https://www.sciencebuddies.org/science- ... Q&from=TSW
Hi there, in the above experiment could you please help me explain in a scientific way why the crystals in the cool room form first and there are the most of them, but they are the smallest the medium temp room is the middle one and the hottest take the longest to form , but are the biggest, and least in number
Thanks for your help in advance
Chris
Crystal Experiment
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barretttomlinson
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Re: Crystal Experiment
Hi Chris,
You should try reading the experimental writeup very carefully and look at the linked pages in the bibliography section to discover the answer to your question.
I will try to give you a short explanation here.
For most salts, including the ones in the experiment you are doing, the amount of salt that will dissolve in a specific amount of water increases as the water gets hotter. A solution that contains as much salt as possible at a given temperature is called a saturated solution. If you cool down a saturated solution as you do in this experiment, as the temperature decreases the solution cannot contain all the salt in a dissolved state so some of the salt has to come out of the solution. This happens by the dissolved salt forming crystals. The crystals form until the solution returns to a saturated state for the cooler temperature.
When a hot solution is placed in a room cooler than the solution is, the solution transfers heat to the air in the room, thereby becoming cooler. How fast this happens is proportional to how big a temperature difference there is between the room air and the solution. This means that a solution in a cold room loses heat much faster than the solution does in a hot room. If the solution is losing heat faster, it must get rid of dissolved salt faster, so crystals must form faster. Crystals can only grow at the surface between the solution and crystal, and they can only grow so fast. This means the rate at which salt can crystalize out of solution depends on how much surface area is available at the surface of the crystals. It turns out that lots of small crystals have much more surface area than one large crystal, so if lots of salt must come out of solution quickly then lots of small crystals must be formed. If the solution is cooling very slowly and there is only one crystal already formed, the solution can grow that one crystal fast enough to stay just saturated at all times(the best crystals are usually formed under these conditions).
I hope all this makes sense to you.
I wish you great success on your project.
Barrett L Tomlinson
You should try reading the experimental writeup very carefully and look at the linked pages in the bibliography section to discover the answer to your question.
I will try to give you a short explanation here.
For most salts, including the ones in the experiment you are doing, the amount of salt that will dissolve in a specific amount of water increases as the water gets hotter. A solution that contains as much salt as possible at a given temperature is called a saturated solution. If you cool down a saturated solution as you do in this experiment, as the temperature decreases the solution cannot contain all the salt in a dissolved state so some of the salt has to come out of the solution. This happens by the dissolved salt forming crystals. The crystals form until the solution returns to a saturated state for the cooler temperature.
When a hot solution is placed in a room cooler than the solution is, the solution transfers heat to the air in the room, thereby becoming cooler. How fast this happens is proportional to how big a temperature difference there is between the room air and the solution. This means that a solution in a cold room loses heat much faster than the solution does in a hot room. If the solution is losing heat faster, it must get rid of dissolved salt faster, so crystals must form faster. Crystals can only grow at the surface between the solution and crystal, and they can only grow so fast. This means the rate at which salt can crystalize out of solution depends on how much surface area is available at the surface of the crystals. It turns out that lots of small crystals have much more surface area than one large crystal, so if lots of salt must come out of solution quickly then lots of small crystals must be formed. If the solution is cooling very slowly and there is only one crystal already formed, the solution can grow that one crystal fast enough to stay just saturated at all times(the best crystals are usually formed under these conditions).
I hope all this makes sense to you.
I wish you great success on your project.
Barrett L Tomlinson