 The Chemistry of Water 2
Hopefully you've noticed by now that, in addition to the required topics, such as the periodic table, we also like to cover what we call “softer” topics in this book, ones that connect chemistry a little more closely to people's
everyday lives.
To that end, in this second chapter on water, we have chosen to focus on solubility, specifically, that of salt and sugar. How these substances get into sea salt remains a mystery, whereas with
sugar, it is as familiar to us as it can possibly be.
But how do they get out again? In this case, it’s the other way around, because, for example, seawater is spread out over vast areas in countries with high levels of solar radiation, and once the H2O content
has evaporated, the salt can be gathered.
And what about sugar? Can it even be separated from the water again, or does it just evaporate along with it? In any case, the term 'solubility' does not always mean the same thing in chemistry. It remains true that
when the sugar evaporates, there isn't just one layer of sugar left.
Have you ever heard of rock sugar, or used it to enhance your tea? And if you read mystery novels, have you ever come across a description of that crackling sound when hot East Frisian tea comes into contact with
rock sugar and makes those kinds of noises?
It's important to note that the rock sugar pieces are larger than when, as we do, you spoon rock sugar into a cup of tea that's already been filled. They are cold, and the hot tea causes fine stress cracks to form, and it is
precisely this process that creates the effect.
However, ChatGPT also points out a second physical-chemical effect. It is the slow pace that makes the sweetness more pronounced as you savor your tea. So by no means should you dissolve the rock sugar cube as
quickly as possible before drinking.
| Sugar cubes make a sound before they disappear. |
Sugar crystallizes when the water in which it was dissolved evaporates. However, crystal formation is dependent on a certain amount of dissolved sugar. In principle, however, the molecules retain their composition.
In addition, unlike with salt, the heat must not be too intense. That's when you actually get a chemical reaction. The sugar caramelizes and eventually decomposes. However, that has little to do with the production of brown
sugar.
In the case of salt, the solution also causes Natrium and Clor to separate, with the individual ions being surrounded and stabilized by water. After the water evaporates, they come back together.
The solubility of table salt in cold water is already quite high, while that of sucrose, the main component of sugar, is significantly lower. Here, it increases sharply with temperature, but by no means as sharply with table
salt.
Temperature, therefore, plays a minor role in the solubility and evaporation of salt. It is always the same, whereas the solubility of sugar decreases very sharply as the temperature drops.
| 
