Solubility Question

I make homemade jams, and one of the steps is to add sugar to boiling fruit. The amount of sugar can be quite large for some fruit. Sometimes the level of the fruit is high enough that it would seem that adding that sugar would bring the level of the liquid above the top of the pot. But the sugar dissolves in the fruit juices, and even though the level goes up, it is not to the extent that would be intuitive.

My primitive knowledge of Archimedes and water displacement is clearly not going to work here. Can anyone explain this phenomenom to a non-chemist in terms that I might understand?

Thanks, plynck

I’m no chemist, but I always thought of it as the sugar filling in the gaps. The resulting stuff is thicker, right?

I seem to remember that, in general, volume is not conserved when a substance is dissolving into another substance. There are classroom demonstrations where a chemist will poor a nearly full beaker of liquid into a nearly full beaker of another liquid without overflowing the second beaker, with no noticeable chemical reaction.

I suspect it is a bit of an illusion?

from the world reknowned sucrose calculator website

1g of sugar and 1 g of water as a solution has a density of 1.227 and thus a total volume of 1.63 cm3. Now solid sugar has a density of 1.58 so separately they would have a volume of 1 (water) + 0.63 (sugar) = 1.63 cm3. So there is no overall volume change on mixing equal amounts of sugar and water.

Similar results hold for other concentrations.

However granulated sugar only has a density of about 0.8 or about half what solid sugar is. Thus it looks as though you are adding a lot more volume of sugar than you really are.