Is it gas, liquid or solid?

Question

A glass cylinder contains 1 mole of water under piston.
How can we tell if water is in gaseous, liquid or solid state,
if we are allowed to use any measurement instrument?

Answer 1

Liquid water is relatively incompressable, too, though. If you can measure the temp and pressure of the water, you can figure the state.

Answer 2

Gas (steam) is compressible. Push on the piston; if it compresses, you have a gas.

Then, presuming the cylinder is not completely filled with either solid (ice) or liquid:

Turn the cylinder on its side. If the CG is found to be near the center of the length of the cylinder, then it contains liquid water. This results because water seeks the lowest level; so it will distribute evenly along the length of the cylinder while it is on its side.

If the CG is found to be closer to one end or the other, then the water is a solid. This results because we presumed the cylinder was only partially filled; so the ice mass would not be evenly distributed along the length of the cylinder. (There is an exception to this...if the ice were formed while the cylinder was on its side, the ice would also be uniformly distributed. In that rare case, just to make sure, we could rotate the cylinder 90 deg on its length-wise axis while it's on its side. Let go, if the cylinder rotates on its own back to the original orientation, then that's ice. Water would have just stayed on the gravitational bottom while the cylinder was rotated. So a water filled cylinder would not try to rotate back to its original prone orientation around the length-wise axis.)

Fun question.

Answer 3

I'm going to assume that the glass cylinder and piston is fixed, so that the pressure is unknown. But if I assume that the apparatus is in thermal equlibrum so that I can measure its temperature, and if I assume I'm actually able to measure the interior volume of the cylinder, and knowing that it contains 1 mole of water, I can consult the phase chart of water to find out which state it is in.

On the other hand, if the volume cannot be determined precisely (because of ambiguities of glass wall thickness), then there are at least 2 other methods that can be tried. One is checking its optical index of refraction, since that varies with the phase, the other is checking the speed of sound, since that also varies with the phase.

And then we can bring out the big guns and use techniques of Raman spectroscopy to really force the water to give up its secrets.

Addendum: Eyeonthescreen's answer addresses the case where the water is in more than one phase For example, if the cylinder is partially filled with ice, then necessarily the rest of the cylinder is water in other phases. What was the question, again?

Answer 4

The most obvious is to look through the glass!
If you can move the piston and it's compressible, it's a gas.
If you can measure the pressure, volume, and temperature, consult a phase chart. Even then, if the water is just at the freezing point given the PVT, you don't know the phase, since water can be supercooled. The easiest way then is to rotate the cylinder about its axis and see what it does to light. And even then, it could look frozen but still have a liquid interior. At that point, a sonogram is probably the simplest way to tell.

Answer 5

neither the solid or liquid forms of H20 compress easily, but the gaseous form requires much less force to put under pressure.

Answer 6

The amount of resistance to the piston would tell you what state it is in. As the previous poster stated, the temperature would give you a direct answer.

Although...one other factor, I believe the amount of pressure the water is under would affect its state as well.

Answer 7

compress it with the piston, if it is not easily compressed, and breaks, then it's a solid.
any measurement instrument? Take a thermometer, and see what the temperature is. If it's below 0C, then it's solid, if it's between 0 and 100C, then it's a liquid, and if it's above, it's a gas.

Answer 8

Ur...