How do I decide what mass and specific heat capacity to use to find the heat involved when I place a hot ionic solid into water? Do I use the mass of the solid or the water?
1 Answer
Well, the ionic solid will evidently dissolve in the water. Depending on how much ionic solid is dissolved, it may be a good approximation to simply use the specific heat capacity of water and the mass of water.
When there isn't a lot of solid, the solid particles should disperse itself amongst the water molecules (surrounded by them), minimally changing the mass (and volume) of the overall solution.
If it's, say, 5 g of solid in 100 mL of water, then it's probably fine to simply use
(When possible, you should reweigh the solution with the dissolved solid to compare the masses.)
NOTE:
If you use the mass of the solid, then of course, you would underestimate the mass of the solution by quite a lot. You would literally be ignoring the water, which doesn't make sense.
If, say, you have like 25 g of solid urea in 50 mL of water, then you definitely can't simply use the mass of water. Clearly, that would significantly increase the mass (and volume) of the solution.
