How would you determine the density of a solid that is soluble in water such as salt and sugar?

Question

Density

Answer 1

Evaporate the liquid in an evaporating dish and measure the mass of the crystals remaining. Or if the crystals aren't seperate, measure the mass of the dish b4 pouring the liquid in, then measure it again after the liquid is evaporated and then subtract the difference.

Answer 2

The reason why this would be non-trivial is if you have grains of solid and relatively crude measuring devices (compared to the size of the solid).

When you try to directly measure volume, you have 2 issues: 1) the crystal dimensions aren't easy to measure (too small and may be inconveniently shaped) and 2) air gaps.

When the solid is dissolved in water, the air gaps disappear.

Depending on the degree of accuracy, you'll need to measure the temperature since the density of water changes with temp.

But, assume the density of water is 1.00 g/mL.

Add a quantity of your solid to a known volume of water (e.g. 97.0 mL which is calculated to be 97.0 g using density). Remeasure the new volume and the new mass (e.g., 101.0 mL and 103.0 g).

You added 103.0 - 97.0 g = 6.0 g. The volume of solid is presumably 101.0 mL - 97.0 mL = 4.0 mL. The density of the solid is therefore 1.2 g/mL.

That's probably the reasoning/thinking that your text/teacher would like you to follow (and I apologize if you were just sitting in the shower this morning randoming thinking about density concepts... ;-) ).

To make things interesting, it turns out that this method has a major flaw. Namely, solution densities are also dependent on the concentration of the solute and this dependence isn't easy to pre-determine.

Consider this analogy:

There are a bunch of guys in a room. They are relatively unattracted to each other (so that they don't clump together in close contact, but also aren't so repelled that they have enough energy/reason to escape the room). We could characterize the room with "density" or the number of guys present per square meter.

Suppose now that we add in a few attractive girls (and who said chemistry wasn't fun; if you want to be more PC, rephrase this in a gender-neutral manner!). Well, what will happen (and let's keep this a non-fantasy party, so no bonding occurs, just alot of attraction)?

About the only thing you can be sure of is that the "density" will change.

Around the girls, the density will increase as the guys are... attracted and want to get closer. In fact, the guy-girl attraction may be stronger than the guy-guy repulsion and we'd see a net increase in density for the whole solution.

Alternatively, let's imagine that the girls are completely surrounded by a tight clump of guys, so that the next "ring" of guys can't see the girl (hence no attraction) and in fact just see an extremely high density of (repulsive) guys. We could then have a net decrease in density for the whole solution.

Analogies are naturally inexact at some level, but I hope this gives you a picture of the forces in solutions (hey, it's not as good as trashy cable, but it's free...)

Answer 3

Density = mass / volume
So If you know the mass of the solid and the volume there shouldn't be a problem. Evaporating the solution would leave the mass behind leaving you to calculate the density.
OR if you are trying to find the concentration of a solution .. (that is different form density)..there are different ways of finding that.
One if them is mass per volume percentage..
i.e : (grams of solute x 100)/(volume in mililitresof solution).

Answer 4

i just wonder if yu want to know your raw substance density or the pure substance ? any way we can do that very simple we need a dry graduated cylinder ,, weight this cylinder empty then put you substance in that cylinder to the mark shake this cylinder with pencil or rubber bar until no gaps among your substance and weight,, repeat that 3 times and get the average reading ,, yor density will be= the wieght of substance / Volume of your cylinder =grams/ml

Answer 5

You could use another fluid which does not dissolve the solid. I don't know what that might be for salt or sugar. Maybe alcohol or an oil?

Answer 6

Put it on a Ritz cracker.