Making Crystals Using Evaporation
Background
The sun is so hot! This heat is the reason why
evaporation
happens. The thing with evaporation is that whatever was dissolved in the water, is left behind once the water has disappeared. So if water is sweet, the “sweet thing” behind – hey presto – sugar.
But the salt will look different to what you are used to putting on your food. In what way, you ask? Well, I ain't gonna tell ya –but I will help you discover the answer yourself using scientific investigation and experiments...
Let's do science...
The Experiment
The following two experiments will both have similar results. You can do one or the other, or both.
The Aim
To make crystals out of salt/sugar using the process of evaporation.
Experiment 1:
Equipment Needed
Salt
Water
Kettle
Dish (with smooth sides)
Something rough, like a rock or a brick
Tissue or coffee filter
Magnifying glass
A sunny place
Method
Mix the salt into the water until no more will dissolve in it. This is called a
saturated solution
. If you use 125ml water, add 25ml salt. Once you have stirred it there should be some left at the bottom of the container – this means it has not dissolved, so the solution is saturated. Note: more salt will dissolve if hot water is used. No prizes to guess the piece of equipment you should use here - yup, the kettle! WARNING: boiling water has been known to be hot! Ask your parent to help you pour it into the jar, and be careful when mixing the salt or sugar in. Wait for it to cool before doing the next step.
Put the
solution
into a dish. Place the rough object (e.g. rock) into the dish.
Cover the dish with a tissue or coffee filter. This is to prevent dust and other bugs and such from falling into your experiment. Tissue and filter paper will let the water vapor through so evaporation can still take place.
Leave the dish in a safe (where the cat can't knock it over!) and sunny place (this is important because the sun is going to produce the heat for evaporation to happen). A good place is a windowsill.
Wait! Look every day and record any changes in a
log book
. Use a magnifying glass to look at the crystals being formed.
Compare the shape of the crystals with the shape of the salt crystals you use in your food. Write down the difference. As soon as you see crystals forming on the side of the container, take the rock out of the solution and put it into a new container with a new saturated solution. Keep doing this and make notes of the changes that happen to the crystals on the rock.
Leave the original solution, that you have taken the rock out of, to finish evaporating.
Results
This is what you should see happening...
After a couple of days, there will be crystals on the rock (or other rough object). Crystals find it more difficult to grow on smooth surfaces, hence the rock.
These crystals will be bigger than what you are used to seeing. This is because the salt that is still left in the water will carry on joining on to the already formed “seed crystals”.
The crystals will carry on growing on the rock as long as it has fresh saturated solution. (Check out the photo. This is a piece of charcoal with some crystals growing on it.)
The original solution will eventually evaporate away leaving the bottom of the container full of large beautifully shaped salt crystals.
Experiment 2:
Equipment needed
Salt
Water
Kettle
Glass tumbler
Pencil
String
Tissue or coffee filter
Magnifying glass
A sunny place
Method
Dissolve salt into hot water until the water is saturated. (See point one of Part 1 of this experiment for details. Please take note of the WARNING.)
Put the saturated solution in the glass.
Tie the string onto the pencil and then balance the pencil on top of the glass so that the string hangs into the solution.
Cover with the tissue or coffee filter (to keep bugs and dust out).
Check the glass side everyday. When crystals start growing on the side of the glass, make a fresh saturated solution in a fresh container and hang the string in once again.
The Results
This is what you should see happening...
Crystals will start growing on the string. This is your “seed crystal”.
When you change containers the crystals on the string should carry on growing in size.
As long as the solution is saturated, the crystals will carry on growing.
The Conclusion
In both of the above situations, crystals were formed when a the water was allowed to evaporate out of a solution. The crystals were bigger than what we are used to seeing on our dinner tables because the salt particles kept being added onto the original crystal.
(Check out the photos below. Which one is the table salt? Easy to tell the difference, hey?)
Back to "Please pass me the salt" project page
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