SteemSTEM Science fair Entry: beautiful sugar crystals for kids

Trying to get our children interested in science can be at the same time extremely simple and complex. Here I present a chemistry experiment I realised with our son of 6 years old, but that may also be suitable for bigger kids.

Starting question

What happens to sweetened water (a mix of water and sugar, nothing less nothing more) when it is first heated and next cooled down?

Material needed for the experiment:

• 380 g of water
• 1 kg of granulated sugar (or about 1 cup of water for 3 cups of sugar)
• wooden sticks (like skewer)
• clothes pegs
• long drink glasses

Optional: food coloring, food flavor

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Step 1: Preparation of the material

Wet the sticks and roll them into the sugar: let then them dry on a plate. Some use a string with a paper clip attached to one of the ends, but I prefer the solid support of a stick which then allows to reuse the sugar crystals for a real meal / drink.

If desired, put a few drops of food coloring into the glasses and / or artificial flavor. The visual effect is much more beautiful and the aroma brings a touch of fantasy.

Step 2: Dissolution of sugar crystals

Heat the water and gradually add the sugar. Dissolve the sugar by mixing with a wooden spoon until the solution is completely saturated.

Step 3: Final installation and cooling

Once the sugar has completely dissolved, pour the syrup into the glasses.

Let cool and soak the spikes in the glasses, keeping them in the center with a clothes peg.

To protect the crystals from the dust, I cut out squares of cardboard with a hole in the center to let pass the sticks as in the image.

The spikes must not touch the edges or the bottom of the glass.

Then install the glasses in a place where they will remain motionless for the rest of the experience.

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Questions to Zachary (6 years old) and his impressions

What happens to sugar when mixed with water?
The sugar dissolves in water and is transformed. It becomes sweet water.

Can we do the same experiment with cold water?
In cold water, if you put sugar, there comes a time when it will overflow. It dissolves less and less quickly. While in hot water, it does not overflow because it dissolves very quickly and one can put more.

Observations made at day-3:
The crystals formed on the stick that was put in the water and also on the surface of the liquid.

Observations made at day-7:
The longer you wait, more crystals are formed ... The crystals are big enough, we can get them out of the water.

What happened ? Where do the crystals come from? How have they formed?
When the water was very hot we could not see the sugar and when it got cold, it became crystals.

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Scientific explanation of the phenomenon

Sugar consists of sucrose molecules that are linked together. When they encounter water molecules, the latter bonds break down to form new molecules. The solid crystal sugar disappears: it is said to be dissolved.

By heating the water, we increase the amount of sugar that can be dissolved.

When the temperature decreases, the agitation of the molecules also decreases and the sugar is found in too great quantity compared to the amount of molecules of water. The sucrose molecules bind together again on surfaces such as the glass walls, the string, the trombone or the stick.

This consists of crystal formation.

For children, one can compare the binding of water molecules to sugar with two groups of children meeting. A group of very numerous girls meet a group of boy (less numerous) who will mix with each other.

When the water boils, the children run in all directions, everyone is mixed and when the children get tired (the water that cool down), the groups are formed again: some groups will be composed of girls and boys (sweet water), but since there are more girls, some will remain together and form the « crystals ».

_{[image credits: homemade]}

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References

• Ref 1.
• Ref 2.
• Ref 3.
• Ref 4, for the bigger ones.