dissolved in water. Truly pure water does not exist in nature, because water is such a superb solvent (dissolving substance).