how would you set up a simple experiment to test whether salt-crystal growth is affected by tempeture???

Question

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Answer 1

The first guy got it. But I would add that in preparing the saltwater solutions, make sure you have the same amounts of water and salt in both containers. :)

Answer 2

Salt Crystal Growth

Answer 3

1) You can dissolve salt in water until saturation is reached (no more salt is dissolved).
2) put the solution in two or three containers (as many as you want for your experiment).
3) Place the open containers in a) room temperature b) the refrigetator, (c), (d) it will depend on your desing.
4) Expect crystal growth in about a week, but daily observation is required.

Important: Salt crystal growth is affected mostly by evaporation. Evaporation is faster at room temperature and whith high "winds". So to really test for remperature, the containers needs to be open but not wide open so that evaporation is under control. If you have a closed container salt crystals will not grow (just a little bit in the one that is in the refrigerator, since water dissolve more salt at higher temperatures).
So, eventhough the experiment is simple, there are several complications to avoid.

I have done experiments with salt several times. What happens is that crystals will form at the surface (where there is more evaporation, this is the nucleation area) and grow until they sink and they keep growing. Another area where crystals nucleate fast is in the walls but they don't grow much. This is because there is lots of evaporation and so you have thousands of tiny crystals. They start growing upward building up a coating as the water surficial tension keep it wet and it evaporates, repeating the process until it covers about the whole walls of the container. So you endup with two different sizes 1) coating formed by formed by millions of tiny crystals 2) tens to hundreds of mm sized crystals at the bottom.
By the way, if you boil off the water, crystals will nucleate fast but they will grow just a little. The size is bigger than in the coating formed at room temperature.

To preserve the beauty of the crystals stop the experiment before water fully evaporates. Then take the crystals out. If you want to keep them cover them with oil. They are beautiful, but they are fragile.

If you want to discuss anything else, let me know...

Good luck with your experiment. It is fun for teaching purposes...

Bonus: The white color of the salt crystal is due to the amount of fluid inclusions (the salty water trapped when the crystal grew). You will find that there are areas of the crystal that are more trasparent this areas containe less fluid inclusions. Fluid inclusions are important since you can determine the temperature at which a crystal grew and because it can trap spores of bacteria for millions of years. Now scientist are trying to revive the oldest bacteria trap in salt crystal millions of years ago. Isn't that cool...

Answer 4

I did a crystal experiment once. I tied a piece of string (I think it was wool) to a pencil. I filled a cup up with saltwater and placed the pencil on top of the cup (so that the string falls into the water). Then I watched the crystals grow. In your case, I would change the temperature of the water. I hope that helps!

Answer 5

First responder offers a good start. For comparison, set up two jars as above, but put one over a light bulb of suitable power. Put a thermometer in each jar. Then see what happens. You can remove the strings to weigh the crystals from time to time.