Observing Changes In Matter - Sugar!

Lately in science class, we have been studying exothermic and endothermic changes. To put it to the test, we proceeded with a lab using sugar. It showed us what some types of changes look like when it comes to matter. We started off with four sugar cubes, a glass of water, a spoon, mortar and pestle, Bunsen burner (ouch!), test tube, and tongs. Observing the sugar cubes as the easiest. And the sweetest! They looked like any other sugar cubes, but they were in for a beating! We then mashed them up with the mortar and pestle. After this, we observed the sugar, now a powder instead of a cube, again. We then poured the powder into the glass of water. After stirring it for about 20 seconds, the sugar was hardly even visible anymore, but it was still in there. And then came the really fun part!

We carefully put 2 sugar cubes in to the test tube and let our teacher light the Bunsen burner. Carefully holding the test tube over the flame with the tongs, the sugar quickly melted and expanded, filling up more of the test tube as a liquid than as a solid. It bubbled and popped inside and the beige liquid soon turned brown, then black as we pulled the test tube off of the burner. Smoke flew out of it and it didn’t smell so sweet anymore. When we got the "sugar" out of the tube it was hard and crumbled on the table. But i did observe something awfully familiar. The smell of the sugar while it was burning smelled like a marshmallow. So the smell and taste of a marshmallow is actually just the sugar, and not any flavorings.

Again, time to observe. It had small holes, like craters, all over it. Probably from the boiling, I thought. So the changes we made in part a, grinding it, was just a physical change. It didn’t change anything major about it because it's still sugar. When in part B, burning it, it was a chemical change because we cannot un-burn it.