Thames & Kosmos Crystal Creation handleiding

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Thames & Kosmos

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1. EVAPORATION METHOD

The evaporation of a saturated solution is known as the evaporation method. By this method, just the

water evaporates, reducing the quantity of water, while the amount of substance contained in it

remains the same. This means that the solution gradually becomes supersaturated.

2. COOLING METHOD

The cooling of a saturated solution is known as the cooling method. The cooling method works

very quickly. An alum solution that is saturated at 60 °C deposits most of its alum in the form of

crystals when it is cooled to 20 °C. These crystals will be very small and not look very pretty,

however.

A strongly supersaturated solution, in other words, will not produce very nice crystals. It is

better to use a solution that is just barely supersaturated.

The cooling method is good, though, for quickly creating lots of small individual crystals, which

you can then coax along to form larger, prettier crystals by using the evaporation method. Due to

the slow evaporation of water from the container, the solution always stays just barely

supersaturated. This method does require a few days, however.

Crystal Growth

A crystal is built out of very tiny building blocks,

called

unit cells

. These unit cells consist of

molecules

, which are in turn made of

atoms

connected together. Atoms are the smallest

building blocks of all substances. In the case of

crystal salts, these unit cells are electrically

charged, so they are called

ions

A crystal growing in a solution is a very active

building site. The tiny particles whizz around and

look for an ideal spot to settle, which usually

tends to be an edge or a corner. If the landing

spot isn’t right, the particle whizzes on until it

finds the right kind of place where a unit cell is

being formed. Only then will it stay put and

become incorporated into the emerging crystal.

That is how the crystal grows, layer by layer.

Saturated Solution

A solution is said to be saturated when it contains

as much of a substance as can possibly dissolve

in it at a given temperature. A saturated salt

solution, for example, holds 16 g of salt per 100 g

of solution at 20 °C. But if you heat a saturated

solution, it becomes capable of dissolving more of

the substance. If, on the other hand, you cool a

saturated solution, it becomes supersaturated:

Now it contains more salt than it can hold at the

lower temperature. The consequence: Solid salt

will separate out on the bottom of the container

and along the container’s walls — in the form of

crystals. Crystals will only grow out of

supersaturated solutions.

Basic concepts for crystal growers

How to make a supersaturated solution

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